HK1237152B - Network node and method in a wireless telecommunications network - Google Patents

Abstract

A method performed by a network node for managing transmission of one or more CRS subframes. The network node identifies if a cell is actively serving a set of UEs. When the cell is actively serving a set of UEs, which set of UEs is configured for DRX the network node sends CRS over the first bandwidth in one or more CRS subframes which are transmitted in the cell during an onDuration interval of the DRX pattern and/or in one or more CRS subframes where system information is sent and/or in one or more CRS subframes where downlink, DL, data is sent. The network node sends CRS over a second bandwidth, in CRS subframes which are not transmitted in the cell during the onDuration interval of the DRX and/or in the one or more CRS subframes except CRS subframes where system information is sent and/or in the one or more CRS subframes except CRS subframes where DL data is sent, which second bandwidth is reduced in relation to the first bandwidth.

Description

Network node and method in wireless telecommunication network

Technical Field

Embodiments herein relate to a network node and methods therein. Specifically, a method and a network node for managing transmission of a cell reference signal are disclosed.

Background Art

A communication device, such as a user equipment (UE), is enabled to communicate wirelessly in a cellular communication network or wireless communication system (sometimes also referred to as a cellular radio system or cellular network). Communication can be performed, for example, between two UEs, between a UE and a regular phone, and/or between a UE and a server via a radio access network (RAN) and possibly one or more core networks included in the cellular communication network.

To name a few other examples, a UE may also be referred to as a wireless terminal, a mobile terminal and/or a mobile station, a mobile phone, a cellular phone, a laptop computer, a tablet computer, or a surfboard with wireless capabilities. A UE in this context may be, for example, a portable, pocket-storable, handheld, computer-built-in, or vehicle-mounted mobile device that is enabled to communicate voice and/or data with another entity, such as another wireless terminal or a server, via a RAN.

A cellular communication network covers a geographical area divided into cell areas, where each cell area is served by a network node. A cell is a geographical area where a network node provides radio coverage.

A network node may further control several transmission points, for example, including radio units (RRUs). Thus, a cell may include one or more network nodes, each controlling one or more transmission/reception points. A transmission point, also referred to as a transmission/reception point, is an entity that transmits and/or receives radio signals. This entity has a location in space, such as an antenna. A network node is an entity that controls one or more transmission points. Depending on the technology and terminology used, a network node may be, for example, a base station such as a radio base station (RBS), eNB, eNodeB, NodeB, B-node, or base transceiver station (BTS). Base stations may be of different types, such as macro eNodeB, home eNodeB, or pico base station, based on transmission power and, therefore, cell size.

In addition, each network node can support one or several communication technologies. The network node communicates with UEs within range of the network node over an air interface operated by radio frequency. In the context of this disclosure, the term downlink (DL) is used for the transmission path from the base station to the mobile station. The term uplink (UL) is used for the transmission path in the opposite direction (i.e., from the UE to the base station).

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks. In LTE, the cellular communication network is also referred to as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN).

An E-UTRAN cell is defined by certain signals broadcast from the eNB. These signals contain information about the cell that can be used by a UE to connect to the network via the cell. The signals include reference and synchronization signals that the UE uses to find frame timing and physical cell identity, as well as system information that includes parameters related to the entire cell.

Therefore, a UE that needs to connect to the network must first detect a suitable cell, as defined in 3GPP TS 36.304v11.5.0. The UE can be in an idle state, also known as IDLE or radio resource control idle (RRC_IDLE); or in a connected state, which is also known as CONNECTED or radio resource control connected (RRC_CONNECTED). When the UE is in RRC_IDLE, it monitors the paging channel, which is part of the Paging Control Channel (PCCH) at the logical layer, the Paging Channel (PCH) at the transport channel layer, and the Physical Downlink Shared Channel (PDSCH) at the physical channel layer. In doing so, the UE typically also performs a number of radio measurements that the UE uses to evaluate the best cell, such as Reference Signal Received Power (RSRP), Reference Symbol Received Quality (RSRQ), or Received Signal Strength Indicator (RSSI). This is performed by measuring the received reference signal and/or the portion of the spectrum that includes the reference signal sent by the cell. This can also be referred to as "listening" for a suitable cell.

A suitable cell is typically a cell with an RSRQ or RSRP above a certain level. The cell with the highest RSRP or RSRQ may be referred to as the best cell or the most suitable cell. Sensing a suitable cell may include searching for a reference signal transmitted from a network node in an orthogonal frequency division multiplexing (OFDM) subframe. When the most suitable cell is found, the UE performs random access based on the system information for the cell. This is done to transmit a radio resource control (RRC) connection establishment request to the network node. Assuming the random access procedure is successful and the network node receives the request, the network node will respond with an RRC connection establishment message or an RRC connection rejection. The RRC connection establishment message confirms the UE's request and informs it to enter the RRC_CONNECTED state. The RRC connection rejection informs the UE that it may not be able to connect to the cell. In the RRC_CONNECTED state, the parameters required for communication between the network node and the UE are known to the two entities, and data transfer between the two entities is enabled.

When the UE is in the RRC_CONNECTED state, the UE continues to measure RSRP as an input to connected mode mobility decisions, such as, for example, deciding when to perform a handover from one cell to another. These measurements are typically performed in the full bandwidth of a subframe (which may also be referred to as full spectrum).

RSRP is a measure of the signal strength of an LTE cell. It helps the UE rank different cells based on their signal strength, which serves as an input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying the cell-specific reference signal (CRS) across the entire bandwidth. Therefore, RSRP is only measured in OFDM symbols that carry CRS.

The RRC protocol handles control plane signaling at the network layer (also called layer 3) between the UE and a network node, which may also be referred to as a UTRAN or E-UTRAN node. At any one time, only one RRC connection can be open between the UE and a network node.

The network layer may also include:

Connection establishment and release functions,

Broadcasting of system information,

Radio bearer establishment/reconfiguration and release,

RRC connection mobility procedures,

· Paging notification and release,

Outer loop power control.

To support UEs connecting to a cell (also referred to as an access cell), a system information block (SIB) is transmitted in a control channel such as the broadcast control channel (BCCH) logical channel in the downlink, which can be mapped to the PDSCH physical channel. In LTE, a number of different SIBs are defined, characterized by the information they carry. For example, SIB1 carries cell access related parameters, such as information about the operator of the cell, restrictions on what users can access the cell, and allocation of uplink/downlink subframes. SIB1 also carries information about the scheduling of other SIBs.

To reduce UE power consumption, discontinuous reception (DRX) can be implemented. The fundamental mechanism in DRX is a configurable DRX cycle in the UE, also known as a DRX mode. When a DRX cycle is configured, the UE monitors control signaling only during the onDuration interval of the DRX cycle. The onDuration interval can be one or more subframes, which can be referred to as one or more active subframes. During the remaining subframes of the DRX cycle, the UE can shut down its receiver, which can also be referred to as UE sleep, or the offDuration interval of the DRX cycle. This allows for a significant reduction in power consumption: the longer the DRX cycle and the shorter the onDuration interval, the lower the power consumption. In certain situations, if a UE is already scheduled and active for receiving or transmitting data in a subframe, it may be scheduled again in the near future. Waiting until the next active subframe according to the DRX cycle may result in additional delays in transmission. Therefore, to reduce latency, the UE can remain active for a configurable time after being scheduled, which can also be referred to as the activity time or the inactivity timer (DRX-Inactivity Timer) defined in 3GPP TS 36.321 Ch 3.1. The duration of the active time is set by the inactivity timer, which is the duration in downlink subframes from the last successful decoding of the physical downlink control channel (PDCCH) to the duration the UE waits before shutting down and re-entering the offDuration. The UE can restart the inactivity timer after a single successful decoding of the PDCCH for a transmission. The time it takes for the UE to re-enter the offDuration after the last transmission can also be called the inactivity time.

To facilitate handovers to other cells, each network node can store the cell identifiers of cells supported by other network nodes in an address database, so that it knows how to contact the network node of a potential target cell for handover. Each network node serving a cell typically stores in a database the cells with which it has neighbor relationships, i.e., the cells in the area to which UEs frequently perform handovers. Hereinafter, a cell's neighbor relationships are referred to as its "neighbor relationship list."

CRS is a UE-known symbol inserted in the resource elements (REs) of the subframes of the OFDM time and frequency grid and broadcast by the network node. Each RE has an extension in the frequency domain corresponding to an OFDM subcarrier and an extension in the time domain corresponding to an OFDM symbol interval.

The UE uses CRS for downlink channel estimation. Channel estimation is used for demodulation of downlink data when the UE is in RRC_CONNECTED state and is receiving user data and when the UE is in RRC_IDLE state and is reading system information. Due to the latter use case, the network node cannot know whether the UE wants to access the network before the UE performs random access, so even the cells without any UE in RRC connected state must transmit CRS from it. The downlink CRS is inserted into the first and third to last OFDM symbol of each time slot with a frequency domain spacing of six subcarriers. A time slot is a time period of the OFDM time and frequency grid, typically 0.5 milliseconds long. Therefore, a problem with the known technology is that the cells without any UE in RRC connected state still consume power due to the CRS broadcast.

In the case where a network node uses several antennas for transmission and each antenna represents a cell, each antenna must transmit a unique reference signal in order for the UE to connect to that specific cell. When one antenna transmits, the other antennas must be silent so as not to interfere with the first antenna reference signal. In order to reduce interference of reference signals between cells, the position of the CRS is usually shifted in frequency between cells. The CRS can be shifted between 0-5 subcarriers, and for LTE, each subcarrier corresponds to a frequency shift of 15kHz. The frequency shift can be derived from the physical cell identity (cell ID) that is signaled to the UE through the selection of the appropriate primary synchronization channel (PSCH) and secondary synchronization channel (SSCH).

Although this reduces the interference of reference symbols (eg, CRS symbols) between cells, there is a problem that the reference symbols of one cell may interfere with the PDSCH and PDCCH symbols of an adjacent cell.

Therefore, even if a cell does not have any UE in the RRC_CONNECTED state, interference may affect the UE DL throughput in a neighboring cell, especially when the UE is at and/or close to the boundary between cells.

Reducing the power of the CRS can alleviate this problem. However, in order to access a cell, the UE must be able to hear the CRS of the cell, that is, the UE must be able to identify and receive the CRS transmitted from the cell. Therefore, reducing the power of the CRS also reduces the size of the cell, because UEs farther away will no longer hear the CRS sent by the cell. In addition, when the signal-to-interference ratio (SINR) on the CRS decreases, the quality of the channel estimate used for demodulation decreases. Therefore, reducing the power of the CRS leads to degradation of cell edge performance. When the load in the network increases, especially if data is transmitted at a higher power than the CRS, which is usually the case when the impact of CRS interference will be reduced, this degradation will be further exacerbated, resulting in reduced performance of the wireless communication network.

Summary of the Invention

It is therefore an object of embodiments herein to enhance performance in wireless communication networks.

According to a first aspect of embodiments herein, the object is achieved by a method performed by a network node for managing transmission of a Cell Reference Signal, CRS.

The network node operates one or more cells. The network node identifies whether the cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node sends CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in one or more CRS subframes in which system information is sent. The network node also sends CRS on a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in one or more CRS subframes other than the subframes in which system information is sent. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception (DRX), the network node sends CRS on a first bandwidth in one or more CRS subframes transmitted in the cell during the onDuration interval of the DRX mode and/or in one or more CRS subframes in which system information is sent and/or in one or more CRS subframes in which downlink DL data is sent. The network node further transmits the CRS on a second bandwidth in a CRS subframe that is not transmitted in the cell during the onDuration interval of DRX, and/or in one or more CRS subframes other than the CRS subframe in which system information is transmitted, and/or in one or more CRS subframes other than the CRS subframe in which downlink (DL) data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

According to a second aspect of the embodiments of this document, the purpose is achieved by a network node configured to manage the transmission of a cell reference signal (CRS). The network node operates one or more cells. The network node is configured to identify whether the cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node is configured to transmit CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in a CRS subframe in which system information is transmitted. The network node is further configured to transmit CRS on a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in a CRS subframe other than a CRS subframe in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception (DRX), the network node is further configured to transmit a CRS on a first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX mode, and/or in a CRS subframe in which system information is transmitted, and/or in a CRS subframe in which downlink (DL) data is transmitted. The network node is further configured to transmit a CRS on a second bandwidth in a CRS subframe that is not transmitted in the cell during an onDuration interval of the DRX mode, and/or in a CRS subframe other than a CRS subframe in which system information is transmitted, and/or in a CRS subframe other than a CRS subframe in which downlink (DL) data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

By applying the reduced bandwidth mode to CRS transmitted in all subframes except for subframes transmitted during or related to the onDuration in the cell, or subframes in which or related to subframes in which system information such as SIBs are transmitted, power consumption and interference from the cell can be reduced, thereby enhancing the performance of neighboring cells transmitting data. In other words, the reduced bandwidth mode is applied during the period when no data transmission occurs and the UE turns off its receiver and enters a low power mode.

By applying reduced bandwidth mode to CRS in cells that do not serve any UE in RRC connected mode, power consumption and interference from null cells may be reduced, thereby enhancing the performance of cells with UEs in RRC connected mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein are described in more detail with reference to the accompanying drawings, in which:

FIG1 is a schematic block diagram illustrating an embodiment of a wireless communication network.

FIG2 is a schematic block diagram illustrating embodiments of an OFDM subframe.

FIG3 is a flow chart depicting a first embodiment of a method in a network node.

FIG4 is a flow chart depicting a second embodiment of a method in a network node.

FIG5 is a schematic block diagram illustrating embodiments of a network node.

FIG6 a is a scheduling diagram illustrating a first embodiment of the method herein.

FIG6 b is a scheduling diagram illustrating a first embodiment of the method herein.

FIG7 is a schematic block diagram illustrating embodiments of a core network node.

DETAILED DESCRIPTION

the term

The following general terms are used in the examples and are explained below:

Radio network node: In some embodiments, the non-limiting term radio network node is more generally used and refers to any type of network node that serves a UE and/or is connected to other network nodes or network elements, or any radio node from which a UE receives signals. Examples of radio network nodes are Node B, Base Station (BS), MSR radio node such as a Multi-Standard Radio (MSR) BS, eNode B, network controller, Radio Network Controller (RNC), Base Station Controller, relay, donor node controlled relay, Base Transceiver Station (BTS), Access Point (AP), Transmission Point, Transmission Node, RRU, RRH, a node in a Distributed Antenna System (DAS), etc.

Network node: In some embodiments, the more general term "network node" is used, which may correspond to any type of radio network node or any network node that communicates with at least a radio network node. Examples of network nodes are any of the radio network nodes mentioned above, core network nodes (e.g., mobile switching center (MSC), mobility management entity (MME), etc.), operation and maintenance (O&M) center, operation support system (OSS), self-organizing network (SON), positioning node (e.g., evolved serving mobile positioning center (E-SMLC), master data telegraph (MDT), etc.).

User Equipment: In some embodiments, the non-limiting term User Equipment (UE) is used to refer to any type of wireless device that communicates with a radio network node in a cellular communication system or a mobile communication system. Examples of UEs are target devices, device-to-device UEs, machine-type UEs or UEs with machine-to-machine communication capabilities, PDAs, iPADs, tablet computers, mobile terminals, smartphones, laptop embedded equipment (LEEs), laptop mounted equipment (LMEs), USB dongles, etc.

The embodiments herein are also applicable to a multi-point carrier aggregation system.

Note that although terminology from 3GPP LTE has been used in this disclosure to exemplify the embodiments herein, this should not be considered to limit the scope of the embodiments herein to only that system. Other wireless systems including WCDMA, WiMax, UMB, and GSM may also benefit from utilizing the ideas covered by this disclosure.

It should also be noted that terms such as eNodeB and UE should be considered non-restrictive and, in particular, do not imply a hierarchical relationship between the two. In general, "eNodeB" can be considered as device 1 and "UE" can be considered as device 2, and the two devices communicate with each other via some radio channel. In this article, we also focus on wireless transmission in the downlink, but the embodiments herein are equally applicable to the uplink.

In this section, the embodiments of this invention will be described in more detail through a plurality of exemplary embodiments. It should be noted that these embodiments are not mutually exclusive. Components of one embodiment may be assumed to exist in another embodiment by default, and it will be apparent to those skilled in the art how these components may be used in other exemplary embodiments.

1 depicts an example of a wireless communication network 100 according to a first scenario in which embodiments herein may be implemented. The wireless communication network 100 is a wireless communication network such as LTE, E-UTRAN, WCDMA, GSM network, any 3GPP cellular network, Wimax or any cellular network or system.

The wireless communication network 100 includes a plurality of network nodes, two of which (a first network node 110 and a second network node 111) are depicted in FIG1 . The first network node 110 and the second network node 111 are network nodes, each of which can be a transmission point such as a radio base station, for example, an eNB, eNodeB, or a Home NodeB, Home eNodeB, or any other network node capable of serving wireless terminals such as user equipment or machine type communication devices in the wireless communication network. The first network node 110 and the second network node 111 each serve a plurality of cells 130, 131, 132.

Wireless communication network 100 includes a UE set 121, which may include one or more UEs 120. First network node 110 and second network node 111 may each be a transmission point for UE 120. UE 120 is within radio range of first network node 110 and second network node 111, meaning it can hear signals from first network node 110 and second network node 111. One or more UEs 120 may also exist in each cell, and one or more UEs 120 may also be referred to as a UE set 121.

The UE 120 in the UE set 121 may be, for example, a wireless terminal, a wireless device, a mobile wireless terminal or a wireless terminal, a mobile phone, a computer such as a laptop with wireless capabilities, a personal digital assistant (PDA) or a tablet (sometimes called a surfboard), or any other radio network element capable of communicating via a radio link in a wireless communication network. Note that the term wireless terminal used in this document also covers other wireless devices such as machine-to-machine (M2M) devices.

Figure 2 shows an exemplary downlink OFDM time and frequency grid, which may also be referred to as an OFDM subframe. Each subframe includes two time slots. Each time slot includes multiple resource elements (REs) 201 extending in both the time domain (x-axis) and the frequency domain (z-axis). The extension of each RE 201 in the frequency domain may be referred to as a subcarrier, while the extension in the time domain may be referred to as an OFDM symbol. In the time domain, LTE downlink transmissions are organized into 10ms radio frames, where each radio frame includes ten subframes of equal size. Furthermore, resource allocation in LTE may generally be described in terms of physical resource blocks (PRBs) comprising multiple REs. A resource block corresponds to one time slot in the time domain and 12 consecutive subcarriers in the frequency domain.

Downlink and uplink transmissions are dynamically scheduled, i.e., in each subframe, the first network node 110 transmits control information about which UE 120 to or from which data and on which resource blocks the data is transmitted. The control information may include system information, paging messages, and/or random access response messages. One or more PDCCHs may be used to transmit control information for a given UE 120. The control information of the PDCCH is transmitted in the control region of each subframe. Figure 2 shows an exemplary size of a conventional control region of three OFDM symbols allocated for control signaling (e.g., PDCCH). However, the size of the control region may be dynamically adjusted based on the current traffic situation. In the example shown in the figure, only the first OFDM symbol of the three possible OFDM symbols is used for control signaling. In general, the control region may include multiple PDCCHs that carry control information for multiple UEs 120 simultaneously. The REs used for control signaling are represented by wavy lines, and the REs used for CRS are represented by diagonal lines.

UE 120 uses CRS for downlink channel estimation. Channel estimation is used to determine the demodulation of downlink data when UE 120 is in RRC connected state, and when UE 120 is in RRC idle state and is reading system information. Downlink CRS can be inserted into the first and third-to-last OFDM symbols of each time slot with a frequency domain interval of six subcarriers. RSRP is a measurement of the signal strength of an LTE cell, which helps UE 120 to sort between different cells as an input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying cell-specific reference signals (CRS) over the entire bandwidth. Therefore, it is only measured in OFDM symbols carrying CRS.

The subframe also includes data symbols for transmitting user data between the first network node 110 and the UE 120. The data symbols are located in a region following the control region, also called the data region.

A first example of embodiments of a method in a network node 110 for managing transmission of a Cell Reference Signal (CRS) will now be described with reference to the flowchart depicted in Figure 3. The network node 110 operates one or more cells 130, 131, 132 which may or may not serve a set 121 of UEs.

The method may include the following actions, which may be performed in any suitable order: The dashed lines of the boxes in Figure 3 indicate that this operation is not mandatory.

Action 301

The network node 110 identifies whether a cell among the one or more cells 130, 131, 132 is actively serving the set of UEs 121. A cell actively serving the set of UEs 121 may also be referred to as a cell having a set of connected UEs, and a cell not actively serving the set of connected UEs 121 may be referred to as an empty cell. This action 301 may be performed by an identification module 404 within a network node (such as the network node 110). This action corresponds to action 401 described below.

When the network node 110 has identified a cell that is not actively serving the set of UEs 121, the network node performs actions 302 and 303 described below. Although actions 302 and 303 are depicted as following each other, the actions may be performed simultaneously.

Action 302

When the network node 110 has identified cells that are not actively serving the set of UEs 121 , the network node 110 transmits CRS over the first bandwidth in one or more CRS subframes transmitted during paging occasions and/or in one or more CRS subframes transmitting system information.

Action 303

When the network node 110 has identified cells that are not actively serving the set of UEs 121, the network node 110 further transmits CRS using a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in one or more CRS subframes other than subframes in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth.

In another embodiment herein, paging occasions may be sent in one CRS subframe per radio frame with paging only in cells that do not serve the set of UEs 121. Thus, the number of CRS subframes that must be sent with the first bandwidth is reduced, which allows the network node 110 to reduce the bandwidth in a higher number of CRS subframes.

When the network node has identified a cell that is actively serving the set of UEs (121) configured for discontinuous reception (DRX), the network node 110 performs actions 304 and 305 described below. Although actions 304 and 305 are depicted as following each other, the actions may be performed simultaneously.

Action 304

When the network node has identified a cell that is actively serving a set of UEs (121) configured for discontinuous reception (DRX), the network node 110 transmits CRS subframes over a first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX mode, and/or in one or more CRS subframes transmitting system information, and/or in one or more CRS subframes transmitting downlink (DL) data.

In other embodiments, the network node 110 may also transmit the CRS using the first bandwidth in a CRS subframe transmitted immediately before or after the CRS subframe transmitted during the paging occasion and/or in a CRS subframe transmitting system information and/or during the onDuration period and/or in a CRS subframe transmitting DL data.

Action 305

When the network node has identified a cell that is actively serving the set of UEs (121) configured for discontinuous reception (DRX), the network node 110 further transmits a CRS using a second bandwidth in a CRS subframe that is not transmitted in the cell during the onDuration interval of DRX, and/or in one or more CRS subframes other than CRS subframes for transmitting system information, and/or in one or more CRS subframes other than CRS subframes for transmitting DL data. The second bandwidth is reduced relative to the first bandwidth. This action 305 corresponds to action 402 described below, and therefore the embodiments described for action 402 can also be applied to this action 305.

Action 306

When the network node 110 has identified the cell that is actively serving the UE set, the network node 110 may also send a message including a DRX command to the UE set 121. The DRX command indicates the DRX mode for the UE set 121, which may also be referred to as a DRX cycle. The indicated DRX mode is the DRX mode that the UE set 121 will use. For the UEs 120 included in the UE set 121, the onDurations of the DRX modes are aligned so that the UEs 120 have overlapping onDuration intervals. By aligning the onDuration intervals of the UEs 120, the UEs can be grouped, i.e., the UEs will have overlapping onDurations. This has the advantage that the timing of transmitting CRS in the first bandwidth mode can be reduced and the number of subframes in which CRS is transmitted via the second bandwidth is increased. This will further improve the performance of the cell.

This action 306 corresponds to action 403 described below, so the embodiment described for action 403 can also be applied to this action 306 .

By sending a message including a command indicating the onDuration of the DRX mode to all connected UEs in the cell, the UEs can be grouped together, i.e., the UEs are configured with overlapping onDurations. By doing so, the performance of the cell can be further improved because the times when CRS must be transmitted at full bandwidth can be minimized because each UE performs radio measurements such as RSRP, RSRQ, or RSSI in the same time interval.

Another example of an embodiment of a method for managing the transmission of cell reference signals (CRS) in a network node 110 will now be described with reference to the flowchart shown in FIG4 . The network node 110 operates one or more cells and is configured to transmit CRS in a first bandwidth mode during operation. This relates to normal operation. The first bandwidth mode, which may also be referred to as normal bandwidth mode, is used when at least one cell of the network node 110 is serving at least one UE 120 in RRC connected mode and the at least one UE 120 is scheduled to receive data. In normal bandwidth mode, CRS is transmitted over the entire available bandwidth of a DL radio frame (RF), i.e., the CRS is transmitted in all physical resource blocks (PRBs) of the cell.

The method may include the following actions, which may be performed in any suitable order: The dashed lines in the boxes in Figure 4 indicate that this operation is not mandatory.

Action 401

The network node 110 identifies a cell serving a set of UEs 121 (which may also be referred to as a set of connected UEs). The set of UEs 121 is configured for discontinuous reception (DRX). The set of UEs 121 may include one or more UEs 120. The set of UEs 121 is not scheduled by the network node for receiving a transmission from the network node sent in one of the network node's cells. This may mean that the network node has not yet scheduled the set of UEs 121 for receiving a transmission sent from the network node 110 in the cell, or that a certain time (T) has passed since the set of UEs 121 was scheduled for transmission in the UL or DL. The time T may be a time set in a DRX inactivity timer. This action 401 may be performed by an identification module 404 within a network node, such as the network node 110.

Action 402

When the network node 110 has identified a first cell serving a set of UEs 121 that are not scheduled by the network node 110, the network node 110 applies a second bandwidth mode (also referred to as a reduced CRS bandwidth mode) to CRSs in subframes not transmitted in the cell during the onDuration of DRX or in subframes in which system information is transmitted. In another embodiment, the reduced CRS bandwidth mode may also be applied to CRSs transmitted in subframes not transmitted with respect to the onDuration or related to subframes in which system information is transmitted, which may be, for example, subframes directly before or after the onDuration or subframes in which system information is transmitted. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode. The system information may be, for example, a system information block (SIB). This reduced bandwidth mode may also be referred to as a low bandwidth mode. The low bandwidth mode means that the network node 110 does not transmit CRSs in all PRBs of the subframes of the cell. By reducing the bandwidth of the CRSs, i.e., transmitting the CRSs only on a portion of the available bandwidth of the DL radio frame, the overall interference from the CRSs of the cell 130 is reduced. Reducing interference from cell 130 increases throughput in neighboring cells 131 , as well as increasing RRC connections and scheduled UEs 120 .

Studies have shown that when the CRS bandwidth is reduced, mobility measurements (also known as cell evaluation or best cell evaluation, such as RSRP) may be negatively affected. This may cause the UE to make incorrect decisions about which cell it should camp on. When the UE120 performs mobility measurements on a neighboring cell, only a limited part of the bandwidth is considered. This limited part of the bandwidth may be, for example, the center six PRBs of a subframe. However, when the UE performs measurements on the cell in which it camps (which may also be referred to as its own cell), the entire bandwidth is taken into account. If the bandwidth used to send CRS in a cell is reduced, the CRS will only be sent in a part of the bandwidth (e.g., in the center six PRBs). However, RSRP is calculated as the average power of all REs carrying CRS over the entire bandwidth. Since the power of the CRS sent in, for example, the center six PRBs is averaged over the entire bandwidth, not just over the reduced bandwidth, the RSRP of the own cell may appear to be lower than that of the neighboring cell. This may cause the UE to connect to (which may also be referred to as performing handover to) a neighboring cell that appears to be better but is actually worse. This may cause the UE to start performing multiple handovers back and forth between cells, which can also be called a ping-pong effect, because the neighboring cell evaluated only on the central six PRBs will always appear to be better.

To prevent the reduced bandwidth mode from negatively affecting (such as corrupting) mobility measurements (such as cell evaluation or best cell evaluation), subframes transmitted during the onDuration of DRX or subframes in which system information is sent are transmitted first, which may also be referred to as normal bandwidth mode.

In another embodiment, CRS may also be transmitted in normal bandwidth mode in subframes surrounding the subframe transmitted during onDuration. In one embodiment, normal bandwidth mode may apply to multiple subframes before or after the subframe transmitted during onDuration. The number of subframes transmitted in normal bandwidth mode may be up to 25 subframes, including the subframe transmitted during onDuration. The onDuration period may occur over two subframes. In another embodiment, normal bandwidth mode may apply to the four subframes before the onDuration period and the seven subframes after the onDuration period, for a total of thirteen subframes. By transmitting CRS in normal bandwidth mode in subframes surrounding the onDuration period, legacy UEs that do not perform measurements as precisely as modern UEs can measure CRS for channel estimation, even if the measurements are not performed precisely during the onDuration period. Depending on the accuracy of the measurements performed by the UE, the number of subframes in which CRS is transmitted in normal bandwidth mode may be reduced. In another embodiment, normal bandwidth mode may, for example, apply to a subframe preceding the subframe transmitted during onDuration or the subframe in which system information is transmitted. Thus, it can be ensured that the CRS is sent over the entire bandwidth when the UE performs measurements during the onDuration period (ie in normal bandwidth mode). This embodiment is depicted in FIG6 .

In yet another embodiment, the CRS may also be transmitted in normal bandwidth mode during the UE's inactive time.

Having a long DRX cycle (i.e., a long time between DRX onDurations) can further be beneficial because it enables the network node 110 to apply the reduced bandwidth mode over a greater number of subframes. In one embodiment herein, the DRX cycle (which may also be referred to as the period of the DRX pattern) may be in the range of 20ms to 320ms. In another embodiment herein, the DRX cycle may be in the range of 20ms to 80ms. In yet another embodiment, the DRX cycle may be 40ms long. Studies have shown that this is the preferred period at which UEs typically read RSRP in order to assess the channel conditions in the cell to which they are connected.

Action 402 may be performed by a bandwidth adjustment module within a network node, such as network node 110 .

Action 403

In another embodiment herein, network node 110 may send a message to UE set 121, the message including a discontinuous reception (DRX) command. This command indicates a DRX cycle, wherein the onDuration (also referred to as the onDuration interval) of the DRX mode is aligned for the UEs included in UE set 121. Thus, the UEs can be grouped, i.e., the UEs will have overlapping onDurations. This has the advantage of reducing the number of times CRS is transmitted in the first bandwidth mode, further improving cell performance.

In another embodiment herein, the onDuration of the DRX mode can be aligned with the transmission of one or more subframes containing system information, such as system information blocks (SIBs). In another embodiment herein, the onDuration is aligned with SIB 1. Since SIB 1 includes parameters related to cell access and information regarding the scheduling of other SIBs, SIB 1 is transmitted even if the remaining SIBs are not transmitted. Since the number of subframes transmitted in the first bandwidth mode can be further reduced, aligning the onDuration of the set of UEs 121 with the transmission of SIB 1 further improves cell performance. Aligning the onDuration with SIB 1 further reduces losses, as SIB 1 is transmitted with the full CRS bandwidth regardless. SIB 1 can be transmitted with a 20ms period in subframe 5, which may also be referred to as SFN mod 2 = 0. Through forced DRX, a UE can be triggered (which may also be referred to as being incentivized, commanded, forced, or tricked) to always evaluate the status of the current cell when CRS is transmitted in full bandwidth mode and to reduce bandwidth when the connected UE is dormant. The trigger can be sent in a DRX command that sets the onDuration of the DRX cycle. The DRX mode may be applied to the UE 120 in order to trigger the evaluation of RSRP and other measurements for time slots in cases where the network node has transmitted CRS over the entire bandwidth (ie, in normal bandwidth mode).

In another embodiment, the network node 110 may force the UE to enter DRX sleep by sending a 3GPP DRX command MacControlElement (such as defined in 3GPP TS 36.321 v11.5.0 Ch 6.1.3.3 and referred to as a DRX command MAC control element). The MacControl element may include an indication to stop the DRX inactivity timer and/or the onDuration timer.

In other embodiments herein, when the number of connected UEs in a cell exceeds a certain threshold, the alignment of the onDuration of the DRX mode and/or the application of the reduced CRS bandwidth may be deactivated.

Action 403 may be performed by a transmitting module within a network node, such as network node 110. The transmitting module may also be comprised in a radio circuit within a network node, such as the described network node.

In one embodiment herein, a reduced CRS bandwidth mode is applied to CRSs transmitted in any subframe except for subframes in which the network node 110 transmits system information, paging, or random access response messages, or subframes in which the network node 110 assumes that the UE 120 is performing measurements. By applying the reduced CRS bandwidth mode in all subframes except for the aforementioned subframes, interference from the CRS is reduced while allowing the UE 120 in the neighboring cells 131, 132 to hear the CRS from the null cell 130. This is necessary to enable the UE 120 to obtain information about the modulation of the signal so that it can demodulate the downlink control channel of the cell. In this embodiment, the network node 110 may transmit CRSs across the entire bandwidth in subframes in which the network node 110 transmits system information such as SIBs, paging, or random access response messages, or in which the UE 120 is assumed to be performing measurements.

In another embodiment herein, the network node 110 transmits the CRS in PRBs used for transmission of data or control information only in subframes in which the network node 110 transmits system information, paging or random access response messages, or assumes that the UE performs measurements.

The network node 110 may also transmit the CRS in REs adjacent to the REs mapped to the common search space of the PDCCH. Thus, the CRS is transmitted only in the area where the UE is searching for the PDCCH. Consequently, the number of subframes in which the CRS can be transmitted on the second bandwidth increases, further improving the performance of the wireless communication network.

The CRS bandwidth can be further adapted to multiple levels. For LTE, the bandwidth in cell 130 can vary, for example, between 1.4 MHz and 20 MHz. However, other bandwidths are also possible depending on the technology used.

In another embodiment, a hysteresis function may be applied when changing the CRS bandwidth level, thereby avoiding unnecessary switching between bandwidth modes when the cell 130 switches from the first bandwidth mode to the second bandwidth mode.

In another embodiment herein, for services requiring Voice over IP (VoIP) or other "constanton" types, the UE can be moved to the lowest frequency band with the best coverage, while the CRS can be muted on higher frequency bands. Moving voice users on LTE to the lowest frequency band can be beneficial because these users are active and require coverage. This facilitates carrier aggregation.

In another embodiment herein, some UEs may be configured with a channel quality indicator (CQI) on the physical uplink control channel (PUCCH) that may be aligned with the DRX onDuration, while some UEs may not be configured with CQI on the PUCCH. Thus, the onDuration periods may be stacked more closely. Intelligent selection of UEs to be given PUCCH CQIs may be achieved by, for example, looking at the path loss so as not to degrade system coverage. UEs with high path loss may be configured with CQI on the PUCCH, while others may not.

In another embodiment herein, dynamic reconfiguration of paging frames and paging occasions may be performed, thereby reducing CRS transmissions performed in normal bandwidth mode while maintaining sufficient paging capacity.

In another embodiment, coordination over X2 can be performed between interfering cells. Thus, the interfering cells can inform each other which subframes to transmit in reduced bandwidth mode (also referred to as blank subframes) and which subframes to transmit in normal bandwidth mode (also referred to as non-blank subframes). This can enable different network nodes to have different outer loop adjustment values for blank subframes versus non-blank subframes, which can improve link adaptation results.

In other embodiments of the present invention, DL data may be sent to each UE in connected mode with a certain period. This has been shown to increase the stability of measurements (such as RSRP, RSRQ, or RSSI) performed by the UE. DL data may be sent during a period corresponding to the time of the UE's onDuration. Tests have shown that the preferred period for DL data is approximately 2 seconds, i.e., DL data is sent to the DL approximately every 2 seconds. The periodically sent DL data may be any DL data. In one embodiment, a timing advance command (TAC) is sent as periodic DL data. CRS is sent in full bandwidth mode during the transmission of DL data, thereby providing CRS to the UE during the DL transmission and the subsequent inactivity time (also referred to as DRX-Inactivity time).

In other embodiments of this document, the CRS may also be transmitted using the first bandwidth or full bandwidth mode during UL transmission (eg, a subframe for sending UL data).

In other embodiments herein, periodic DL data transmissions may be aligned between connected UEs. Since each DL transmission starts an inactivity timer as defined in 3GPP TS 36.321 v.9.6.0, CRS will be sent to each UE in full bandwidth mode for the duration of the inactivity period. By aligning periodic DL data transmissions between connected UEs, the number of subframes in which full spectrum CRS needs to be transmitted is reduced. This improves the gain when many users are connected by ensuring that the full bandwidth CRS transmitted during each UE's DRX-Inactivity timer coincides in time, thereby maximizing the number of subframes in which CRS can be muted. This may further improve the performance of the cell.

In other embodiments herein, the connected UE may be released and forced into idle mode after an inactivity timer in the network node that monitors UE activity has elapsed (i.e., when the UE has been inactive for a period of time). In embodiments herein, the inactivity timer may be variable. The inactivity timer may be changed based on the number of connected UEs in the cell. When the method for reducing the CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Therefore, a threshold for connected UEs in a cell may be defined. When the total number of connected UEs is below a threshold, the duration of the inactivity timer for the connected UE is reduced compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Therefore, when the method for managing the transmission of CRS is active, the connected UEs are released faster, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments of the present invention, parameters of the method described herein, such as the DRX inactivity timer length, the DRX onDuration period and length (which may also be referred to as the onDuration interval) and/or the TAC/DL data transmission period, may be adapted (which may also be referred to as being tailored or customized) according to different types of UEs. The UE's International Mobile Equipment Identity (IMEI) and/or IMEI Software Version (IMEISV) may be sent from the core network to the network node and may be used as identifiers to distinguish different UE types, such as different brands. In another embodiment, the core network node may identify the brand/type of the UE based on the IMEI or IMEISV and may send the brand of the UE to the network node. The network node may then adapt the parameters of the method based on the received UE type. In another embodiment, the UE and the network node may establish a proprietary protocol that may be used to identify the UE type/brand, for example at the MAC, RLC, PDCP or RRC layer. Based on the UE's identification, the UE may request the network node to adapt the above parameters in a manner that is beneficial to each UE type. The UE type may be identified by comparing the UE's IMEI and/or IMEISV with a database comprising IMEI:s and/or IMEISV:s for different UE types. Depending on the method of identifying the UE, the database may be stored in a network node or a core network node.

In other embodiments of the present invention, the parameters of the function can be adapted based on the mobile speed of the UE. The indication shows that, depending on the speed of the UE, the UE may need to transmit more or fewer CRS:s in the DL. The speed of the UE can be determined by the Doppler estimation performed by the network node (such as, for example, the eNodeB) in the uplink, and can be used as input to modify the parameters of the method in this article, such as the DRX inactivity timer length, the DRX onDuration period and length and/or the TAC/DL data transmission period. These parameters can be adapted so that a larger Doppler (i.e., a higher UE speed) will give the UE more opportunities to read the CRS, while a low Doppler estimate (i.e., a low speed of the UE) will trigger the opposite.

According to a second aspect of the embodiments herein, when a second cell is identified, the second cell is not actively serving any UE, which may also be referred to as serving a UE in IDLE mode, and the network node applies a reduced CRS bandwidth mode to the CRS transmitted in the second cell. In the reduced bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

In another embodiment, when the network node identifies that the cell is serving only UEs in idle mode, the paging frequency can be reduced while transmitting the subframes of these paging occasions with the full CRS bandwidth. In some other embodiments of the present invention, some surrounding subframes (e.g., a previous or subsequent subframe) can also be transmitted with the full CRS bandwidth. In order to minimize the number of subframes transmitted with the full CRS bandwidth, there can be only one paging occasion in each radio frame with paging. This paging occasion can be in subframe 9. Subframes 9 and 0 can be transmitted with full bandwidth only in those radio frames carrying paging, thereby improving the mobility of idle mode. In addition, all subframes including SIBs can be transmitted with the full CRS bandwidth to allow UEs to hear them. Subframes after or before subframe 9 can also be sent with full bandwidth.

To perform the method actions for managing transmission of CRS described above with respect to Figure 4, the network node 110 may include the following arrangement shown in Figure 5. As described above, the network node 110 operates one or more cells and is typically configured to transmit CRS in a first bandwidth mode.

The network node 110 comprises a radio circuit 401 for communicating with the UE 120, a communication circuit 402 for communicating with other network nodes, and a processing module 403. The communication module 402 may be, for example, an X2 interface.

The network node 110 is configured to identify whether the cells 130, 131, 132 are actively serving the set of UEs 121, which may also be referred to as the set of connected UEs, for example by means of an identification module 404. The set of UEs 121 may not be scheduled by the network node 110 for receiving transmissions from the cells. The network node 110 is further configured to, or includes a bandwidth adjustment module 405 configured to, apply a reduced CRS bandwidth pattern for CRSs in the first cell 130 relative to the first bandwidth pattern when the first cell is identified as actively serving the set of UEs 121.

The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to apply the reduced CRS bandwidth mode to CRS transmitted in any subframe except for subframes in which the network node 110 transmits system information, paging or random access response messages, or in which the UE 120 is assumed to perform measurements (such as subframes transmitted during the onDuration of the UE 120). In this embodiment, the network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to transmit CRS over the entire bandwidth of the subframe in subframes in which the network node 110 transmits system information, paging or random access response messages, or in which the UE 120 is assumed to perform measurements (such as subframes transmitted during the onDuration of the UE 120).

In another embodiment herein, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to apply the reduced CRS bandwidth mode to CRS transmitted in any subframe except the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which the UE 120 is assumed to perform measurements (such as a subframe transmitted during the onDuration of the UE 120). In this embodiment, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to transmit the CRS over the entire bandwidth in the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which the UE 120 is assumed to perform measurements (such as a subframe transmitted during the onDuration of the UE 120).

The network node 110 may also be configured, for example by means of the bandwidth adjustment module 405, to further be configured to send CRS only in PRBs used for transmission in subframes in which the network node 110 transmits system information, paging or random access response messages or in which the UE 120 is assumed to perform measurements, such as subframes sent during the onDuration of the UE 120.

In the embodiments herein, the network node 110 may be further configured to transmit CRS only in REs adjacent to REs mapped to the common search space of the PDCCH, for example, by means of the bandwidth adjustment module 405. The common search space includes REs used by the network node 110 to transmit control information that is common to all UEs 120.

The network node 110 may also be configured, for example, by means of the sending module 408, to send a message to all connected UEs in the cell, the message comprising a discontinuous reception (DRX) command. The DRX command may indicate a DRX mode for the connected UEs, wherein the onDuration of the DRX mode may be aligned between the UEs 120. The onDuration may also be aligned with the transmission of one or more subframes comprising a system information block (SIB). The network node may further be configured to apply a second CRS bandwidth mode to CRS in subframes that are not transmitted in the cell during the onDuration. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

The transmitting module 408 may be included in the radio circuit 401 within the network node 110 .

In order to reduce unnecessary switching between bandwidth modes, the network node 110 may also be configured to, or may include a bandwidth adjustment unit 405 further configured to, use a hysteresis function to reduce and/or increase the CRS bandwidth. By using the hysteresis function, when the number of connected UEs 120 changes, the network node 110 may not switch the bandwidth mode immediately, but instead may remain in one bandwidth mode for a period of time after the change in bandwidth mode in the cell has occurred.

In other embodiments of the present invention, the network node 110 may also be configured to, for example, be further configured by means of the bandwidth adjustment module 405 to send DL data to each UE in connected mode with a certain periodicity. Therefore, increased stability of measurements performed by the UE (such as RSRP, RSRQ or RSSI) can be provided. DL data may be sent during a period corresponding to the onDuration time of the UE. Tests have shown that the preferred period for DL data is approximately 2 seconds, i.e., DL data is sent to the UE approximately every 2 seconds. The periodically sent DL data may be any DL data. In one embodiment, a timing advance command (TAC) is sent as periodic DL data. CRS is sent in full bandwidth mode during the transmission of DL data, thereby providing CRS to the UE during the DL transmission and the subsequent inactivity time (also referred to as DRX-Inactivity time).

In other embodiments of the present invention, the network node 110 may also be configured to, for example, be further configured by means of the bandwidth adjustment module 405 to align the periodic DL data transmissions between connected UEs. Since each DL transmission starts the DRX inactivity timer as defined in 3GPPTS 36.321 v.9.6.0, CRS will be sent to each UE in full-bandwidth mode for the duration of the inactivity period. By aligning the periodic DL data transmissions between connected UEs, the number of subframes in which full-spectrum CRS needs to be sent is reduced. This improves the gain when many users are connected by ensuring that the full-bandwidth CRS sent during each UE DRX-Inactivity timer overlaps in time and thereby maximizes the number of subframes in which CRS can be muted. This can further improve the performance of the cell.

In other embodiments of the present invention, the network node 110 may be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to start an inactivity timer that releases the connected UE and forces the UE to enter idle mode after a certain period of inactivity. The inactivity timer may be variable. When the method for reducing the CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Therefore, a threshold value for connected UEs in a cell may be defined. When the total number of connected UEs is below a threshold, the duration of the inactivity timer for the connected UE is reduced compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Therefore, when the method for managing the transmission of CRS is active, the connected UEs are released faster, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments herein, the network node 110 may be configured to, for example, further be configured to, according to different types of UEs, adapt or tailor parameters of the methods described herein, such as DRX inactivity timer length, DRX onDuration periodicity and length, and/or TAC/DL data transmission period. The network node 110 may also be configured to, for example, further be configured to, according to different types of UEs, identify/distinguish different UE types based on the UE's IMEI that may be received by the network node 110 from the core network node, for example, by means of the identification module 404.

The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to adapt the parameters of the method according to the brand/type of the UE received and identified by the core network node based on the UE's IMEI. The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to establish a proprietary protocol for identifying the UE type, for example, at the media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), or RRC layer. Based on the identification of the UE, the network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to adapt the above parameters in a manner that is beneficial to each UE type.

In other embodiments herein, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to adapt parameters of the method based on the UE's speed. The indication indicates that, depending on the UE's speed, the UE may need to transmit more or fewer CRSs in the DL. The network node 110 may also be further configured, for example, by means of the bandwidth adjustment module 405, to perform Doppler estimation in the UL to determine the UE's speed. The network node 110 may also be further configured, for example, by means of the bandwidth adjustment module 405, to modify parameters of the method herein based on the Doppler estimation, such as the DRX inactivity timer length, the DRX onDuration period and length, and/or the TAC/DL data transmission period. The parameters may be adapted such that a greater Doppler (i.e., a higher speed of the UE 120) provides the UE 120 with more opportunities to read CRSs, while a lower Doppler estimate (i.e., a lower speed of the UE 120) triggers the opposite.

In other embodiments, the network node 110 may be further configured to receive the IMEI of the UE 120 or the identified type of the UE 120 from the core network node 140, for example by means of the receiving module 407. The receiving module may be included in the communication circuit 402.

The embodiments for managing CRS transmission herein can be implemented by one or more processors (such as the processing module 403 in the network node 110 depicted in FIG5 ) together with computer program code for performing the functions and actions of the embodiments herein. The above program code can also be provided as a computer program product, for example, in the form of a data carrier carrying computer program code for executing the embodiments herein when loaded into the network node 110. One such carrier can be in the form of a CD ROM disc. However, other data carriers such as memory sticks are also feasible. The computer program code can also be provided on a server as pure program code and downloaded to the network node 110 and/or core network node.

The network node 110 may further comprise a memory 406 comprising one or more memory units. The memory 406 is arranged for storing acquired information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

Figures 6a and 6b disclose scheduling diagrams for DRX and bandwidth modes according to two embodiments of the above method. To prevent the reduced bandwidth mode from negatively impacting (such as corrupting) mobility measurements such as cell evaluation or best cell evaluation, subframes transmitted during the onDuration of the DRX mode or subframes transmitting system information are transmitted in the first bandwidth mode (also referred to as the full bandwidth mode).

Figure 6a discloses an embodiment of the method, wherein the CRS is transmitted over full bandwidth over a total of thirteen subframes arranged around the subframe of onDuration. Four of the thirteen subframes are located before the two subframes of each onDuration, and seven of these subframes are located after each onDuration. A reduced bandwidth mode is applied to the remaining subframes of the radio frame. Tests have shown that some legacy UEs may not perform measurements as accurately as other UEs and may start measurements briefly before or after onDuration. By transmitting the CRS in normal bandwidth mode in multiple subframes located around onDuration, it is ensured that such less accurate UEs are able to measure the CRS in order to perform channel estimation, even if the measurements are not performed exactly during the onDuration.

FIG6 b shows another embodiment of a method in which the number of subframes in which CRS is transmitted using the full bandwidth is reduced. In this embodiment, the normal bandwidth mode is applied only to subframes transmitted during the onDuration period or one subframe before the subframe in which system information is transmitted. Thus, the number of subframes in which CRS can be transmitted using the reduced bandwidth is increased, further improving network performance. This embodiment can be used when UE 120 connected to a cell provides high-precision measurements.

The network node 110 may adapt the number of subframes in which CRS is transmitted over the full bandwidth based on the type of UE 120 connected to the cell. The type of UE 120 may be identified based on an identifier such as IMEI or the brand/type of UE 120.

Some of the method actions for managing the transmission of CRS described above with respect to FIG3 may be performed by core network node 140. Core network node 140 may include the following arrangement depicted in FIG7. Core network node 140 may include communication circuitry 601 and a processing module 602 for communicating with other network nodes. Communication circuitry 601 may be, for example, an X2 interface.

The core network node 140 may be configured to identify/distinguish different UE brands/types based on the UE's IMEI, for example, by means of the identification module 603 . The identification module 603 may be included in the processing unit 602 .

The core network node 140 may also be configured to send an indication of the brand/type to the network node, for example, by means of a sending module 604. The indication may be the IMEI of the UE or the brand/type of the UE identified by the core network node 140. The sending module 604 may be included in the communication circuit 601.

The embodiments for managing CRS transmission herein can be implemented by one or more processors (such as the processing module 602 in the core network node shown in FIG7 ) together with computer program code for performing the functions and actions of the embodiments herein. The above program code can also be provided as a computer program product, for example, in the form of a data carrier carrying the computer program code for executing the embodiments herein when loaded into the core network node. One such carrier can be in the form of a CD ROM disk. However, other data carriers such as memory sticks are also feasible. The computer program code can also be provided on a server as pure program code and downloaded to the network node 110 and/or the core network node.

The network node 110 may further comprise a memory 406 comprising one or more memory units. The memory 406 is arranged for storing obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

The core network node may further comprise a memory 605 comprising one or more memory units. The memory 605 is arranged for storing obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the core network node.

Those skilled in the art will also understand that the identification modules 404, 603 and bandwidth adjustment module 405 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, which are stored in, for example, memory 406, 660 and executed by one or more processors such as processing units 403, 602 as described above. One or more of these processors and other digital hardware may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed across several separate components, whether packaged separately or assembled into a system-on-chip (SoC).

When the word "comprise" or "comprising" is used, it should be interpreted as non-limiting, ie meaning "consisting at least of. . . . . "

When the word "set" is used herein, it should be interpreted to mean "one or more."

The embodiments herein are not limited to the preferred embodiments described above. Various substitutions, modifications, and equivalents may be used. Therefore, the above embodiments should not be considered to limit the scope of the present invention, which is defined by the appended claims.

Network node and method in wireless telecommunication network

Technical Field

Embodiments herein relate to a network node and methods therein. Specifically, a method and a network node for managing transmission of a cell reference signal are disclosed.

Background Art

A communication device, such as a user equipment (UE), is enabled to communicate wirelessly in a cellular communication network or wireless communication system (sometimes also referred to as a cellular radio system or cellular network). Communication can be performed, for example, between two UEs, between a UE and a regular phone, and/or between a UE and a server via a radio access network (RAN) and possibly one or more core networks included in the cellular communication network.

To name a few other examples, a UE may also be referred to as a wireless terminal, a mobile terminal and/or a mobile station, a mobile phone, a cellular phone, a laptop computer, a tablet computer, or a surfboard with wireless capabilities. A UE in this context may be, for example, a portable, pocket-storable, handheld, computer-built-in, or vehicle-mounted mobile device that is enabled to communicate voice and/or data with another entity, such as another wireless terminal or a server, via a RAN.

A cellular communication network covers a geographical area divided into cell areas, where each cell area is served by a network node. A cell is a geographical area where a network node provides radio coverage.

A network node may further control several transmission points, for example, including radio units (RRUs). Thus, a cell may include one or more network nodes, each controlling one or more transmission/reception points. A transmission point, also referred to as a transmission/reception point, is an entity that transmits and/or receives radio signals. This entity has a location in space, such as an antenna. A network node is an entity that controls one or more transmission points. Depending on the technology and terminology used, a network node may be, for example, a base station such as a radio base station (RBS), eNB, eNodeB, NodeB, B-node, or base transceiver station (BTS). Base stations may be of different types, such as macro eNodeB, home eNodeB, or pico base station, based on transmission power and, therefore, cell size.

In addition, each network node can support one or several communication technologies. The network node communicates with UEs within range of the network node over an air interface operated by radio frequency. In the context of this disclosure, the term downlink (DL) is used for the transmission path from the base station to the mobile station. The term uplink (UL) is used for the transmission path in the opposite direction (i.e., from the UE to the base station).

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks. In LTE, the cellular communication network is also referred to as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN).

An E-UTRAN cell is defined by certain signals broadcast from the eNB. These signals contain information about the cell that can be used by a UE to connect to the network via the cell. The signals include reference and synchronization signals that the UE uses to find frame timing and physical cell identity, as well as system information that includes parameters related to the entire cell.

Therefore, a UE that needs to connect to the network must first detect a suitable cell, as defined in 3GPP TS 36.304v11.5.0. The UE can be in an idle state, also known as IDLE or radio resource control idle (RRC_IDLE); or in a connected state, which is also known as CONNECTED or radio resource control connected (RRC_CONNECTED). When the UE is in RRC_IDLE, it monitors the paging channel, which is part of the Paging Control Channel (PCCH) at the logical layer, the Paging Channel (PCH) at the transport channel layer, and the Physical Downlink Shared Channel (PDSCH) at the physical channel layer. In doing so, the UE typically also performs a number of radio measurements that the UE uses to evaluate the best cell, such as Reference Signal Received Power (RSRP), Reference Symbol Received Quality (RSRQ), or Received Signal Strength Indicator (RSSI). This is performed by measuring the received reference signal and/or the portion of the spectrum that includes the reference signal sent by the cell. This can also be referred to as "listening" for a suitable cell.

A suitable cell is typically a cell with an RSRQ or RSRP above a certain level. The cell with the highest RSRP or RSRQ may be referred to as the best cell or the most suitable cell. Sensing a suitable cell may include searching for a reference signal transmitted from a network node in an orthogonal frequency division multiplexing (OFDM) subframe. When the most suitable cell is found, the UE performs random access based on the system information for the cell. This is done to transmit a radio resource control (RRC) connection establishment request to the network node. Assuming the random access procedure is successful and the network node receives the request, the network node will respond with an RRC connection establishment message or an RRC connection rejection. The RRC connection establishment message confirms the UE's request and informs it to enter the RRC_CONNECTED state. The RRC connection rejection informs the UE that it may not be able to connect to the cell. In the RRC_CONNECTED state, the parameters required for communication between the network node and the UE are known to the two entities, and data transfer between the two entities is enabled.

When the UE is in the RRC_CONNECTED state, the UE continues to measure RSRP as an input to connected mode mobility decisions, such as, for example, deciding when to perform a handover from one cell to another. These measurements are typically performed in the full bandwidth of a subframe (which may also be referred to as full spectrum).

RSRP is a measure of the signal strength of an LTE cell. It helps the UE rank different cells based on their signal strength, which serves as an input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying the cell-specific reference signal (CRS) across the entire bandwidth. Therefore, RSRP is only measured in OFDM symbols that carry CRS.

The RRC protocol handles control plane signaling at the network layer (also called layer 3) between the UE and a network node, which may also be referred to as a UTRAN or E-UTRAN node. At any one time, only one RRC connection can be open between the UE and a network node.

The network layer may also include:

Connection establishment and release functions,

Broadcasting of system information,

Radio bearer establishment/reconfiguration and release,

RRC connection mobility procedures,

· Paging notification and release,

Outer loop power control.

To support UEs connecting to a cell (also referred to as an access cell), a system information block (SIB) is transmitted in a control channel such as the broadcast control channel (BCCH) logical channel in the downlink, which can be mapped to the PDSCH physical channel. In LTE, a number of different SIBs are defined, characterized by the information they carry. For example, SIB1 carries cell access related parameters, such as information about the operator of the cell, restrictions on what users can access the cell, and allocation of uplink/downlink subframes. SIB1 also carries information about the scheduling of other SIBs.

To reduce UE power consumption, discontinuous reception (DRX) can be implemented. The fundamental mechanism in DRX is a configurable DRX cycle in the UE, also known as a DRX mode. When a DRX cycle is configured, the UE monitors control signaling only during the onDuration interval of the DRX cycle. The onDuration interval can be one or more subframes, which can be referred to as one or more active subframes. During the remaining subframes of the DRX cycle, the UE can shut down its receiver, which can also be referred to as UE sleep, or the offDuration interval of the DRX cycle. This allows for a significant reduction in power consumption: the longer the DRX cycle and the shorter the onDuration interval, the lower the power consumption. In certain situations, if a UE is already scheduled and active for receiving or transmitting data in a subframe, it may be scheduled again in the near future. Waiting until the next active subframe according to the DRX cycle may result in additional delays in transmission. Therefore, to reduce latency, the UE can remain active for a configurable time after being scheduled, which can also be referred to as the activity time or the inactivity timer (DRX-Inactivity Timer) defined in 3GPP TS 36.321 Ch 3.1. The duration of the active time is set by the inactivity timer, which is the duration in downlink subframes from the last successful decoding of the physical downlink control channel (PDCCH) to the duration the UE waits before shutting down and re-entering the offDuration. The UE can restart the inactivity timer after a single successful decoding of the PDCCH for a transmission. The time it takes for the UE to re-enter the offDuration after the last transmission can also be called the inactivity time.

To facilitate handovers to other cells, each network node can store the cell identifiers of cells supported by other network nodes in an address database, so that it knows how to contact the network node of a potential target cell for handover. Each network node serving a cell typically stores in a database the cells with which it has neighbor relationships, i.e., the cells in the area to which UEs frequently perform handovers. Hereinafter, a cell's neighbor relationships are referred to as its "neighbor relationship list."

CRS is a UE-known symbol inserted in the resource elements (REs) of the subframes of the OFDM time and frequency grid and broadcast by the network node. Each RE has an extension in the frequency domain corresponding to an OFDM subcarrier and an extension in the time domain corresponding to an OFDM symbol interval.

The UE uses CRS for downlink channel estimation. Channel estimation is used for demodulation of downlink data when the UE is in RRC_CONNECTED state and is receiving user data and when the UE is in RRC_IDLE state and is reading system information. Due to the latter use case, the network node cannot know whether the UE wants to access the network before the UE performs random access, so even the cells without any UE in RRC connected state must transmit CRS from it. The downlink CRS is inserted into the first and third to last OFDM symbol of each time slot with a frequency domain spacing of six subcarriers. A time slot is a time period of the OFDM time and frequency grid, typically 0.5 milliseconds long. Therefore, a problem with the known technology is that the cells without any UE in RRC connected state still consume power due to the CRS broadcast.

In the case where a network node uses several antennas for transmission and each antenna represents a cell, each antenna must transmit a unique reference signal in order for the UE to connect to that specific cell. When one antenna transmits, the other antennas must be silent so as not to interfere with the first antenna reference signal. In order to reduce interference of reference signals between cells, the position of the CRS is usually shifted in frequency between cells. The CRS can be shifted between 0-5 subcarriers, and for LTE, each subcarrier corresponds to a frequency shift of 15kHz. The frequency shift can be derived from the physical cell identity (cell ID) that is signaled to the UE through the selection of the appropriate primary synchronization channel (PSCH) and secondary synchronization channel (SSCH).

Although this reduces the interference of reference symbols (eg, CRS symbols) between cells, there is a problem that the reference symbols of one cell may interfere with the PDSCH and PDCCH symbols of an adjacent cell.

Therefore, even if a cell does not have any UE in the RRC_CONNECTED state, interference may affect the UE DL throughput in a neighboring cell, especially when the UE is at and/or close to the boundary between cells.

Reducing the power of the CRS can alleviate this problem. However, in order to access a cell, the UE must be able to hear the CRS of the cell, that is, the UE must be able to identify and receive the CRS transmitted from the cell. Therefore, reducing the power of the CRS also reduces the size of the cell, because UEs farther away will no longer hear the CRS sent by the cell. In addition, when the signal-to-interference ratio (SINR) on the CRS decreases, the quality of the channel estimate used for demodulation decreases. Therefore, reducing the power of the CRS leads to degradation of cell edge performance. When the load in the network increases, especially if data is transmitted at a higher power than the CRS, which is usually the case when the impact of CRS interference will be reduced, this degradation will be further exacerbated, resulting in reduced performance of the wireless communication network.

Summary of the Invention

It is therefore an object of embodiments herein to enhance performance in wireless communication networks.

According to a first aspect of embodiments herein, the object is achieved by a method performed by a network node for managing transmission of a Cell Reference Signal, CRS.

The network node operates one or more cells. The network node identifies whether the cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node sends CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in one or more CRS subframes in which system information is sent. The network node also sends CRS on a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in one or more CRS subframes other than the subframes in which system information is sent. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception (DRX), the network node sends CRS on a first bandwidth in one or more CRS subframes transmitted in the cell during the onDuration interval of the DRX mode and/or in one or more CRS subframes in which system information is sent and/or in one or more CRS subframes in which downlink DL data is sent. The network node further transmits the CRS on a second bandwidth in a CRS subframe that is not transmitted in the cell during the onDuration interval of DRX, and/or in one or more CRS subframes other than the CRS subframe in which system information is transmitted, and/or in one or more CRS subframes other than the CRS subframe in which downlink (DL) data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

According to a second aspect of the embodiments of this document, the purpose is achieved by a network node configured to manage the transmission of a cell reference signal (CRS). The network node operates one or more cells. The network node is configured to identify whether the cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node is configured to transmit CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in a CRS subframe in which system information is transmitted. The network node is further configured to transmit CRS on a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in a CRS subframe other than a CRS subframe in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception (DRX), the network node is further configured to transmit a CRS on a first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX mode, and/or in a CRS subframe in which system information is transmitted, and/or in a CRS subframe in which downlink (DL) data is transmitted. The network node is further configured to transmit a CRS on a second bandwidth in a CRS subframe that is not transmitted in the cell during an onDuration interval of the DRX mode, and/or in a CRS subframe other than a CRS subframe in which system information is transmitted, and/or in a CRS subframe other than a CRS subframe in which downlink (DL) data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

By applying the reduced bandwidth mode to CRS transmitted in all subframes except for subframes transmitted during or related to the onDuration in the cell, or subframes in which or related to subframes in which system information such as SIBs are transmitted, power consumption and interference from the cell can be reduced, thereby enhancing the performance of neighboring cells transmitting data. In other words, the reduced bandwidth mode is applied during the period when no data transmission occurs and the UE turns off its receiver and enters a low power mode.

By applying reduced bandwidth mode to CRS in cells that do not serve any UE in RRC connected mode, power consumption and interference from null cells may be reduced, thereby enhancing the performance of cells with UEs in RRC connected mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein are described in more detail with reference to the accompanying drawings, in which:

FIG1 is a schematic block diagram illustrating an embodiment of a wireless communication network.

FIG2 is a schematic block diagram illustrating embodiments of an OFDM subframe.

FIG3 is a flow chart depicting a first embodiment of a method in a network node.

FIG4 is a flow chart depicting a second embodiment of a method in a network node.

FIG5 is a schematic block diagram illustrating embodiments of a network node.

FIG6 a is a scheduling diagram illustrating a first embodiment of the method herein.

FIG6 b is a scheduling diagram illustrating a first embodiment of the method herein.

FIG7 is a schematic block diagram illustrating embodiments of a core network node.

DETAILED DESCRIPTION

the term

The following general terms are used in the examples and are explained below:

Radio network node: In some embodiments, the non-limiting term radio network node is more generally used and refers to any type of network node that serves a UE and/or is connected to other network nodes or network elements, or any radio node from which a UE receives signals. Examples of radio network nodes are Node B, Base Station (BS), MSR radio node such as a Multi-Standard Radio (MSR) BS, eNode B, network controller, Radio Network Controller (RNC), Base Station Controller, relay, donor node controlled relay, Base Transceiver Station (BTS), Access Point (AP), Transmission Point, Transmission Node, RRU, RRH, a node in a Distributed Antenna System (DAS), etc.

Network node: In some embodiments, the more general term "network node" is used, which may correspond to any type of radio network node or any network node that communicates with at least a radio network node. Examples of network nodes are any of the radio network nodes mentioned above, core network nodes (e.g., mobile switching center (MSC), mobility management entity (MME), etc.), operation and maintenance (O&M) center, operation support system (OSS), self-organizing network (SON), positioning node (e.g., evolved serving mobile positioning center (E-SMLC), master data telegraph (MDT), etc.).

User Equipment: In some embodiments, the non-limiting term User Equipment (UE) is used to refer to any type of wireless device that communicates with a radio network node in a cellular communication system or a mobile communication system. Examples of UEs are target devices, device-to-device UEs, machine-type UEs or UEs with machine-to-machine communication capabilities, PDAs, iPADs, tablet computers, mobile terminals, smartphones, laptop embedded equipment (LEEs), laptop mounted equipment (LMEs), USB dongles, etc.

The embodiments herein are also applicable to a multi-point carrier aggregation system.

Note that although terminology from 3GPP LTE has been used in this disclosure to exemplify the embodiments herein, this should not be considered to limit the scope of the embodiments herein to only that system. Other wireless systems including WCDMA, WiMax, UMB, and GSM may also benefit from utilizing the ideas covered by this disclosure.

It should also be noted that terms such as eNodeB and UE should be considered non-restrictive and, in particular, do not imply a hierarchical relationship between the two. In general, "eNodeB" can be considered as device 1 and "UE" can be considered as device 2, and the two devices communicate with each other via some radio channel. In this article, we also focus on wireless transmission in the downlink, but the embodiments herein are equally applicable to the uplink.

In this section, the embodiments of this invention will be described in more detail through a plurality of exemplary embodiments. It should be noted that these embodiments are not mutually exclusive. Components of one embodiment may be assumed to exist in another embodiment by default, and it will be apparent to those skilled in the art how these components may be used in other exemplary embodiments.

1 depicts an example of a wireless communication network 100 according to a first scenario in which embodiments herein may be implemented. The wireless communication network 100 is a wireless communication network such as LTE, E-UTRAN, WCDMA, GSM network, any 3GPP cellular network, Wimax or any cellular network or system.

The wireless communication network 100 includes a plurality of network nodes, two of which (a first network node 110 and a second network node 111) are depicted in FIG1 . The first network node 110 and the second network node 111 are network nodes, each of which can be a transmission point such as a radio base station, for example, an eNB, eNodeB, or a Home NodeB, Home eNodeB, or any other network node capable of serving wireless terminals such as user equipment or machine type communication devices in the wireless communication network. The first network node 110 and the second network node 111 each serve a plurality of cells 130, 131, 132.

Wireless communication network 100 includes a UE set 121, which may include one or more UEs 120. First network node 110 and second network node 111 may each be a transmission point for UE 120. UE 120 is within radio range of first network node 110 and second network node 111, meaning it can hear signals from first network node 110 and second network node 111. One or more UEs 120 may also exist in each cell, and one or more UEs 120 may also be referred to as a UE set 121.

The UE 120 in the UE set 121 may be, for example, a wireless terminal, a wireless device, a mobile wireless terminal or a wireless terminal, a mobile phone, a computer such as a laptop with wireless capabilities, a personal digital assistant (PDA) or a tablet (sometimes called a surfboard), or any other radio network element capable of communicating via a radio link in a wireless communication network. Note that the term wireless terminal used in this document also covers other wireless devices such as machine-to-machine (M2M) devices.

Figure 2 shows an exemplary downlink OFDM time and frequency grid, which may also be referred to as an OFDM subframe. Each subframe includes two time slots. Each time slot includes multiple resource elements (REs) 201 extending in both the time domain (x-axis) and the frequency domain (z-axis). The extension of each RE 201 in the frequency domain may be referred to as a subcarrier, while the extension in the time domain may be referred to as an OFDM symbol. In the time domain, LTE downlink transmissions are organized into 10ms radio frames, where each radio frame includes ten subframes of equal size. Furthermore, resource allocation in LTE may generally be described in terms of physical resource blocks (PRBs) comprising multiple REs. A resource block corresponds to one time slot in the time domain and 12 consecutive subcarriers in the frequency domain.

Downlink and uplink transmissions are dynamically scheduled, i.e., in each subframe, the first network node 110 transmits control information about which UE 120 to or from which data and on which resource blocks the data is transmitted. The control information may include system information, paging messages, and/or random access response messages. One or more PDCCHs may be used to transmit control information for a given UE 120. The control information of the PDCCH is transmitted in the control region of each subframe. Figure 2 shows an exemplary size of a conventional control region of three OFDM symbols allocated for control signaling (e.g., PDCCH). However, the size of the control region may be dynamically adjusted based on the current traffic situation. In the example shown in the figure, only the first OFDM symbol of the three possible OFDM symbols is used for control signaling. In general, the control region may include multiple PDCCHs that carry control information for multiple UEs 120 simultaneously. The REs used for control signaling are represented by wavy lines, and the REs used for CRS are represented by diagonal lines.

UE 120 uses CRS for downlink channel estimation. Channel estimation is used to determine the demodulation of downlink data when UE 120 is in RRC connected state, and when UE 120 is in RRC idle state and is reading system information. Downlink CRS can be inserted into the first and third-to-last OFDM symbols of each time slot with a frequency domain interval of six subcarriers. RSRP is a measurement of the signal strength of an LTE cell, which helps UE 120 to sort between different cells as an input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying cell-specific reference signals (CRS) over the entire bandwidth. Therefore, it is only measured in OFDM symbols carrying CRS.

The subframe also includes data symbols for transmitting user data between the first network node 110 and the UE 120. The data symbols are located in a region following the control region, also called the data region.

A first example of embodiments of a method in a network node 110 for managing transmission of a Cell Reference Signal (CRS) will now be described with reference to the flowchart depicted in Figure 3. The network node 110 operates one or more cells 130, 131, 132 which may or may not serve a set 121 of UEs.

The method may include the following actions, which may be performed in any suitable order: The dashed lines of the boxes in Figure 3 indicate that this operation is not mandatory.

Action 301

The network node 110 identifies whether a cell among the one or more cells 130, 131, 132 is actively serving the set of UEs 121. A cell actively serving the set of UEs 121 may also be referred to as a cell having a set of connected UEs, and a cell not actively serving the set of connected UEs 121 may be referred to as an empty cell. This action 301 may be performed by an identification module 404 within a network node (such as the network node 110). This action corresponds to action 401 described below.

When the network node 110 has identified a cell that is not actively serving the set of UEs 121, the network node performs actions 302 and 303 described below. Although actions 302 and 303 are depicted as following each other, the actions may be performed simultaneously.

Action 302

When the network node 110 has identified cells that are not actively serving the set of UEs 121 , the network node 110 transmits CRS over the first bandwidth in one or more CRS subframes transmitted during paging occasions and/or in one or more CRS subframes transmitting system information.

Action 303

When the network node 110 has identified cells that are not actively serving the set of UEs 121, the network node 110 further transmits CRS using a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in one or more CRS subframes other than subframes in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth.

In another embodiment herein, paging occasions may be sent in one CRS subframe per radio frame with paging only in cells that do not serve the set of UEs 121. Thus, the number of CRS subframes that must be sent with the first bandwidth is reduced, which allows the network node 110 to reduce the bandwidth in a higher number of CRS subframes.

When the network node has identified a cell that is actively serving the set of UEs (121) configured for discontinuous reception (DRX), the network node 110 performs actions 304 and 305 described below. Although actions 304 and 305 are depicted as following each other, the actions may be performed simultaneously.

Action 304

When the network node has identified a cell that is actively serving a set of UEs (121) configured for discontinuous reception (DRX), the network node 110 transmits CRS subframes over a first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX mode, and/or in one or more CRS subframes transmitting system information, and/or in one or more CRS subframes transmitting downlink (DL) data.

In other embodiments, the network node 110 may also transmit the CRS using the first bandwidth in a CRS subframe transmitted immediately before or after the CRS subframe transmitted during the paging occasion and/or in a CRS subframe transmitting system information and/or during the onDuration period and/or in a CRS subframe transmitting DL data.

Action 305

When the network node has identified a cell that is actively serving the set of UEs (121) configured for discontinuous reception (DRX), the network node 110 further transmits a CRS using a second bandwidth in a CRS subframe that is not transmitted in the cell during the onDuration interval of DRX, and/or in one or more CRS subframes other than CRS subframes for transmitting system information, and/or in one or more CRS subframes other than CRS subframes for transmitting DL data. The second bandwidth is reduced relative to the first bandwidth. This action 305 corresponds to action 402 described below, and therefore the embodiments described for action 402 can also be applied to this action 305.

Action 306

When the network node 110 has identified the cell that is actively serving the UE set, the network node 110 may also send a message including a DRX command to the UE set 121. The DRX command indicates the DRX mode for the UE set 121, which may also be referred to as a DRX cycle. The indicated DRX mode is the DRX mode that the UE set 121 will use. For the UEs 120 included in the UE set 121, the onDurations of the DRX modes are aligned so that the UEs 120 have overlapping onDuration intervals. By aligning the onDuration intervals of the UEs 120, the UEs can be grouped, i.e., the UEs will have overlapping onDurations. This has the advantage that the timing of transmitting CRS in the first bandwidth mode can be reduced and the number of subframes in which CRS is transmitted via the second bandwidth is increased. This will further improve the performance of the cell.

This action 306 corresponds to action 403 described below, so the embodiment described for action 403 can also be applied to this action 306 .

By sending a message including a command indicating the onDuration of the DRX mode to all connected UEs in the cell, the UEs can be grouped together, i.e., the UEs are configured with overlapping onDurations. By doing so, the performance of the cell can be further improved because the times when CRS must be transmitted at full bandwidth can be minimized because each UE performs radio measurements such as RSRP, RSRQ, or RSSI in the same time interval.

Another example of an embodiment of a method for managing the transmission of cell reference signals (CRS) in a network node 110 will now be described with reference to the flowchart shown in FIG4 . The network node 110 operates one or more cells and is configured to transmit CRS in a first bandwidth mode during operation. This relates to normal operation. The first bandwidth mode, which may also be referred to as normal bandwidth mode, is used when at least one cell of the network node 110 is serving at least one UE 120 in RRC connected mode and the at least one UE 120 is scheduled to receive data. In normal bandwidth mode, CRS is transmitted over the entire available bandwidth of a DL radio frame (RF), i.e., the CRS is transmitted in all physical resource blocks (PRBs) of the cell.

The method may include the following actions, which may be performed in any suitable order: The dashed lines in the boxes in Figure 4 indicate that this operation is not mandatory.

Action 401

The network node 110 identifies a cell serving a set of UEs 121 (which may also be referred to as a set of connected UEs). The set of UEs 121 is configured for discontinuous reception (DRX). The set of UEs 121 may include one or more UEs 120. The set of UEs 121 is not scheduled by the network node for receiving a transmission from the network node sent in one of the network node's cells. This may mean that the network node has not yet scheduled the set of UEs 121 for receiving a transmission sent from the network node 110 in the cell, or that a certain time (T) has passed since the set of UEs 121 was scheduled for transmission in the UL or DL. The time T may be a time set in a DRX inactivity timer. This action 401 may be performed by an identification module 404 within a network node, such as the network node 110.

Action 402

When the network node 110 has identified a first cell serving a set of UEs 121 that are not scheduled by the network node 110, the network node 110 applies a second bandwidth mode (also referred to as a reduced CRS bandwidth mode) to CRSs in subframes not transmitted in the cell during the onDuration of DRX or in subframes in which system information is transmitted. In another embodiment, the reduced CRS bandwidth mode may also be applied to CRSs transmitted in subframes not transmitted with respect to the onDuration or related to subframes in which system information is transmitted, which may be, for example, subframes directly before or after the onDuration or subframes in which system information is transmitted. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode. The system information may be, for example, a system information block (SIB). This reduced bandwidth mode may also be referred to as a low bandwidth mode. The low bandwidth mode means that the network node 110 does not transmit CRSs in all PRBs of the subframes of the cell. By reducing the bandwidth of the CRSs, i.e., transmitting the CRSs only on a portion of the available bandwidth of the DL radio frame, the overall interference from the CRSs of the cell 130 is reduced. Reducing interference from cell 130 increases throughput in neighboring cells 131 , as well as increasing RRC connections and scheduled UEs 120 .

Studies have shown that when the CRS bandwidth is reduced, mobility measurements (also known as cell evaluation or best cell evaluation, such as RSRP) may be negatively affected. This may cause the UE to make incorrect decisions about which cell it should camp on. When the UE120 performs mobility measurements on a neighboring cell, only a limited part of the bandwidth is considered. This limited part of the bandwidth may be, for example, the center six PRBs of a subframe. However, when the UE performs measurements on the cell in which it camps (which may also be referred to as its own cell), the entire bandwidth is taken into account. If the bandwidth used to send CRS in a cell is reduced, the CRS will only be sent in a part of the bandwidth (e.g., in the center six PRBs). However, RSRP is calculated as the average power of all REs carrying CRS over the entire bandwidth. Since the power of the CRS sent in, for example, the center six PRBs is averaged over the entire bandwidth, not just over the reduced bandwidth, the RSRP of the own cell may appear to be lower than that of the neighboring cell. This may cause the UE to connect to (which may also be referred to as performing handover to) a neighboring cell that appears to be better but is actually worse. This may cause the UE to start performing multiple handovers back and forth between cells, which can also be called a ping-pong effect, because the neighboring cell evaluated only on the central six PRBs will always appear to be better.

To prevent the reduced bandwidth mode from negatively affecting (such as corrupting) mobility measurements (such as cell evaluation or best cell evaluation), subframes transmitted during the onDuration of DRX or subframes in which system information is sent are transmitted first, which may also be referred to as normal bandwidth mode.

In another embodiment, CRS may also be transmitted in normal bandwidth mode in subframes surrounding the subframe transmitted during onDuration. In one embodiment, normal bandwidth mode may apply to multiple subframes before or after the subframe transmitted during onDuration. The number of subframes transmitted in normal bandwidth mode may be up to 25 subframes, including the subframe transmitted during onDuration. The onDuration period may occur over two subframes. In another embodiment, normal bandwidth mode may apply to the four subframes before the onDuration period and the seven subframes after the onDuration period, for a total of thirteen subframes. By transmitting CRS in normal bandwidth mode in subframes surrounding the onDuration period, legacy UEs that do not perform measurements as precisely as modern UEs can measure CRS for channel estimation, even if the measurements are not performed precisely during the onDuration period. Depending on the accuracy of the measurements performed by the UE, the number of subframes in which CRS is transmitted in normal bandwidth mode may be reduced. In another embodiment, normal bandwidth mode may, for example, apply to a subframe preceding the subframe transmitted during onDuration or the subframe in which system information is transmitted. Thus, it can be ensured that the CRS is sent over the entire bandwidth when the UE performs measurements during the onDuration period (ie in normal bandwidth mode). This embodiment is depicted in FIG6 .

In yet another embodiment, the CRS may also be transmitted in normal bandwidth mode during the UE's inactive time.

Having a long DRX cycle (i.e., a long time between DRX onDurations) can further be beneficial because it enables the network node 110 to apply the reduced bandwidth mode over a greater number of subframes. In one embodiment herein, the DRX cycle (which may also be referred to as the period of the DRX pattern) may be in the range of 20ms to 320ms. In another embodiment herein, the DRX cycle may be in the range of 20ms to 80ms. In yet another embodiment, the DRX cycle may be 40ms long. Studies have shown that this is the preferred period at which UEs typically read RSRP in order to assess the channel conditions in the cell to which they are connected.

Action 402 may be performed by a bandwidth adjustment module within a network node, such as network node 110 .

Action 403

In another embodiment herein, network node 110 may send a message to UE set 121, the message including a discontinuous reception (DRX) command. This command indicates a DRX cycle, wherein the onDuration (also referred to as the onDuration interval) of the DRX mode is aligned for the UEs included in UE set 121. Thus, the UEs can be grouped, i.e., the UEs will have overlapping onDurations. This has the advantage of reducing the number of times CRS is transmitted in the first bandwidth mode, further improving cell performance.

In another embodiment herein, the onDuration of the DRX mode can be aligned with the transmission of one or more subframes containing system information, such as system information blocks (SIBs). In another embodiment herein, the onDuration is aligned with SIB 1. Since SIB 1 includes parameters related to cell access and information regarding the scheduling of other SIBs, SIB 1 is transmitted even if the remaining SIBs are not transmitted. Since the number of subframes transmitted in the first bandwidth mode can be further reduced, aligning the onDuration of the set of UEs 121 with the transmission of SIB 1 further improves cell performance. Aligning the onDuration with SIB 1 further reduces losses, as SIB 1 is transmitted with the full CRS bandwidth regardless. SIB 1 can be transmitted with a 20ms period in subframe 5, which may also be referred to as SFN mod 2 = 0. Through forced DRX, a UE can be triggered (which may also be referred to as being incentivized, commanded, forced, or tricked) to always evaluate the status of the current cell when CRS is transmitted in full bandwidth mode and to reduce bandwidth when the connected UE is dormant. The trigger can be sent in a DRX command that sets the onDuration of the DRX cycle. The DRX mode may be applied to the UE 120 in order to trigger the evaluation of RSRP and other measurements for time slots in cases where the network node has transmitted CRS over the entire bandwidth (ie, in normal bandwidth mode).

In another embodiment, the network node 110 may force the UE to enter DRX sleep by sending a 3GPP DRX command MacControlElement (such as defined in 3GPP TS 36.321 v11.5.0 Ch 6.1.3.3 and referred to as a DRX command MAC control element). The MacControl element may include an indication to stop the DRX inactivity timer and/or the onDuration timer.

In other embodiments herein, when the number of connected UEs in a cell exceeds a certain threshold, the alignment of the onDuration of the DRX mode and/or the application of the reduced CRS bandwidth may be deactivated.

Action 403 may be performed by a transmitting module within a network node, such as network node 110. The transmitting module may also be comprised in a radio circuit within a network node, such as the described network node.

In one embodiment herein, a reduced CRS bandwidth mode is applied to CRSs transmitted in any subframe except for subframes in which the network node 110 transmits system information, paging, or random access response messages, or subframes in which the network node 110 assumes that the UE 120 is performing measurements. By applying the reduced CRS bandwidth mode in all subframes except for the aforementioned subframes, interference from the CRS is reduced while allowing the UE 120 in the neighboring cells 131, 132 to hear the CRS from the null cell 130. This is necessary to enable the UE 120 to obtain information about the modulation of the signal so that it can demodulate the downlink control channel of the cell. In this embodiment, the network node 110 may transmit CRSs across the entire bandwidth in subframes in which the network node 110 transmits system information such as SIBs, paging, or random access response messages, or in which the UE 120 is assumed to be performing measurements.

In another embodiment herein, the network node 110 transmits the CRS in PRBs used for transmission of data or control information only in subframes in which the network node 110 transmits system information, paging or random access response messages, or assumes that the UE performs measurements.

The network node 110 may also transmit the CRS in REs adjacent to the REs mapped to the common search space of the PDCCH. Thus, the CRS is transmitted only in the area where the UE is searching for the PDCCH. Consequently, the number of subframes in which the CRS can be transmitted on the second bandwidth increases, further improving the performance of the wireless communication network.

The CRS bandwidth can be further adapted to multiple levels. For LTE, the bandwidth in cell 130 can vary, for example, between 1.4 MHz and 20 MHz. However, other bandwidths are also possible depending on the technology used.

In another embodiment, a hysteresis function may be applied when changing the CRS bandwidth level, thereby avoiding unnecessary switching between bandwidth modes when the cell 130 switches from the first bandwidth mode to the second bandwidth mode.

In another embodiment herein, for services requiring Voice over IP (VoIP) or other "constanton" types, the UE can be moved to the lowest frequency band with the best coverage, while the CRS can be muted on higher frequency bands. Moving voice users on LTE to the lowest frequency band can be beneficial because these users are active and require coverage. This facilitates carrier aggregation.

In another embodiment herein, some UEs may be configured with a channel quality indicator (CQI) on the physical uplink control channel (PUCCH) that may be aligned with the DRX onDuration, while some UEs may not be configured with CQI on the PUCCH. Thus, the onDuration periods may be stacked more closely. Intelligent selection of UEs to be given PUCCH CQIs may be achieved by, for example, looking at the path loss so as not to degrade system coverage. UEs with high path loss may be configured with CQI on the PUCCH, while others may not.

In another embodiment herein, dynamic reconfiguration of paging frames and paging occasions may be performed, thereby reducing CRS transmissions performed in normal bandwidth mode while maintaining sufficient paging capacity.

In another embodiment, coordination over X2 can be performed between interfering cells. Thus, the interfering cells can inform each other which subframes to transmit in reduced bandwidth mode (also referred to as blank subframes) and which subframes to transmit in normal bandwidth mode (also referred to as non-blank subframes). This can enable different network nodes to have different outer loop adjustment values for blank subframes versus non-blank subframes, which can improve link adaptation results.

In other embodiments of the present invention, DL data may be sent to each UE in connected mode with a certain period. This has been shown to increase the stability of measurements (such as RSRP, RSRQ, or RSSI) performed by the UE. DL data may be sent during a period corresponding to the time of the UE's onDuration. Tests have shown that the preferred period for DL data is approximately 2 seconds, i.e., DL data is sent to the DL approximately every 2 seconds. The periodically sent DL data may be any DL data. In one embodiment, a timing advance command (TAC) is sent as periodic DL data. CRS is sent in full bandwidth mode during the transmission of DL data, thereby providing CRS to the UE during the DL transmission and the subsequent inactivity time (also referred to as DRX-Inactivity time).

In other embodiments of this document, the CRS may also be transmitted using the first bandwidth or full bandwidth mode during UL transmission (eg, a subframe for sending UL data).

In other embodiments herein, periodic DL data transmissions may be aligned between connected UEs. Since each DL transmission starts an inactivity timer as defined in 3GPP TS 36.321 v.9.6.0, CRS will be sent to each UE in full bandwidth mode for the duration of the inactivity period. By aligning periodic DL data transmissions between connected UEs, the number of subframes in which full spectrum CRS needs to be transmitted is reduced. This improves the gain when many users are connected by ensuring that the full bandwidth CRS transmitted during each UE's DRX-Inactivity timer coincides in time, thereby maximizing the number of subframes in which CRS can be muted. This may further improve the performance of the cell.

In other embodiments herein, the connected UE may be released and forced into idle mode after an inactivity timer in the network node that monitors UE activity has elapsed (i.e., when the UE has been inactive for a period of time). In embodiments herein, the inactivity timer may be variable. The inactivity timer may be changed based on the number of connected UEs in the cell. When the method for reducing the CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Therefore, a threshold for connected UEs in a cell may be defined. When the total number of connected UEs is below a threshold, the duration of the inactivity timer for the connected UE is reduced compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Therefore, when the method for managing the transmission of CRS is active, the connected UEs are released faster, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments of the present invention, parameters of the method described herein, such as the DRX inactivity timer length, the DRX onDuration period and length (which may also be referred to as the onDuration interval) and/or the TAC/DL data transmission period, may be adapted (which may also be referred to as being tailored or customized) according to different types of UEs. The UE's International Mobile Equipment Identity (IMEI) and/or IMEI Software Version (IMEISV) may be sent from the core network to the network node and may be used as identifiers to distinguish different UE types, such as different brands. In another embodiment, the core network node may identify the brand/type of the UE based on the IMEI or IMEISV and may send the brand of the UE to the network node. The network node may then adapt the parameters of the method based on the received UE type. In another embodiment, the UE and the network node may establish a proprietary protocol that may be used to identify the UE type/brand, for example at the MAC, RLC, PDCP or RRC layer. Based on the UE's identification, the UE may request the network node to adapt the above parameters in a manner that is beneficial to each UE type. The UE type may be identified by comparing the UE's IMEI and/or IMEISV with a database comprising IMEI:s and/or IMEISV:s for different UE types. Depending on the method of identifying the UE, the database may be stored in a network node or a core network node.

In other embodiments of the present invention, the parameters of the function can be adapted based on the mobile speed of the UE. The indication shows that, depending on the speed of the UE, the UE may need to transmit more or fewer CRS:s in the DL. The speed of the UE can be determined by the Doppler estimation performed by the network node (such as, for example, the eNodeB) in the uplink, and can be used as input to modify the parameters of the method in this article, such as the DRX inactivity timer length, the DRX onDuration period and length and/or the TAC/DL data transmission period. These parameters can be adapted so that a larger Doppler (i.e., a higher UE speed) will give the UE more opportunities to read the CRS, while a low Doppler estimate (i.e., a low speed of the UE) will trigger the opposite.

According to a second aspect of the embodiments herein, when a second cell is identified, the second cell is not actively serving any UE, which may also be referred to as serving a UE in IDLE mode, and the network node applies a reduced CRS bandwidth mode to the CRS transmitted in the second cell. In the reduced bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

In another embodiment, when the network node identifies that the cell is serving only UEs in idle mode, the paging frequency can be reduced while transmitting the subframes of these paging occasions with the full CRS bandwidth. In some other embodiments of the present invention, some surrounding subframes (e.g., a previous or subsequent subframe) can also be transmitted with the full CRS bandwidth. In order to minimize the number of subframes transmitted with the full CRS bandwidth, there can be only one paging occasion in each radio frame with paging. This paging occasion can be in subframe 9. Subframes 9 and 0 can be transmitted with full bandwidth only in those radio frames carrying paging, thereby improving the mobility of idle mode. In addition, all subframes including SIBs can be transmitted with the full CRS bandwidth to allow UEs to hear them. Subframes after or before subframe 9 can also be sent with full bandwidth.

To perform the method actions for managing transmission of CRS described above with respect to Figure 4, the network node 110 may include the following arrangement shown in Figure 5. As described above, the network node 110 operates one or more cells and is typically configured to transmit CRS in a first bandwidth mode.

The network node 110 comprises a radio circuit 401 for communicating with the UE 120, a communication circuit 402 for communicating with other network nodes, and a processing module 403. The communication module 402 may be, for example, an X2 interface.

The network node 110 is configured to identify whether the cells 130, 131, 132 are actively serving the set of UEs 121, which may also be referred to as the set of connected UEs, for example by means of an identification module 404. The set of UEs 121 may not be scheduled by the network node 110 for receiving transmissions from the cells. The network node 110 is further configured to, or includes a bandwidth adjustment module 405 configured to, apply a reduced CRS bandwidth pattern for CRSs in the first cell 130 relative to the first bandwidth pattern when the first cell is identified as actively serving the set of UEs 121.

The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to apply the reduced CRS bandwidth mode to CRS transmitted in any subframe except for subframes in which the network node 110 transmits system information, paging or random access response messages, or in which the UE 120 is assumed to perform measurements (such as subframes transmitted during the onDuration of the UE 120). In this embodiment, the network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to transmit CRS over the entire bandwidth of the subframe in subframes in which the network node 110 transmits system information, paging or random access response messages, or in which the UE 120 is assumed to perform measurements (such as subframes transmitted during the onDuration of the UE 120).

In another embodiment herein, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to apply the reduced CRS bandwidth mode to CRS transmitted in any subframe except the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which the UE 120 is assumed to perform measurements (such as a subframe transmitted during the onDuration of the UE 120). In this embodiment, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to transmit the CRS over the entire bandwidth in the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which the UE 120 is assumed to perform measurements (such as a subframe transmitted during the onDuration of the UE 120).

The network node 110 may also be configured, for example by means of the bandwidth adjustment module 405, to further be configured to send CRS only in PRBs used for transmission in subframes in which the network node 110 transmits system information, paging or random access response messages or in which the UE 120 is assumed to perform measurements, such as subframes sent during the onDuration of the UE 120.

In the embodiments herein, the network node 110 may be further configured to transmit CRS only in REs adjacent to REs mapped to the common search space of the PDCCH, for example, by means of the bandwidth adjustment module 405. The common search space includes REs used by the network node 110 to transmit control information that is common to all UEs 120.

The network node 110 may also be configured, for example, by means of the sending module 408, to send a message to all connected UEs in the cell, the message comprising a discontinuous reception (DRX) command. The DRX command may indicate a DRX mode for the connected UEs, wherein the onDuration of the DRX mode may be aligned between the UEs 120. The onDuration may also be aligned with the transmission of one or more subframes comprising a system information block (SIB). The network node may further be configured to apply a second CRS bandwidth mode to CRS in subframes that are not transmitted in the cell during the onDuration. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

The transmitting module 408 may be included in the radio circuit 401 within the network node 110 .

In order to reduce unnecessary switching between bandwidth modes, the network node 110 may also be configured to, or may include a bandwidth adjustment unit 405 further configured to, use a hysteresis function to reduce and/or increase the CRS bandwidth. By using the hysteresis function, when the number of connected UEs 120 changes, the network node 110 may not switch the bandwidth mode immediately, but instead may remain in one bandwidth mode for a period of time after the change in bandwidth mode in the cell has occurred.

In other embodiments of the present invention, the network node 110 may also be configured to, for example, be further configured by means of the bandwidth adjustment module 405 to send DL data to each UE in connected mode with a certain periodicity. Therefore, increased stability of measurements performed by the UE (such as RSRP, RSRQ or RSSI) can be provided. DL data may be sent during a period corresponding to the onDuration time of the UE. Tests have shown that the preferred period for DL data is approximately 2 seconds, i.e., DL data is sent to the UE approximately every 2 seconds. The periodically sent DL data may be any DL data. In one embodiment, a timing advance command (TAC) is sent as periodic DL data. CRS is sent in full bandwidth mode during the transmission of DL data, thereby providing CRS to the UE during the DL transmission and the subsequent inactivity time (also referred to as DRX-Inactivity time).

In other embodiments of the present invention, the network node 110 may also be configured to, for example, be further configured by means of the bandwidth adjustment module 405 to align the periodic DL data transmissions between connected UEs. Since each DL transmission starts the DRX inactivity timer as defined in 3GPPTS 36.321 v.9.6.0, CRS will be sent to each UE in full-bandwidth mode for the duration of the inactivity period. By aligning the periodic DL data transmissions between connected UEs, the number of subframes in which full-spectrum CRS needs to be sent is reduced. This improves the gain when many users are connected by ensuring that the full-bandwidth CRS sent during each UE DRX-Inactivity timer overlaps in time and thereby maximizes the number of subframes in which CRS can be muted. This can further improve the performance of the cell.

In other embodiments of the present invention, the network node 110 may be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to start an inactivity timer that releases the connected UE and forces the UE to enter idle mode after a certain period of inactivity. The inactivity timer may be variable. When the method for reducing the CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Therefore, a threshold value for connected UEs in a cell may be defined. When the total number of connected UEs is below a threshold, the duration of the inactivity timer for the connected UE is reduced compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Therefore, when the method for managing the transmission of CRS is active, the connected UEs are released faster, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments herein, the network node 110 may be configured to, for example, further be configured to, according to different types of UEs, adapt or tailor parameters of the methods described herein, such as DRX inactivity timer length, DRX onDuration periodicity and length, and/or TAC/DL data transmission period. The network node 110 may also be configured to, for example, further be configured to, according to different types of UEs, identify/distinguish different UE types based on the UE's IMEI that may be received by the network node 110 from the core network node, for example, by means of the identification module 404.

The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to adapt the parameters of the method according to the brand/type of the UE received and identified by the core network node based on the UE's IMEI. The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to establish a proprietary protocol for identifying the UE type, for example, at the media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), or RRC layer. Based on the identification of the UE, the network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to adapt the above parameters in a manner that is beneficial to each UE type.

In other embodiments herein, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to adapt parameters of the method based on the UE's speed. The indication indicates that, depending on the UE's speed, the UE may need to transmit more or fewer CRSs in the DL. The network node 110 may also be further configured, for example, by means of the bandwidth adjustment module 405, to perform Doppler estimation in the UL to determine the UE's speed. The network node 110 may also be further configured, for example, by means of the bandwidth adjustment module 405, to modify parameters of the method herein based on the Doppler estimation, such as the DRX inactivity timer length, the DRX onDuration period and length, and/or the TAC/DL data transmission period. The parameters may be adapted such that a greater Doppler (i.e., a higher speed of the UE 120) provides the UE 120 with more opportunities to read CRSs, while a lower Doppler estimate (i.e., a lower speed of the UE 120) triggers the opposite.

In other embodiments, the network node 110 may be further configured to receive the IMEI of the UE 120 or the identified type of the UE 120 from the core network node 140, for example by means of the receiving module 407. The receiving module may be included in the communication circuit 402.

The embodiments for managing CRS transmission herein can be implemented by one or more processors (such as the processing module 403 in the network node 110 depicted in FIG5 ) together with computer program code for performing the functions and actions of the embodiments herein. The above program code can also be provided as a computer program product, for example, in the form of a data carrier carrying computer program code for executing the embodiments herein when loaded into the network node 110. One such carrier can be in the form of a CD ROM disc. However, other data carriers such as memory sticks are also feasible. The computer program code can also be provided on a server as pure program code and downloaded to the network node 110 and/or core network node.

The network node 110 may further comprise a memory 406 comprising one or more memory units. The memory 406 is arranged for storing acquired information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

Figures 6a and 6b disclose scheduling diagrams for DRX and bandwidth modes according to two embodiments of the above method. To prevent the reduced bandwidth mode from negatively impacting (such as corrupting) mobility measurements such as cell evaluation or best cell evaluation, subframes transmitted during the onDuration of the DRX mode or subframes transmitting system information are transmitted in the first bandwidth mode (also referred to as the full bandwidth mode).

Figure 6a discloses an embodiment of the method, wherein the CRS is transmitted over full bandwidth over a total of thirteen subframes arranged around the subframe of onDuration. Four of the thirteen subframes are located before the two subframes of each onDuration, and seven of these subframes are located after each onDuration. A reduced bandwidth mode is applied to the remaining subframes of the radio frame. Tests have shown that some legacy UEs may not perform measurements as accurately as other UEs and may start measurements briefly before or after onDuration. By transmitting the CRS in normal bandwidth mode in multiple subframes located around onDuration, it is ensured that such less accurate UEs are able to measure the CRS in order to perform channel estimation, even if the measurements are not performed exactly during the onDuration.

FIG6 b shows another embodiment of a method in which the number of subframes in which CRS is transmitted using the full bandwidth is reduced. In this embodiment, the normal bandwidth mode is applied only to subframes transmitted during the onDuration period or one subframe before the subframe in which system information is transmitted. Thus, the number of subframes in which CRS can be transmitted using the reduced bandwidth is increased, further improving network performance. This embodiment can be used when UE 120 connected to a cell provides high-precision measurements.

The network node 110 may adapt the number of subframes in which CRS is transmitted over the full bandwidth based on the type of UE 120 connected to the cell. The type of UE 120 may be identified based on an identifier such as IMEI or the brand/type of UE 120.

Some of the method actions for managing the transmission of CRS described above with respect to FIG3 may be performed by core network node 140. Core network node 140 may include the following arrangement depicted in FIG7. Core network node 140 may include communication circuitry 601 and a processing module 602 for communicating with other network nodes. Communication circuitry 601 may be, for example, an X2 interface.

The core network node 140 may be configured to identify/distinguish different UE brands/types based on the UE's IMEI, for example, by means of the identification module 603 . The identification module 603 may be included in the processing unit 602 .

The core network node 140 may also be configured to send an indication of the brand/type to the network node, for example, by means of a sending module 604. The indication may be the IMEI of the UE or the brand/type of the UE identified by the core network node 140. The sending module 604 may be included in the communication circuit 601.

The embodiments for managing CRS transmission herein can be implemented by one or more processors (such as the processing module 602 in the core network node shown in FIG7 ) together with computer program code for performing the functions and actions of the embodiments herein. The above program code can also be provided as a computer program product, for example, in the form of a data carrier carrying the computer program code for executing the embodiments herein when loaded into the core network node. One such carrier can be in the form of a CD ROM disk. However, other data carriers such as memory sticks are also feasible. The computer program code can also be provided on a server as pure program code and downloaded to the network node 110 and/or the core network node.

The network node 110 may further comprise a memory 406 comprising one or more memory units. The memory 406 is arranged for storing obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

The core network node may further comprise a memory 605 comprising one or more memory units. The memory 605 is arranged for storing obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the core network node.

Those skilled in the art will also understand that the identification modules 404, 603 and bandwidth adjustment module 405 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, which are stored in, for example, memory 406, 660 and executed by one or more processors such as processing units 403, 602 as described above. One or more of these processors and other digital hardware may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed across several separate components, whether packaged separately or assembled into a system-on-chip (SoC).

When the word "comprise" or "comprising" is used, it should be interpreted as non-limiting, ie meaning "consisting at least of. . . . . "

When the word "set" is used herein, it should be interpreted to mean "one or more."

The embodiments herein are not limited to the preferred embodiments described above. Various substitutions, modifications, and equivalents may be used. Therefore, the above embodiments should not be considered to limit the scope of the present invention, which is defined by the appended claims.

Technical Field

Embodiments herein relate to a network node and methods therein. Specifically, a method and a network node for managing transmission of a cell reference signal are disclosed.

Background Art

A communication device, such as a user equipment (UE), is enabled to communicate wirelessly in a cellular communication network or wireless communication system (sometimes also referred to as a cellular radio system or cellular network). Communication can be performed, for example, between two UEs, between a UE and a regular phone, and/or between a UE and a server via a radio access network (RAN) and possibly one or more core networks included in the cellular communication network.

To name a few other examples, a UE may also be referred to as a wireless terminal, a mobile terminal and/or a mobile station, a mobile phone, a cellular phone, a laptop computer, a tablet computer, or a surfboard with wireless capabilities. A UE in this context may be, for example, a portable, pocket-storable, handheld, computer-built-in, or vehicle-mounted mobile device that is enabled to communicate voice and/or data with another entity, such as another wireless terminal or a server, via a RAN.

A cellular communication network covers a geographical area divided into cell areas, where each cell area is served by a network node. A cell is a geographical area where a network node provides radio coverage.

A network node may further control several transmission points, for example, including radio units (RRUs). Thus, a cell may include one or more network nodes, each controlling one or more transmission/reception points. A transmission point, also referred to as a transmission/reception point, is an entity that transmits and/or receives radio signals. This entity has a location in space, such as an antenna. A network node is an entity that controls one or more transmission points. Depending on the technology and terminology used, a network node may be, for example, a base station such as a radio base station (RBS), eNB, eNodeB, NodeB, B-node, or base transceiver station (BTS). Base stations may be of different types, such as macro eNodeB, home eNodeB, or pico base station, based on transmission power and, therefore, cell size.

In addition, each network node can support one or several communication technologies. The network node communicates with UEs within range of the network node over an air interface operated by radio frequency. In the context of this disclosure, the term downlink (DL) is used for the transmission path from the base station to the mobile station. The term uplink (UL) is used for the transmission path in the opposite direction (i.e., from the UE to the base station).

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks. In LTE, the cellular communication network is also referred to as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN).

An E-UTRAN cell is defined by certain signals broadcast from the eNB. These signals contain information about the cell that can be used by a UE to connect to the network via the cell. The signals include reference and synchronization signals that the UE uses to find frame timing and physical cell identity, as well as system information that includes parameters related to the entire cell.

Therefore, a UE that needs to connect to the network must first detect a suitable cell, as defined in 3GPP TS 36.304v11.5.0. The UE can be in an idle state, also known as IDLE or radio resource control idle (RRC_IDLE); or in a connected state, which is also known as CONNECTED or radio resource control connected (RRC_CONNECTED). When the UE is in RRC_IDLE, it monitors the paging channel, which is part of the Paging Control Channel (PCCH) at the logical layer, the Paging Channel (PCH) at the transport channel layer, and the Physical Downlink Shared Channel (PDSCH) at the physical channel layer. In doing so, the UE typically also performs a number of radio measurements that the UE uses to evaluate the best cell, such as Reference Signal Received Power (RSRP), Reference Symbol Received Quality (RSRQ), or Received Signal Strength Indicator (RSSI). This is performed by measuring the received reference signal and/or the portion of the spectrum that includes the reference signal sent by the cell. This can also be referred to as "listening" for a suitable cell.

A suitable cell is typically a cell with an RSRQ or RSRP above a certain level. The cell with the highest RSRP or RSRQ may be referred to as the best cell or the most suitable cell. Sensing a suitable cell may include searching for a reference signal transmitted from a network node in an orthogonal frequency division multiplexing (OFDM) subframe. When the most suitable cell is found, the UE performs random access based on the system information for the cell. This is done to transmit a radio resource control (RRC) connection establishment request to the network node. Assuming the random access procedure is successful and the network node receives the request, the network node will respond with an RRC connection establishment message or an RRC connection rejection. The RRC connection establishment message confirms the UE's request and informs it to enter the RRC_CONNECTED state. The RRC connection rejection informs the UE that it may not be able to connect to the cell. In the RRC_CONNECTED state, the parameters required for communication between the network node and the UE are known to the two entities, and data transfer between the two entities is enabled.

When the UE is in the RRC_CONNECTED state, the UE continues to measure RSRP as an input to connected mode mobility decisions, such as, for example, deciding when to perform a handover from one cell to another. These measurements are typically performed in the full bandwidth of a subframe (which may also be referred to as full spectrum).

RSRP is a measure of the signal strength of an LTE cell. It helps the UE rank different cells based on their signal strength, which serves as an input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying the cell-specific reference signal (CRS) across the entire bandwidth. Therefore, RSRP is only measured in OFDM symbols that carry CRS.

The RRC protocol handles control plane signaling at the network layer (also called layer 3) between the UE and a network node, which may also be referred to as a UTRAN or E-UTRAN node. At any one time, only one RRC connection can be open between the UE and a network node.

The network layer may also include:

Connection establishment and release functions,

Broadcasting of system information,

Radio bearer establishment/reconfiguration and release,

RRC connection mobility procedures,

· Paging notification and release,

Outer loop power control.

To support UEs connecting to a cell (also referred to as an access cell), a system information block (SIB) is transmitted in a control channel such as the broadcast control channel (BCCH) logical channel in the downlink, which can be mapped to the PDSCH physical channel. In LTE, a number of different SIBs are defined, characterized by the information they carry. For example, SIB1 carries cell access related parameters, such as information about the operator of the cell, restrictions on what users can access the cell, and allocation of uplink/downlink subframes. SIB1 also carries information about the scheduling of other SIBs.

To reduce UE power consumption, discontinuous reception (DRX) can be implemented. The fundamental mechanism in DRX is a configurable DRX cycle in the UE, also known as a DRX mode. When a DRX cycle is configured, the UE monitors control signaling only during the onDuration interval of the DRX cycle. The onDuration interval can be one or more subframes, which can be referred to as one or more active subframes. During the remaining subframes of the DRX cycle, the UE can shut down its receiver, which can also be referred to as UE sleep, or the offDuration interval of the DRX cycle. This allows for a significant reduction in power consumption: the longer the DRX cycle and the shorter the onDuration interval, the lower the power consumption. In certain situations, if a UE is already scheduled and active for receiving or transmitting data in a subframe, it may be scheduled again in the near future. Waiting until the next active subframe according to the DRX cycle may result in additional delays in transmission. Therefore, to reduce latency, the UE can remain active for a configurable time after being scheduled, which can also be referred to as the activity time or the inactivity timer (DRX-Inactivity Timer) defined in 3GPP TS 36.321 Ch 3.1. The duration of the active time is set by the inactivity timer, which is the duration in downlink subframes from the last successful decoding of the physical downlink control channel (PDCCH) to the duration the UE waits before shutting down and re-entering the offDuration. The UE can restart the inactivity timer after a single successful decoding of the PDCCH for a transmission. The time it takes for the UE to re-enter the offDuration after the last transmission can also be called the inactivity time.

To facilitate handovers to other cells, each network node can store the cell identifiers of cells supported by other network nodes in an address database, so that it knows how to contact the network node of a potential target cell for handover. Each network node serving a cell typically stores in a database the cells with which it has neighbor relationships, i.e., the cells in the area to which UEs frequently perform handovers. Hereinafter, a cell's neighbor relationships are referred to as its "neighbor relationship list."

CRS is a UE-known symbol inserted in the resource elements (REs) of the subframes of the OFDM time and frequency grid and broadcast by the network node. Each RE has an extension in the frequency domain corresponding to an OFDM subcarrier and an extension in the time domain corresponding to an OFDM symbol interval.

The UE uses CRS for downlink channel estimation. Channel estimation is used for demodulation of downlink data when the UE is in RRC_CONNECTED state and is receiving user data and when the UE is in RRC_IDLE state and is reading system information. Due to the latter use case, the network node cannot know whether the UE wants to access the network before the UE performs random access, so even the cells without any UE in RRC connected state must transmit CRS from it. The downlink CRS is inserted into the first and third to last OFDM symbol of each time slot with a frequency domain spacing of six subcarriers. A time slot is a time period of the OFDM time and frequency grid, typically 0.5 milliseconds long. Therefore, a problem with the known technology is that the cells without any UE in RRC connected state still consume power due to the CRS broadcast.

In the case where a network node uses several antennas for transmission and each antenna represents a cell, each antenna must transmit a unique reference signal in order for the UE to connect to that specific cell. When one antenna transmits, the other antennas must be silent so as not to interfere with the first antenna reference signal. In order to reduce interference of reference signals between cells, the position of the CRS is usually shifted in frequency between cells. The CRS can be shifted between 0-5 subcarriers, and for LTE, each subcarrier corresponds to a frequency shift of 15kHz. The frequency shift can be derived from the physical cell identity (cell ID) that is signaled to the UE through the selection of the appropriate primary synchronization channel (PSCH) and secondary synchronization channel (SSCH).

Although this reduces the interference of reference symbols (eg, CRS symbols) between cells, there is a problem that the reference symbols of one cell may interfere with the PDSCH and PDCCH symbols of an adjacent cell.

Therefore, even if a cell does not have any UE in the RRC_CONNECTED state, interference may affect the UE DL throughput in a neighboring cell, especially when the UE is at and/or close to the boundary between cells.

Reducing the power of the CRS can alleviate this problem. However, in order to access a cell, the UE must be able to hear the CRS of the cell, that is, the UE must be able to identify and receive the CRS transmitted from the cell. Therefore, reducing the power of the CRS also reduces the size of the cell, because UEs farther away will no longer hear the CRS sent by the cell. In addition, when the signal-to-interference ratio (SINR) on the CRS decreases, the quality of the channel estimate used for demodulation decreases. Therefore, reducing the power of the CRS leads to degradation of cell edge performance. When the load in the network increases, especially if data is transmitted at a higher power than the CRS, which is usually the case when the impact of CRS interference will be reduced, this degradation will be further exacerbated, resulting in reduced performance of the wireless communication network.

Summary of the Invention

It is therefore an object of embodiments herein to enhance performance in wireless communication networks.

According to a first aspect of embodiments herein, the object is achieved by a method performed by a network node for managing transmission of a Cell Reference Signal, CRS.

The network node operates one or more cells. The network node identifies whether the cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node sends CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in one or more CRS subframes in which system information is sent. The network node also sends CRS on a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in one or more CRS subframes other than the subframes in which system information is sent. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception (DRX), the network node sends CRS on a first bandwidth in one or more CRS subframes transmitted in the cell during the onDuration interval of the DRX mode and/or in one or more CRS subframes in which system information is sent and/or in one or more CRS subframes in which downlink DL data is sent. The network node further transmits the CRS on a second bandwidth in a CRS subframe that is not transmitted in the cell during the onDuration interval of DRX, and/or in one or more CRS subframes other than the CRS subframe in which system information is transmitted, and/or in one or more CRS subframes other than the CRS subframe in which downlink (DL) data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

According to a second aspect of the embodiments of this document, the purpose is achieved by a network node configured to manage the transmission of a cell reference signal (CRS). The network node operates one or more cells. The network node is configured to identify whether the cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node is configured to transmit CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in a CRS subframe in which system information is transmitted. The network node is further configured to transmit CRS on a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in a CRS subframe other than a CRS subframe in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception (DRX), the network node is further configured to transmit a CRS on a first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX mode, and/or in a CRS subframe in which system information is transmitted, and/or in a CRS subframe in which downlink (DL) data is transmitted. The network node is further configured to transmit a CRS on a second bandwidth in a CRS subframe that is not transmitted in the cell during an onDuration interval of the DRX mode, and/or in a CRS subframe other than a CRS subframe in which system information is transmitted, and/or in a CRS subframe other than a CRS subframe in which downlink (DL) data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

By applying the reduced bandwidth mode to CRS transmitted in all subframes except for subframes transmitted during or related to the onDuration in the cell, or subframes in which or related to subframes in which system information such as SIBs are transmitted, power consumption and interference from the cell can be reduced, thereby enhancing the performance of neighboring cells transmitting data. In other words, the reduced bandwidth mode is applied during the period when no data transmission occurs and the UE turns off its receiver and enters a low power mode.

By applying reduced bandwidth mode to CRS in cells that do not serve any UE in RRC connected mode, power consumption and interference from null cells may be reduced, thereby enhancing the performance of cells with UEs in RRC connected mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein are described in more detail with reference to the accompanying drawings, in which:

FIG1 is a schematic block diagram illustrating an embodiment of a wireless communication network.

FIG2 is a schematic block diagram illustrating embodiments of an OFDM subframe.

FIG3 is a flow chart depicting a first embodiment of a method in a network node.

FIG4 is a flow chart depicting a second embodiment of a method in a network node.

FIG5 is a schematic block diagram illustrating embodiments of a network node.

FIG6 a is a scheduling diagram illustrating a first embodiment of the method herein.

FIG6 b is a scheduling diagram illustrating a first embodiment of the method herein.

FIG7 is a schematic block diagram illustrating embodiments of a core network node.

DETAILED DESCRIPTION

the term

The following general terms are used in the examples and are explained below:

Radio network node: In some embodiments, the non-limiting term radio network node is more generally used and refers to any type of network node that serves a UE and/or is connected to other network nodes or network elements, or any radio node from which a UE receives signals. Examples of radio network nodes are Node B, Base Station (BS), MSR radio node such as a Multi-Standard Radio (MSR) BS, eNode B, network controller, Radio Network Controller (RNC), Base Station Controller, relay, donor node controlled relay, Base Transceiver Station (BTS), Access Point (AP), Transmission Point, Transmission Node, RRU, RRH, a node in a Distributed Antenna System (DAS), etc.

Network node: In some embodiments, the more general term "network node" is used, which may correspond to any type of radio network node or any network node that communicates with at least a radio network node. Examples of network nodes are any of the radio network nodes mentioned above, core network nodes (e.g., mobile switching center (MSC), mobility management entity (MME), etc.), operation and maintenance (O&M) center, operation support system (OSS), self-organizing network (SON), positioning node (e.g., evolved serving mobile positioning center (E-SMLC), master data telegraph (MDT), etc.).

User Equipment: In some embodiments, the non-limiting term User Equipment (UE) is used to refer to any type of wireless device that communicates with a radio network node in a cellular communication system or a mobile communication system. Examples of UEs are target devices, device-to-device UEs, machine-type UEs or UEs with machine-to-machine communication capabilities, PDAs, iPADs, tablet computers, mobile terminals, smartphones, laptop embedded equipment (LEEs), laptop mounted equipment (LMEs), USB dongles, etc.

The embodiments herein are also applicable to a multi-point carrier aggregation system.

Note that although terminology from 3GPP LTE has been used in this disclosure to exemplify the embodiments herein, this should not be considered to limit the scope of the embodiments herein to only that system. Other wireless systems including WCDMA, WiMax, UMB, and GSM may also benefit from utilizing the ideas covered by this disclosure.

It should also be noted that terms such as eNodeB and UE should be considered non-restrictive and, in particular, do not imply a hierarchical relationship between the two. In general, "eNodeB" can be considered as device 1 and "UE" can be considered as device 2, and the two devices communicate with each other via some radio channel. In this article, we also focus on wireless transmission in the downlink, but the embodiments herein are equally applicable to the uplink.

In this section, the embodiments of this invention will be described in more detail through a plurality of exemplary embodiments. It should be noted that these embodiments are not mutually exclusive. Components of one embodiment may be assumed to exist in another embodiment by default, and it will be apparent to those skilled in the art how these components may be used in other exemplary embodiments.

1 depicts an example of a wireless communication network 100 according to a first scenario in which embodiments herein may be implemented. The wireless communication network 100 is a wireless communication network such as LTE, E-UTRAN, WCDMA, GSM network, any 3GPP cellular network, Wimax or any cellular network or system.

The wireless communication network 100 includes a plurality of network nodes, two of which (a first network node 110 and a second network node 111) are depicted in FIG1 . The first network node 110 and the second network node 111 are network nodes, each of which can be a transmission point such as a radio base station, for example, an eNB, eNodeB, or a Home NodeB, Home eNodeB, or any other network node capable of serving wireless terminals such as user equipment or machine type communication devices in the wireless communication network. The first network node 110 and the second network node 111 each serve a plurality of cells 130, 131, 132.

Wireless communication network 100 includes a UE set 121, which may include one or more UEs 120. First network node 110 and second network node 111 may each be a transmission point for UE 120. UE 120 is within radio range of first network node 110 and second network node 111, meaning it can hear signals from first network node 110 and second network node 111. One or more UEs 120 may also exist in each cell, and one or more UEs 120 may also be referred to as a UE set 121.

The UE 120 in the UE set 121 may be, for example, a wireless terminal, a wireless device, a mobile wireless terminal or a wireless terminal, a mobile phone, a computer such as a laptop with wireless capabilities, a personal digital assistant (PDA) or a tablet (sometimes called a surfboard), or any other radio network element capable of communicating via a radio link in a wireless communication network. Note that the term wireless terminal used in this document also covers other wireless devices such as machine-to-machine (M2M) devices.

Figure 2 shows an exemplary downlink OFDM time and frequency grid, which may also be referred to as an OFDM subframe. Each subframe includes two time slots. Each time slot includes multiple resource elements (REs) 201 extending in both the time domain (x-axis) and the frequency domain (z-axis). The extension of each RE 201 in the frequency domain may be referred to as a subcarrier, while the extension in the time domain may be referred to as an OFDM symbol. In the time domain, LTE downlink transmissions are organized into 10ms radio frames, where each radio frame includes ten subframes of equal size. Furthermore, resource allocation in LTE may generally be described in terms of physical resource blocks (PRBs) comprising multiple REs. A resource block corresponds to one time slot in the time domain and 12 consecutive subcarriers in the frequency domain.

Downlink and uplink transmissions are dynamically scheduled, i.e., in each subframe, the first network node 110 transmits control information about which UE 120 to or from which data and on which resource blocks the data is transmitted. The control information may include system information, paging messages, and/or random access response messages. One or more PDCCHs may be used to transmit control information for a given UE 120. The control information of the PDCCH is transmitted in the control region of each subframe. Figure 2 shows an exemplary size of a conventional control region of three OFDM symbols allocated for control signaling (e.g., PDCCH). However, the size of the control region may be dynamically adjusted based on the current traffic situation. In the example shown in the figure, only the first OFDM symbol of the three possible OFDM symbols is used for control signaling. In general, the control region may include multiple PDCCHs that carry control information for multiple UEs 120 simultaneously. The REs used for control signaling are represented by wavy lines, and the REs used for CRS are represented by diagonal lines.

UE 120 uses CRS for downlink channel estimation. Channel estimation is used to determine the demodulation of downlink data when UE 120 is in RRC connected state, and when UE 120 is in RRC idle state and is reading system information. Downlink CRS can be inserted into the first and third-to-last OFDM symbols of each time slot with a frequency domain interval of six subcarriers. RSRP is a measurement of the signal strength of an LTE cell, which helps UE 120 to sort between different cells as an input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying cell-specific reference signals (CRS) over the entire bandwidth. Therefore, it is only measured in OFDM symbols carrying CRS.

The subframe also includes data symbols for transmitting user data between the first network node 110 and the UE 120. The data symbols are located in a region following the control region, also called the data region.

A first example of embodiments of a method in a network node 110 for managing transmission of a Cell Reference Signal (CRS) will now be described with reference to the flowchart depicted in Figure 3. The network node 110 operates one or more cells 130, 131, 132 which may or may not serve a set 121 of UEs.

The method may include the following actions, which may be performed in any suitable order: The dashed lines of the boxes in Figure 3 indicate that this operation is not mandatory.

Action 301

The network node 110 identifies whether a cell among the one or more cells 130, 131, 132 is actively serving the set of UEs 121. A cell actively serving the set of UEs 121 may also be referred to as a cell having a set of connected UEs, and a cell not actively serving the set of connected UEs 121 may be referred to as an empty cell. This action 301 may be performed by an identification module 404 within a network node (such as the network node 110). This action corresponds to action 401 described below.

When the network node 110 has identified a cell that is not actively serving the set of UEs 121, the network node performs actions 302 and 303 described below. Although actions 302 and 303 are depicted as following each other, the actions may be performed simultaneously.

Action 302

When the network node 110 has identified cells that are not actively serving the set of UEs 121 , the network node 110 transmits CRS over the first bandwidth in one or more CRS subframes transmitted during paging occasions and/or in one or more CRS subframes transmitting system information.

Action 303

When the network node 110 has identified cells that are not actively serving the set of UEs 121, the network node 110 further transmits CRS using a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in one or more CRS subframes other than subframes in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth.

In another embodiment herein, paging occasions may be sent in one CRS subframe per radio frame with paging only in cells that do not serve the set of UEs 121. Thus, the number of CRS subframes that must be sent with the first bandwidth is reduced, which allows the network node 110 to reduce the bandwidth in a higher number of CRS subframes.

When the network node has identified a cell that is actively serving the set of UEs (121) configured for discontinuous reception (DRX), the network node 110 performs actions 304 and 305 described below. Although actions 304 and 305 are depicted as following each other, the actions may be performed simultaneously.

Action 304

When the network node has identified a cell that is actively serving a set of UEs (121) configured for discontinuous reception (DRX), the network node 110 transmits CRS subframes over a first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX mode, and/or in one or more CRS subframes transmitting system information, and/or in one or more CRS subframes transmitting downlink (DL) data.

In other embodiments, the network node 110 may also transmit the CRS using the first bandwidth in a CRS subframe transmitted immediately before or after the CRS subframe transmitted during the paging occasion and/or in a CRS subframe transmitting system information and/or during the onDuration period and/or in a CRS subframe transmitting DL data.

Action 305

When the network node has identified a cell that is actively serving the set of UEs (121) configured for discontinuous reception (DRX), the network node 110 further transmits a CRS using a second bandwidth in a CRS subframe that is not transmitted in the cell during the onDuration interval of DRX, and/or in one or more CRS subframes other than CRS subframes for transmitting system information, and/or in one or more CRS subframes other than CRS subframes for transmitting DL data. The second bandwidth is reduced relative to the first bandwidth. This action 305 corresponds to action 402 described below, and therefore the embodiments described for action 402 can also be applied to this action 305.

Action 306

When the network node 110 has identified the cell that is actively serving the UE set, the network node 110 may also send a message including a DRX command to the UE set 121. The DRX command indicates the DRX mode for the UE set 121, which may also be referred to as a DRX cycle. The indicated DRX mode is the DRX mode that the UE set 121 will use. For the UEs 120 included in the UE set 121, the onDurations of the DRX modes are aligned so that the UEs 120 have overlapping onDuration intervals. By aligning the onDuration intervals of the UEs 120, the UEs can be grouped, i.e., the UEs will have overlapping onDurations. This has the advantage that the timing of transmitting CRS in the first bandwidth mode can be reduced and the number of subframes in which CRS is transmitted via the second bandwidth is increased. This will further improve the performance of the cell.

This action 306 corresponds to action 403 described below, so the embodiment described for action 403 can also be applied to this action 306 .

By sending a message including a command indicating the onDuration of the DRX mode to all connected UEs in the cell, the UEs can be grouped together, i.e., the UEs are configured with overlapping onDurations. By doing so, the performance of the cell can be further improved because the times when CRS must be transmitted at full bandwidth can be minimized because each UE performs radio measurements such as RSRP, RSRQ, or RSSI in the same time interval.

Another example of an embodiment of a method for managing the transmission of cell reference signals (CRS) in a network node 110 will now be described with reference to the flowchart shown in FIG4 . The network node 110 operates one or more cells and is configured to transmit CRS in a first bandwidth mode during operation. This relates to normal operation. The first bandwidth mode, which may also be referred to as normal bandwidth mode, is used when at least one cell of the network node 110 is serving at least one UE 120 in RRC connected mode and the at least one UE 120 is scheduled to receive data. In normal bandwidth mode, CRS is transmitted over the entire available bandwidth of a DL radio frame (RF), i.e., the CRS is transmitted in all physical resource blocks (PRBs) of the cell.

The method may include the following actions, which may be performed in any suitable order: The dashed lines in the boxes in Figure 4 indicate that this operation is not mandatory.

Action 401

The network node 110 identifies a cell serving a set of UEs 121 (which may also be referred to as a set of connected UEs). The set of UEs 121 is configured for discontinuous reception (DRX). The set of UEs 121 may include one or more UEs 120. The set of UEs 121 is not scheduled by the network node for receiving a transmission from the network node sent in one of the network node's cells. This may mean that the network node has not yet scheduled the set of UEs 121 for receiving a transmission sent from the network node 110 in the cell, or that a certain time (T) has passed since the set of UEs 121 was scheduled for transmission in the UL or DL. The time T may be a time set in a DRX inactivity timer. This action 401 may be performed by an identification module 404 within a network node, such as the network node 110.

Action 402

When the network node 110 has identified a first cell serving a set of UEs 121 that are not scheduled by the network node 110, the network node 110 applies a second bandwidth mode (also referred to as a reduced CRS bandwidth mode) to CRSs in subframes not transmitted in the cell during the onDuration of DRX or in subframes in which system information is transmitted. In another embodiment, the reduced CRS bandwidth mode may also be applied to CRSs transmitted in subframes not transmitted with respect to the onDuration or related to subframes in which system information is transmitted, which may be, for example, subframes directly before or after the onDuration or subframes in which system information is transmitted. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode. The system information may be, for example, a system information block (SIB). This reduced bandwidth mode may also be referred to as a low bandwidth mode. The low bandwidth mode means that the network node 110 does not transmit CRSs in all PRBs of the subframes of the cell. By reducing the bandwidth of the CRSs, i.e., transmitting the CRSs only on a portion of the available bandwidth of the DL radio frame, the overall interference from the CRSs of the cell 130 is reduced. Reducing interference from cell 130 increases throughput in neighboring cells 131 , as well as increasing RRC connections and scheduled UEs 120 .

Studies have shown that when the CRS bandwidth is reduced, mobility measurements (also known as cell evaluation or best cell evaluation, such as RSRP) may be negatively affected. This may cause the UE to make incorrect decisions about which cell it should camp on. When the UE120 performs mobility measurements on a neighboring cell, only a limited part of the bandwidth is considered. This limited part of the bandwidth may be, for example, the center six PRBs of a subframe. However, when the UE performs measurements on the cell in which it camps (which may also be referred to as its own cell), the entire bandwidth is taken into account. If the bandwidth used to send CRS in a cell is reduced, the CRS will only be sent in a part of the bandwidth (e.g., in the center six PRBs). However, RSRP is calculated as the average power of all REs carrying CRS over the entire bandwidth. Since the power of the CRS sent in, for example, the center six PRBs is averaged over the entire bandwidth, not just over the reduced bandwidth, the RSRP of the own cell may appear to be lower than that of the neighboring cell. This may cause the UE to connect to (which may also be referred to as performing handover to) a neighboring cell that appears to be better but is actually worse. This may cause the UE to start performing multiple handovers back and forth between cells, which can also be called a ping-pong effect, because the neighboring cell evaluated only on the central six PRBs will always appear to be better.

To prevent the reduced bandwidth mode from negatively affecting (such as corrupting) mobility measurements (such as cell evaluation or best cell evaluation), subframes transmitted during the onDuration of DRX or subframes in which system information is sent are transmitted first, which may also be referred to as normal bandwidth mode.

In another embodiment, CRS may also be transmitted in normal bandwidth mode in subframes surrounding the subframe transmitted during onDuration. In one embodiment, normal bandwidth mode may apply to multiple subframes before or after the subframe transmitted during onDuration. The number of subframes transmitted in normal bandwidth mode may be up to 25 subframes, including the subframe transmitted during onDuration. The onDuration period may occur over two subframes. In another embodiment, normal bandwidth mode may apply to the four subframes before the onDuration period and the seven subframes after the onDuration period, for a total of thirteen subframes. By transmitting CRS in normal bandwidth mode in subframes surrounding the onDuration period, legacy UEs that do not perform measurements as precisely as modern UEs can measure CRS for channel estimation, even if the measurements are not performed precisely during the onDuration period. Depending on the accuracy of the measurements performed by the UE, the number of subframes in which CRS is transmitted in normal bandwidth mode may be reduced. In another embodiment, normal bandwidth mode may, for example, apply to a subframe preceding the subframe transmitted during onDuration or the subframe in which system information is transmitted. Thus, it can be ensured that the CRS is sent over the entire bandwidth when the UE performs measurements during the onDuration period (ie in normal bandwidth mode). This embodiment is depicted in FIG6 .

In yet another embodiment, the CRS may also be transmitted in normal bandwidth mode during the UE's inactive time.

Having a long DRX cycle (i.e., a long time between DRX onDurations) can further be beneficial because it enables the network node 110 to apply the reduced bandwidth mode over a greater number of subframes. In one embodiment herein, the DRX cycle (which may also be referred to as the period of the DRX pattern) may be in the range of 20ms to 320ms. In another embodiment herein, the DRX cycle may be in the range of 20ms to 80ms. In yet another embodiment, the DRX cycle may be 40ms long. Studies have shown that this is the preferred period at which UEs typically read RSRP in order to assess the channel conditions in the cell to which they are connected.

Action 402 may be performed by a bandwidth adjustment module within a network node, such as network node 110 .

Action 403

In another embodiment herein, network node 110 may send a message to UE set 121, the message including a discontinuous reception (DRX) command. This command indicates a DRX cycle, wherein the onDuration (also referred to as the onDuration interval) of the DRX mode is aligned for the UEs included in UE set 121. Thus, the UEs can be grouped, i.e., the UEs will have overlapping onDurations. This has the advantage of reducing the number of times CRS is transmitted in the first bandwidth mode, further improving cell performance.

In another embodiment herein, the onDuration of the DRX mode can be aligned with the transmission of one or more subframes containing system information, such as system information blocks (SIBs). In another embodiment herein, the onDuration is aligned with SIB 1. Since SIB 1 includes parameters related to cell access and information regarding the scheduling of other SIBs, SIB 1 is transmitted even if the remaining SIBs are not transmitted. Since the number of subframes transmitted in the first bandwidth mode can be further reduced, aligning the onDuration of the set of UEs 121 with the transmission of SIB 1 further improves cell performance. Aligning the onDuration with SIB 1 further reduces losses, as SIB 1 is transmitted with the full CRS bandwidth regardless. SIB 1 can be transmitted with a 20ms period in subframe 5, which may also be referred to as SFN mod 2 = 0. Through forced DRX, a UE can be triggered (which may also be referred to as being incentivized, commanded, forced, or tricked) to always evaluate the status of the current cell when CRS is transmitted in full bandwidth mode and to reduce bandwidth when the connected UE is dormant. The trigger can be sent in a DRX command that sets the onDuration of the DRX cycle. The DRX mode may be applied to the UE 120 in order to trigger the evaluation of RSRP and other measurements for time slots in cases where the network node has transmitted CRS over the entire bandwidth (ie, in normal bandwidth mode).

In another embodiment, the network node 110 may force the UE to enter DRX sleep by sending a 3GPP DRX command MacControlElement (such as defined in 3GPP TS 36.321 v11.5.0 Ch 6.1.3.3 and referred to as a DRX command MAC control element). The MacControl element may include an indication to stop the DRX inactivity timer and/or the onDuration timer.

In other embodiments herein, when the number of connected UEs in a cell exceeds a certain threshold, the alignment of the onDuration of the DRX mode and/or the application of the reduced CRS bandwidth may be deactivated.

Action 403 may be performed by a transmitting module within a network node, such as network node 110. The transmitting module may also be comprised in a radio circuit within a network node, such as the described network node.

In one embodiment herein, a reduced CRS bandwidth mode is applied to CRSs transmitted in any subframe except for subframes in which the network node 110 transmits system information, paging, or random access response messages, or subframes in which the network node 110 assumes that the UE 120 is performing measurements. By applying the reduced CRS bandwidth mode in all subframes except for the aforementioned subframes, interference from the CRS is reduced while allowing the UE 120 in the neighboring cells 131, 132 to hear the CRS from the null cell 130. This is necessary to enable the UE 120 to obtain information about the modulation of the signal so that it can demodulate the downlink control channel of the cell. In this embodiment, the network node 110 may transmit CRSs across the entire bandwidth in subframes in which the network node 110 transmits system information such as SIBs, paging, or random access response messages, or in which the UE 120 is assumed to be performing measurements.

In another embodiment herein, the network node 110 transmits the CRS in PRBs used for transmission of data or control information only in subframes in which the network node 110 transmits system information, paging or random access response messages, or assumes that the UE performs measurements.

The network node 110 may also transmit the CRS in REs adjacent to the REs mapped to the common search space of the PDCCH. Thus, the CRS is transmitted only in the area where the UE is searching for the PDCCH. Consequently, the number of subframes in which the CRS can be transmitted on the second bandwidth increases, further improving the performance of the wireless communication network.

The CRS bandwidth can be further adapted to multiple levels. For LTE, the bandwidth in cell 130 can vary, for example, between 1.4 MHz and 20 MHz. However, other bandwidths are also possible depending on the technology used.

In another embodiment, a hysteresis function may be applied when changing the CRS bandwidth level, thereby avoiding unnecessary switching between bandwidth modes when the cell 130 switches from the first bandwidth mode to the second bandwidth mode.

In another embodiment herein, for services requiring Voice over IP (VoIP) or other "constanton" types, the UE can be moved to the lowest frequency band with the best coverage, while the CRS can be muted on higher frequency bands. Moving voice users on LTE to the lowest frequency band can be beneficial because these users are active and require coverage. This facilitates carrier aggregation.

In another embodiment herein, some UEs may be configured with a channel quality indicator (CQI) on the physical uplink control channel (PUCCH) that may be aligned with the DRX onDuration, while some UEs may not be configured with CQI on the PUCCH. Thus, the onDuration periods may be stacked more closely. Intelligent selection of UEs to be given PUCCH CQIs may be achieved by, for example, looking at the path loss so as not to degrade system coverage. UEs with high path loss may be configured with CQI on the PUCCH, while others may not.

In another embodiment herein, dynamic reconfiguration of paging frames and paging occasions may be performed, thereby reducing CRS transmissions performed in normal bandwidth mode while maintaining sufficient paging capacity.

In another embodiment, coordination over X2 can be performed between interfering cells. Thus, the interfering cells can inform each other which subframes to transmit in reduced bandwidth mode (also referred to as blank subframes) and which subframes to transmit in normal bandwidth mode (also referred to as non-blank subframes). This can enable different network nodes to have different outer loop adjustment values for blank subframes versus non-blank subframes, which can improve link adaptation results.

In other embodiments of the present invention, DL data may be sent to each UE in connected mode with a certain period. This has been shown to increase the stability of measurements (such as RSRP, RSRQ, or RSSI) performed by the UE. DL data may be sent during a period corresponding to the time of the UE's onDuration. Tests have shown that the preferred period for DL data is approximately 2 seconds, i.e., DL data is sent to the DL approximately every 2 seconds. The periodically sent DL data may be any DL data. In one embodiment, a timing advance command (TAC) is sent as periodic DL data. CRS is sent in full bandwidth mode during the transmission of DL data, thereby providing CRS to the UE during the DL transmission and the subsequent inactivity time (also referred to as DRX-Inactivity time).

In other embodiments of this document, the CRS may also be transmitted using the first bandwidth or full bandwidth mode during UL transmission (eg, a subframe for sending UL data).

In other embodiments herein, periodic DL data transmissions may be aligned between connected UEs. Since each DL transmission starts an inactivity timer as defined in 3GPP TS 36.321 v.9.6.0, CRS will be sent to each UE in full bandwidth mode for the duration of the inactivity period. By aligning periodic DL data transmissions between connected UEs, the number of subframes in which full spectrum CRS needs to be transmitted is reduced. This improves the gain when many users are connected by ensuring that the full bandwidth CRS transmitted during each UE's DRX-Inactivity timer coincides in time, thereby maximizing the number of subframes in which CRS can be muted. This may further improve the performance of the cell.

In other embodiments herein, the connected UE may be released and forced into idle mode after an inactivity timer in the network node that monitors UE activity has elapsed (i.e., when the UE has been inactive for a period of time). In embodiments herein, the inactivity timer may be variable. The inactivity timer may be changed based on the number of connected UEs in the cell. When the method for reducing the CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Therefore, a threshold for connected UEs in a cell may be defined. When the total number of connected UEs is below a threshold, the duration of the inactivity timer for the connected UE is reduced compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Therefore, when the method for managing the transmission of CRS is active, the connected UEs are released faster, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments of the present invention, parameters of the method described herein, such as the DRX inactivity timer length, the DRX onDuration period and length (which may also be referred to as the onDuration interval) and/or the TAC/DL data transmission period, may be adapted (which may also be referred to as being tailored or customized) according to different types of UEs. The UE's International Mobile Equipment Identity (IMEI) and/or IMEI Software Version (IMEISV) may be sent from the core network to the network node and may be used as identifiers to distinguish different UE types, such as different brands. In another embodiment, the core network node may identify the brand/type of the UE based on the IMEI or IMEISV and may send the brand of the UE to the network node. The network node may then adapt the parameters of the method based on the received UE type. In another embodiment, the UE and the network node may establish a proprietary protocol that may be used to identify the UE type/brand, for example at the MAC, RLC, PDCP or RRC layer. Based on the UE's identification, the UE may request the network node to adapt the above parameters in a manner that is beneficial to each UE type. The UE type may be identified by comparing the UE's IMEI and/or IMEISV with a database comprising IMEI:s and/or IMEISV:s for different UE types. Depending on the method of identifying the UE, the database may be stored in a network node or a core network node.

In other embodiments of the present invention, the parameters of the function can be adapted based on the mobile speed of the UE. The indication shows that, depending on the speed of the UE, the UE may need to transmit more or fewer CRS:s in the DL. The speed of the UE can be determined by the Doppler estimation performed by the network node (such as, for example, the eNodeB) in the uplink, and can be used as input to modify the parameters of the method in this article, such as the DRX inactivity timer length, the DRX onDuration period and length and/or the TAC/DL data transmission period. These parameters can be adapted so that a larger Doppler (i.e., a higher UE speed) will give the UE more opportunities to read the CRS, while a low Doppler estimate (i.e., a low speed of the UE) will trigger the opposite.

According to a second aspect of the embodiments herein, when a second cell is identified, the second cell is not actively serving any UE, which may also be referred to as serving a UE in IDLE mode, and the network node applies a reduced CRS bandwidth mode to the CRS transmitted in the second cell. In the reduced bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

In another embodiment, when the network node identifies that the cell is serving only UEs in idle mode, the paging frequency can be reduced while transmitting the subframes of these paging occasions with the full CRS bandwidth. In some other embodiments of the present invention, some surrounding subframes (e.g., a previous or subsequent subframe) can also be transmitted with the full CRS bandwidth. In order to minimize the number of subframes transmitted with the full CRS bandwidth, there can be only one paging occasion in each radio frame with paging. This paging occasion can be in subframe 9. Subframes 9 and 0 can be transmitted with full bandwidth only in those radio frames carrying paging, thereby improving the mobility of idle mode. In addition, all subframes including SIBs can be transmitted with the full CRS bandwidth to allow UEs to hear them. Subframes after or before subframe 9 can also be sent with full bandwidth.

To perform the method actions for managing transmission of CRS described above with respect to Figure 4, the network node 110 may include the following arrangement shown in Figure 5. As described above, the network node 110 operates one or more cells and is typically configured to transmit CRS in a first bandwidth mode.

The network node 110 comprises a radio circuit 401 for communicating with the UE 120, a communication circuit 402 for communicating with other network nodes, and a processing module 403. The communication module 402 may be, for example, an X2 interface.

The network node 110 is configured to identify whether the cells 130, 131, 132 are actively serving the set of UEs 121, which may also be referred to as the set of connected UEs, for example by means of an identification module 404. The set of UEs 121 may not be scheduled by the network node 110 for receiving transmissions from the cells. The network node 110 is further configured to, or includes a bandwidth adjustment module 405 configured to, apply a reduced CRS bandwidth pattern for CRSs in the first cell 130 relative to the first bandwidth pattern when the first cell is identified as actively serving the set of UEs 121.

The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to apply the reduced CRS bandwidth mode to CRS transmitted in any subframe except for subframes in which the network node 110 transmits system information, paging or random access response messages, or in which the UE 120 is assumed to perform measurements (such as subframes transmitted during the onDuration of the UE 120). In this embodiment, the network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to transmit CRS over the entire bandwidth of the subframe in subframes in which the network node 110 transmits system information, paging or random access response messages, or in which the UE 120 is assumed to perform measurements (such as subframes transmitted during the onDuration of the UE 120).

In another embodiment herein, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to apply the reduced CRS bandwidth mode to CRS transmitted in any subframe except the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which the UE 120 is assumed to perform measurements (such as a subframe transmitted during the onDuration of the UE 120). In this embodiment, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to transmit the CRS over the entire bandwidth in the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which the UE 120 is assumed to perform measurements (such as a subframe transmitted during the onDuration of the UE 120).

The network node 110 may also be configured, for example by means of the bandwidth adjustment module 405, to further be configured to send CRS only in PRBs used for transmission in subframes in which the network node 110 transmits system information, paging or random access response messages or in which the UE 120 is assumed to perform measurements, such as subframes sent during the onDuration of the UE 120.

In the embodiments herein, the network node 110 may be further configured to transmit CRS only in REs adjacent to REs mapped to the common search space of the PDCCH, for example, by means of the bandwidth adjustment module 405. The common search space includes REs used by the network node 110 to transmit control information that is common to all UEs 120.

The network node 110 may also be configured, for example, by means of the sending module 408, to send a message to all connected UEs in the cell, the message comprising a discontinuous reception (DRX) command. The DRX command may indicate a DRX mode for the connected UEs, wherein the onDuration of the DRX mode may be aligned between the UEs 120. The onDuration may also be aligned with the transmission of one or more subframes comprising a system information block (SIB). The network node may further be configured to apply a second CRS bandwidth mode to CRS in subframes that are not transmitted in the cell during the onDuration. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

The transmitting module 408 may be included in the radio circuit 401 within the network node 110 .

In order to reduce unnecessary switching between bandwidth modes, the network node 110 may also be configured to, or may include a bandwidth adjustment unit 405 further configured to, use a hysteresis function to reduce and/or increase the CRS bandwidth. By using the hysteresis function, when the number of connected UEs 120 changes, the network node 110 may not switch the bandwidth mode immediately, but instead may remain in one bandwidth mode for a period of time after the change in bandwidth mode in the cell has occurred.

In other embodiments of the present invention, the network node 110 may also be configured to, for example, be further configured by means of the bandwidth adjustment module 405 to send DL data to each UE in connected mode with a certain periodicity. Therefore, increased stability of measurements performed by the UE (such as RSRP, RSRQ or RSSI) can be provided. DL data may be sent during a period corresponding to the onDuration time of the UE. Tests have shown that the preferred period for DL data is approximately 2 seconds, i.e., DL data is sent to the UE approximately every 2 seconds. The periodically sent DL data may be any DL data. In one embodiment, a timing advance command (TAC) is sent as periodic DL data. CRS is sent in full bandwidth mode during the transmission of DL data, thereby providing CRS to the UE during the DL transmission and the subsequent inactivity time (also referred to as DRX-Inactivity time).

In other embodiments of the present invention, the network node 110 may also be configured to, for example, be further configured by means of the bandwidth adjustment module 405 to align the periodic DL data transmissions between connected UEs. Since each DL transmission starts the DRX inactivity timer as defined in 3GPPTS 36.321 v.9.6.0, CRS will be sent to each UE in full-bandwidth mode for the duration of the inactivity period. By aligning the periodic DL data transmissions between connected UEs, the number of subframes in which full-spectrum CRS needs to be sent is reduced. This improves the gain when many users are connected by ensuring that the full-bandwidth CRS sent during each UE DRX-Inactivity timer overlaps in time and thereby maximizes the number of subframes in which CRS can be muted. This can further improve the performance of the cell.

In other embodiments of the present invention, the network node 110 may be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to start an inactivity timer that releases the connected UE and forces the UE to enter idle mode after a certain period of inactivity. The inactivity timer may be variable. When the method for reducing the CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Therefore, a threshold value for connected UEs in a cell may be defined. When the total number of connected UEs is below a threshold, the duration of the inactivity timer for the connected UE is reduced compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Therefore, when the method for managing the transmission of CRS is active, the connected UEs are released faster, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments herein, the network node 110 may be configured to, for example, further be configured to, according to different types of UEs, adapt or tailor parameters of the methods described herein, such as DRX inactivity timer length, DRX onDuration periodicity and length, and/or TAC/DL data transmission period. The network node 110 may also be configured to, for example, further be configured to, according to different types of UEs, identify/distinguish different UE types based on the UE's IMEI that may be received by the network node 110 from the core network node, for example, by means of the identification module 404.

The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to adapt the parameters of the method according to the brand/type of the UE received and identified by the core network node based on the UE's IMEI. The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to establish a proprietary protocol for identifying the UE type, for example, at the media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), or RRC layer. Based on the identification of the UE, the network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to adapt the above parameters in a manner that is beneficial to each UE type.

In other embodiments herein, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to adapt parameters of the method based on the UE's speed. The indication indicates that, depending on the UE's speed, the UE may need to transmit more or fewer CRSs in the DL. The network node 110 may also be further configured, for example, by means of the bandwidth adjustment module 405, to perform Doppler estimation in the UL to determine the UE's speed. The network node 110 may also be further configured, for example, by means of the bandwidth adjustment module 405, to modify parameters of the method herein based on the Doppler estimation, such as the DRX inactivity timer length, the DRX onDuration period and length, and/or the TAC/DL data transmission period. The parameters may be adapted such that a greater Doppler (i.e., a higher speed of the UE 120) provides the UE 120 with more opportunities to read CRSs, while a lower Doppler estimate (i.e., a lower speed of the UE 120) triggers the opposite.

In other embodiments, the network node 110 may be further configured to receive the IMEI of the UE 120 or the identified type of the UE 120 from the core network node 140, for example by means of the receiving module 407. The receiving module may be included in the communication circuit 402.

The embodiments for managing CRS transmission herein can be implemented by one or more processors (such as the processing module 403 in the network node 110 depicted in FIG5 ) together with computer program code for performing the functions and actions of the embodiments herein. The above program code can also be provided as a computer program product, for example, in the form of a data carrier carrying computer program code for executing the embodiments herein when loaded into the network node 110. One such carrier can be in the form of a CD ROM disc. However, other data carriers such as memory sticks are also feasible. The computer program code can also be provided on a server as pure program code and downloaded to the network node 110 and/or core network node.

The network node 110 may further comprise a memory 406 comprising one or more memory units. The memory 406 is arranged for storing acquired information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

Figures 6a and 6b disclose scheduling diagrams for DRX and bandwidth modes according to two embodiments of the above method. To prevent the reduced bandwidth mode from negatively impacting (such as corrupting) mobility measurements such as cell evaluation or best cell evaluation, subframes transmitted during the onDuration of the DRX mode or subframes transmitting system information are transmitted in the first bandwidth mode (also referred to as the full bandwidth mode).

Figure 6a discloses an embodiment of the method, wherein the CRS is transmitted over full bandwidth over a total of thirteen subframes arranged around the subframe of onDuration. Four of the thirteen subframes are located before the two subframes of each onDuration, and seven of these subframes are located after each onDuration. A reduced bandwidth mode is applied to the remaining subframes of the radio frame. Tests have shown that some legacy UEs may not perform measurements as accurately as other UEs and may start measurements briefly before or after onDuration. By transmitting the CRS in normal bandwidth mode in multiple subframes located around onDuration, it is ensured that such less accurate UEs are able to measure the CRS in order to perform channel estimation, even if the measurements are not performed exactly during the onDuration.

FIG6 b shows another embodiment of a method in which the number of subframes in which CRS is transmitted using the full bandwidth is reduced. In this embodiment, the normal bandwidth mode is applied only to subframes transmitted during the onDuration period or one subframe before the subframe in which system information is transmitted. Thus, the number of subframes in which CRS can be transmitted using the reduced bandwidth is increased, further improving network performance. This embodiment can be used when UE 120 connected to a cell provides high-precision measurements.

The network node 110 may adapt the number of subframes in which CRS is transmitted over the full bandwidth based on the type of UE 120 connected to the cell. The type of UE 120 may be identified based on an identifier such as IMEI or the brand/type of UE 120.

Some of the method actions for managing the transmission of CRS described above with respect to FIG3 may be performed by core network node 140. Core network node 140 may include the following arrangement depicted in FIG7. Core network node 140 may include communication circuitry 601 and a processing module 602 for communicating with other network nodes. Communication circuitry 601 may be, for example, an X2 interface.

The core network node 140 may be configured to identify/distinguish different UE brands/types based on the UE's IMEI, for example, by means of the identification module 603 . The identification module 603 may be included in the processing unit 602 .

The core network node 140 may also be configured to send an indication of the brand/type to the network node, for example, by means of a sending module 604. The indication may be the IMEI of the UE or the brand/type of the UE identified by the core network node 140. The sending module 604 may be included in the communication circuit 601.

The embodiments for managing CRS transmission herein can be implemented by one or more processors (such as the processing module 602 in the core network node shown in FIG7 ) together with computer program code for performing the functions and actions of the embodiments herein. The above program code can also be provided as a computer program product, for example, in the form of a data carrier carrying the computer program code for executing the embodiments herein when loaded into the core network node. One such carrier can be in the form of a CD ROM disk. However, other data carriers such as memory sticks are also feasible. The computer program code can also be provided on a server as pure program code and downloaded to the network node 110 and/or the core network node.

The network node 110 may further comprise a memory 406 comprising one or more memory units. The memory 406 is arranged for storing obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

The core network node may further comprise a memory 605 comprising one or more memory units. The memory 605 is arranged for storing obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the core network node.

Those skilled in the art will also understand that the identification modules 404, 603 and bandwidth adjustment module 405 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, which are stored in, for example, memory 406, 660 and executed by one or more processors such as processing units 403, 602 as described above. One or more of these processors and other digital hardware may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed across several separate components, whether packaged separately or assembled into a system-on-chip (SoC).

When the word "comprise" or "comprising" is used, it should be interpreted as non-limiting, ie meaning "consisting at least of. . . . . "

When the word "set" is used herein, it should be interpreted to mean "one or more."

The embodiments herein are not limited to the preferred embodiments described above. Various substitutions, modifications, and equivalents may be used. Therefore, the above embodiments should not be considered to limit the scope of the present invention, which is defined by the appended claims.

Technical Field

Embodiments herein relate to a network node and methods therein. Specifically, a method and a network node for managing transmission of a cell reference signal are disclosed.

Background Art

A communication device, such as a user equipment (UE), is enabled to communicate wirelessly in a cellular communication network or wireless communication system (sometimes also referred to as a cellular radio system or cellular network). Communication can be performed, for example, between two UEs, between a UE and a regular phone, and/or between a UE and a server via a radio access network (RAN) and possibly one or more core networks included in the cellular communication network.

To name a few other examples, a UE may also be referred to as a wireless terminal, a mobile terminal and/or a mobile station, a mobile phone, a cellular phone, a laptop computer, a tablet computer, or a surfboard with wireless capabilities. A UE in this context may be, for example, a portable, pocket-storable, handheld, computer-built-in, or vehicle-mounted mobile device that is enabled to communicate voice and/or data with another entity, such as another wireless terminal or a server, via a RAN.

A cellular communication network covers a geographical area divided into cell areas, where each cell area is served by a network node. A cell is a geographical area where a network node provides radio coverage.

A network node may further control several transmission points, for example, including radio units (RRUs). Thus, a cell may include one or more network nodes, each controlling one or more transmission/reception points. A transmission point, also referred to as a transmission/reception point, is an entity that transmits and/or receives radio signals. This entity has a location in space, such as an antenna. A network node is an entity that controls one or more transmission points. Depending on the technology and terminology used, a network node may be, for example, a base station such as a radio base station (RBS), eNB, eNodeB, NodeB, B-node, or base transceiver station (BTS). Base stations may be of different types, such as macro eNodeB, home eNodeB, or pico base station, based on transmission power and, therefore, cell size.

In addition, each network node can support one or several communication technologies. The network node communicates with UEs within range of the network node over an air interface operated by radio frequency. In the context of this disclosure, the term downlink (DL) is used for the transmission path from the base station to the mobile station. The term uplink (UL) is used for the transmission path in the opposite direction (i.e., from the UE to the base station).

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks. In LTE, the cellular communication network is also referred to as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN).

An E-UTRAN cell is defined by certain signals broadcast from the eNB. These signals contain information about the cell that can be used by a UE to connect to the network via the cell. The signals include reference and synchronization signals that the UE uses to find frame timing and physical cell identity, as well as system information that includes parameters related to the entire cell.

Therefore, a UE that needs to connect to the network must first detect a suitable cell, as defined in 3GPP TS 36.304v11.5.0. The UE can be in an idle state, also known as IDLE or radio resource control idle (RRC_IDLE); or in a connected state, which is also known as CONNECTED or radio resource control connected (RRC_CONNECTED). When the UE is in RRC_IDLE, it monitors the paging channel, which is part of the Paging Control Channel (PCCH) at the logical layer, the Paging Channel (PCH) at the transport channel layer, and the Physical Downlink Shared Channel (PDSCH) at the physical channel layer. In doing so, the UE typically also performs a number of radio measurements that the UE uses to evaluate the best cell, such as Reference Signal Received Power (RSRP), Reference Symbol Received Quality (RSRQ), or Received Signal Strength Indicator (RSSI). This is performed by measuring the received reference signal and/or the portion of the spectrum that includes the reference signal sent by the cell. This can also be referred to as "listening" for a suitable cell.

A suitable cell is typically a cell with an RSRQ or RSRP above a certain level. The cell with the highest RSRP or RSRQ may be referred to as the best cell or the most suitable cell. Sensing a suitable cell may include searching for a reference signal transmitted from a network node in an orthogonal frequency division multiplexing (OFDM) subframe. When the most suitable cell is found, the UE performs random access based on the system information for the cell. This is done to transmit a radio resource control (RRC) connection establishment request to the network node. Assuming the random access procedure is successful and the network node receives the request, the network node will respond with an RRC connection establishment message or an RRC connection rejection. The RRC connection establishment message confirms the UE's request and informs it to enter the RRC_CONNECTED state. The RRC connection rejection informs the UE that it may not be able to connect to the cell. In the RRC_CONNECTED state, the parameters required for communication between the network node and the UE are known to the two entities, and data transfer between the two entities is enabled.

When the UE is in the RRC_CONNECTED state, the UE continues to measure RSRP as an input to connected mode mobility decisions, such as, for example, deciding when to perform a handover from one cell to another. These measurements are typically performed in the full bandwidth of a subframe (which may also be referred to as full spectrum).

RSRP is a measure of the signal strength of an LTE cell. It helps the UE rank different cells based on their signal strength, which serves as an input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying the cell-specific reference signal (CRS) across the entire bandwidth. Therefore, RSRP is only measured in OFDM symbols that carry CRS.

The RRC protocol handles control plane signaling at the network layer (also called layer 3) between the UE and a network node, which may also be referred to as a UTRAN or E-UTRAN node. At any one time, only one RRC connection can be open between the UE and a network node.

The network layer may also include:

Connection establishment and release functions,

Broadcasting of system information,

Radio bearer establishment/reconfiguration and release,

RRC connection mobility procedures,

· Paging notification and release,

Outer loop power control.

To support UEs connecting to a cell (also referred to as an access cell), a system information block (SIB) is transmitted in a control channel such as the broadcast control channel (BCCH) logical channel in the downlink, which can be mapped to the PDSCH physical channel. In LTE, a number of different SIBs are defined, characterized by the information they carry. For example, SIB1 carries cell access related parameters, such as information about the operator of the cell, restrictions on what users can access the cell, and allocation of uplink/downlink subframes. SIB1 also carries information about the scheduling of other SIBs.

To reduce UE power consumption, discontinuous reception (DRX) can be implemented. The fundamental mechanism in DRX is a configurable DRX cycle in the UE, also known as a DRX mode. When a DRX cycle is configured, the UE monitors control signaling only during the onDuration interval of the DRX cycle. The onDuration interval can be one or more subframes, which can be referred to as one or more active subframes. During the remaining subframes of the DRX cycle, the UE can shut down its receiver, which can also be referred to as UE sleep, or the offDuration interval of the DRX cycle. This allows for a significant reduction in power consumption: the longer the DRX cycle and the shorter the onDuration interval, the lower the power consumption. In certain situations, if a UE is already scheduled and active for receiving or transmitting data in a subframe, it may be scheduled again in the near future. Waiting until the next active subframe according to the DRX cycle may result in additional delays in transmission. Therefore, to reduce latency, the UE can remain active for a configurable time after being scheduled, which can also be referred to as the activity time or the inactivity timer (DRX-Inactivity Timer) defined in 3GPP TS 36.321 Ch 3.1. The duration of the active time is set by the inactivity timer, which is the duration in downlink subframes from the last successful decoding of the physical downlink control channel (PDCCH) to the duration the UE waits before shutting down and re-entering the offDuration. The UE can restart the inactivity timer after a single successful decoding of the PDCCH for a transmission. The time it takes for the UE to re-enter the offDuration after the last transmission can also be called the inactivity time.

To facilitate handovers to other cells, each network node can store the cell identifiers of cells supported by other network nodes in an address database, so that it knows how to contact the network node of a potential target cell for handover. Each network node serving a cell typically stores in a database the cells with which it has neighbor relationships, i.e., the cells in the area to which UEs frequently perform handovers. Hereinafter, a cell's neighbor relationships are referred to as its "neighbor relationship list."

CRS is a UE-known symbol inserted in the resource elements (REs) of the subframes of the OFDM time and frequency grid and broadcast by the network node. Each RE has an extension in the frequency domain corresponding to an OFDM subcarrier and an extension in the time domain corresponding to an OFDM symbol interval.

The UE uses CRS for downlink channel estimation. Channel estimation is used for demodulation of downlink data when the UE is in RRC_CONNECTED state and is receiving user data and when the UE is in RRC_IDLE state and is reading system information. Due to the latter use case, the network node cannot know whether the UE wants to access the network before the UE performs random access, so even the cells without any UE in RRC connected state must transmit CRS from it. The downlink CRS is inserted into the first and third to last OFDM symbol of each time slot with a frequency domain spacing of six subcarriers. A time slot is a time period of the OFDM time and frequency grid, typically 0.5 milliseconds long. Therefore, a problem with the known technology is that the cells without any UE in RRC connected state still consume power due to the CRS broadcast.

In the case where a network node uses several antennas for transmission and each antenna represents a cell, each antenna must transmit a unique reference signal in order for the UE to connect to that specific cell. When one antenna transmits, the other antennas must be silent so as not to interfere with the first antenna reference signal. In order to reduce interference of reference signals between cells, the position of the CRS is usually shifted in frequency between cells. The CRS can be shifted between 0-5 subcarriers, and for LTE, each subcarrier corresponds to a frequency shift of 15kHz. The frequency shift can be derived from the physical cell identity (cell ID) that is signaled to the UE through the selection of the appropriate primary synchronization channel (PSCH) and secondary synchronization channel (SSCH).

Although this reduces the interference of reference symbols (eg, CRS symbols) between cells, there is a problem that the reference symbols of one cell may interfere with the PDSCH and PDCCH symbols of an adjacent cell.

Therefore, even if a cell does not have any UE in the RRC_CONNECTED state, interference may affect the UE DL throughput in a neighboring cell, especially when the UE is at and/or close to the boundary between cells.

Reducing the power of the CRS can alleviate this problem. However, in order to access a cell, the UE must be able to hear the CRS of the cell, that is, the UE must be able to identify and receive the CRS transmitted from the cell. Therefore, reducing the power of the CRS also reduces the size of the cell, because UEs farther away will no longer hear the CRS sent by the cell. In addition, when the signal-to-interference ratio (SINR) on the CRS decreases, the quality of the channel estimate used for demodulation decreases. Therefore, reducing the power of the CRS leads to degradation of cell edge performance. When the load in the network increases, especially if data is transmitted at a higher power than the CRS, which is usually the case when the impact of CRS interference will be reduced, this degradation will be further exacerbated, resulting in reduced performance of the wireless communication network.

Summary of the Invention

It is therefore an object of embodiments herein to enhance performance in wireless communication networks.

According to a first aspect of embodiments herein, the object is achieved by a method performed by a network node for managing transmission of a Cell Reference Signal, CRS.

The network node operates one or more cells. The network node identifies whether the cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node sends CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in one or more CRS subframes in which system information is sent. The network node also sends CRS on a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in one or more CRS subframes other than the subframes in which system information is sent. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception (DRX), the network node sends CRS on a first bandwidth in one or more CRS subframes transmitted in the cell during the onDuration interval of the DRX mode and/or in one or more CRS subframes in which system information is sent and/or in one or more CRS subframes in which downlink DL data is sent. The network node further transmits the CRS on a second bandwidth in a CRS subframe that is not transmitted in the cell during the onDuration interval of DRX, and/or in one or more CRS subframes other than the CRS subframe in which system information is transmitted, and/or in one or more CRS subframes other than the CRS subframe in which downlink (DL) data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

According to a second aspect of the embodiments of this document, the purpose is achieved by a network node configured to manage the transmission of a cell reference signal (CRS). The network node operates one or more cells. The network node is configured to identify whether the cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node is configured to transmit CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in a CRS subframe in which system information is transmitted. The network node is further configured to transmit CRS on a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in a CRS subframe other than a CRS subframe in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception (DRX), the network node is further configured to transmit a CRS on a first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX mode, and/or in a CRS subframe in which system information is transmitted, and/or in a CRS subframe in which downlink (DL) data is transmitted. The network node is further configured to transmit a CRS on a second bandwidth in a CRS subframe that is not transmitted in the cell during an onDuration interval of the DRX mode, and/or in a CRS subframe other than a CRS subframe in which system information is transmitted, and/or in a CRS subframe other than a CRS subframe in which downlink (DL) data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

By applying the reduced bandwidth mode to CRS transmitted in all subframes except for subframes transmitted during or related to the onDuration in the cell, or subframes in which or related to subframes in which system information such as SIBs are transmitted, power consumption and interference from the cell can be reduced, thereby enhancing the performance of neighboring cells transmitting data. In other words, the reduced bandwidth mode is applied during the period when no data transmission occurs and the UE turns off its receiver and enters a low power mode.

By applying reduced bandwidth mode to CRS in cells that do not serve any UE in RRC connected mode, power consumption and interference from null cells may be reduced, thereby enhancing the performance of cells with UEs in RRC connected mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein are described in more detail with reference to the accompanying drawings, in which:

FIG1 is a schematic block diagram illustrating an embodiment of a wireless communication network.

FIG2 is a schematic block diagram illustrating embodiments of an OFDM subframe.

FIG3 is a flow chart depicting a first embodiment of a method in a network node.

FIG4 is a flow chart depicting a second embodiment of a method in a network node.

FIG5 is a schematic block diagram illustrating embodiments of a network node.

FIG6 a is a scheduling diagram illustrating a first embodiment of the method herein.

FIG6 b is a scheduling diagram illustrating a first embodiment of the method herein.

FIG7 is a schematic block diagram illustrating embodiments of a core network node.

DETAILED DESCRIPTION

the term

The following general terms are used in the examples and are explained below:

Radio network node: In some embodiments, the non-limiting term radio network node is more generally used and refers to any type of network node that serves a UE and/or is connected to other network nodes or network elements, or any radio node from which a UE receives signals. Examples of radio network nodes are Node B, Base Station (BS), MSR radio node such as a Multi-Standard Radio (MSR) BS, eNode B, network controller, Radio Network Controller (RNC), Base Station Controller, relay, donor node controlled relay, Base Transceiver Station (BTS), Access Point (AP), Transmission Point, Transmission Node, RRU, RRH, a node in a Distributed Antenna System (DAS), etc.

Network node: In some embodiments, the more general term "network node" is used, which may correspond to any type of radio network node or any network node that communicates with at least a radio network node. Examples of network nodes are any of the radio network nodes mentioned above, core network nodes (e.g., mobile switching center (MSC), mobility management entity (MME), etc.), operation and maintenance (O&M) center, operation support system (OSS), self-organizing network (SON), positioning node (e.g., evolved serving mobile positioning center (E-SMLC), master data telegraph (MDT), etc.).

User Equipment: In some embodiments, the non-limiting term User Equipment (UE) is used to refer to any type of wireless device that communicates with a radio network node in a cellular communication system or a mobile communication system. Examples of UEs are target devices, device-to-device UEs, machine-type UEs or UEs with machine-to-machine communication capabilities, PDAs, iPADs, tablet computers, mobile terminals, smartphones, laptop embedded equipment (LEEs), laptop mounted equipment (LMEs), USB dongles, etc.

The embodiments herein are also applicable to a multi-point carrier aggregation system.

Note that although terminology from 3GPP LTE has been used in this disclosure to exemplify the embodiments herein, this should not be considered to limit the scope of the embodiments herein to only that system. Other wireless systems including WCDMA, WiMax, UMB, and GSM may also benefit from utilizing the ideas covered by this disclosure.

It should also be noted that terms such as eNodeB and UE should be considered non-restrictive and, in particular, do not imply a hierarchical relationship between the two. In general, "eNodeB" can be considered as device 1 and "UE" can be considered as device 2, and the two devices communicate with each other via some radio channel. In this article, we also focus on wireless transmission in the downlink, but the embodiments herein are equally applicable to the uplink.

In this section, the embodiments of this invention will be described in more detail through a plurality of exemplary embodiments. It should be noted that these embodiments are not mutually exclusive. Components of one embodiment may be assumed to exist in another embodiment by default, and it will be apparent to those skilled in the art how these components may be used in other exemplary embodiments.

1 depicts an example of a wireless communication network 100 according to a first scenario in which embodiments herein may be implemented. The wireless communication network 100 is a wireless communication network such as LTE, E-UTRAN, WCDMA, GSM network, any 3GPP cellular network, Wimax or any cellular network or system.

The wireless communication network 100 includes a plurality of network nodes, two of which (a first network node 110 and a second network node 111) are depicted in FIG1 . The first network node 110 and the second network node 111 are network nodes, each of which can be a transmission point such as a radio base station, for example, an eNB, eNodeB, or a Home NodeB, Home eNodeB, or any other network node capable of serving wireless terminals such as user equipment or machine type communication devices in the wireless communication network. The first network node 110 and the second network node 111 each serve a plurality of cells 130, 131, 132.

Wireless communication network 100 includes a UE set 121, which may include one or more UEs 120. First network node 110 and second network node 111 may each be a transmission point for UE 120. UE 120 is within radio range of first network node 110 and second network node 111, meaning it can hear signals from first network node 110 and second network node 111. One or more UEs 120 may also exist in each cell, and one or more UEs 120 may also be referred to as a UE set 121.

The UE 120 in the UE set 121 may be, for example, a wireless terminal, a wireless device, a mobile wireless terminal or a wireless terminal, a mobile phone, a computer such as a laptop with wireless capabilities, a personal digital assistant (PDA) or a tablet (sometimes called a surfboard), or any other radio network element capable of communicating via a radio link in a wireless communication network. Note that the term wireless terminal used in this document also covers other wireless devices such as machine-to-machine (M2M) devices.

Figure 2 shows an exemplary downlink OFDM time and frequency grid, which may also be referred to as an OFDM subframe. Each subframe includes two time slots. Each time slot includes multiple resource elements (REs) 201 extending in both the time domain (x-axis) and the frequency domain (z-axis). The extension of each RE 201 in the frequency domain may be referred to as a subcarrier, while the extension in the time domain may be referred to as an OFDM symbol. In the time domain, LTE downlink transmissions are organized into 10ms radio frames, where each radio frame includes ten subframes of equal size. Furthermore, resource allocation in LTE may generally be described in terms of physical resource blocks (PRBs) comprising multiple REs. A resource block corresponds to one time slot in the time domain and 12 consecutive subcarriers in the frequency domain.

Downlink and uplink transmissions are dynamically scheduled, i.e., in each subframe, the first network node 110 transmits control information about which UE 120 to or from which data and on which resource blocks the data is transmitted. The control information may include system information, paging messages, and/or random access response messages. One or more PDCCHs may be used to transmit control information for a given UE 120. The control information of the PDCCH is transmitted in the control region of each subframe. Figure 2 shows an exemplary size of a conventional control region of three OFDM symbols allocated for control signaling (e.g., PDCCH). However, the size of the control region may be dynamically adjusted based on the current traffic situation. In the example shown in the figure, only the first OFDM symbol of the three possible OFDM symbols is used for control signaling. In general, the control region may include multiple PDCCHs that carry control information for multiple UEs 120 simultaneously. The REs used for control signaling are represented by wavy lines, and the REs used for CRS are represented by diagonal lines.

UE 120 uses CRS for downlink channel estimation. Channel estimation is used to determine the demodulation of downlink data when UE 120 is in RRC connected state, and when UE 120 is in RRC idle state and is reading system information. Downlink CRS can be inserted into the first and third-to-last OFDM symbols of each time slot with a frequency domain interval of six subcarriers. RSRP is a measurement of the signal strength of an LTE cell, which helps UE 120 to sort between different cells as an input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying cell-specific reference signals (CRS) over the entire bandwidth. Therefore, it is only measured in OFDM symbols carrying CRS.

The subframe also includes data symbols for transmitting user data between the first network node 110 and the UE 120. The data symbols are located in a region following the control region, also called the data region.

A first example of embodiments of a method in a network node 110 for managing transmission of a Cell Reference Signal (CRS) will now be described with reference to the flowchart depicted in Figure 3. The network node 110 operates one or more cells 130, 131, 132 which may or may not serve a set 121 of UEs.

The method may include the following actions, which may be performed in any suitable order: The dashed lines of the boxes in Figure 3 indicate that this operation is not mandatory.

Action 301

The network node 110 identifies whether a cell among the one or more cells 130, 131, 132 is actively serving the set of UEs 121. A cell actively serving the set of UEs 121 may also be referred to as a cell having a set of connected UEs, and a cell not actively serving the set of connected UEs 121 may be referred to as an empty cell. This action 301 may be performed by an identification module 404 within a network node (such as the network node 110). This action corresponds to action 401 described below.

When the network node 110 has identified a cell that is not actively serving the set of UEs 121, the network node performs actions 302 and 303 described below. Although actions 302 and 303 are depicted as following each other, the actions may be performed simultaneously.

Action 302

When the network node 110 has identified cells that are not actively serving the set of UEs 121 , the network node 110 transmits CRS over the first bandwidth in one or more CRS subframes transmitted during paging occasions and/or in one or more CRS subframes transmitting system information.

Action 303

When the network node 110 has identified cells that are not actively serving the set of UEs 121, the network node 110 further transmits CRS using a second bandwidth in one or more CRS subframes that are not transmitted during a paging occasion and/or in one or more CRS subframes other than subframes in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth.

In another embodiment herein, paging occasions may be sent in one CRS subframe per radio frame with paging only in cells that do not serve the set of UEs 121. Thus, the number of CRS subframes that must be sent with the first bandwidth is reduced, which allows the network node 110 to reduce the bandwidth in a higher number of CRS subframes.

When the network node has identified a cell that is actively serving the set of UEs (121) configured for discontinuous reception (DRX), the network node 110 performs actions 304 and 305 described below. Although actions 304 and 305 are depicted as following each other, the actions may be performed simultaneously.

Action 304

When the network node has identified a cell that is actively serving a set of UEs (121) configured for discontinuous reception (DRX), the network node 110 transmits CRS subframes over a first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX mode, and/or in one or more CRS subframes transmitting system information, and/or in one or more CRS subframes transmitting downlink (DL) data.

In other embodiments, the network node 110 may also transmit the CRS using the first bandwidth in a CRS subframe transmitted immediately before or after the CRS subframe transmitted during the paging occasion and/or in a CRS subframe transmitting system information and/or during the onDuration period and/or in a CRS subframe transmitting DL data.

Action 305

When the network node has identified a cell that is actively serving the set of UEs (121) configured for discontinuous reception (DRX), the network node 110 further transmits a CRS using a second bandwidth in a CRS subframe that is not transmitted in the cell during the onDuration interval of DRX, and/or in one or more CRS subframes other than CRS subframes for transmitting system information, and/or in one or more CRS subframes other than CRS subframes for transmitting DL data. The second bandwidth is reduced relative to the first bandwidth. This action 305 corresponds to action 402 described below, and therefore the embodiments described for action 402 can also be applied to this action 305.

Action 306

When the network node 110 has identified the cell that is actively serving the UE set, the network node 110 may also send a message including a DRX command to the UE set 121. The DRX command indicates the DRX mode for the UE set 121, which may also be referred to as a DRX cycle. The indicated DRX mode is the DRX mode that the UE set 121 will use. For the UEs 120 included in the UE set 121, the onDurations of the DRX modes are aligned so that the UEs 120 have overlapping onDuration intervals. By aligning the onDuration intervals of the UEs 120, the UEs can be grouped, i.e., the UEs will have overlapping onDurations. This has the advantage that the timing of transmitting CRS in the first bandwidth mode can be reduced and the number of subframes in which CRS is transmitted via the second bandwidth is increased. This will further improve the performance of the cell.

This action 306 corresponds to action 403 described below, so the embodiment described for action 403 can also be applied to this action 306 .

By sending a message including a command indicating the onDuration of the DRX mode to all connected UEs in the cell, the UEs can be grouped together, i.e., the UEs are configured with overlapping onDurations. By doing so, the performance of the cell can be further improved because the times when CRS must be transmitted at full bandwidth can be minimized because each UE performs radio measurements such as RSRP, RSRQ, or RSSI in the same time interval.

Another example of an embodiment of a method for managing the transmission of cell reference signals (CRS) in a network node 110 will now be described with reference to the flowchart shown in FIG4 . The network node 110 operates one or more cells and is configured to transmit CRS in a first bandwidth mode during operation. This relates to normal operation. The first bandwidth mode, which may also be referred to as normal bandwidth mode, is used when at least one cell of the network node 110 is serving at least one UE 120 in RRC connected mode and the at least one UE 120 is scheduled to receive data. In normal bandwidth mode, CRS is transmitted over the entire available bandwidth of a DL radio frame (RF), i.e., the CRS is transmitted in all physical resource blocks (PRBs) of the cell.

The method may include the following actions, which may be performed in any suitable order: The dashed lines in the boxes in Figure 4 indicate that this operation is not mandatory.

Action 401

The network node 110 identifies a cell serving a set of UEs 121 (which may also be referred to as a set of connected UEs). The set of UEs 121 is configured for discontinuous reception (DRX). The set of UEs 121 may include one or more UEs 120. The set of UEs 121 is not scheduled by the network node for receiving a transmission from the network node sent in one of the network node's cells. This may mean that the network node has not yet scheduled the set of UEs 121 for receiving a transmission sent from the network node 110 in the cell, or that a certain time (T) has passed since the set of UEs 121 was scheduled for transmission in the UL or DL. The time T may be a time set in a DRX inactivity timer. This action 401 may be performed by an identification module 404 within a network node, such as the network node 110.

Action 402

When the network node 110 has identified a first cell serving a set of UEs 121 that are not scheduled by the network node 110, the network node 110 applies a second bandwidth mode (also referred to as a reduced CRS bandwidth mode) to CRSs in subframes not transmitted in the cell during the onDuration of DRX or in subframes in which system information is transmitted. In another embodiment, the reduced CRS bandwidth mode may also be applied to CRSs transmitted in subframes not transmitted with respect to the onDuration or related to subframes in which system information is transmitted, which may be, for example, subframes directly before or after the onDuration or subframes in which system information is transmitted. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode. The system information may be, for example, a system information block (SIB). This reduced bandwidth mode may also be referred to as a low bandwidth mode. The low bandwidth mode means that the network node 110 does not transmit CRSs in all PRBs of the subframes of the cell. By reducing the bandwidth of the CRSs, i.e., transmitting the CRSs only on a portion of the available bandwidth of the DL radio frame, the overall interference from the CRSs of the cell 130 is reduced. Reducing interference from cell 130 increases throughput in neighboring cells 131 , as well as increasing RRC connections and scheduled UEs 120 .

Studies have shown that when the CRS bandwidth is reduced, mobility measurements (also known as cell evaluation or best cell evaluation, such as RSRP) may be negatively affected. This may cause the UE to make incorrect decisions about which cell it should camp on. When the UE120 performs mobility measurements on a neighboring cell, only a limited part of the bandwidth is considered. This limited part of the bandwidth may be, for example, the center six PRBs of a subframe. However, when the UE performs measurements on the cell in which it camps (which may also be referred to as its own cell), the entire bandwidth is taken into account. If the bandwidth used to send CRS in a cell is reduced, the CRS will only be sent in a part of the bandwidth (e.g., in the center six PRBs). However, RSRP is calculated as the average power of all REs carrying CRS over the entire bandwidth. Since the power of the CRS sent in, for example, the center six PRBs is averaged over the entire bandwidth, not just over the reduced bandwidth, the RSRP of the own cell may appear to be lower than that of the neighboring cell. This may cause the UE to connect to (which may also be referred to as performing handover to) a neighboring cell that appears to be better but is actually worse. This may cause the UE to start performing multiple handovers back and forth between cells, which can also be called a ping-pong effect, because the neighboring cell evaluated only on the central six PRBs will always appear to be better.

To prevent the reduced bandwidth mode from negatively affecting (such as corrupting) mobility measurements (such as cell evaluation or best cell evaluation), subframes transmitted during the onDuration of DRX or subframes in which system information is sent are transmitted first, which may also be referred to as normal bandwidth mode.

In another embodiment, CRS may also be transmitted in normal bandwidth mode in subframes surrounding the subframe transmitted during onDuration. In one embodiment, normal bandwidth mode may apply to multiple subframes before or after the subframe transmitted during onDuration. The number of subframes transmitted in normal bandwidth mode may be up to 25 subframes, including the subframe transmitted during onDuration. The onDuration period may occur over two subframes. In another embodiment, normal bandwidth mode may apply to the four subframes before the onDuration period and the seven subframes after the onDuration period, for a total of thirteen subframes. By transmitting CRS in normal bandwidth mode in subframes surrounding the onDuration period, legacy UEs that do not perform measurements as precisely as modern UEs can measure CRS for channel estimation, even if the measurements are not performed precisely during the onDuration period. Depending on the accuracy of the measurements performed by the UE, the number of subframes in which CRS is transmitted in normal bandwidth mode may be reduced. In another embodiment, normal bandwidth mode may, for example, apply to a subframe preceding the subframe transmitted during onDuration or the subframe in which system information is transmitted. Thus, it can be ensured that the CRS is sent over the entire bandwidth when the UE performs measurements during the onDuration period (ie in normal bandwidth mode). This embodiment is depicted in FIG6 .

In yet another embodiment, the CRS may also be transmitted in normal bandwidth mode during the UE's inactive time.

Having a long DRX cycle (i.e., a long time between DRX onDurations) can further be beneficial because it enables the network node 110 to apply the reduced bandwidth mode over a greater number of subframes. In one embodiment herein, the DRX cycle (which may also be referred to as the period of the DRX pattern) may be in the range of 20ms to 320ms. In another embodiment herein, the DRX cycle may be in the range of 20ms to 80ms. In yet another embodiment, the DRX cycle may be 40ms long. Studies have shown that this is the preferred period at which UEs typically read RSRP in order to assess the channel conditions in the cell to which they are connected.

Action 402 may be performed by a bandwidth adjustment module within a network node, such as network node 110 .

Action 403

In another embodiment herein, network node 110 may send a message to UE set 121, the message including a discontinuous reception (DRX) command. This command indicates a DRX cycle, wherein the onDuration (also referred to as the onDuration interval) of the DRX mode is aligned for the UEs included in UE set 121. Thus, the UEs can be grouped, i.e., the UEs will have overlapping onDurations. This has the advantage of reducing the number of times CRS is transmitted in the first bandwidth mode, further improving cell performance.

In another embodiment herein, the onDuration of the DRX mode can be aligned with the transmission of one or more subframes containing system information, such as system information blocks (SIBs). In another embodiment herein, the onDuration is aligned with SIB 1. Since SIB 1 includes parameters related to cell access and information regarding the scheduling of other SIBs, SIB 1 is transmitted even if the remaining SIBs are not transmitted. Since the number of subframes transmitted in the first bandwidth mode can be further reduced, aligning the onDuration of the set of UEs 121 with the transmission of SIB 1 further improves cell performance. Aligning the onDuration with SIB 1 further reduces losses, as SIB 1 is transmitted with the full CRS bandwidth regardless. SIB 1 can be transmitted with a 20ms period in subframe 5, which may also be referred to as SFN mod 2 = 0. Through forced DRX, a UE can be triggered (which may also be referred to as being incentivized, commanded, forced, or tricked) to always evaluate the status of the current cell when CRS is transmitted in full bandwidth mode and to reduce bandwidth when the connected UE is dormant. The trigger can be sent in a DRX command that sets the onDuration of the DRX cycle. The DRX mode may be applied to the UE 120 in order to trigger the evaluation of RSRP and other measurements for time slots in cases where the network node has transmitted CRS over the entire bandwidth (ie, in normal bandwidth mode).

In another embodiment, the network node 110 may force the UE to enter DRX sleep by sending a 3GPP DRX command MacControlElement (such as defined in 3GPP TS 36.321 v11.5.0 Ch 6.1.3.3 and referred to as a DRX command MAC control element). The MacControl element may include an indication to stop the DRX inactivity timer and/or the onDuration timer.

In other embodiments herein, when the number of connected UEs in a cell exceeds a certain threshold, the alignment of the onDuration of the DRX mode and/or the application of the reduced CRS bandwidth may be deactivated.

Action 403 may be performed by a transmitting module within a network node, such as network node 110. The transmitting module may also be comprised in a radio circuit within a network node, such as the described network node.

In one embodiment herein, a reduced CRS bandwidth mode is applied to CRSs transmitted in any subframe except for subframes in which the network node 110 transmits system information, paging, or random access response messages, or subframes in which the network node 110 assumes that the UE 120 is performing measurements. By applying the reduced CRS bandwidth mode in all subframes except for the aforementioned subframes, interference from the CRS is reduced while allowing the UE 120 in the neighboring cells 131, 132 to hear the CRS from the null cell 130. This is necessary to enable the UE 120 to obtain information about the modulation of the signal so that it can demodulate the downlink control channel of the cell. In this embodiment, the network node 110 may transmit CRSs across the entire bandwidth in subframes in which the network node 110 transmits system information such as SIBs, paging, or random access response messages, or in which the UE 120 is assumed to be performing measurements.

In another embodiment herein, the network node 110 transmits the CRS in PRBs used for transmission of data or control information only in subframes in which the network node 110 transmits system information, paging or random access response messages, or assumes that the UE performs measurements.

The network node 110 may also transmit the CRS in REs adjacent to the REs mapped to the common search space of the PDCCH. Thus, the CRS is transmitted only in the area where the UE is searching for the PDCCH. Consequently, the number of subframes in which the CRS can be transmitted on the second bandwidth increases, further improving the performance of the wireless communication network.

The CRS bandwidth can be further adapted to multiple levels. For LTE, the bandwidth in cell 130 can vary, for example, between 1.4 MHz and 20 MHz. However, other bandwidths are also possible depending on the technology used.

In another embodiment, a hysteresis function may be applied when changing the CRS bandwidth level, thereby avoiding unnecessary switching between bandwidth modes when the cell 130 switches from the first bandwidth mode to the second bandwidth mode.

In another embodiment herein, for services requiring Voice over IP (VoIP) or other "constanton" types, the UE can be moved to the lowest frequency band with the best coverage, while the CRS can be muted on higher frequency bands. Moving voice users on LTE to the lowest frequency band can be beneficial because these users are active and require coverage. This facilitates carrier aggregation.

In another embodiment herein, some UEs may be configured with a channel quality indicator (CQI) on the physical uplink control channel (PUCCH) that may be aligned with the DRX onDuration, while some UEs may not be configured with CQI on the PUCCH. Thus, the onDuration periods may be stacked more closely. Intelligent selection of UEs to be given PUCCH CQIs may be achieved by, for example, looking at the path loss so as not to degrade system coverage. UEs with high path loss may be configured with CQI on the PUCCH, while others may not.

In another embodiment herein, dynamic reconfiguration of paging frames and paging occasions may be performed, thereby reducing CRS transmissions performed in normal bandwidth mode while maintaining sufficient paging capacity.

In another embodiment, coordination over X2 can be performed between interfering cells. Thus, the interfering cells can inform each other which subframes to transmit in reduced bandwidth mode (also referred to as blank subframes) and which subframes to transmit in normal bandwidth mode (also referred to as non-blank subframes). This can enable different network nodes to have different outer loop adjustment values for blank subframes versus non-blank subframes, which can improve link adaptation results.

In other embodiments of the present invention, DL data may be sent to each UE in connected mode with a certain period. This has been shown to increase the stability of measurements (such as RSRP, RSRQ, or RSSI) performed by the UE. DL data may be sent during a period corresponding to the time of the UE's onDuration. Tests have shown that the preferred period for DL data is approximately 2 seconds, i.e., DL data is sent to the DL approximately every 2 seconds. The periodically sent DL data may be any DL data. In one embodiment, a timing advance command (TAC) is sent as periodic DL data. CRS is sent in full bandwidth mode during the transmission of DL data, thereby providing CRS to the UE during the DL transmission and the subsequent inactivity time (also referred to as DRX-Inactivity time).

In other embodiments of this document, the CRS may also be transmitted using the first bandwidth or full bandwidth mode during UL transmission (eg, a subframe for sending UL data).

In other embodiments herein, periodic DL data transmissions may be aligned between connected UEs. Since each DL transmission starts an inactivity timer as defined in 3GPP TS 36.321 v.9.6.0, CRS will be sent to each UE in full bandwidth mode for the duration of the inactivity period. By aligning periodic DL data transmissions between connected UEs, the number of subframes in which full spectrum CRS needs to be transmitted is reduced. This improves the gain when many users are connected by ensuring that the full bandwidth CRS transmitted during each UE's DRX-Inactivity timer coincides in time, thereby maximizing the number of subframes in which CRS can be muted. This may further improve the performance of the cell.

In other embodiments herein, the connected UE may be released and forced into idle mode after an inactivity timer in the network node that monitors UE activity has elapsed (i.e., when the UE has been inactive for a period of time). In embodiments herein, the inactivity timer may be variable. The inactivity timer may be changed based on the number of connected UEs in the cell. When the method for reducing the CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Therefore, a threshold for connected UEs in a cell may be defined. When the total number of connected UEs is below a threshold, the duration of the inactivity timer for the connected UE is reduced compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Therefore, when the method for managing the transmission of CRS is active, the connected UEs are released faster, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments of the present invention, parameters of the method described herein, such as the DRX inactivity timer length, the DRX onDuration period and length (which may also be referred to as the onDuration interval) and/or the TAC/DL data transmission period, may be adapted (which may also be referred to as being tailored or customized) according to different types of UEs. The UE's International Mobile Equipment Identity (IMEI) and/or IMEI Software Version (IMEISV) may be sent from the core network to the network node and may be used as identifiers to distinguish different UE types, such as different brands. In another embodiment, the core network node may identify the brand/type of the UE based on the IMEI or IMEISV and may send the brand of the UE to the network node. The network node may then adapt the parameters of the method based on the received UE type. In another embodiment, the UE and the network node may establish a proprietary protocol that may be used to identify the UE type/brand, for example at the MAC, RLC, PDCP or RRC layer. Based on the UE's identification, the UE may request the network node to adapt the above parameters in a manner that is beneficial to each UE type. The UE type may be identified by comparing the UE's IMEI and/or IMEISV with a database comprising IMEI:s and/or IMEISV:s for different UE types. Depending on the method of identifying the UE, the database may be stored in a network node or a core network node.

In other embodiments of the present invention, the parameters of the function can be adapted based on the mobile speed of the UE. The indication shows that, depending on the speed of the UE, the UE may need to transmit more or fewer CRS:s in the DL. The speed of the UE can be determined by the Doppler estimation performed by the network node (such as, for example, the eNodeB) in the uplink, and can be used as input to modify the parameters of the method in this article, such as the DRX inactivity timer length, the DRX onDuration period and length and/or the TAC/DL data transmission period. These parameters can be adapted so that a larger Doppler (i.e., a higher UE speed) will give the UE more opportunities to read the CRS, while a low Doppler estimate (i.e., a low speed of the UE) will trigger the opposite.

According to a second aspect of the embodiments herein, when a second cell is identified, the second cell is not actively serving any UE, which may also be referred to as serving a UE in IDLE mode, and the network node applies a reduced CRS bandwidth mode to the CRS transmitted in the second cell. In the reduced bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

In another embodiment, when the network node identifies that the cell is serving only UEs in idle mode, the paging frequency can be reduced while transmitting the subframes of these paging occasions with the full CRS bandwidth. In some other embodiments of the present invention, some surrounding subframes (e.g., a previous or subsequent subframe) can also be transmitted with the full CRS bandwidth. In order to minimize the number of subframes transmitted with the full CRS bandwidth, there can be only one paging occasion in each radio frame with paging. This paging occasion can be in subframe 9. Subframes 9 and 0 can be transmitted with full bandwidth only in those radio frames carrying paging, thereby improving the mobility of idle mode. In addition, all subframes including SIBs can be transmitted with the full CRS bandwidth to allow UEs to hear them. Subframes after or before subframe 9 can also be sent with full bandwidth.

To perform the method actions for managing transmission of CRS described above with respect to Figure 4, the network node 110 may include the following arrangement shown in Figure 5. As described above, the network node 110 operates one or more cells and is typically configured to transmit CRS in a first bandwidth mode.

The network node 110 comprises a radio circuit 401 for communicating with the UE 120, a communication circuit 402 for communicating with other network nodes, and a processing module 403. The communication module 402 may be, for example, an X2 interface.

The network node 110 is configured to identify whether the cells 130, 131, 132 are actively serving the set of UEs 121, which may also be referred to as the set of connected UEs, for example by means of an identification module 404. The set of UEs 121 may not be scheduled by the network node 110 for receiving transmissions from the cells. The network node 110 is further configured to, or includes a bandwidth adjustment module 405 configured to, apply a reduced CRS bandwidth pattern for CRSs in the first cell 130 relative to the first bandwidth pattern when the first cell is identified as actively serving the set of UEs 121.

The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to apply the reduced CRS bandwidth mode to CRS transmitted in any subframe except for subframes in which the network node 110 transmits system information, paging or random access response messages, or in which the UE 120 is assumed to perform measurements (such as subframes transmitted during the onDuration of the UE 120). In this embodiment, the network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to transmit CRS over the entire bandwidth of the subframe in subframes in which the network node 110 transmits system information, paging or random access response messages, or in which the UE 120 is assumed to perform measurements (such as subframes transmitted during the onDuration of the UE 120).

In another embodiment herein, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to apply the reduced CRS bandwidth mode to CRS transmitted in any subframe except the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which the UE 120 is assumed to perform measurements (such as a subframe transmitted during the onDuration of the UE 120). In this embodiment, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to transmit the CRS over the entire bandwidth in the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which the UE 120 is assumed to perform measurements (such as a subframe transmitted during the onDuration of the UE 120).

The network node 110 may also be configured, for example by means of the bandwidth adjustment module 405, to further be configured to send CRS only in PRBs used for transmission in subframes in which the network node 110 transmits system information, paging or random access response messages or in which the UE 120 is assumed to perform measurements, such as subframes sent during the onDuration of the UE 120.

In the embodiments herein, the network node 110 may be further configured to transmit CRS only in REs adjacent to REs mapped to the common search space of the PDCCH, for example, by means of the bandwidth adjustment module 405. The common search space includes REs used by the network node 110 to transmit control information that is common to all UEs 120.

The network node 110 may also be configured, for example, by means of the sending module 408, to send a message to all connected UEs in the cell, the message comprising a discontinuous reception (DRX) command. The DRX command may indicate a DRX mode for the connected UEs, wherein the onDuration of the DRX mode may be aligned between the UEs 120. The onDuration may also be aligned with the transmission of one or more subframes comprising a system information block (SIB). The network node may further be configured to apply a second CRS bandwidth mode to CRS in subframes that are not transmitted in the cell during the onDuration. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

The transmitting module 408 may be included in the radio circuit 401 within the network node 110 .

In order to reduce unnecessary switching between bandwidth modes, the network node 110 may also be configured to, or may include a bandwidth adjustment unit 405 further configured to, use a hysteresis function to reduce and/or increase the CRS bandwidth. By using the hysteresis function, when the number of connected UEs 120 changes, the network node 110 may not switch the bandwidth mode immediately, but instead may remain in one bandwidth mode for a period of time after the change in bandwidth mode in the cell has occurred.

In other embodiments of the present invention, the network node 110 may also be configured to, for example, be further configured by means of the bandwidth adjustment module 405 to send DL data to each UE in connected mode with a certain periodicity. Therefore, increased stability of measurements performed by the UE (such as RSRP, RSRQ or RSSI) can be provided. DL data may be sent during a period corresponding to the onDuration time of the UE. Tests have shown that the preferred period for DL data is approximately 2 seconds, i.e., DL data is sent to the UE approximately every 2 seconds. The periodically sent DL data may be any DL data. In one embodiment, a timing advance command (TAC) is sent as periodic DL data. CRS is sent in full bandwidth mode during the transmission of DL data, thereby providing CRS to the UE during the DL transmission and the subsequent inactivity time (also referred to as DRX-Inactivity time).

In other embodiments of the present invention, the network node 110 may also be configured to, for example, be further configured by means of the bandwidth adjustment module 405 to align the periodic DL data transmissions between connected UEs. Since each DL transmission starts the DRX inactivity timer as defined in 3GPPTS 36.321 v.9.6.0, CRS will be sent to each UE in full-bandwidth mode for the duration of the inactivity period. By aligning the periodic DL data transmissions between connected UEs, the number of subframes in which full-spectrum CRS needs to be sent is reduced. This improves the gain when many users are connected by ensuring that the full-bandwidth CRS sent during each UE DRX-Inactivity timer overlaps in time and thereby maximizes the number of subframes in which CRS can be muted. This can further improve the performance of the cell.

In other embodiments of the present invention, the network node 110 may be configured, for example, by means of the bandwidth adjustment module 405, to further be configured to start an inactivity timer that releases the connected UE and forces the UE to enter idle mode after a certain period of inactivity. The inactivity timer may be variable. When the method for reducing the CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Therefore, a threshold value for connected UEs in a cell may be defined. When the total number of connected UEs is below a threshold, the duration of the inactivity timer for the connected UE is reduced compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Therefore, when the method for managing the transmission of CRS is active, the connected UEs are released faster, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments herein, the network node 110 may be configured to, for example, further be configured to, according to different types of UEs, adapt or tailor parameters of the methods described herein, such as DRX inactivity timer length, DRX onDuration periodicity and length, and/or TAC/DL data transmission period. The network node 110 may also be configured to, for example, further be configured to, according to different types of UEs, identify/distinguish different UE types based on the UE's IMEI that may be received by the network node 110 from the core network node, for example, by means of the identification module 404.

The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to adapt the parameters of the method according to the brand/type of the UE received and identified by the core network node based on the UE's IMEI. The network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to establish a proprietary protocol for identifying the UE type, for example, at the media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), or RRC layer. Based on the identification of the UE, the network node 110 may also be configured, for example, by means of the bandwidth adjustment module 405, to adapt the above parameters in a manner that is beneficial to each UE type.

In other embodiments herein, the network node 110 may be further configured, for example, by means of the bandwidth adjustment module 405, to adapt parameters of the method based on the UE's speed. The indication indicates that, depending on the UE's speed, the UE may need to transmit more or fewer CRSs in the DL. The network node 110 may also be further configured, for example, by means of the bandwidth adjustment module 405, to perform Doppler estimation in the UL to determine the UE's speed. The network node 110 may also be further configured, for example, by means of the bandwidth adjustment module 405, to modify parameters of the method herein based on the Doppler estimation, such as the DRX inactivity timer length, the DRX onDuration period and length, and/or the TAC/DL data transmission period. The parameters may be adapted such that a greater Doppler (i.e., a higher speed of the UE 120) provides the UE 120 with more opportunities to read CRSs, while a lower Doppler estimate (i.e., a lower speed of the UE 120) triggers the opposite.

In other embodiments, the network node 110 may be further configured to receive the IMEI of the UE 120 or the identified type of the UE 120 from the core network node 140, for example by means of the receiving module 407. The receiving module may be included in the communication circuit 402.

The embodiments for managing CRS transmission herein can be implemented by one or more processors (such as the processing module 403 in the network node 110 depicted in FIG5 ) together with computer program code for performing the functions and actions of the embodiments herein. The above program code can also be provided as a computer program product, for example, in the form of a data carrier carrying computer program code for executing the embodiments herein when loaded into the network node 110. One such carrier can be in the form of a CD ROM disc. However, other data carriers such as memory sticks are also feasible. The computer program code can also be provided on a server as pure program code and downloaded to the network node 110 and/or core network node.

The network node 110 may further comprise a memory 406 comprising one or more memory units. The memory 406 is arranged for storing acquired information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

Figures 6a and 6b disclose scheduling diagrams for DRX and bandwidth modes according to two embodiments of the above method. To prevent the reduced bandwidth mode from negatively impacting (such as corrupting) mobility measurements such as cell evaluation or best cell evaluation, subframes transmitted during the onDuration of the DRX mode or subframes transmitting system information are transmitted in the first bandwidth mode (also referred to as the full bandwidth mode).

Figure 6a discloses an embodiment of the method, wherein the CRS is transmitted over full bandwidth over a total of thirteen subframes arranged around the subframe of onDuration. Four of the thirteen subframes are located before the two subframes of each onDuration, and seven of these subframes are located after each onDuration. A reduced bandwidth mode is applied to the remaining subframes of the radio frame. Tests have shown that some legacy UEs may not perform measurements as accurately as other UEs and may start measurements briefly before or after onDuration. By transmitting the CRS in normal bandwidth mode in multiple subframes located around onDuration, it is ensured that such less accurate UEs are able to measure the CRS in order to perform channel estimation, even if the measurements are not performed exactly during the onDuration.

FIG6 b shows another embodiment of a method in which the number of subframes in which CRS is transmitted using the full bandwidth is reduced. In this embodiment, the normal bandwidth mode is applied only to subframes transmitted during the onDuration period or one subframe before the subframe in which system information is transmitted. Thus, the number of subframes in which CRS can be transmitted using the reduced bandwidth is increased, further improving network performance. This embodiment can be used when UE 120 connected to a cell provides high-precision measurements.

The network node 110 may adapt the number of subframes in which CRS is transmitted over the full bandwidth based on the type of UE 120 connected to the cell. The type of UE 120 may be identified based on an identifier such as IMEI or the brand/type of UE 120.

Some of the method actions for managing the transmission of CRS described above with respect to FIG3 may be performed by core network node 140. Core network node 140 may include the following arrangement depicted in FIG7. Core network node 140 may include communication circuitry 601 and a processing module 602 for communicating with other network nodes. Communication circuitry 601 may be, for example, an X2 interface.

The core network node 140 may be configured to identify/distinguish different UE brands/types based on the UE's IMEI, for example, by means of the identification module 603 . The identification module 603 may be included in the processing unit 602 .

The core network node 140 may also be configured to send an indication of the brand/type to the network node, for example, by means of a sending module 604. The indication may be the IMEI of the UE or the brand/type of the UE identified by the core network node 140. The sending module 604 may be included in the communication circuit 601.

The embodiments for managing CRS transmission herein can be implemented by one or more processors (such as the processing module 602 in the core network node shown in FIG7 ) together with computer program code for performing the functions and actions of the embodiments herein. The above program code can also be provided as a computer program product, for example, in the form of a data carrier carrying the computer program code for executing the embodiments herein when loaded into the core network node. One such carrier can be in the form of a CD ROM disk. However, other data carriers such as memory sticks are also feasible. The computer program code can also be provided on a server as pure program code and downloaded to the network node 110 and/or the core network node.

The network node 110 may further comprise a memory 406 comprising one or more memory units. The memory 406 is arranged for storing obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

The core network node may further comprise a memory 605 comprising one or more memory units. The memory 605 is arranged for storing obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the core network node.

Those skilled in the art will also understand that the identification modules 404, 603 and bandwidth adjustment module 405 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, which are stored in, for example, memory 406, 660 and executed by one or more processors such as processing units 403, 602 as described above. One or more of these processors and other digital hardware may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed across several separate components, whether packaged separately or assembled into a system-on-chip (SoC).

When the word "comprise" or "comprising" is used, it should be interpreted as non-limiting, ie meaning "consisting at least of. . . . . "

When the word "set" is used herein, it should be interpreted to mean "one or more."

The embodiments herein are not limited to the preferred embodiments described above. Various substitutions, modifications, and equivalents may be used. Therefore, the above embodiments should not be considered to limit the scope of the present invention, which is defined by the appended claims.

Claims (20)

1. A method performed by a network node (110) for managing the transmission of one or more cell-specific reference signal (CRS) subframes, wherein the network node (110) operates one or more cells (130, 131, 132), the method comprising:

Identifier (301) indicates whether one or more cells in the cell are actively serving a set of user equipment (UE) (121);

When the cell has been identified as not actively serving the UE set (121),

(302) CRS is transmitted on the first bandwidth in one or more CRS subframes transmitted during paging timing and/or in one or more CRS subframes in which system information is transmitted.

In one or more CRS subframes not transmitted during a paging event, and/or in one or more CRS subframes other than those in which system information is transmitted, a (303) CRS is transmitted on a second bandwidth, the second bandwidth being reduced relative to the first bandwidth; and

When the cell has been identified as actively serving the UE set (121), the UE set (121) is configured to receive DRX discontinuously.

(304) CRS is transmitted on the first bandwidth in one or more CRS subframes transmitted in the cell during the DRX mode enable duration interval, and/or in one or more CRS subframes in which system information is transmitted, and/or in one or more CRS subframes in which downlink DL data is transmitted.

(305) CRS is transmitted on the second bandwidth in a CRS subframe that is not transmitted in the cell during the DRX activation duration interval, and/or in one or more CRS subframes other than those in which system information is transmitted, and/or in one or more CRS subframes other than those in which downlink DL data is transmitted, the second bandwidth being reduced relative to the first bandwidth.

2. The method according to claim 1, wherein when the cell is actively serving the UE set (121), the method further comprises:

Send (306) a message including a DRX command to the UE set (121), the DRX command indicating the DRX mode for the UE set (121), wherein the on-duration of the DRX mode is aligned for the UEs (120) included in the UE set (121) so that the UEs (120) have overlapping on-duration time intervals.

3. The method of claim 1, wherein the CRS is also transmitted on the first bandwidth in the CRS subframe transmitted during the paging timing, and/or in the CRS subframe in which system information is transmitted, and/or in the CRS subframe during the open duration time interval, and/or in the CRS subframe in which DL data is transmitted immediately before or after the CRS subframe in which it is transmitted.

4. The method according to any one of claims 1-3, wherein the paging timing is transmitted only in a CRS subframe of each radio frame having paging in the cell that is not currently serving the UE set (121).

5. The method according to any one of claims 1-3, wherein the activation duration time interval of the DRX mode is aligned with the transmission of one or more CRS subframes including system information.

6. The method of claim 5, wherein the activation duration of the DRX mode is aligned with the transmission of system information block 1SIB1.

7. The method according to any one of claims 1-3, wherein the CRS is further transmitted with a first bandwidth in one or more CRS subframes before and/or after the subframe in which the CRS is transmitted during the on-duration time interval of the DRX mode.

8. The method according to any one of claims 1-3, wherein the alignment of the DRX mode of the UE (120) is deactivated when a threshold of the connected UE (120) in each cell is exceeded.

9. The method according to any one of claims 1-3, wherein the inactivity timer of the DRX mode is variable such that the UE (120) connected to the cell when the number of connected UEs (120) is less than the threshold has a shorter inactivity timer than the UE (120) connected to the cell when the number of connected UEs (120) in the cell exceeds the threshold.

10. The method according to any one of claims 1-3, wherein the length of the active timer of the DRX mode, and/or the period of the on-duration time interval of the DRX mode, and/or the period of the DL data are adaptable to different types of UEs based on the UE identifier (120).

11. The method according to any one of claims 1-3, wherein the second bandwidth is reduced to the bandwidth of six central physical resource blocks (PRBs).

12. A network node (110) for managing the transmission of a cell reference signal (CRS), wherein the network node (110) is configured to operate one or more cells, the network node (110) being configured to:

Identify whether the cell is actively serving the UE set (121);

When the network node has identified that the cell is not actively serving the UE set (121), CRS is transmitted on the first bandwidth in one or more CRS subframes transmitted during the paging opportunity and/or in CRS subframes where system information is transmitted.

In one or more CRS subframes not transmitted during a paging event, and/or in CRS subframes other than those in which system information is transmitted, a CRS is transmitted on a second bandwidth, the second bandwidth being reduced relative to the first bandwidth; and

When the network node has identified that the cell is actively serving the UE set (120), the UE set (120) is configured to receive DRX discontinuously, transmitting CRS on the first bandwidth in one or more CRS subframes transmitted in the cell during the DRX mode enable duration interval, and/or in CRS subframes where system information is transmitted, and/or in CRS subframes where downlink DL data is transmitted.

CRS is transmitted on the second bandwidth in CRS subframes that are not transmitted in the cell during the DRX mode activation duration interval, and/or in CRS subframes other than those in which system information is transmitted, and/or in CRS subframes other than those in which downlink DL data is transmitted, the second bandwidth being reduced relative to the first bandwidth.

13. The network node (110) according to claim 12, wherein the network node (110) is further configured to:

A message including a DRX command is sent to the UE set (121), the command indicating the DRX mode for the UE set (121), wherein the on-duration time interval of the DRX mode is aligned for the UEs (120) included in the UE set (121) so that the UEs (120) have overlapping on-duration time intervals.

14. The network node (110) of claim 12, wherein the network node (110) is further configured to: transmit CRS on the first bandwidth in the CRS subframe transmitted during paging timing, and/or in the CRS subframe in which system information is transmitted, and/or in the CRS subframe transmitted immediately before or after the CRS subframe in which downlink DL data is transmitted during the open duration time interval.

15. The network node (110) according to any one of claims 12 to 14, wherein the network node (110) is further configured to: transmit paging in only one CRS subframe of each radio frame having paging in a cell not serving the UE set (121).

16. The network node (110) according to any one of claims 12 to 14, wherein the network node (110) is further configured to: apply the first bandwidth mode to one or more subframes before and/or after the subframe in which the system information is transmitted during the on-duration time interval of the DRX mode.

17. The network node (110) according to any one of claims 13 to 14, wherein the network node (110) is further configured to: deactivate the alignment of the DRX mode of the UE (120) when a threshold of the connected UE (120) in each cell is exceeded.

18. The network node (110) according to any one of claims 12 to 14, wherein the network node (110) is further configured to: send a message including a DRX mode having a variable inactivity timer, such that the UE (120) connected to the cell when the number of connected UEs (120) is less than the threshold has a shorter inactivity timer than the UE (120) connected to the cell when the number of connected UEs (120) in the cell exceeds the threshold.

19. The network node (110) according to any one of claims 12 to 14, wherein the network node (110) is further configured to: adapt the length of the active timer of the DRX mode, and/or the period of the on-duration time interval of the DRX mode, and/or the period of the DL data to different types of UEs (120) based on the UE identifier.

20. The network node (110) according to any one of claims 12 to 14, wherein the network node (110) is further configured to reduce the second bandwidth to the bandwidth of six central physical resource blocks (PRBs).