KR20140077679A - Method for cluster-based adaptive joint transmission - Google Patents

Abstract

The present invention relates to a cluster-based adaptive joint transmission method. The method includes: setting a wireless LAN cluster for combined transmission; checking a reception SINR of STAs connected to an AP belonging to the set wireless LAN cluster to check whether an outgoing STA exists; If there is an STA in which the outage occurs, calculating a data rate of a specific STA when only an AP having the largest interference channel size participates in the joint transmission to estimate whether or not the outage is generated; Calculating the data rate of the STA when the AP having the next largest interference channel participates in the combined transmission and re-predicting whether the outage is generated; and if the outage is not predicted, And informing the STA of whether or not to transmit the combined data.

Description

[0001] METHOD FOR CLUSTER-BASED ADAPTIVE JOINT TRANSMISSION [0002]

The present invention relates to a cluster-based adaptive combining transmission method, and more particularly, to a cluster-based adaptive combining transmission method considering environment characteristics of a wireless LAN network to control an interference problem in a wireless LAN network environment will be.

Recently, the data demand of users is increasing due to the rapid spread of portable wireless devices and the rapid increase of wireless data traffic such as high-quality video transmission. In the past, in order to increase the data demand, a method of installing a large number of APs (Access Points) was used. However, this method causes a decrease in the size of a cell and interference between adjacent APs, resulting in deterioration of the overall system performance. Therefore, it is necessary to study the technology to efficiently control the interference problem of the wireless LAN environment in the development of the high-speed wireless communication system.

Meanwhile, Joint Transmission refers to a technique in which transmitting nodes cooperate and transmit for a specific user simultaneously in order to improve performance of users located at a cell boundary. Cooperative transmitting nodes share data to be sent to one receiving node and transmit to one receiving node at the same time. It is a technology that can improve the performance of users with a low signal-to-noise ratio (SNR) at cell boundaries because they can receive desired signals through interference channels that previously served as interference. In addition to cooperative transmission, technologies such as dynamic point selection, coordinated scheduling and coordinated beamforming are included in Coordinated Multi-Point (CoMP) and applied to the LTE advanced standard .

The joint transmission scheme according to the prior art has been studied to be applied in a cellular environment. This is the technology applied under the name CoMP in the LTE Advanced Standard. Therefore, it is basically a technology that considers the environment in which the cell is arranged well.

However, it can be said that the indoor wireless LAN network environment is difficult to apply the joint transmission scheme considered in the existing cellular environment because of the indiscriminate arrangement of the AP and the overlapped cell structure.

In the existing WLAN standard, when the STA (station) receives the information sent by the AP correctly, the STA sends ACK information to the AP. However, when the STA does not decode the received data correctly, the STA does not send ACK information to the AP The AP has determined that the STA has not received the information and has retransmitted the same information to guarantee the decoding reliability of the STA. However, as the retransmission is repeated several times, transmission delay occurs, and the AP has to discard the data. Therefore, the joint transmission method can be considered as a method for ensuring the decoding reliability of the STA without retransmission.

Therefore, the present invention proposes a method for ensuring the optimal scenario and the decoding reliability of the STA that can be applied to a wireless LAN environment, and a clue to solve the interference problem in a wireless LAN environment, which has recently become a serious problem, .

To this end, the present invention provides a cluster-based adaptive combining transmission method considering environment characteristics of a wireless LAN network to control an interference problem in a wireless LAN network environment.

In the present invention, in order to satisfy the data rate threshold required by the STA, several APs perform joint transmission at the same time, thereby reducing the decoding problem of the STA due to interference.

The problems to be solved by the present invention are not limited to those mentioned above, and another problem to be solved can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a joint transmission method including: setting a wireless LAN cluster for combined transmission; checking a reception SINR of STAs connected to an AP belonging to the set wireless LAN cluster to determine whether an STA in which the outage occurs is present Calculating a data rate of a specific STA when only an AP having the largest interference channel size participates in a binding transmission when the STA exists; If the outage of the STA that received the combined transmission is confirmed, when the AP having the next largest interference channel participates in the combined transmission, the data rate of the STA is calculated, And if the outage of the STA that received the combined transmission is not confirmed, the AP and the STA in the RNC cluster are notified of the combined transmission It can include.

According to the embodiment of the present invention, the combined transmission scheme applied in the existing mobile communication environment reduces the interference problem in the wireless LAN environment through the method of the present invention. In the existing mobile communication environment, because the cell is configured regularly, the size of the interference channel is almost similar to that of the user channel, and the interference channel is likely to be larger due to irregular AP placement in the wireless LAN environment. Will result in improved performance. In addition, in the conventional WLAN system, if the outage of the STA occurs and the decoding is not properly performed, the AP resends the packet and resolved it. However, this retransmission causes a time delay, and if the time delay continues, the data is discarded. In consideration of this point, when several APs simultaneously transmit to a specific STA and provide a retransmission effect, the STA outage is not displayed without time delay, thereby solving the interference problem in the wireless LAN environment.

In addition, since the wireless LAN environment can configure a cluster of APs and perform combined transmission in a narrow area, a backhaul delay or a signal processing overhead is relatively more than a mobile communication environment . In the conventional mobile communication environment, it is not necessary to set a criterion for selecting a node to participate in a combined transmission due to a formal cell structure. However, since a wireless LAN environment has many cell structures in which APs are overlapped, Can be an important issue.

Therefore, in the present invention, a cluster for combined transmission is configured in consideration of the characteristics of the wireless LAN structure. In addition, it provides an adaptive dynamic coupled transmission AP selection scheme that ensures the required data rate threshold of the STA to improve data rate and transmission efficiency and reduce backhaul delay. This method improves the decoding reliability of the STA. In addition, when an outage occurs in a plurality of STAs, the performance of a plurality of STAs that fail to properly decode due to an outage occurring in the cluster is transmitted to the AP Can be improved by cooperative transmission.

1 shows an example of a wireless LAN network arrangement in an urban area.
FIG. 2 shows a network state in a combined transmission in a wireless LAN network in an urban area.
FIG. 3 is a flowchart illustrating a cluster-based adaptive joint transmission method according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating a network state prior to combined transmission in a wireless LAN network in an urban area.
5 illustrates a network situation after selecting a first AP for a combined transmission in a wireless LAN network in an urban area.
FIG. 6 shows a change in network status after selecting a combined transmission AP in a wireless LAN network in an urban area.
FIG. 7 shows a network situation when a plurality of STAs request a combined transmission in a wireless LAN network in an urban area.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions in the embodiments of the present invention, which may vary depending on the intention of the user, the intention or the custom of the operator. Therefore, the definition should be based on the contents throughout this specification.

As shown in Fig. 1, many APs are irregularly installed in a city center area such as a subway station having a large floating population. It can be seen that there are a large number of APs that cause co-channel interference (CCI) due to a large number of APs installed irregularly and having the same wireless LAN operating channel. Since so many APs are installed irregularly, the amount of interference received by users is increased. As can be seen in FIG. 1, in STA1, it is desired to transmit only in AP1. In AP4, 5, and 6, interference is caused by STA1. However, if the joint transmission scheme is introduced in FIG. 1, the interference sources to the STA1 can send the signal desired by the STA1 as shown in FIG. 2, thereby improving the decoding reliability. However, if all the APs send the information that STA1 wants by the route that acts as the interferer, it can not use the radio resources optimally and because there is no opportunity to transmit information to other STAs It may lead to performance degradation from the system-wide point of view.

In the case of the combined communication method in the conventional cellular environment, since the cells are arranged in a planned manner, a user at a cell boundary can clearly know which base station receives a signal. However, in the case of a wireless LAN network environment, as shown in FIG. 1, since the number of APs that interfere with each other due to indiscreet installation and transmission of APs changes constantly, Is very important. In addition, the increase of the interference sources due to the irrelevant arrangement of the WLAN APs results in various combined transmission paths. If the optimum path is selected among the various combined transmission paths, the decoding reliability is improved without retransmission, Can solve the interference problem and improve the overall system performance.

FIG. 3 is a flowchart illustrating a cluster-based adaptive joint transmission method according to an embodiment of the present invention.

As described above, the adaptive joint transmission method according to the embodiment of the present invention includes a step of setting a wireless LAN cluster for combined transmission (S110), a reception SINR of STAs connected to an AP belonging to a set wireless LAN cluster A step S140 of checking whether there is an STA in which an outage occurs or a step S140 in which each AP independently performs transmission in the existing WLAN method when the STA in which the outage occurs does not exist, (S150, S160) whether the outage is generated by calculating a data rate of a specific STA when only the AP having the largest interference channel size participates in the joint transmission when the STA in which the outage occurs exists; (S170, S160) of estimating the occurrence rate of the outage by calculating the data rate of the STA when the AP having the next largest interference channel participates in the combined transmission, And notifying the AP and the STA in the RNC cluster of whether or not the connection is transmitted (S180).

Hereinafter, a cluster-based adaptive combining transmission method according to an embodiment of the present invention will be described in detail.

First, a wireless LAN cluster for combined transmission is set up and configured. Basically, for combined transmission, all the APs need to know the information desired by the user who wants to receive the information through the combined transmission. The RNC (Radio Network Controller) serves as the backbone of such information exchange, (Backhaul network). An important consideration when configuring a WLAN cluster for combined transmissions is to minimize the time delay when information is shared over the backhaul. In order to prevent deterioration of the overall performance of the system, the delays for information transmission should be roughly the same. In order to minimize the delay of information sharing, it is determined that the APs constituting the cluster should be connected to one RNC. Eventually, the backhaul delay that exchanges information plays an important role in determining the number of APs in the cluster.

Then, a signal-to-interference plus noise ratio (SINR) of the STA is measured.

Once the combined transport cluster is configured, it checks the received SINR of all STAs associated with the APs in the cluster. The method of checking the SINR is as follows.

)에 미만하는 값을 가져서 수신기에서 디코딩을 제대로 수행할 수 없는 상황을 의미한다. 이를 수학식으로 나타내면 아래의 수학식 1과 같다.First, APs belonging to the cluster perform transmission without cooperation to each STA. If an outage occurs in one or more STAs in the cluster, the AP switches to the joint transmission mode. Here, the outage means that the current data rate is the reference data rate threshold value (

), Which means that the receiver can not perform the decoding properly. This can be expressed by the following equation (1).

)을 사용자가 요구하는 정보의 양에 따라 동적으로 정해진다.The reference reception SINR threshold is the QoS data rate of each STA (

) Is dynamically determined according to the amount of information required by the user.

Next, a combined transmission mode is performed. After measuring the reception SINR of the STA as described above, when one or more STAs have an SINR value that is less than the reference due to the influence of the interference signal and the outage occurs, the combined transmission mode starts. If there is an STA that is below the reference in the joint transmission mode, the APs interfering with the STA share the data to be transmitted from the RNC to the STA that is under reference to improve the decoding reliability of the STA. However, if all of the APs in the cluster that are interfering with the STA are performing joint transmissions, then there is a high probability that they exceed the STA's threshold data rate threshold. That is, wireless resources are inefficiently used from the viewpoint of the entire network. In other words, when the data rate threshold of the STA is determined to be the required amount of data, the number of APs to perform cooperating is determined optimally so that the RNC satisfies the data rate threshold value so that no outage occurs.

In addition, if the transmission is performed through cooperation, the most appropriate number of cooperating APs is required in order to reduce a combining delay occurring when a receiving STA combines signals transmitted from different APs. Also, if the number of APs that need to share information through the RNC increases more than necessary, time delay problems such as backhaul delay may occur even if there are APs in the same cluster. For this reason, the method for determining the number of APs to perform combined transmission should be determined optimally considering the required data rate threshold of the STA and the channel value from the AP to the STA acting as an interference. First, the RNC needs to know the required data rate threshold of the STA to be combined and the channel value to this STA in each AP. Based on these values, the RNC determines the number of cooperating APs to prevent the STA from leaving the outage by determining the interference channel value of the AP and the STA. Here, the interference channel value is a value considering not only rayleigh fading but also large scale fading including pathloss. For example, if only the AP with the largest interference channel value satisfies the required data rate threshold of the STA when the cooperative transmission is performed, the AP with the largest value of the interference channel is originally associated with the STA Only the AP can perform the combined transmission. However, if it is assumed that the transmission is performed only in the AP having the greatest interference channel value, if it is determined that the STA does not satisfy the required data rate threshold value, it is assumed that the AP having the large interference channel value is included in the cooperative transmission. It is determined whether or not the text threshold value is satisfied. In this way, an appropriate number of APs must be determined and participated in the combined transmission in order to obtain data rates above the STA's required data rate threshold. If there are a large number of STAs that can not exceed the reference SINR value in the cluster, the STA supporting the joint transmission first supports the joint transmission, and the procedure for performing joint transmission for each STA proceeds according to the above method.

Hereinafter, a description will be made of an exemplary procedure for performing a combined transmission mode according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating a network before joining transmission in a wireless LAN network in a city area to explain a starting process of a combined transmission mode according to a cluster-based adaptive combining transmission method according to an embodiment of the present invention.

)을 만족하지 못하여 아우티지가 되면 결합 전송 모드를 시작한다.When STA1 receives information from AP1, it receives interference from AP4,5,6. If the received SINR of the STA1 is smaller than its requested data rate (

) Is not satisfied, and when it becomes outage, it starts the combined transmission mode.

5 is a diagram illustrating a network situation after selecting a first AP for a combined transmission in a wireless LAN network in an urban area for explaining a combined transmission AP selection process according to a cluster-based adaptive combining transmission method according to an embodiment of the present invention to be.

If the size of the channels caused by the interference to the STA1 is defined as Equation (3), the AP5 shares the information from the RNC to the STA1 and performs the combined transmission with the AP1.

값이 작아서 수학식 4와 같이 STA1가 여전히 아우티지가 발생하는 경우 RNC는 디코딩 신뢰도를 만족시키기 위해 AP5 이외에 결합 전송을 위한 AP를 추가해야 한다.If the required data rate threshold value of STA1 is high as shown in Equation 4 below

If the STA1 still generates an outage as shown in Equation (4), the RNC must add an AP for combined transmission in addition to AP5 to satisfy the decoding reliability.

이라고 가정할 때 AP6도 도 6과 같이 결합 전송에 참여한다.The criterion that the RNC adds the AP for the combined transmission is a channel value considering both the large scale fading and the small scale fading. In FIG. 5, if the outage still occurs, the second largest channel value

AP6 also participates in the combined transmission as shown in FIG.

는 분산된 AP_k에서 하나의 STA_i으로 정보를 송신할 때 일관(coherently)되게 채널 값이 더해지게 하기 위한 위상 회전(phase rotation) 보정 프리코딩 메트릭스(precoding matrix) 이다. 여기서, 채널 값이 일관되게 더해지게 프리코딩 메트릭스를 만들더라도 각기 다른 송신기에서 수신기로의 전달 딜레이(propagation delay) 등의 문제로 인해 수신기에서의 연결(combining)에 영향을 줄 수 있다.In Equation (4)

Is a phase rotation corrected precoding matrix for coherently adding channel values when transmitting information from a distributed AP _k to one STA _i . Here, even if a precoding matrix is made to consistently add channel values, it may affect combining in the receiver due to problems such as propagation delays from different transmitters to receivers.

6 is a diagram illustrating a change in a network status after selecting a combined transmission AP in a wireless LAN network in an urban area.

If the requested data rate threshold of STA1 is satisfied by the combined transmission of AP5, AP6, and AP1 as shown in FIG. 6 and Equation (5) below, there is no further AP participation for combined transmission for backhaul delay and efficient use of resources.

When determining the number of APs for combined transmission in order to guarantee the value of the interference channel and the requested data rate threshold of the STA, the RNC judges whether or not the STA is outgoing by assuming transmission from the AP with the best interference channel, The AP with the largest interference channel value performs the concatenated transmission sequentially.

The RNC internally checks the QoS value of each STA and the channel value to each AP-STA, and dynamically determines whether a few APs should perform combined transmission to determine whether the STA's outage will occur.

After the final determination, it notifies APs and STAs belonging to the inside of the cluster whether or not the combined transmission is performed.

When there are many STAs in which the outage occurs, as shown in FIG. 7, the STA performs the joint transmission in the TDMA scheme. If there are several STAs in the cluster that require joint transmission, it is possible to perform joint transmission of the STA requesting transmission first, and then performing joint transmission of the requested STA. The method of selecting a combined transmission AP for a specific STA at a moment follows the procedure described in the selection process of the combined transmission AP.

Combinations of the steps of the flowcharts appended to the present invention may be performed by computer program instructions. These computer program instructions may be loaded into a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus so that the instructions, which are executed via a processor of a computer or other programmable data processing apparatus, Lt; / RTI > These computer program instructions may also be stored in a computer usable or computer readable memory capable of directing a computer or other programmable data processing apparatus to implement the functionality in a particular manner so that the computer usable or computer readable memory It is also possible to produce manufacturing items that contain instruction means for performing the functions described in each step of the flowchart. Computer program instructions may also be stored on a computer or other programmable data processing equipment so that a series of operating steps may be performed on a computer or other programmable data processing equipment to create a computer- It is also possible for the instructions to perform the processing equipment to provide steps for executing the functions described in each step of the flowchart.

In addition, each step may represent a module, segment, or portion of code that includes one or more executable instructions for executing the specified logical function (s). It should also be noted that in some alternative embodiments, the functions mentioned in the steps may occur out of order. For example, the two steps shown in succession may in fact be performed substantially concurrently, or the steps may sometimes be performed in reverse order according to the corresponding function.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (1)

Establishing a wireless LAN cluster for combined transmission,
Checking a reception SINR of STAs connected to an AP belonging to the set WLAN cluster to check whether there is an STA in which the outage occurs;
If there is an STA in which the outage occurs, calculating a data rate of a specific STA when only an AP having the largest interference channel size participates in joint transmission,
Estimating occurrence of the outage by calculating the data rate of the STA when the AP having the next largest interference channel participates in the combined transmission,
And notifying the AP and the STA in the RNC cluster of whether or not the outage is not generated.

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