KR102118916B1 - Method for cluster-based adaptive joint transmission - Google Patents

Abstract

The present invention relates to a cluster-based adaptive combined transmission method. The disclosed combined transmission method comprises: setting a wireless LAN cluster for combined transmission, and checking received SINRs of STAs connected to APs belonging to the configured wireless LAN cluster to check whether an STA having an outage exists or not, When the STA having the outage exists, calculating the data rate of a specific STA when only the AP having the largest interference channel size participates in the combined transmission, and predicting whether the outage occurs, and when the outage is predicted When the AP having the next largest interference channel size participates in the combined transmission, calculating the STA data rate to predict the occurrence of the outage again, and when the occurrence of the outage is predicted, the AP in the RNC cluster And notifying the STA whether the combination is transmitted.

Description

METHOD FOR CLUSTER-BASED ADAPTIVE JOINT TRANSMISSION}

The present invention relates to a cluster-based adaptive combined transmission method, and more particularly, to a cluster-based adaptive combined transmission method considering environmental characteristics of a WLAN network in order to control interference problems in a WLAN network environment. will be.

2. Description of the Related Art Recently, a user's data demand is increasing due to the rapid spread of portable wireless devices and the rapid increase in wireless data traffic such as high-definition video transmission. Previously, a method of installing a large number of APs (Access Points) was used to increase the amount of data required. However, this method reduced the size of the cell and caused interference between adjacent APs, resulting in a decrease in overall system performance. Therefore, it can be said that research into a technique for efficiently controlling the interference problem in the wireless LAN environment is essential for the development of a high-speed wireless communication system.

On the other hand, joint transmission (Joint Transmission) is a technique in which transmission nodes cooperate and simultaneously transmit for a specific user to improve performance of users located at a cell boundary. The transmitting nodes that cooperate share data to be transmitted to one receiving node, and simultaneously transmit the data to one receiving node. It is a technology that can improve the performance of users with a low signal-to-noise ratio (SNR) at the cell boundary because a desired signal can be received through an interference channel that has been used as interference. In addition to combined transmission, technologies such as dynamic point selection, coordinated scheduling, and coordinated beamforming are included in CoMP (Coordinated Multi-Point) and applied to LTE advanced standards. .

The combined transmission method according to the prior art has been studied to be applied in a cellular environment. That is the technology applied under the name CoMP in the LTE Advanced standard. Therefore, it can be said that it is basically a technology that considers an environment in which cells are well-planned.

However, it can be said that the indoor wireless LAN network environment has difficulty in applying the combined transmission scheme considered in the existing cellular environment as it is due to the indiscriminate arrangement of the AP and the overlapped cell structure.

In the existing WLAN standard, when the STA (station) properly receives the information sent by the AP, the STA sends the ACK information to the AP, whereas the STA does not send the ACK information to the AP when the received data is not properly decoded. Then, the AP determines that the STA has not received the information and retransmits the same information, thereby guaranteeing the decoding reliability of the STA. However, as retransmission is performed several times, a transmission delay occurs, and the AP is forced to discard the data, so a combined transmission method may be considered as a method for guaranteeing the decoding reliability of the STA without retransmission.

Therefore, in the present invention, by providing an optimal scenario in which the combined transmission scheme can be applied to a wireless LAN environment and a method for ensuring decoding reliability of the STA, a clue to solve the interference problem in the wireless LAN environment, which has recently emerged as a serious problem, is provided. Want to provide.

To this end, the present invention provides a cluster-based adaptive combined transmission method in consideration of environmental characteristics of a WLAN network in order to control interference problems in a WLAN network environment.

In the present invention, multiple APs simultaneously perform combined transmission to satisfy a data rate threshold required by the STA, thereby reducing the decoding problem of the STA due to interference.

The problem to be solved of the present invention is not limited to those mentioned above, and another problem to be solved that is not mentioned will be clearly understood by those having ordinary knowledge to which the present invention belongs from the following description.

In one aspect of the present invention, a combined transmission method comprises: setting a wireless LAN cluster for combined transmission, and checking the received SINR of STAs connected to an AP belonging to the configured wireless LAN cluster to determine whether an STA with an outage occurs. Checking, and if the STA where the outage occurs, calculating the data rate of a specific STA when only the AP having the largest interference channel size participates in the combined transmission, and determining whether the STA that received the combined transmission is an outage. Checking, and when the outage of the STA receiving the combined transmission is confirmed, when the AP having the next largest interference channel size participates in the combined transmission, the STA calculates the data rate of the STA to receive the combined transmission again. A step of checking and notifying the AP and the STA in the RNC cluster whether or not the binding is transmitted may be included when the outage of the STA receiving the combined transmission is not confirmed.

According to an embodiment of the present invention, a combined transmission method applied in an existing mobile communication environment reduces interference problems in a wireless LAN environment through the method of the present invention. In the existing mobile communication environment, since the cells are regularly configured, the size of the interference channel and the channel of the user are almost the same, whereas the WLAN environment is more likely to have a larger interference channel due to irregular AP placement. When you do, it brings an improvement in performance. In addition, in the existing WLAN system, when an STA outage occurs and decoding is not properly performed, the AP retransmits the problem and resolves this. However, this retransmission sometimes causes a time delay, and if the time delay persists, data is discarded. Considering this, if multiple APs simultaneously transmit to a specific STA and give a retransmission effect, interference of the STA environment is solved by preventing the STA from appearing without a time delay.

In addition, in a wireless LAN environment, a backhaul delay or signal processing overhead is relatively higher than that of a mobile communication environment because a radio network controller (RNC) can configure a cluster of APs and perform combined transmission in a small area. It can be seen as small. In the conventional mobile communication environment, the combined transmission does not need to determine the criteria for node selection to participate in the combined transmission due to the standardized cell structure, but in the WLAN environment, the APs to participate in the combined transmission because the multiple APs often have overlapped cell structures. The criteria for selecting can be an important issue.

Therefore, in the present invention, a cluster for combined transmission is configured in consideration of the characteristics of the WLAN structure. In addition, it provides an adaptive dynamic combined transmission AP selection scheme that guarantees the required data rate threshold of the STA in order to improve data rate and transmission efficiency and reduce backhaul delay. Through this method, the decoding reliability of the STA is improved. In addition, when the outage occurs in a plurality of STAs, the STAs that first request the combined transmission send information through the combined transmission in order, thereby generating an outage in the cluster and performing performance of the multiple STAs that have not properly decoded the AP. It can be improved by their cooperative transmission.

1 shows an example of a WLAN network deployment in an urban area.
Figure 2 shows the network situation when combined transmission in a wireless LAN network in the downtown area.
3 is a flowchart illustrating a cluster-based adaptive combined transmission method according to an embodiment of the present invention.
4 shows a network situation before combined transmission in a wireless LAN network in an urban area.
5 shows the network situation after selecting the first AP for the combined transmission in the wireless LAN network in the downtown area.
6 shows a change in network conditions after selecting a combined transmission AP in a wireless LAN network in an urban area.
7 shows a network situation when several STAs request combined transmission in a wireless LAN network in an urban area.

Advantages and features of the present invention, and methods for achieving them will be clarified with reference to embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention pertains. It is provided to fully inform the holder of the scope of the invention, and the invention is only defined by the scope of the claims.

In describing embodiments of the present invention, when it is determined that a detailed description of known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, terms to be described later are terms defined in consideration of functions in an embodiment of the present invention, which may vary according to a user's or operator's intention or practice. Therefore, the definition should be made based on the contents throughout this specification.

In the downtown area, such as a subway station with many floating populations, many APs are irregularly installed as shown in FIG. 1. It can be seen that there are a lot of APs that cause co-channel interference (CCI) due to the fact that many APs are installed irregularly and have the same WLAN operation channel. Since many APs are installed irregularly, the amount of interference received by users has also increased. As can be seen in FIG. 1, STA1 wants to receive transmission only from AP1, but it can be seen that AP4,5,6 interferes with STA1 communication because it affects interference like a dotted line. However, if a combined transmission scheme is introduced in FIG. 1, interference sources affecting STA1 can be transmitted as desired by STA1 as shown in FIG. 2, thereby improving decoding reliability. However, if all APs transmit information desired by STA1 through a path acting as an interference source, radio resources are not optimally used and there is no opportunity to transmit information to other STAs (all APs acting as interference sources perform combined transmissions). Rather, it may cause a decrease in performance from the overall system point of view.

In the case of the combined communication method in the existing cellular environment, since the cells are intentionally arranged, it is possible to clearly know which base station a user at the cell boundary will receive a signal from. However, in the case of a wireless LAN network environment, as shown in FIG. 1, the number of interfering APs is constantly changing due to the indiscriminate installation and transmission situation of APs, thereby determining which AP to participate in combined transmission to improve decoding reliability. Is very important. In addition, the increase of interference sources due to the indiscriminate arrangement of the wireless LAN APs has created various combined transmission paths. If the optimal path is selected from the various combined transmission paths, decoding reliability is improved without retransmission, and the wireless LAN environment. It can also solve the interference problem and improve the overall system performance.

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

As shown in this, the adaptive combined transmission method according to an embodiment of the present invention comprises: setting a WLAN cluster for combined transmission (S110); and checking received SINRs of STAs connected to APs belonging to the configured WLAN cluster. Step (S120, S130) of determining whether there is an STA where the outage occurs and each AP independently transmitting in the existing WLAN method when the STA where the outage occurs does not exist (S140) And, if there is an STA where the outage occurs, predicting whether the outage occurs by calculating the data rate of a specific STA when only the AP having the largest interference channel size participates in the combined transmission (S150, S160). When the occurrence of is predicted, when the AP having the largest interference channel size participates in the combined transmission, calculating the STA's data rate to predict the occurrence of outage again (S170, S160), and the outage of outage occurs If predicted, the step of notifying whether the AP and the STA in the RNC cluster are transmitted (S180).

Hereinafter, the cluster-based adaptive combined 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 and configured. Basically, for the combined transmission, all APs need to know all the information desired by the user who wants to receive the information through the combined transmission. The central role of such information exchange is called RNC (Radio Network Controller), and connecting the RNC and the AP is a backhaul. It is called a network (Backhaul Network). An important point to consider when configuring a wireless LAN cluster for combined transmission is to minimize the time delay when information is shared through a backhaul. In order to prevent deterioration of overall system performance, the delay for transmitting information should be roughly similar. In order to minimize the delay of information sharing, it is determined that APs constituting a cluster should be connected to one RNC. Eventually, the delay of the backhaul exchanging information plays an important role in determining the number of APs included in the cluster.

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

After the combined transmission cluster is configured, the received SINR of all STAs connected to the AP belonging to the cluster is checked. The method of checking 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 a cluster perform transmission without cooperation to each STA, and if an outage occurs in one or more STAs in the cluster, the AP switches to a combined transmission mode. Here, the current data rate is the reference data rate threshold (

), which means that the receiver cannot properly decode. If this is expressed as an equation, it is as shown in equation 1 below.

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

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

Next, a combined transmission mode is performed. As described above, after measuring the received SINR of the STA, when one or more STAs have an SINR value that is less than the standard due to the influence of the interference signal, when the outage occurs, the combined transmission mode starts. In the combined transmission mode, if there is an under-standard STA, APs interfering with the STA to improve decoding reliability of the STA share data to be transmitted to an under-standard STA from the RNC and perform combined transmission. However, if all of the APs included in the cluster and interfering with the STA perform the combined transmission, it is highly likely to satisfy the STA's reference data rate threshold. That is, radio resources were used inefficiently from the whole network point of view. In other words, when the STA's data rate threshold is determined to be the required amount of data, the RNC optimally determines the number of APs to cooperate to satisfy this data rate threshold so that no outage occurs.

In addition, the most appropriate number of cooperating APs is required to reduce the combining delay that occurs when the receiving STA combines signals transmitted from different APs when the transmission is performed through performing the cooperation. In addition, if the number of APs that need to share information through the RNC increases more than necessary, a time delay problem such as a backhaul delay may occur even in an AP existing in the same cluster. For this reason, the method of determining the number of APs to perform the combined transmission should be optimally determined by taking into consideration a complex channel value from the AP to the STA, which acts as interference with the required data rate threshold of the STA. First, the RNC needs to know the required data rate threshold of the STA to be combined and the channel value from each AP to this STA. Based on these values, the RNC determines the number of cooperative APs to prevent the STA from being placed as an outlook and determines the interference channel values of the AP and the STA. Here, the interference channel value is a value that considers not only Rayleigh fading but also large scale fading including pathloss. For example, if only the AP having the largest interference channel value can satisfy the STA's required data rate threshold when performing cooperative transmission, the AP with the largest interference channel value is originally associated with the STA. Only the AP needs to perform combined transmission. However, if it is determined that transmission is performed only on the AP having the largest interference channel value, and it is determined that the STA does not satisfy the required data rate threshold, the AP having the second largest interference channel value is also assumed to participate in the cooperative transmission and then requested data. It is determined whether the rate threshold is satisfied. In this way, in order to obtain a data rate above the required data rate threshold of the STA, an appropriate number of APs must be determined to participate in the combined transmission. If there are a large number of STAs that do not exceed the reference SINR value in the cluster, the STA that first requested the combined transmission is supported through the combined transmission, and the procedure of performing the combined transmission for each STA proceeds according to the method described above.

Hereinafter, a process of performing a combined transmission mode according to an embodiment of the present invention will be described by way of example.

FIG. 4 is a diagram illustrating a network situation before a combined transmission in a wireless LAN network in a downtown area to describe a process of starting a combined transmission mode according to a cluster-based adaptive combined 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 STA1 is its own requested data rate (Equation 2 below)

) Is not satisfied, and when it becomes an outage, the combined transmission mode is started.

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

If the size of the channels affecting STA1 is defined as in Equation 3 below, AP5 shares information from RNC to STA1 to perform combined transmission with 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 of STA1 is high as shown in Equation 4 below,

If STA1 still has an outage as shown in Equation 4 because the value is small, the RNC needs to add an AP for combined transmission in addition to AP5 to satisfy decoding reliability.

이라고 가정할 때 AP6도 도 6과 같이 결합 전송에 참여한다.A criterion for the RNC to add an AP for combined transmission is a channel value considering both large scale and small scale fading. In Fig. 5, if the outage still occurs, having the second largest channel value

Assuming that AP6 also participates in the combined transmission as shown in FIG. 6.

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 above

Is a phase rotation correction precoding matrix for coherently adding channel values when transmitting information from a distributed AP _k to one STA _i . Here, even if the precoding metrics are created such that the channel values are consistently added, the coupling at the receiver may be affected due to problems such as propagation delay from different transmitters to the receiver.

6 is a view showing a change in network conditions after selecting a combined transmission AP in a wireless LAN network in an urban area.

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

When determining the number of APs for combined transmission in order to ensure the value of the interference channel and the required data rate threshold of the STA, the RNC determines whether the STA is out of reach and assumes the outage by assuming the transmission from the AP with the best interference channel. When is generated, the AP having the second largest interference channel sequentially performs combined transmission.

RNC internally grasps the QoS value of each STA and the channel value of each AP-STA, and dynamically determines whether the STA's outage does not occur when several APs transmit the combined transmission.

After the final determination, the AP and the STAs belonging to the cluster are notified of the combination transmission.

When there are a large number of STAs with outages, as shown in FIG. 7, combined transmission is performed in a TDMA scheme. If there are multiple STAs that need to be combined and transmitted within the cluster, the STA may first perform the combined transmission of the requesting STA and then perform the combined transmission of the requested STA. The method for selecting a combined transmission AP for a specific STA at one moment follows the procedure described in the selection process of the combined transmission AP.

Combinations of each step of the flowchart attached to the present invention may be performed by computer program instructions. Since these computer program instructions may be mounted on a processor of a general purpose computer, special purpose computer, or other programmable data processing equipment, those instructions performed through a processor of a computer or other programmable data processing equipment are described in each step of the flowchart. It creates a means to do them. These computer program instructions can also be stored in computer readable or computer readable memory that can be oriented to a computer or other programmable data processing equipment to implement a function in a particular way, so that computer readable or computer readable memory It is also possible for the instructions stored in to produce an article of manufacture containing instructions means for performing the functions described in each step of the flowchart. Computer program instructions can also be mounted on a computer or other programmable data processing equipment, so a series of operational steps are performed on a computer or other programmable data processing equipment to create a process that is executed by the computer to generate a computer or other programmable data. It is also possible for instructions to perform processing equipment to provide steps for performing the functions described in each step of the flowchart.

Further, 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, it is also possible that the functions mentioned in the steps occur out of order. For example, the two steps shown in succession may in fact be performed substantially simultaneously, or the steps may sometimes be performed in reverse order depending on the corresponding function.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the claims below, and all technical thoughts within the equivalent range should be interpreted as being included in the scope of the present invention.

Claims (10)

In the combined transmission method performed by a radio network controller (RNC),
Setting a wireless LAN cluster for combined transmission;
Checking the received signal-to-interference plus noise ratio (SINR) of one or more STAs (Stations) connected to a first access point (AP) belonging to the set WLAN cluster to determine whether an STA with an outage exists ;
Determining a plurality of STAs based on an order of a combination transmission request among a plurality of STAs when there are a plurality of STAs with an outage among the STAs;
Determining a second AP having the largest interference channel value for the STA when the STA with the outage occurs among the STAs;
Predicting whether an outage occurs by calculating a data rate of the STA when the second AP participates in a combined transmission with the first AP; And
If it is predicted that the STA does not generate an outage, notifying the first AP and the STA of the combined transmission of the second AP.
Containing,
Cluster-based adaptive combined transmission method.
According to claim 1,
The step of confirming the presence of the STA where the outage occurs is,
Determining whether an outage occurs in the STA based on the data rate and the reference data rate threshold of the STA
Including,
The reference data rate threshold is dynamically determined according to the amount of information that the first AP intends to transmit to the STA,
Cluster-based adaptive combined transmission method.
According to claim 1,
When combined transmission is performed, receiving data to be transmitted from the first AP to the STA;
Transmitting the data to the second AP participating in the combined transmission
Further comprising,
The data is transmitted to the STA by the first AP and the second AP,
Cluster-based adaptive combined transmission method.
delete According to claim 1,
The interference channel value between the STA and the second AP is,
Calculated based on Rayleigh fading and large scale fading,
Cluster-based adaptive combined transmission method.
delete delete According to claim 1,
Even when the second AP participates in the combined transmission, when the occurrence of the outage is predicted to the STA, the third AP having the next largest size of the interference channel value may further participate in the combined transmission. Determining; And
Re-predicting whether the outage occurs by calculating a data rate of the STA for the combined transmission in which the third AP participates.
Further comprising,
Cluster-based adaptive combined transmission method.
In the method for receiving information from a plurality of AP (Access Point) through a combined transmission, performed by a STA (station),
Calculating a signal-to-interference plus noise ratio (SINR) for a first AP connected to the STA;
Transmitting the SINR to a radio network controller (RNC) connected to the plurality of APs-The first AP and the second AP to transmit the information to the STA among the plurality of APs are determined by the RNC, The second AP has the largest interference channel value for the STA -;
Receiving data from the first AP and the second AP, respectively, through combined transmission; And
Decoding the information based on data received from the first AP and data received from the second AP
Including,
When there are a plurality of STAs where the outage occurs, the order of the combined transmission of the STAs is determined by the RNC based on the order of the combined transmission requests among the plurality of STAs.
Method of receiving information through combined transmission.
The method of claim 9,
Starting the combined transmission mode when the calculated SINR does not satisfy the required data rate.
Further comprising,
Method of receiving information through combined transmission.

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