JP7664355B2 - Control of modulation and coding schemes for transmissions between a base station and a user device - Google Patents

Description

The present invention relates to the field of cellular networks, in particular to the evolution of LTE networks, and more particularly to networks including LTE networks and evolved LTE networks.

Further developments are being made on LTE, for example for Beyond 4G (B4G) wireless systems which are assumed to be commercially available in 2020. However, evolutions of LTE may be introduced at any date within a new release.

LTE achieves a peak bit rate of 30 bps/Hz using 64QAM modulation and 8x8 MIMO transmission. As a result, B4G requires higher order modulation than 64QAM, e.g., 256QAM, to meet future requirements. Higher order modulation is suitable for e.g. relay backhaul due to better channel quality and better radio frequency (RF) characteristics that are easier to achieve for relays than for user equipment (UE) or separate indoor cells, where the UE is closer to the access point and thus has a good link to the access point and there is little or no interference from other access points due to attenuation by walls.

The determination of modulation order for LTE Release 10 is described in TS 36.213 V10.3, chapter 7.1.7 and CQI definition, chapter 7.2.3. In LTE (and LTE-Advanced), the theoretical spectral efficiency is limited by 64QAM modulation. Extensions to 256QAM provide improved spectral efficiency.

The LTE standard defines MCS (modulation and coding scheme) index and modulation tables and CQI (channel quality indicator) tables, which are used to determine and select the appropriate modulation and coding scheme. Currently the tables support up to 64QAM. The question is how to introduce 256QAM extensions, or other higher order modulation extensions for LTE, while maintaining backward compatibility and avoiding significant complexity.

Improved and flexible systems and methods are desired that are adapted to allow extension to higher order modulations while maintaining backward compatibility for LTE. In particular, it is desired to maintain the signaling format and, more particularly, to use the same number of bits as in the case where a different encoding scheme needs to be used and potentially so-called blind decoding should be applied.

The above-mentioned needs are met by the subject matter based on the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

According to a first aspect of the present invention, there is provided a method of controlling a modulation and coding scheme for transmissions between a base station and a user equipment, the modulation and coding scheme being selectable based on a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a first maximum modulation order, or a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a second maximum modulation order. The method comprises selecting, by the base station, the first modulation and coding scheme table or the second modulation and coding scheme table, and controlling, by the base station, the modulation and coding scheme for transmissions between the base station and the user equipment based on the selected modulation and coding scheme table.

This aspect of the invention is based on the idea of extending the modulation and coding scheme table to higher order modulations while maintaining backward compatibility. The first table supports, for example, up to 64QAM (Quadrature Amplitude Modulation) and the second table supports, for example, up to 256QAM or other higher order modulation extensions. Note that although 256QAM is explicitly mentioned here, other modulations of higher orders than those used in the first table can also be used, for example 128QAM, or in general higher order modulation and coding schemes (MCS), characterized by the modulation order or the coding scheme or both.

The idea of this method is to introduce higher order modulations while still supporting the Modulation and Coding Scheme (MCS) tables introduced for lower modulation orders.

The term "modulation order" as used herein is determined by the number of different symbols that can be transmitted using it. In general, the MCS also allows for different code rates and therefore dictates the average number of payload bits that can be transmitted per symbol. The first maximum modulation order and the second maximum modulation order may be the same or different.

The term "modulation and coding scheme table" refers to the MCS table defined in LTE, which is used to determine and select the appropriate modulation and coding scheme. The second table is an extended MCS table based on the MCS defined in LTE, but includes entries corresponding to higher order modulations. For example, backward compatibility is ensured by making the first table exactly as currently defined in the LTE standard.

The first and second tables may differ in some respects. For example, one table may be biased towards low MCS and the second table may be biased towards high MCS values. For example, one table may have more MCS values below a certain threshold MCS. Also, the density of MCS values at low MCS may be higher in one table, or the centroid or average of MCS values may be lower in one table. In one embodiment, one table is a mirror image of the other, e.g., mirrored at a middle MCS.

The term "base station" in this document refers to any kind of physical entity that can communicate with user equipment or other network equipment by selecting a modulation and coding scheme from such an MCS table. A base station in this document may be any kind of network equipment providing the required functionality for the method or may be a transceiver node communicating with a central entity. A base station is, for example, a NodeB or an eNB.

The base station may explicitly inform the UE about the change in the MCS table used or may inform the UE as part of the capability enquiry procedure and select the MCS table implicitly.

According to one embodiment of the present invention, the second maximum modulation order is higher than the first maximum modulation order. In particular, the first maximum modulation order corresponds to 64QAM, and the second maximum modulation order corresponds to 256QAM.

Note that other modulation orders can also be used, e.g., 128QAM.

Furthermore, the first table contains a small number of high MCSs to allow for a quick reaction if the channel suddenly becomes good.

According to yet another embodiment of the present invention, the maximum modulation order corresponds to the highest modulation and coding scheme (MCS). Moreover, the highest modulation and coding scheme is the same for both tables.

According to yet another embodiment of the present invention, the method further includes determining, by the base station, actual channel conditions of a wireless transmission channel used for transmission between the base station and the user equipment, determining, by the base station, a maximum supported modulation order based on the determined actual channel conditions, and selecting, by the base station, the first modulation and coding scheme table or the second modulation and coding scheme table based on a comparison of the maximum supported modulation order with the first maximum modulation order and the second maximum modulation order.

If the actual channel conditions do not support higher order modulation or the user equipment (UE) cannot support higher order modulation, the base station performs modulation and coding for transmission based on a first table. If the actual channel conditions are good enough for higher order modulation and the UE supports higher order modulation, the base station performs modulation and coding based on a second table that supports higher order modulation, for example, up to 256QAM.

According to yet another embodiment of the present invention, the method further includes transmitting information representing the selected modulation and coding scheme table to the user equipment.

The base station provides the UE with a signal containing information about the selected MCS table to be used. The UE then performs further actions, such as CQI reporting, based on that information.

According to yet another embodiment of the present invention, the transmission of information to the user equipment is based on radio resource control signaling.

By using a common signaling link, the UE is easily informed about the selected MCS table. This information is also included in any information signal that comprises the UE's information on other resource control considerations.

According to yet another embodiment of the present invention, the transmission of information to the user equipment is based on implicit signaling.

This refers to the case where the UE receives information from the base station and determines the selected MCS table based on that information. This is the case, for example, as part of a capability enquiry procedure that also makes capabilities available to the eNB. During this type of configuration procedure, where the eNB determines the UE's capabilities, the tables are switched and the UE is informed implicitly without specific signaling.

According to yet another embodiment of the present invention, the method includes receiving confirmation information from the user equipment indicating the change made to the selected modulation and coding scheme table.

The base station performs the change from one table to the selected MCS table after receiving the confirmation signal from the UE. The confirmation signal thus represents the final change of the MCS table performed by the base station.

According to yet another embodiment of the present invention, the first modulation and coding scheme table and the second modulation and coding scheme table each include a common subset of equal entries located at the same positions in the first modulation and coding scheme table and the second modulation and coding scheme table. In particular, the method includes, after transmitting information representative of a selected modulation and coding scheme table to the user equipment and before receiving confirmation information from the user equipment, controlling a modulation and coding scheme for transmission between the base station and the user equipment based on the selected modulation and coding scheme table based on the common subset of entries.

By using a common entry in both MCS tables, the base station will use the common entry unless there is a confirmation signal from the UE. This has the advantage that there are no misunderstandings or incorrect modulation and coding, since both parts (base station and UE) use the same modulation and coding scheme (albeit possibly using different tables).

According to yet another embodiment of the present invention, controlling the initial transmission between the base station and the user equipment is based on a first modulation and coding scheme table.

The base station and UE use the MCS table with the lowest maximum modulation order at the beginning of each communication. This has the effect that each communication starts with the same table, and then the base station decides whether to change the MCS table. Then, if the UE can support an MCS table that supports a higher modulation order, the change is made based on the actual channel conditions.

According to yet another embodiment of the present invention, the bits carrying the modulation and coding scheme index are the same for the first modulation and coding scheme table and the second modulation and coding scheme table.

Thus, forward compatibility is guaranteed without the need to change the existing form of the MCS table or the coding and transmission mechanisms used to convey the selections from that table. In a more particular embodiment, the tables have the same size. In particular, a portion of the first MCS table and the second MCS table are equal, providing the common entries mentioned above. Entries of the first MCS table associated with a very low modulation order are exchanged (redefined) for the second MCS table, which includes a higher order modulation.

According to yet another embodiment of the present invention, the actual channel conditions are determined based on a selectable channel quality indicator based on a first channel quality indicator table supporting a first maximum modulation order or based on a second channel quality indicator table supporting a second maximum modulation order, the method comprising receiving, by a base station, a channel quality indicator from a user equipment, and determining, by the base station, actual channel conditions of a wireless transmission channel used for transmission between the base station and the user equipment based on the received channel quality indicator.

Similar to the MCS table, the CQI table is also selected based on the selection of the MCS table. When there is a switch or change from the first MCS table to the second MCS table, there is also a change from the first CQI table to the second CQI table. Thus, the UE determines the CQI based on the table corresponding to the selected MCS table.

According to yet another embodiment of the present invention, the method includes selecting, by the base station, a first channel quality indicator table or a second channel quality indicator table based on the selected modulation and coding scheme table, and transmitting information representative of the selected channel quality indicator table to the user equipment.

The information of the selected CQI table is provided to the UE by the base station. Alternatively, the information may be provided implicitly by notifying the user equipment of the selected MCS table.

According to yet another embodiment of the present invention, the first channel quality indicator table and the second channel quality indicator table each include a common subset of equal entries located at the same positions in the first channel quality indicator table and the second channel quality indicator table.

Similar to the MCS table, the CQI table also contains a common subset, thus ensuring that there is no misunderstanding between the UE and the base station during handover.

According to a second aspect of the present invention, there is provided a base station for controlling a modulation and coding scheme for transmissions between the base station and a user device, the modulation and coding scheme being selectable based on a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a first maximum modulation order or a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a second maximum modulation order. The base station comprises a selection unit for selecting the first modulation and coding scheme table or the second modulation and coding scheme table, and a control unit for controlling the modulation and coding scheme for transmissions between the base station and the user device based on the selected modulation and coding scheme table.

A base station is any type of access point or attachment point capable of providing wireless access to a cellular network system. Thus, wireless access is provided to user equipment or other network devices that can communicate wirelessly. The base station may be a NodeB, eNB, Home NodeB or HeNB, or other type of access point or multi-hop node or relay. Base stations are used in particular for B4G, LTE or 3GPP cells and communications.

The base station includes a receiving unit, e.g., a receiver, as known to those skilled in the art. The base station also includes a transmitting or transmission unit, e.g., a transmitter. The receiver and transmitter may be implemented as a single unit, e.g., a transceiver. The transceiver, or receiving unit-transmitting unit, is adapted to communicate with user equipment via an antenna.

The base station further comprises a selection unit and a control unit, which may be implemented as a single unit or may be implemented as part of a standard control unit, such as a CPU or a microcontroller.

In one embodiment, the base station further comprises a determination unit for determining actual channel conditions of a wireless transmission channel used for transmission between the base station and the user equipment and for determining a maximum supported modulation order based on the determined actual channel conditions. The selection unit selects the first modulation and coding scheme table or the second modulation and coding scheme table based on a comparison of the maximum supported modulation order with the first maximum modulation order and the second maximum modulation order.

The decision unit may be implemented as a separate unit or as part of a standard control unit such as a CPU or microcontroller.

A User Equipment (UE) is any type of communication end device capable of connecting to the base stations described herein. A UE may be, among others, a cellular mobile telephone, a personal digital assistant (PDA), a notebook computer, a printer, and/or any other mobile communication device.

The user equipment comprises a receiving unit or receiver for receiving signals from the base station. The user equipment comprises a transmitting unit for transmitting signals. The transmitting unit is a transmitter as known to those skilled in the art. The receiver and transmitting unit may be implemented as a single unit, for example a transceiver. The transceiver, or the receiver and transmitting unit, are arranged to communicate with the base station via an antenna.

The user equipment further comprises a control unit for controlling and configuring the transmission based on information received from the base station representing the selected MCS table. This control unit may be implemented as a separate unit or as part of a standard control unit, for example a CPU or a microcontroller.

According to a third aspect of the present invention, there is provided a cellular network system. The cellular network system includes the base station described above.

In general, herein, the method and embodiments of the method according to the first aspect include performing one or more functions as described with respect to the second or third aspect or embodiments thereof. Vice versa, the base station or cellular network system and embodiments thereof according to the second and third aspects include a unit or apparatus for performing one or more functions as described with respect to the first aspect or embodiments thereof.

According to a fourth aspect of the presently disclosed subject matter, there is provided a computer program for controlling a modulation and coding scheme for transmissions between a base station and a user equipment, the computer program being for controlling the method described in the first aspect or an embodiment thereof when executed by a data processor assembly.

The term computer program as used herein is equivalent to the terms program elements and/or computer readable media containing instructions for controlling a computer system to coordinate the execution of the methods described above.

A computer program is implemented as computer readable instruction code, for example, using a suitable programming language such as JAVA, C++, and stored on a computer readable medium (removable disk, volatile or non-volatile memory, embedded memory/processor, etc.). The instruction code serves to program a computer or other programmable device to perform the intended functions. Computer programs are available from a network such as the World Wide Web from which they can be downloaded.

The subject matter disclosed herein may be implemented by means of a computer program, respectively software. However, the subject matter disclosed herein may also be implemented by means of one or more specific electronic circuits, respectively hardware. Furthermore, the subject matter disclosed herein may also be implemented in a hybrid form, i.e. a combination of software and hardware modules.

Having described exemplary embodiments of the subject matter disclosed herein, the following provides a detailed description of a cellular network system, a base station, and a method for controlling a modulation and coding scheme for transmission between a base station and a user device. It is noted that combinations of features relating to different aspects of the subject matter disclosed herein are of course also possible. In particular, certain embodiments are described with reference to an apparatus-type embodiment, while other embodiments are described with reference to a method-type embodiment. However, those skilled in the art will appreciate from the above and following description that, unless otherwise indicated, in addition to combinations of features belonging to one aspect, combinations between features relating to different aspects or embodiments, for example, combinations between features of an apparatus-type embodiment and a method-type embodiment, are also considered to be disclosed with this application.

The above-mentioned aspects and embodiments, as well as further aspects and embodiments of the present invention, will become apparent from the following examples and will be described with reference to the drawings, to which the present invention is not limited. It should be noted that in different drawings, the same or similar elements are designated by the same reference characters.

1 illustrates a cellular network system in accordance with an exemplary embodiment of the invention. Simulations of the spectral efficiency for 64QAM and 256QAM are shown. Simulations of the spectral efficiency of 4x4 MIMO and 2x2 MIMO for 64QAM and 256QAM, respectively, are presented. 1 illustrates a base station and user equipment in a cellular network system in accordance with an exemplary embodiment of the present invention.

Embodiments of the subject matter disclosed herein are described below with reference to the accompanying drawings and with reference to current standards such as LTE and their further developments. However, reference to current standards is for illustrative purposes only and does not limit the scope of the claims thereto.

Figure 1 shows a cellular network system 100. A user equipment 102 is served by a first cell 103 of the cellular network system. The first cell is designated by a base station 101.

Transmissions and communications between the base station and the user equipment are controlled based on a modulation and coding scheme that can be selected based on a first modulation and coding scheme table that includes entries corresponding to a plurality of modulation and coding schemes with a first maximum modulation order, or based on a second modulation and coding scheme table that includes entries corresponding to a plurality of modulation and coding schemes with a second maximum modulation order. In one embodiment, the second maximum modulation order is higher (e.g., up to 256QAM) than the first maximum modulation order (e.g., up to 64QAM).

The base station determines actual channel conditions of a radio transmission channel used for transmission between the base station and the user equipment. The base station then determines a maximum supported modulation order based on the determined actual channel conditions, and finally based on information from the user equipment on which modulation orders can be supported by the user equipment. The base station then selects the first modulation and coding scheme table or the second modulation and coding scheme table based on a comparison of the maximum supported modulation order with the first maximum modulation order and the second maximum modulation order. Thus, the modulation and coding scheme (MCS) for transmission between the base station and the user equipment is controlled based on the selected modulation and coding scheme table.

The base station may also select a table based on other information, for example predefined selection criteria.

In LTE (and LTE-Advanced), the theoretical spectral efficiency is limited by 64QAM modulation. Figure 2 shows the simulated LTE-Advanced throughput (reference number 201) (code rate 8/9) for 8x8 MIMO and modulation limited to 64QAM in a spatially uncorrelated 1-tap Rayleigh channel. For comparison, Figure 2 also plots the spectral efficiency obtained with an extension to 256QAM (reference number 202). It is clear that the extension to 256QAM starts to have an effect in the SNR range of approximately 25 dB. In this figure, the average SINR is plotted against the throughput. Even if the average is lower than that region, the channel conditions are still good for a while, regardless of whether 256QAM gives a gain due to fading.

The throughput of LTE is also limited by the MCS in more practical scenarios (e.g., relay backhaul cases) where high spatial channel correlation occurs, limiting the use of large ranks. This is shown in Fig. 3, where the spectral efficiency for 2x2 and 4x4 MIMO schemes with adaptive rank and MCS selection in a high spectral correlation scenario is plotted as a function of the average signal-to-noise ratio. For both 2x2 and 4x4 schemes, two curves are shown, one where the MCS is limited to 64QAM (2x2: 304, 4x4: 302) and the other where the MCS is extended to 256QAM (2x2: 303, 4x4: 301). It is clear that the extension to 256QAM already increases the throughput from an SNR range of almost 10 dB in these scenarios. This means that the throughput is already at risk of being significantly lower than the maximum throughput possible with 64QAM.

The question is how to introduce 256QAM for LTE while maintaining backward compatibility and avoiding significant complexity. The addition of 256QAM needs to be done both to the MCS index and modulation tables defined in the LTE standard and to the CQI tables.

In Release 10, a new DCI format 2c was added to support closed-loop MIMO up to 8 layers. One simple solution would be to define a new DCI format for 256QAM (and use more than 6 bits for the modulation and coding scheme field of the DCI). This is not a desirable solution since it would double the number of DCI formats and significantly increase the complexity. In UMTS too, the extension from 16QAM to 64QAM is done by adding one extra signaling bit [R1-070635 R1-070570]. The extra bit can be provided by defining a new DCI format at the expense of worse decoding performance and more blind decoding, or at least by defining more arbitrary DCI sizes. Alternatively, bits can be "stolen" from some other signaling to limit the possibility of bits being stolen from a code allocation table that only supports half as many entries when 64QAM is enabled, for example in HSDPA.

Another possible solution is to take the existing MCS/CQI index table as a basis and switch its usage to only use a subset of the current MCS values, for example dropping every third one to make room for additional 256QAM values. This is a crude adaptation to channel conditions, which is undesirable. Hereinafter, this method is referred to as sub-sampling.

The idea of the method described here is to define a new procedure that allows the use of 256QAM in good channel conditions using the existing DCI format. For this purpose, an additional new MCS and CQI index table with an extension to 256QAM ( _Qm = 8) is created. This new table has the same size as the normal one. The decision whether the original index table or the table with the 256QAM extension is used is decided by the base station (or eNB), and the switch is indicated to the UE in a signaling message or in an implicit way.

In one embodiment, there is a common index area common to both the original table and the table with 256QAM extension, where the MCS/CQI index, modulation order and TBS index are the same and in the same position in both tables. Only this common MCS index area is used while switching tables to avoid ambiguity.

In one embodiment, the MCS/CQI index table with 256QAM extension is created so that room for 256QAM related TB (Transport Block) sizes is taken from the originally low TB size. Furthermore, there are some common modulation/TB sizes in the common MCS index area from the low range modulations where the extended 256QAM table is used and set for the situation where the channel condition drops rapidly. These indexes can be sub-sampled from the low TBS area.

A two-stage switching procedure is provided for CQI index table switching to ensure that the switching is visible to the UE and that it does not use ambiguous table entries during the switching. The MCS table is pre-switched to the 256QAM version.

There are also some common modulation/TB sizes in the common MCS index area from the higher range modulations designated for situations where 256QAM must be used quickly, e.g. before a clear selection is made during initial call setup, or to allow a fast reaction towards good quality.

The second table described here for the MCS and CQI index table is generated corresponding to 36.213 table 7.1.7-1, but with an extension to 256QAM (Q _m =8). One option is that the original table 7.1.7-1 and the table with the 256QAM extension are switched by the eNB with an RRC message (alternatively, MAC or control signaling messages can also be considered). In this case, the algorithm responsible for this switching is eNB vendor specific, but obviously takes into account the CQI report from the UE. The UE is responsible for switching the MCS index table based on the RRC message and sending a confirmation to the eNB regarding the received RRC message (the confirmation is not essential, but helps to avoid backward compatibility issues, since UEs that do not support the switching do not acknowledge the command).

Since RRC messages take about 100-200 ms to become effective at the UE (higher layer processing delays are not standardized and depend on how often they are retransmitted in case of detection errors) and there is uncertainty associated with the start time when (1) RRC messages are lost and (2) a new configuration is used by the UE, there must be a common MCS index area in both tables that allows data scheduling during the uncertainty period. This ensures that the MCS from that area is correctly understood regardless of whether a switch has already been made or not. This common area is continuous, i.e. has consecutive MCS entries, allowing fine adaptation during the switch. The MCS index, modulation order and TBS index are identical in both MCS index tables for this area. For example, during the RRC procedure to switch tables, only this common MCS index area can be used before the eNB receives confirmation from the UE that it has received the RRC message to switch MCS index tables. This common index area is also used when implicit table switching is used, in which case only the common area can be used during the implicit switching procedure.

In addition, there are some common low modulation/TB sizes in the common MCS index area for situations where the extended 256QAM table is used and the channel condition drops rapidly. The TB size required to send the switch command is available in the common MCS index area.

A new TB size is introduced into the MCS/CQI index table with 256QAM extension to increase the spectral efficiency in 256QAM.
- Room for these new TB sizes can be taken from the current lower TB sizes (QPSK and possibly lower 16QAM).
The reserved TBS size for 256QAM is also in the common MCS area for low modulation. This MCS is used for retransmissions in poor channel conditions, especially if the previous initial transmission was made with a higher MCS, especially with a higher modulation order, or with a different number of designated resources. However, there is no need to reserve an entry for the included 256QAM.
There are also some 256QAM entries in the common area for situations like call setup where it is useful to use 256QAM quickly (at the expense of losing forward compatibility and having fewer entries available in the "normal" range). Such a default "compromise" MCS table, where sub-sampling is used to obtain a high dynamic range, can be used as soon as the eNB is aware of the UE's capabilities. The switch from the legacy table, i.e. with a low maximum modulation order, to the compromise table, i.e. with a high maximum modulation order, can be done implicitly as part of the capability enquiry procedure that makes the capabilities available to the eNB. An explicit switch to a table focused on low or high MCS is then made, but also to a sub-sampled table if the channel conditions change too quickly to realize an explicit switch.

An example of a modulation table with MCS index and 256QAM extension is shown in Table 1. MCS indexes 12 to 31 refer to the continuous common MCS index area. MCS indexes 0, 5 and 10 refer to the sub-sampled low modulation common MCS index area, and MCS indexes 1 to 4, 6 to 9 and 1 refer to the 256QAM extension.

Similar to the MCS index table, a new CQI index table with 256QAM extension and common index area is used. The CQI table is switched with the same RRC message that is responsible for the MCS index table switching. In another case, the CQI table is switched implicitly. The eNB is responsible for handling possible error situations that arise due to the UE not knowing which table to use at the exact time during this RRC procedure. The eNB can, for example, simply ignore non-common CQI indexes and round them to the nearest common index or take a risk and decide based on heuristics which table is most likely to be associated. Such error cases arise because, in contrast to MCS selection, where the eNB initiates the change and therefore can avoid ambiguous entries during the switch, with CQI the UE is unaware of the impending switch and therefore cannot avoid it (unless it avoids it all the time, which is pointless). To increase the chances that the eNB will choose the right decision in case of ambiguous table entries, the minimum difference in TBS with respect to MCS index must be maximized. This is the case in Table 1, since the entries are arranged to increase the TBS for both 256 and QAM cases. If the 256QAM case were in the reverse order, then for MCS index 9, the TBS would be 26 (for 256QAM) or 8 (for QPSK), i.e. the difference would be 26-8=18, whereas in Table 1 the difference would be 33-8=25. The larger this difference is, the less likely the eNB will be unable to use the heuristic (e.g. if the channel really changes by that amount of 25 steps). For the same reason, it is beneficial to place the reserved 256QAM entry at the highest MCS index, i.e. for MCS index 11 in Table 1. The reserved entry only concerns the downlink, not the uplink. Therefore, in the uplink table, it can easily be dropped and replaced with the normal entry for QAM (TBS10 in Table 1).

To avoid ambiguous CQI reports during the switching time, a two-stage switching procedure can be used: in a first command, the eNB informs the switching. Then, the UE uses only CQI reports from the common MCS area. In a second command, the eNB commands the execution of the switching. Then, the UE uses the high MCS table completely. Now, despite the fact that there are two ambiguous periods, there is no risk of misunderstanding. That is, during both ambiguous periods, the UE uses either a well-defined MCS table (the original one during the first ambiguous period and the final one during the second period) or only MCS from the common MCS area, in which there is no risk of misunderstanding. This is because the entries from the common MCS area are coded identically in both tables. This makes the order of the entries in the high MCS area non-contiguous, but this is not very complicated and can be solved, for example, by implementing a lookup table.

The message flow according to this embodiment is as follows.
1) eNB to UE: RRC message to switch MCS tables and restrict CQI reporting to common index areas. The eNB uses only common index areas for MCS.
2) UE to eNB: Confirmation (and implicit message), the eNB now uses the full index area of the new MCS table, and the eNB knows that the UE uses the new CQI table (initially only the common index area).
3) eNB to UE: Confirm, the UE now uses the complete index area of the new CQI table.

Even though there are actually two handshakes, instead of using four messages, there are only two, because the intermediate messages have two meanings in both the CQI and MCS tables.

Another solution to avoid ambiguous CQI reports is to allow the UE to initiate the table switch for CQI and the eNB to initiate the switch for MCS. Thus, at all times, the originator of the message can switch to the corresponding table and therefore restrict the use to a common index area during the ambiguous period.

To indicate the UE's capability to support 256QAM, a new UE category including 256QAM is needed. If the UE does not support 256QAM, the above process and the MCS/CQI index table with 256QAM extension are not used. Alternatively, the eNB can send a switch command and decide to respond regardless of whether the UE supports 256QAM or not. In the initial access phase, the eNB does not yet know the UE's capability, so 256QAM and therefore MCS tables with higher modulation orders should not be used.

The above process can be used to extend to higher MCS. It can also be extended to cover and switch between more than two tables. A common MCS represented in more than one table must always be in the same position. There can be differences in the size and shape of the common index area between the tables, for example allowing different tables to have different levels of sub-sampling. For example, there are three tables: low, medium and high. The medium table can contain every other MCS entry in the low modulation area, while the high table uses only every third entry (similar to table 1), which are selected from those also present in the medium table. This is possible because 2 is a factor of 4, so the sub-sampling of the high table must not select every second or fourth entry that does not fit. This may also be used for table 1, which covers a wide range of CQI values.

The proposed solution has a number of advantages: The existing DCI format design remains unchanged. It allows supporting 256QAM for each DL DCI format while maintaining the existing DCI blind decoding burden at the UE. The proposed scheme provides a means for the eNB to easily avoid complex error cases due to signaling errors. The proposed design allows the basic functionality of the existing DL resource allocation (CQI/MCS index table) to remain unchanged. Hence, the impact on the DL scheduler operation is only minimal.

Figure 4 illustrates a cellular network system 400 according to an exemplary embodiment of the present invention. The cellular network system includes a base station 101 and a user device 102 served by the base station.

Below, the base station is described together with the decision unit. However, it should be noted that the decision unit is optional.

The base station comprises a determination unit 402 for determining actual channel conditions of a radio transmission channel used for transmission between the base station 101 and the user equipment 102 and for determining a maximum supported modulation order based on the determined actual channel conditions. The base station further comprises a selection unit 403 for selecting a first modulation and coding scheme table or a second modulation and coding scheme table based on a predefined criterion or based on a comparison of the maximum supported modulation order with the first maximum modulation order and the second maximum modulation order. The base station further comprises a control unit 404 for controlling a modulation and coding scheme for transmission between the base station and the user equipment based on the selected modulation and coding scheme table.

A base station is any type of access point or attachment point capable of providing wireless access to a cellular network system. Thus, wireless access is provided to user equipment or other network devices that can communicate wirelessly. The base station may be a NodeB, eNB, Home NodeB or HeNB, or other type of access point.

The base station includes a receiving unit, e.g., a receiver, as known to those skilled in the art. The base station also includes a transmitting or transmission unit, e.g., a transmitter. The receiver and transmitter may be implemented as a single unit, e.g., a transceiver 401. The transceiver, or receiving unit-transmitting unit, is adapted to communicate with user equipment via an antenna.

The decision unit 402, the selection unit 403 and the control unit 404 may be implemented as a single unit or may be implemented as part of a standard control unit, such as, for example, a CPU or a microcontroller.

A User Equipment (UE) is any type of communication end device capable of connecting to the base stations described herein. A UE may be, among others, a cellular mobile telephone, a personal digital assistant (PDA), a notebook computer, a printer, and/or any other mobile communication device.

The user equipment comprises a receiving unit or receiver for receiving signals from the base station. The user equipment comprises a transmitting unit for transmitting signals. The transmitting unit is a transmitter as known to those skilled in the art. The receiver and transmitting unit may be implemented as a single unit, for example a transceiver 405. The transceiver, or the receiver and transmitting unit, is adapted to communicate with the base station via an antenna.

The user equipment further comprises a control unit 406 for controlling and configuring transmissions based on information received from the base station representing the selected MCS table. This control unit may be implemented as a separate unit or may be part of a standard control unit, for example a CPU or a microcontroller.

With respect to the subject matter disclosed herein, certain embodiments may refer to "base station," "eNB," etc., with the understanding that each of these references is considered to implicitly disclose the general term "network component," or in other embodiments, the term "network access node." Other terms relating to specific standards or specific communications technologies are also considered to implicitly disclose each of the general terms along with their desired functionality.

Furthermore, it should be noted that the base stations disclosed herein are not limited to the dedicated entities described in some embodiments. Rather, the subject matter described herein may be implemented in a variety of ways at various locations in a communications network while still providing the desired functionality.

According to embodiments of the present invention, the suitable entities (e.g., components, units and devices) disclosed herein, e.g., a decision unit, may be provided, at least in part, in the form of respective computer programs enabling a processor device to perform the functionality of the respective entities disclosed herein. According to other embodiments, the suitable entities disclosed herein may be provided in hardware. According to other hybrid embodiments, some entities are provided in software while other entities are provided in hardware.

It should be noted that the entities (e.g., components, units, and devices) disclosed herein are not limited to the dedicated entities described in some embodiments. Rather, the subject matter disclosed herein can be implemented in various ways and with various granularities at the device level while still providing the desired functionality. Furthermore, it should be noted that, according to embodiments, a separate entity (e.g., a software module, a hardware module, or a hybrid module) may be provided for each function disclosed herein. According to other embodiments, an entity (e.g., a software module, a hardware module, or a hybrid module (combined software/hardware module)) is configured to provide two or more functions disclosed herein.

It should be noted that the term "comprises" does not exclude other elements or steps. Also, features from different embodiments described above can be combined in further refinements of the invention. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

100: Cellular network system 101: Base station 102: User equipment 103: Cell 201: 8x8 MIMO with 64QAM
202: 8x8 MIMO with 256QAM
301: 4x4 MIMO with 256QAM
302: 4x4 MIMO with 64QAM
303: 2x2 MIMO with 256QAM
304: 2x2 MIMO with 64QAM
400: Cellular network system 401: Base station transceiver 402: Base station determination unit 403: Base station selection unit 404: Base station control unit 405: User equipment transceiver 406: User equipment control unit

Claims (18)

A method for performing communication between a base station (101) and a user equipment (102) by said user equipment, comprising:
transmitting, by the user equipment, a channel quality indicator selectable by the user equipment based on a first channel quality indicator table supporting a maximum modulation order corresponding to 64QAM or a second channel quality indicator table supporting a maximum modulation order corresponding to 256QAM;
receiving radio resource control signaling from the base station including first information indicating a selected modulation and coding scheme table, the selected modulation and coding scheme table being selected from a modulation and coding scheme table including a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a maximum modulation order corresponding to 64 QAM or a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a maximum modulation order corresponding to 256 QAM;
receiving second information from the base station indicating a selected channel quality indicator table, the selected channel quality indicator table being the first channel quality indicator table or the second channel quality indicator table, selected from channel quality indicator tables including the first channel quality indicator table and the second channel quality indicator table;
performing, by the user equipment, the communication between the base station and the user equipment in accordance with a modulation and coding scheme controlled by the base station based on the selected modulation and coding scheme table;
The method includes: The method of claim 1, wherein the bits carrying the modulation and coding scheme index are the same for the first modulation and coding scheme table and the second modulation and coding scheme table. The method of claim 2, wherein the bits carrying the modulation and coding scheme index are bits in a downlink control information (DCI) format. 1. A method for controlling a modulation and coding scheme for communications between a base station and a user equipment, comprising the steps of:
receiving, by the base station, from the user equipment, a channel quality indicator selectable by the user equipment based on a first channel quality indicator table supporting a maximum modulation order corresponding to 64 QAM or a second channel quality indicator table supporting a maximum modulation order corresponding to 256 QAM;
selecting, by the base station based on the received channel quality indicator, from a modulation and coding scheme table comprising a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a maximum modulation order corresponding to 64 QAM or a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a maximum modulation order corresponding to 256 QAM, based on the received channel quality indicator;
transmitting, by the base station, radio resource control signaling to the user equipment, the radio resource control signaling including first information indicative of the selected modulation and coding scheme table;
selecting, by the base station, the first channel quality indicator table or the second channel quality indicator table from a channel quality indicator table including the first channel quality indicator table and the second channel quality indicator table;
determining, by said base station, actual channel conditions of a wireless transmission channel used for said communication based on said channel quality indicator;
transmitting second information indicative of the selected channel quality indicator table by the base station to the user equipment;
controlling, by the base station, the modulation and coding scheme for the communication between the base station and the user equipment based on the selected modulation and coding scheme table;
The method includes: The method of claim 4, wherein the bits carrying the modulation and coding scheme index are the same for the first modulation and coding scheme table and the second modulation and coding scheme table. The method of claim 5, wherein the bits carrying the modulation and coding scheme index are bits in a downlink control information (DCI) format. The method of any of claims 4 to 6, wherein the selection by the base station of the first channel quality indicator table or the second channel quality indicator table is based on the selected modulation and coding scheme table. The method according to any of claims 4 to 7, wherein selecting the modulation and coding scheme table is based on the actual channel conditions. The method according to any one of claims 1 to 8, wherein the second information indicative of the selected channel quality indicator table is implicitly provided by informing the user equipment of the selected modulation and coding scheme table. The method according to any one of claims 1 to 9, wherein the communication between the base station and the user equipment is in accordance with LTE or evolved LTE. A computer-readable medium having stored thereon instructions which, when executed by a data processor assembly, cause a user device to perform the method of any one of claims 1 to 3. A computer-readable medium having stored thereon instructions which, when executed by a data processor assembly, cause a base station to perform the method of any one of claims 4 to 8. A user device,
a transmitting unit adapted to transmit a channel quality indicator selectable by the user equipment based on a first channel quality indicator table supporting a maximum modulation order corresponding to 64 QAM or a second channel quality indicator table supporting a maximum modulation order corresponding to 256 QAM;
a receiving unit adapted to receive from a base station a radio resource control signaling including first information indicative of a selected modulation and coding scheme table, the selected modulation and coding scheme table being a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes with a maximum modulation order corresponding to 64QAM, or a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes with a maximum modulation order corresponding to 256QAM, the selected modulation and coding scheme table being from a modulation and coding scheme table including the first modulation and coding scheme table and the second modulation and coding scheme table, and further adapted to receive from the base station a second information indicative of a selected channel quality indicator table, the selected channel quality indicator table being the first channel quality indicator table or the second channel quality indicator table, the selected channel quality indicator table being from a channel quality indicator table including the first channel quality indicator table and the second channel quality indicator table;
a control unit (406) adapted to control communication between the base station and the user equipment in accordance with a modulation and coding scheme controlled by the base station based on the selected modulation and coding scheme table;
A user device comprising: The user equipment of claim 13, wherein the bits carrying the modulation and coding scheme index are the same for the first modulation and coding scheme table and the second modulation and coding scheme table. The user equipment of claim 14, wherein the bits carrying the modulation and coding scheme index are bits in a downlink control information (DCI) format. A user equipment according to any one of claims 13 to 15, wherein the second information indicative of the selected channel quality indicator table is implicitly provided by informing the user equipment of the selected modulation and coding scheme table. a base station for controlling a modulation and coding scheme for communications between said base station and a user equipment,
a receiving unit adapted to receive from a user equipment by a base station a channel quality indicator selectable by the user equipment based on a first channel quality indicator table supporting a maximum modulation order corresponding to 64 QAM or a second channel quality indicator table supporting a maximum modulation order corresponding to 256 QAM;
a selection unit (403) adapted to select, based on the received channel quality indicator, a first modulation and coding scheme table including an entry corresponding to a plurality of modulation and coding schemes with a maximum modulation order corresponding to 64QAM or a second modulation and coding scheme table including an entry corresponding to a plurality of modulation and coding schemes with a maximum modulation order corresponding to 256QAM from a modulation and coding scheme table including the first modulation and coding scheme table and the second modulation and coding scheme table, and to select the first channel quality indicator table or the second channel quality indicator table from a channel quality indicator table including the first channel quality indicator table and the second channel quality indicator table;
a determining unit configured to determine actual channel conditions of a wireless transmission channel used for said communication based on said channel quality indicator;
a transmitting unit configured to transmit radio resource control signaling to the user equipment, the radio resource control signaling including first information indicative of the selected modulation and coding scheme table, and to transmit second information indicative of the selected channel quality indicator table to the user equipment;
a control unit (404) adapted to control the modulation and coding scheme for the transmission between the base station and the user equipment based on the selected modulation and coding scheme table;
A base station equipped with The base station of claim 17, wherein the communication between the base station and the user equipment is in accordance with LTE or evolved LTE.

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