KR101884635B1 - Appratus of distributed downlink resourse allocation for densely deployed ofdma wlan and method of the same - Google Patents

Abstract

A distributed downlink resource allocation apparatus in an OFDMA-based dense wireless LAN environment including a first access point, a second access point positioned adjacent to the first access point, and a plurality of terminals concatenated to each access point, A distributed downlink resource allocation method is disclosed. The downlink resource allocation method includes the steps of: a first access point collecting resource allocation information and signal strength information of a neighboring second access point that the terminal receives from the terminal; acquiring resource allocation information and signal strength information of the second access point; , Calculating a normalized throughput (u _t ) and a normalized fairness (u _f ) using the allocation matrix Y and generating an allocation matrix Y and allocating resources so that the utility (u) is maximized.

Description

[0001] APPARATUS FOR DISTRIBUTED DOWNLINK RESOURCE ALLOCATION FOR DENSELY DEPLOYED OFDMA WLAN AND METHOD OF THE SAME [0002]

The present invention relates to an apparatus and method for distributed downlink resource allocation in an OFDMA-based dense wireless LAN environment, and more particularly, to a method and apparatus for collecting resource allocation information and signal strength of neighboring access points, And more particularly, to an apparatus and a method for allocating resources so as to maximize utility.

The present invention proposes a distributed downlink resource allocation technique in an OFDMA-based dense wireless LAN environment.

The number of personal terminals such as smart phones, laptops, and multimedia devices is rapidly increasing. Most of these devices send and receive data through a wireless local area network (WLAN), and thus there is an increasing interest in improving the performance of the wireless LAN.

In order to improve the performance of wireless LAN, IEEE 802.11n supports 4x4 multiple input multiple output (MIMO) and IEEE802.11ac, the latest wireless LAN standard, supports 8x8 MIMO to improve the throughput of the wireless LAN physical layer have. However, since the improvement of the throughput of the medium access layer is relatively low, an efficient algorithm of the medium access layer is required.

For this purpose, throughput enhancement techniques of a large number of medium access layers have been studied. Orthogonal Frequency-Division Multiple Access (OFDMA) is a typical medium access layer throughput enhancement technique, which enables diversity in time, space, and frequency to be achieved to improve throughput. OFDMA is already applied in 4G cellular network, Wireless Metropolitan Area Network (WMAN), and Ultra Mobile Broadband (UMB), but it will be applied first in IEEE 802.11ax which is a draft stage in wireless LAN environment.

In the current wireless LAN environment, the number of personal terminals and access points (APs) is explosively increasing. Therefore, IEEE 802.11ax considers improvement of overall network throughput rather than increase of throughput rate of terminals to terminals . However, since the wireless LAN environment is not a network managed by a small number of service providers such as a cellular network, it is difficult to manage each AP. Therefore, a centralized optimization technique is very difficult.

Therefore, a more efficient resource allocation scheme is needed to solve the problems that may occur in a wireless LAN environment.

Japanese Patent Application No. 10-0924834 proposes a downlink scheduling control information transmission method using a channel coding scheme, in particular, a bitmap pattern capable of transmitting control information, but a method of deriving such control information is disclosed not.

Open No. 10-2013-0110588 discloses an OFDMA resource allocation method in a multi-cell environment, in particular, a method for improving cell edge performance by adjusting inter-cell interference. However, There is a problem that it is difficult to use in a distributed environment such as a wireless LAN environment.

Japanese Patent Application No. 10-0848655 proposes a distributed OFDMA resource allocation method in a multi-cell environment. In particular, a technique for minimizing co-channel interference (CCI) between neighboring cells through optimization of transmission power between subcarriers is disclosed However, consideration of which sub-carrier is to be allocated to a terminal is not suitable for application to a dense wireless LAN environment because it is proposed to maximize the yield.

The present invention proposes a distributed downlink resource allocation algorithm. In this algorithm, each AP defines a 'utility' function in a distributed manner and establishes an optimization problem that maximizes it. The utility function reflects the fairness measure between the throughput and the throughput of the AP, and it is made up of parameters that can be adjusted to maximize throughput and maximize fairness. In addition, we need a modified Clear-To-Send (M-CTS) frame structure for the neighboring APs in order to establish the optimization problem.

Korean Patent Publication No. 10-0924834 Korean Laid-Open Publication No. 10-2013-0110588 Korean Patent Publication No. 10-0848655

 Nan Bao, Junchao Li, Weiwei Xia, and Lianfeng Shen. "QoS-aware Resource Allocation Algorithm for OFDMA-WLAN integrated system," in IEEE Wireless Communications and Networking Conference (WCNC), 2013, pp. 807-812  T. Mishima, S. Miyamoto, S. Sampei, and W. Jiang, "Novel DCF-based Multi-User MAC Protocol and Dynamic Resource Allocation for OFDMA WLAN Systems," in International Conference on Computing, Communications and Networking (ICNC) 2013, pp. 616-620  C. Wang and W. H. Kuo, "A utility-based resource allocation scheme for IEEE 802.11 WLANs," Networks, vol. 20, no. 7, pp. 1743-1758, 2014.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus and a method for allocating downlink resources to a mobile station by establishing an optimization problem in which each access point (AP) defines a utility function and maximizes the utility function.

It is another object of the present invention to provide an apparatus and method for allocating downlink resources that can maximize the throughput and fairness of an access point.

According to another aspect of the present invention, there is provided a method for allocating resource allocation information and signal strength of a neighboring access point for distributed downlink resource allocation in an OFDMA-based dense wireless LAN environment, ) Frame structure.

In an OFDMA-based dense wireless LAN environment including a first access point, a second access point positioned adjacent to the first access point, and a plurality of terminals concatenated to each access point, The method for allocating downlink resources by an access point includes collecting resource allocation information and signal strength information of a neighboring access point from a terminal connected to the first access point by the first access point, Calculating a normalized throughput (u _t ) by using the resource allocation information of the second access point and the signal strength information of the second access point, the first access point The resource allocation information of the first access point and the signal strength information of the second access point, (U _f ), and allocating the first access point to satisfy a constraint condition that two or more terminals concatenated to the first access point do not occupy the same sub-channel, Generating a matrix Y and allocating resources.

According to the apparatus and method for intrusion detection of a vehicle according to an embodiment of the present invention, the efficiency of downlink resource allocation in an OFDMA-based dense wireless LAN environment can be maximized.

In addition, according to the wireless LAN environment, maximization of throughput and maximization of fairness can be controlled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to more fully understand the drawings recited in the detailed description of the present invention, a detailed description of each drawing is provided.
1 is a diagram illustrating an entire system including a resource allocation apparatus according to an embodiment.
2 is a block diagram illustrating a resource allocation apparatus according to an exemplary embodiment of the present invention.
3 is a flowchart illustrating a distributed downlink resource allocation method using the distributed downlink resource allocation apparatus shown in FIG.
FIG. 4A shows a CTS frame defined in IEEE 802.11, and FIG. 4B shows a modified CTS (M-CTS) frame proposed in the present invention.
FIG. 5 shows an example of transmission using an M-CTS frame in which a Target RSSI subfield and an RU allocation subfield are added.
6 shows a simple example of an OFDMA system based on a resource allocation method according to an embodiment of the present invention.
7 and 8 show the throughput and the fairness measure of the proposed technique and the comparison technique according to the change of the number of APs.
FIG. 9 shows the change of the throughput and the fairness according to the change of alpha, and FIGS. 10 and 11 show the throughput and the fairness change according to the AP density.

It is to be understood that the specific structural or functional description of embodiments of the present invention disclosed herein is for illustrative purposes only and is not intended to limit the scope of the inventive concept But may be embodied in many different forms and is not limited to the embodiments set forth herein.

The embodiments according to the concept of the present invention can make various changes and can take various forms, so that the embodiments are illustrated in the drawings and described in detail herein. It is not intended to be exhaustive or to limit the invention to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms may be named for the purpose of distinguishing one element from another, for example, without departing from the scope of the right according to the concept of the present invention, the first element may be referred to as a second element, The component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that no other element exists in between.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "having" and the like are used to specify that there are features, numbers, steps, operations, elements, parts or combinations thereof described herein, But do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the meaning of the context in the relevant art and, unless explicitly defined herein, are to be interpreted as ideal or overly formal Do not.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings attached hereto.

1 is a diagram illustrating an entire system 10 including a resource allocation apparatus according to an embodiment.

The apparatus and method for distributed downlink resource allocation in an OFDMA-based dense wireless LAN environment according to an embodiment of the present invention assume an OFDMA wireless LAN environment in which a plurality of single hop BSS (basic service set) exist.

Referring to FIG. 1, the terminal a1 and the terminal a2 are connected to AP a, and the terminal b1 and the terminal b2 are connected to AP b. That is, each access point (AP) has a network structure of providing a service to a plurality of terminals, for example, a plurality of stations (STAs) connected to each access point (AP) and collecting information.

The circles represent the transmission range of the AP, and the overlapped portions of the circles indicate the overlapped transmission range of the two APs. When the AP a allocates the resource allocation information and the signal strength of the AP b from the terminal a 2, it receives the downlink resource allocation from the terminal a 2 through the modified CTS (M-CTS) frame proposed in the present invention Based on this, a resource allocation optimization problem is established and downlink OFDMA transmission is performed accordingly. Similarly, the AP b establishes a resource allocation optimization problem using the resource allocation information and the signal strength of the adjacent AP a received from the terminal b 1.

That is, the AP a can improve the performance of the network by allocating the optimal radio resources using the resource allocation information and the signal strength of the adjacent AP b received from the terminal a 2.

2 is a functional block diagram of a distributed downlink resource allocation apparatus 100 in an OFDMA-based dense wireless LAN environment according to an exemplary embodiment.

Referring to FIG. 2, the resource allocation apparatus 100 includes a collecting unit 110, an allocating unit 120, and a transmitting unit 130.

The resource allocation apparatus 100 may operate as an access point (AP).

The collection unit 110 of the resource allocation apparatus 100 may control a station connected to the resource allocation apparatus 100 for optimized resource allocation and collect resource allocation information and signal strength of neighboring APs from the established terminals .

The allocating unit 120 calculates the normalized throughput u _t and the normalized fairness u _f using the resource allocation information and the signal strength information of the neighbor AP and calculates the normalized throughput u _t and the normalized fairness (u _f ), and establishes an optimization problem that maximizes the utility (u), thereby allocating downlink resources to the UE.

The transmitting unit 130 may transmit the allocation information to the established terminals.

In addition, the resource allocation apparatus 100 according to an exemplary embodiment may further include a storage unit for storing resource allocation information and signal strength information received from the UE.

Hereinafter, a method for allocating a distributed downlink resource in an OFDMA-based dense wireless LAN environment according to an embodiment of the present invention will be described in detail with reference to FIG. 3 to FIG.

3 is a flowchart illustrating a distributed downlink resource allocation method using the distributed downlink resource allocation apparatus shown in FIG.

Referring to FIG. 3, the resource allocation apparatus 100 receives the resource allocation information of the neighbor AP from the established terminal 200 and the strength information of the signal received from the neighbor AP (S100). Specifically, the resource allocation apparatus 100 transmits an RTS frame to the terminal 200, and the terminal 200 overhearing transmission of another adjacent AP transmits resource allocation information (RU allocation information) And transmits a modified CTS (M-CTS) frame including signal strength information (intensity of noise) to the resource allocation apparatus 100. [ That is, the terminal 200 that has received the transmission of another adjacent AP stores the RU allocation information and the strength of the signal contained in the transmission of the eavesdropping, Upon receiving an RTS frame from the allocation apparatus 100, the MS 200 transmits a modified CTS (M-CTS) frame including resource allocation (RU allocation) information and signal strength information to the resource allocation apparatus 100 .

1, the terminal a2, which receives the AP b, stores the RU allocation information and the strength of the signal contained in the transmission r, and then transmits the RTS frame from the AP a And transmits an M-CTS frame including the M-CTS frame to the AP a when it is received.

The M-CTS frame structure proposed by the present invention for collecting RU allocation information and the strength of a signal of an adjacent AP is as follows.

FIG. 4A shows a CTS frame defined in IEEE 802.11, and FIG. 4B shows a modified CTS (M-CTS) frame proposed in the present invention.

The present invention proposes an M-CTS frame to which a Target RSSI subfield and an RU allocation subfield are added.

The Target RSSI subfield is a subfield indicating the intensity of the signal received. It is composed of 8 bits, and the intensity of the signal can be divided into 256 steps (that is, 2 8). The Target RSSI subfield is a field originally proposed in the IEEE 802.11ax draft, which is currently in progress. In the 802.11ax, a trigger frame (Trigger) used by the AP to request transmission to the UEs or used as a ready-to- frame, but it is not used in the CTS frame.

The RU Allocation subfield is a subfield indicating how a resource unit (RU), which is a transmission unit of an OFDMA wireless LAN system, is allocated, and is not supported in a subfield or CTS frame supported by IEEE 802.11ax Draft.

FIG. 5 shows an example of transmission using an M-CTS frame in which a Target RSSI subfield and an RU allocation subfield are added. FIG. 5 is based on the operation example of FIG. t denotes the data transmission time to be influenced by the adjacent AP, which can be known through reception of the M-CTS frame. T represents the length of the PLCP protocol data unit (PPDU). The terminal b1 hears the frame transmitted from the AP a, stores the RU allocation and the target RSSI information separately, receives the RTS frame from the AP b, and transmits the attached information to the M-CTS frame.

The AP b receiving the M-CTS frame can know the transmission information of the neighboring AP and the influences received from the neighboring AP, and the OFDMA resource, that is, the resource unit (RU) is distributed using the resource allocation technique proposed in the present invention .

Next, the resource allocation apparatus 100 allocates AP Adjacent to the resource allocation information of AP And allocates resources using the strength information of the signal received from the base station S200 ).

6 shows a simple example of an OFDMA system based on a resource allocation method according to an embodiment of the present invention. One PPDU consists of several sub-channels on the frequency axis and several time slots on the time axis. A resource allocation unit is defined as a resource unit, which is defined as one subchannel and one time slot.

N denotes the number of terminals responding to the RTS of the AP with the existing CTS or the modified CTS (M-CTS). M is defined as the number of sub-channels. N should be less than or equal to M. B is the total channel bandwidth. That is, B / M means the bandwidth of one subchannel.

Y denotes an allocation matrix, and is a matrix to be derived from the resource allocation algorithm. An N × M matrix of 0 and 1, where the element y _{n , m} of matrix Y is defined as 1 when terminal n occupies subchannel m, and 0 otherwise. Also, I is an interference matrix and is a real N × M matrix. The element i _{n , m} of matrix I represents the strength of interference experienced by terminal n on subchannel m and is derived from the Target RSSI subfield. Next, S denotes a signal matrix, which represents the strength of a signal received by the terminal n on the subchannel m.

The step S200 of allocating downlink resources in the resource allocation apparatus 100 includes calculating a normalized throughput u _t using resource allocation information and signal strength information of a neighbor AP S210, Calculating a normalized fairness (u _f ) using the resource allocation information and the signal strength information (S230), generating an allocation matrix Y so as to maximize the utility (u) while satisfying a predetermined constraint condition, (S250).

Specifically, calculating the normalized throughput (u _t ) includes calculating a throughput (c) that can be derived from an arbitrary allocation matrix, calculating a theoretical maximum throughput (c *) excluding fairness, and And calculating the normalized throughput u _t using Equation 1 below.

The process of calculating the throughput (c) that can be derived from an arbitrary allocation matrix is as follows.

First, a Signal-to-Interference plus Noise Ratio (SINR _{n , m} ) is calculated when the n-th UE occupies the m-th subchannel. The SINR _{n , m,} which can be obtained when the terminal n occupies the subchannel m _, is given by Equation 2 below.

In Equation (2), N _{0n , m} means thermal noise, and f [mW] means that f is a milli-watts scale unit.

Next, by using equation (3) below, n capacity of the second terminal can be obtained from the m-th sub-channel (capacity: c _{n, m),} i.e. the terminal n c _n, the kepa city that can be obtained from the sub-channel m _(m ).

In this case, B denotes the bandwidth of the entire channel, and thus B / M denotes the bandwidth of one unit subchannel.

Next, the total capacity c _n obtainable by the terminal n is calculated using the following Equation 4, and the total capacity c obtained from one PPDU using the following mathematical expression 5, that is, (C) that can be derived from the allocation matrix.

The theoretical maximum available capacity (c *), which excludes fairness, may be the total capacity when the AP allocates resources (RUs) with the highest SINR to the UE in descending order.

Next, the step of calculating the normalized fairness (u _f ) is a step of calculating a fairness index (f) between a total capacity (c _n ) obtainable by the nth UE, all the subchannels are sequentially allocated to all UEs And calculating the normalized fairness (u _f ) using the following Equation (6): " (6) "

n the total capacity of the second terminal to obtain (c _n) Fairness Index (f), i.e. the total capacity Jain's fairness index (f) between (c _n) of the terminal between a can be calculated by using Equation 7 below.

Next, the resource allocation apparatus 100 generates an allocation matrix Y so as to maximize the utility (u) while satisfying a certain constraint condition, and allocates resources (S250).

Specifically, utility (u) can be derived as Equation (8) below using normalized throughput (u _t ) and normalized fairness (u _f ).

α is a weighting factor that is a variable that can control the priority between throughput and fairness. The closer to 1 is, the higher the total throughput becomes, and on the contrary, the closer to 0 is, the higher the fairness between throughput becomes.

The optimization problem can be expressed as Equation (9) below.

The constraint condition of the optimization problem means that two or more UEs can not occupy the same subchannel.

That is, the resource allocation apparatus 100 generates the allocation matrix Y (y _{n , m} ) so as to maximize the utility (u) while satisfying the constraint condition, and transmits the allocation matrix Y (y _{n , m} ) to at least one terminal Allocate resources.

7 and 8 show the throughput and the fairness measure of the proposed technique and the comparison technique according to the change of the number of APs. As a comparison method for performance evaluation, selfish technique and arbitrary technique are defined. The selfish technique is a technique for allocating from a terminal-subchannel with the highest SINR, and an arbitrary technique is a technique for arbitrarily allocating under conditions satisfying a constraint condition.

Referring to FIGS. 7 and 8, as the number of APs increases, the throughput of the proposed scheme and the comparison scheme increases, but the rate of increase decreases. In the resource allocation method according to the present invention, when? Is 0.1, the throughput rate of 16.9% ~ 27.0% is lower than that of the selfish method, but the fairness scale is the highest.

Fig. 9 shows the change of the throughput and the fairness according to the change of alpha. When α is low, the fairness (fairness) of the utility function becomes larger, and the resource unit (RU) of the OFDMA is distributed relatively fairly. As a result, the fairness measure is high but the sum of the throughput is low. On the contrary, when the α is high, the UEs with high SINR monopolize the resource unit (RU), so that the fairness measure is low but the sum of the throughputs is high.

Figures 10 and 11 illustrate throughput and fairness trends according to AP density.

Figures 8 and 9 below show throughput and fairness according to how dense the AP is deployed.

r / r0 on the x-axis represents the ratio of the distance between the APs and the transmission range. If r / r0 equals 1, APs are accurately spaced by the transmission range. If r / r0 equals 2, the transmission range overlaps This means the situation has been completely separated without.

As the r / r0 increases, that is, as the APs are arranged more steeply, the throughput of both the proposed scheme and the comparison scheme increases. This is because the interference decreases as the distance between the APs decreases, and the overall SINRs rise can see.

Similar to FIG. 7, when α is low, the throughput is somewhat lower than that of the selfish technique, but the fairness is superior.

The distributed downlink resource allocation method in the OFDMA-based dense wireless LAN environment can be implemented in a general-purpose digital computer that can be created as a program that can be executed by a computer and operates the program using a computer-readable recording medium .

For example, a program stored in a recording medium and assigned to an access point in downlink resources in an OFDMA-based dense wireless LAN environment, the program causing a computer to execute the steps of: An instruction set that collects allocation information and intensity information of a signal received from a neighboring access point from the terminal, an instruction set that calculates a normalized throughput (u _t ) using the collected information, a normalized fairness u _f ), and a set of instructions for generating an allocation matrix Y and allocating resources so that the utility u can be maximized while satisfying certain constraints.

The program for allocating the downlink resources is stored in the recording medium. The recording medium may be a magnetic storage medium (for example, a ROM, a floppy disk, a hard disk, etc.), an optical reading medium (for example, ). ≪ / RTI > In addition, the recording medium may be distributed and distributed to a network-connected computer system so that a computer-readable instruction set can be stored and executed in a distributed manner.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

100: resource allocation device, access point
110: collecting unit 120: assigning unit
130:

Claims (7)

The OFDMA-based dense wireless LAN environment includes a first access point, a second access point located adjacent to the first access point, and a plurality of terminals concatenated to the respective access points,
Collecting resource allocation information and signal strength information of a neighboring access point from a terminal connected to the first access point by the first access point;
Calculating a normalized throughput (u _t ) using the resource allocation information of the second access point and the signal strength information of the second access point;
Calculating a normalized fairness (u _f ) using the resource allocation information of the second access point and the signal strength information of the second access point; And
The first access point generates an allocation matrix Y such that the two or more UEs concatenated to the first access point satisfy the constraint condition that the same subchannel is not occupied and the utility (u) is maximized based on the following equation And allocating resources to the access point.
(Equation)

(n is the number of terminals responding to the RTS of the first access point, M is the number of subchannels, y _{n , m} is a variable capable of adjusting the priority between the throughput and the fairness, An element of the NXM matrix Y having a value of '1' when occupying a subchannel, and '0' otherwise) The method according to claim 1,
The step of calculating the normalized throughput (u _t )
Calculating a throughput (c) that can be derived from an arbitrary allocation matrix;
Calculating a theoretical maximum throughput (c *) excluding fairness; And
And calculating the normalized throughput (u _t ) using the following equation: < EMI ID = 17.0 >

3. The method of claim 2,
The process of calculating the throughput (c) that can be derived from an arbitrary allocation matrix,
calculating a signal-to-interference plus noise ratio (SINR _{n , m} ) when the n-th terminal occupies the m-th subchannel;
Calculating a capacity (capacity: c _{n , m} ) of the n-th terminal from the m-th subchannel using the following equation:

(Where B is the bandwidth of the entire channel)
calculating a total capacity (c _n ) obtainable by the nth terminal; And

Calculating a total capacity (c) obtainable from one PPDU; and

Wherein the access point allocates downlink resources. 3. The method of claim 2,
The process of calculating the theoretical maximum throughput (c *), which excludes fairness,
Wherein the first access point is a total capacity when resources that can have the highest signal-to-interference and noise ratio (SINR) are allocated to the terminals concluded with the first access point in descending order.
Wherein the access point allocates downlink resources. The method of claim 3,
The step of calculating the normalized fairness (u _f )
Calculating a fairness index (f) between the total capacity (c _n ) obtainable by the n-th terminal using the following equation;

Calculating a fairness index (f *) when all subchannels are sequentially allocated to all UEs; And
And calculating the normalized fairness (u _f ) using the following equation: < EMI ID ₌ 17.0 >

The method according to claim 1,
The step of collecting the resource allocation information and the signal strength information of the second access point comprises:
The first access point transmitting a request to send (RTS) frame to a plurality of terminals; And
A modified CTS (Modified Clear to Send) message including resource allocation information and signal strength information contained in the transmission of the second access point from at least one terminal that the first access point tries to transmit the second access point, : M-CTS) frame, wherein the access point allocates downlink resources. The method according to claim 6,
Wherein the modified CTS frame allocates a downlink resource to an access point including an RU allocation subfield including a target RSSI subfield including strength information of a coded signal and resource information (RU) allocation information.

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