KR101428812B1 - Method and apparatus for down link data transmission/reception in wireless communication networks - Google Patents

Abstract

In the present invention, a terminal receiving downlink data in a collaborative wireless communication system using a multi-input / output antenna estimates a downlink channel for each of a plurality of base stations belonging to the same cluster, To-interference and noise ratio (SINR) in each of the estimated downlink channels among a plurality of transmission modes according to the selected transmission mode, and selects the transmission mode maximizing a signal-to-interference and noise ratio (SINR) Feedback information to the at least one base station among the plurality of base stations, and receives the downlink data from the at least one base station in the selected transmission mode.

High-speed packet communication, mobile communication system, multi-input / output antenna system, MIMO, network MIMO, collaborative communications

Description

TECHNICAL FIELD [0001] The present invention relates to a method and apparatus for transmitting and receiving downlink data in a wireless communication network,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system using multiple input / output antennas, and more particularly, to a method and an apparatus for transmitting and receiving cooperative data between base stations for downlink data transmission.

In order to provide high-speed and high-quality data service in wireless communication, a multiple-input multiple-output (MIMO) system using multiple antennas at a transmitter and a receiver has been proposed. In the MIMO technique, spatial multiplexing (hereinafter, referred to as SM) is a technique of simultaneously forming a plurality of spatial subchannels between a transmitter and a receiver, independently transmitting data for each spatial subchannel, It is possible to increase the data transmission capacity in the mobile communication system. Also, space division multiple access (SDMA) techniques can increase the transmission capacity of a system by sending data streams to multiple receivers simultaneously.

SM and SDMA require spatial processing in the transmitter and the receiver in the system to which the technology is applied. To do this, the transmitter and receiver have MIMO channel state information (CSI) between the transmitter and the receiver . In particular, in order to operate the SM and SDMA technologies operating in the downlink, the BTS has downlink MIMO channel information from n _T transmit antennas of a base transceiver station (BTS) to n _R receive antennas of an access terminal .

Since the frequency division multiplexing (FDD) system uses different frequency bands for the downlink and the uplink, in order to have the downlink CSI in the BTS, the AT estimates the downlink channel and estimates the downlink CSI Feedback to the BTS. However, since the transmission of full channel information (full CSI) to the BTS requires transmission of a large amount of reverse link information, multi-antenna techniques for effectively using SM and SDMA techniques using only minimum feedback information have been proposed.

Figure 1 illustrates a conventional multi-antenna technique.

As shown in FIG. 1, conventional multi-antenna technologies are technologies focused on spatially removing or suppressing the same cell interference, which is an interference between data streams transmitted simultaneously in the same cell. In particular, the conventional SDMA technique forms n _T beams for each BTS and performs independent scheduling for each BTS in order to select an AT to transmit data through each beam. However, when the ATs selected by the independent scheduling of the respective BTSs are located in areas where the service areas of adjacent BTSs overlap with each other, inter-cell interference significantly increases, thereby degrading service reception performance. In order to overcome such disadvantages, in recent years, a multi-antenna technique has been used, and a network MIMO or a collaborative MIMO (MIMO) scheme for suppressing interference in the same cell as well as inter- There is a need for research on technology.

FIG. 2 is intended to illustrate the concept of a collaborative SDMA technique to which the present invention is applied.

In the collaborative SDMA technique, adjacent BTSs capable of exchanging interference between other cells are connected to a cluster scheduler 210 through a high-speed broadband wired communication network. Each BTS delivers the channel information fed back from the ATs to the cluster scheduler 210 via the wired communication network. The cluster scheduler 210 schedules and transmits scheduling information for all ATs belonging to the cluster, . The cluster scheduler 210 informs schedulers of corresponding BTSs of the ATs to transmit data in each BTS selected by the scheduling, weight information to be used by the ATs, and MCS (modulation and coding scheme) information of data to be transmitted to the ATs, The scheduler of each BTS finally refers to the information delivered from the cluster scheduler 210, finally determines the ATs to transmit data in the BTS, the weights to be used by the ATs, and the MCS of the data to be transmitted to the ATs, And transmits the data to the ATs according to the information.

In order to operate the collaborative SDMA technology in the FDD wireless communication network, a scheduling technique for effectively suppressing inter-cell interference using only partial channel information transmitted from an AT through a limited feedback channel of the reverse link, and an SDMA technique therefor Is required. In addition, in the wireless communication network, collaborative ATs (hereinafter, referred to as C-ATs) capable of applying collaborative MIMO techniques overlap service areas of neighboring BTSs and non-collaborative ATs and collaborative scheduling and SDMA technology applicable to both C-AT and NC-AT are required because NC-ATs are mixed. That is, there is a need for a collaborative SDMA and scheduling technology for C-ATs compatible with existing SDMA and scheduling technologies for NC-ATs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cooperative wireless communication system in which adjacent BTSs are connected to each other through a high-speed wired communication network using an FDD scheme, using only partial channel information transmitted from an AT through a limited feedback channel of a reverse link , A cooperative SDMA technique for effectively suppressing other cell interference by an adjacent BTS, and a new data transmission / reception method and apparatus for cooperative BF.

Also, a problem to be solved by the present invention is to provide a method and system for providing a coexistence of cooperative ATs in a service area of a plurality of BTSs and non-cooperative ATs in an exclusive service area of a single BTS, And to provide a new method and apparatus for collaborative SDMA.

Another object of the present invention is to provide a new method and apparatus for optimizing a cluster transmission mode selection and feedback scheme for cooperative SDMA according to the capacity of an uplink feedback channel allowed in the system.

A method according to an embodiment of the present invention is a method for a UE to receive downlink data in a collaborative wireless communication system using a multi-input / output antenna, the method comprising the steps of: A transmission mode for maximizing a signal-to-interference and noise ratio (SINR) in each of the estimated downlink channels among a plurality of transmission modes according to a combination of a pre-code matrix, The method comprising the steps of: feedbacking information on the selected transmission mode and SINR when using the selected transmission mode to at least one base station among the plurality of base stations; And receiving the downlink data.

Another method according to an embodiment of the present invention comprises: A method for transmitting downlink data in a base station in a collaborative wireless communication system using a multiple input / output antenna, the method comprising: receiving feedback information from each of a plurality of terminals; Selecting a terminal group having a maximum priority by performing scheduling for each of the generated terminals based on information about a mode of the terminal group; Determining a transmission mode to be used by the terminals belonging to the selected terminal group and a modulation level of downlink data to be transmitted to terminals belonging to the selected terminal group based on the determined transmission mode and the determined modulation level, And transmits the downlink data to terminals belonging to It includes forward.

Another method according to an embodiment of the present invention comprises: A method for receiving a downlink data in a collaborative wireless communication system using a multiple input / output antenna, the method comprising: estimating a downlink channel for each of a plurality of base stations belonging to the same cluster; Determining interference weights that maximize signal-to-interference and noise ratio (SINR) of the base station and interference weights to the interfering base stations; and determining the determined signal weights, the determined interference weights, Feedback information on the reception SINR to the base station; and receiving the downlink data according to the decided signal weights from the base station.

Another method according to an embodiment of the present invention comprises: A method for transmitting downlink data in a base station in a collaborative wireless communication system using a multiple input / output antenna, the method comprising: receiving feedback information from each of a plurality of terminals; Determining a scheduling priority of the plurality of UEs using a signal-to-interference and noise ratio (SINR); determining a scheduling priority of the UEs based on the determined signal weights and interference Selecting a terminal to transmit downlink data from among the plurality of terminals and determining a signal weight and a modulation level to be used by the selected terminal, and transmitting the downlink data to the selected terminal, wherein the scheduling is performed to minimize interference between base stations using interference weights of the base stations, The selected weight and the modulation level determine the selected terminal It comprises the step of transmitting the downlink data.

An apparatus according to an embodiment of the present invention is a terminal apparatus for receiving downlink data in a collaborative wireless communication system using a multi-input / output antenna, wherein a downlink channel for each of a plurality of base stations belonging to the same cluster A control unit for selecting a transmission mode for maximizing a signal-to-interference and noise ratio (SINR) in each of the estimated downlink channels among a plurality of transmission modes according to a combination of pre-code matrices; A feedback transmitter for feeding back information on the selected transmission mode and SINR when using the selected transmission mode to at least one base station among the plurality of base stations; And a receiver for receiving link data.
Another apparatus according to an embodiment of the present invention includes: A base station apparatus for transmitting downlink data in a collaborative wireless communication system using a multiple input / output antenna, the base station apparatus comprising: a feedback receiver for receiving feedback information from each of a plurality of terminals; And generates scheduling for each of the generated terminal groups to select a terminal group having the highest priority, and transmits the selected terminal group to the selected terminal group A control unit for determining a modulation level of downlink data to be transmitted to terminals belonging to the selected terminal group and a transmission mode for using terminals belonging to the selected terminal group according to the determined transmission mode and the determined modulation level, Lt; RTI ID = 0.0 > downlink < / RTI & And a transmission unit.
Another apparatus according to an embodiment of the present invention includes: A terminal apparatus for receiving downlink data in a collaborative wireless communication system using a multiple input / output antenna, the terminal apparatus estimating a downlink channel for each of a plurality of base stations belonging to the same cluster, Comprising: a controller for determining a signal weight of a base station that maximizes a signal-to-interference and noise ratio (SINR) at an interference base station and an interference weight that maximizes interference to interfering base stations; And a receiver for receiving the downlink data according to the determined signal weights from the base station.

Another apparatus according to an embodiment of the present invention includes: A base station apparatus for transmitting downlink data in a collaborative wireless communication system using a multi-input / output antenna, the base station apparatus comprising: a feedback receiver for receiving feedback information from each of a plurality of terminals; A method of determining a scheduling priority of a plurality of UEs using a signal-to-interference and noise ratio (SINR), determining signaling weights of base stations included in the determined scheduling priority, A controller for selecting a terminal to transmit downlink data among the plurality of terminals and determining a signal weight and a modulation level to be used by the selected terminal based on the interference weight; And to the selected terminal according to the modulation level Group includes data transfer unit configured to transfer the DL data.

Effects obtained by representative ones of the inventions disclosed below will be briefly described as follows.

In a cooperative wireless communication system using an FDD scheme, only inter-cell interference is effectively suppressed by using partial channel information transmitted from an AT through a limited feedback channel of a reverse link, The system transmission capacity can be significantly improved.

The cooperative SDMA technique proposed by the present invention is a scheme in which data transmission in a single BTS is extended to data transmission by a plurality of cooperative BTSs in a precoder codebook based SDMA technology, Cooperative ATs and cooperative ATs in the service area of multiple BTSs. Therefore, it is fully compatible with the existing precoder codebook-based SDMA technology.

The present invention also provides a method of selecting a cluster transmission mode for maximizing the signal-to-noise ratio for each link among the cluster transmission modes predetermined between the BTS and the AT, and a method of selecting the same transmission mode for each cluster transmission mode in the cluster scheduler A transmission mode for performing scheduling for ATs and providing a maximum scheduling priority and a scheme for selecting ATs to transmit data can improve the transmission capacity of a cluster by maximizing a multiuser diversity gain using minimum feedback information .

The " single cluster transmission mode selection and feedback scheme "and the" G transmission mode selection and feedback scheme "proposed by the present invention can be classified into an optimal feedback scheme for cooperative SDMA To be selected.

In addition, the cooperative BF technique proposed in the present invention is a cooperative radio communication system using an FDD scheme in which information on weight vectors and main interference weight vectors used for signal transmission and transmitted through a limited feedback channel on the reverse link, , It is possible to improve the system transmission capacity for ATs for cell edges by suppressing collision between beams formed by the weights used in each BTS.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an operation principle of an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 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 of the present invention, and may be changed according to the intentions or customs of the user, the operator, and the like. Therefore, the definition should be based on the contents throughout this specification.

The present invention proposes a cooperative SDMA (hereinafter referred to as C-SDMA) technique that effectively suppresses interference between neighboring cells by neighboring BTS based on SDMA technology using an existing precoder codebook in an FDD system.

In the embodiment of the present invention, each BTS uses n _T transmit antennas, all ATs use n _R receive antennas, and a forward link cluster consisting of three adjacent BTSs with K users per each BTS is assumed . However, the present invention is not limited to this and can be extended to a cluster including any number of BTSs.

Let x _{m be} the (n _T x 1) sized transmission signal vector of the mth BTS, y _{m, k be} the (n _R x 1) sized received signal vector of the k th AT belonging to the m th BTS, Assuming selective fading, the received signal at the k < th > AT can be expressed by Equation (1) below.

는 i번째 간섭 BTS로부터 m번째 BTS의

번째 AT로의 평균 SNR을 나타낸다. H_m,k는 k번째 AT가 속한 m번째 BTS로부터 수신한 (n_T×n_R) 크기의 복소 채널 행렬을,

는 i번째 간섭 BTS로부터 m번째 BTS의 k번째 AT로의 (n_T×n_R) 크기의 복소 채널 행렬을 나타내며, n_m,k는 (n_R×1) 크기의 AWGN(Additive White Gaussian Noise) 벡터를 나타낸다. 또한, F와 G_i는 각각 m번째 BTS와 i번째 간섭 BTS에서 사용하는 (n_T×n_R) 크기의 프리코딩 행렬을 나타내며, i_i는 i번째 간섭 BTS의 신호 벡터이다.Where γ _{m, k} is the average signal-to-noise ratio (SNR) received from the mth BTS to which the kth AT belongs,

Lt; RTI ID = 0.0 > BTS < / RTI >

Th < / RTI > AT. H _{m, k} denotes a complex channel matrix of size (n _T × n _R ) received from the m th BTS to which the k th AT belongs,

Is i-th from the interfering BTS to the k-th AT of the m-th BTS (n _T × n _R) denotes a complex channel matrix of size, n _{m, k} are (n _R × 1) size of the AWGN (Additive White Gaussian Noise) vector . Also, F and G _i represent precoding matrices of size (n _T × n _R ) used in the m th BTS and i th interfering BTS, respectively, and i _i is the signal vector of the ith interfering BTS.

을 추정할 수 없으며, 따라서 간섭 BTS로부터의 하향 링크 채널은 순수한 타 셀 간섭으로 간주된다. 그러므로 해당 NC-AT는 비협동 SDMA(이하, NC-SDMA) 기술로 동작을 하게 되며, 이러한 경우 해당 NC-AT는 기존의 프리코더 코드북 기반의 SDMA 기술과 동일하게 동작한다. The operation of the NC-AT in this C-SDMA system will be described.
If the downlink sounding reference signal received from the BTS is equal to or higher than a reference value, the NC-AT estimates the downlink channel using the downlink sounding reference signal. If the NC-AT receives the downlink sounding reference signal transmitted from the BTS to which the NC-AT belongs and does not receive a sounding reference signal from the interference BTS in the cluster, the corresponding NC-

And therefore the downlink channel from the interfering BTS is considered to be purely another cell interference. Therefore, the corresponding NC-AT operates with the non-cooperative SDMA (hereinafter referred to as NC-SDMA) technology. In this case, the NC-AT operates in the same manner as the existing precoder codebook based SDMA technology.

The detailed operation of NC-AT is as follows.

The k-th NC-AT estimates the downlink channel signal H _{m, k} using the downlink sounding reference signal transmitted at the m-th BTS. The NC-AT uses the estimated downlink channel signal to select a precoding matrix that maximizes the multiuser diversity gain in the link between the m-th BTS and the k-th AT.

에서, 해당 BTS의 시스템 용량을 최대화하는 하나의 프리코딩 행렬을 선택하여 사용한다. 이를 위해 AT는 코드북 F에 속한 G개의 프리코딩 행렬에 대해, n_T개의 송신 데이터 스트림들에 대한 수신 SINR(signal-to-interference and noise ratio)을 계산한다. AT가 사용하는 수신 알고리즘에 따라 계산된 (n_T×n_R) 크기의 수신 가중치 행렬을

라 하면, AT가 코드북 F의 g번째 프리코딩 행렬 F_g를 사용할 경우, AT는 송신 신호 벡터 x_m의 n번째 데이터 심볼

을 다음 수학식 2와 같이 복구한다.SDMA technique of using a precoder codebook is a codebook consisting of G (n _T × n _R) of the size of the precoding matrix

, A single precoding matrix for maximizing the system capacity of the BTS is selected and used. For this, the AT computes the received signal-to-interference and noise ratio (SINR) for n _T transmit data streams for the G precoding matrices in the codebook F. Calculated in accordance with the received algorithm that uses the AT (n _T × n _R) a received weight matrix of size

, The AT uses the g th precoding matrix F _g of the codebook F, the AT computes the nth data symbol of the transmission signal vector x _m

Is restored as shown in the following equation (2).

의 SINR

은 다음 수학식 3과 같다.The recovered symbol < RTI ID = 0.0 >

Of the SINR

Is expressed by the following equation (3).

여기서, 수학식 3의 분모의 첫 번째 항은 m번째 BTS에서 동시에 전송되는 개의 데이터 스트림으로부터 받는 동일 셀의 간섭을 나타내며, 두 번째 항은 두 개의 간섭 BTS로부터 하향 링크 채널 행렬 에 의해서 받는 타 셀의 간섭을 나타낸다.

The first term of the denominator of Equation (3) represents the interference of the same cell received from the data streams transmitted simultaneously in the mth BTS, and the second term represents interference of the other cells received from the two interference BTSs by the downlink channel matrix. Indicates interference.

을 이용하여, m번째 BTS와 k번째 AT간의 링크에서 다중 사용자 다이버시티 이득을 최대화하는 프리코딩 행렬

를 다음 수학식 4와 같이 결정한다. AT is calculated

, A precoding matrix for maximizing the multi-user diversity gain in the link between the m < th > BTS and the k <

Is determined according to the following equation (4).

과

로 송신할 경우 수신 가능한 n_T 데이터 스트림에 대한 SINR,

을 m번째 BTS로 역방향 링크 피드백 채널을 통해 알려준다. 정리하면, AT는 BTS로 다음의 정보들을 역방향 링크 피드백 채널을 통해 전송한다.According to Equation (4), AT selects a precoding matrix for maximizing the SINR of the stream with the largest SINR among n _T streams in each link. The kth AT represents the index in the codebook of the selected precoding matrix

and

The SINR for the n _T data streams that can be received,

To the m < th > BTS via the reverse link feedback channel. In summary, the AT transmits the following information to the BTS over the reverse link feedback channel.

를 나타내는 전송 모드 정보(1) The AT operates as NC-SDMA, and the index in the codebook including the selected precoding matrix by the AT

≪ / RTI >

로 데이터 송신할 경우, AT에서 수신하는 n_T개의 데이터 스트림들의 SINR 정보(2) The BTS selects the precoding matrix selected by the AT

SINR < / RTI > information of n _T data streams received at the AT,

Next, the operation of the C-AT for C-SDMA according to the embodiment of the present invention will be described.

을 추정할 수 있을 경우, 해당 C-AT는 C-SDMA로 동작할 수 있다. 이는 해당 C-AT가 클러스터 내의 간섭 BTS들에서 수신하는 사운딩 기준 신호가 기준치 이상으로 수신될 때 가능하다. 따라서, C-AT의 채널 환경에 따라서 C-AT가 하향 링크 MIMO 채널을 추정할 수 있는 collaborative BTS(이하, C-BTS)의 수는 달라진다. 각 C-AT들이 처한 채널 환경에 따라, non-collaborative로 동작을 하는 AT인 NC-AT와 두 개의 C-BTS들간의 collaborative 전송을 원하는 AT인 C2-AT, 그리고 세 개의 C-BTS들간의 collaborative 전송을 원하는 C3-AT들로 구분할 수 있다.The k-th C-AT of the m-th BTS is a downlink MIMO channel matrix from adjacent interfering BTSs in the cluster

, The corresponding C-AT can operate as C-SDMA. This is possible when the C-AT receives a sounding reference signal that is received at the interfering BTSs in the cluster above a reference value. Therefore, the number of the collaborative BTS (hereinafter referred to as C-BTS) in which the C-AT can estimate the downlink MIMO channel depends on the channel environment of the C-AT. According to the channel environment in which each C-AT is located, the NC-AT which is a non-collaborative AT, the C2-AT which is an AT which desires collaborative transmission between two C-BTSs, and the collaborative And the C3-ATs desired to be transmitted.

를 추정한다고 가정하면, m번째 BTS와 인접한 두 개의 BTS로 구성된 BTS 클러스터의 3n_T개의 송신 안테나들로부터 동시에 전송된 (3n_T×1) 크기의 신호 벡터 X가 m번째 BTS의 k번째 AT에서 수신되는 신호 벡터 Y_m,k는 다음 수학식 5와 같다.Hereinafter, the C-SDMA for the C3-AT including the m-th BTS including the k-th AT belongs to the ro-number of the C-BTS will be described as an example. That is, it is assumed that the AT can estimate the downlink MIMO channel from the two BTSs adjacent to the mth BTS. The kth AT of the m-th BTS receives the downlink MIMO channel matrix from the two adjacent interfering BTSs

(3n _T × 1) signal vector X transmitted simultaneously from the 3n _T transmit antennas of the BTS cluster consisting of two BTSs adjacent to the m th BTS is received at the k th AT of the m th BTS The signal vector Y _{m, k} is given by the following equation (5).

는 (n_R×3n_T) 크기의 C-BTS 클러스터에 속한 3개의 C-BTS로부터 m번째 BTS의 k번째 AT로의 유효한(effective) 하향 링크 채널 행렬을 나타내며, C-BTS들로부터 수신된 사운딩 기준 신호를 이용하여 AT에서 H_m,k와

를 각각 추정할 수 있기 때문에, m번째 BTS가 사용할 프리코딩 행렬 F와 클러스터 내의 두 개의 간섭 BTS가 사용하는 프리코딩 행렬

를 알고 있으면,

를 계산할 수 있다. 또한 수하식 5에서

이고

이다.Where Y _{m, k} is the received signal vector of size (n _R × 1), N _{m, k} is the noise vector of size (n _R × 1).

Denotes an effective downlink channel matrix from three C-BTSs in the C-BTS cluster of size (n _R x 3n _T ) to the kth AT of the m-th BTS, and the sounding received from the C- Using the reference signal, H _{m, k} and

The precoding matrix F to be used by the m-th BTS and the precoding matrix used by the two interference BTSs in the cluster

If you know,

Can be calculated. In addition,

ego

to be.

를 동시에 결정해야 함을 보여준다. 모든 BTS들은 G개의 프리코딩 행렬로 이루어진 프리코더 코드북

에서 하나의 프리코딩 행렬을 선택하여 사용하기 때문에, AT는 G³개의 모든 가능한 프리코딩 행렬 조합들 중에서 다중 사용자 다이버시티 이득을 최대화하는 프리코딩 행렬 조합을 선택한다. 본 발명에서는 이러한 각각의 프리코딩 행렬 조합을 클러스터 전송 모드라고 정의한다. Equation (5) represents a precoding matrix F to be used by the m-th BTS that maximizes the multi-user diversity gain in the link between kth ATs of the m-th BTS from the C-BTS cluster and a precoding matrix

Should be determined at the same time. All BTSs include a precoder codebook < RTI ID = 0.0 >

The AT selects a precoding matrix combination that maximizes the multi-user diversity gain among all the G ³ possible precoding matrix combinations. In the present invention, each combination of these precoding matrices is defined as a cluster transmission mode.

를 사용하고, C-BTS의 수가 세 개인 C3-AT를 위한, 가능한 8개의 클러스터 전송 모드는 다음 수학식 6과 같다.For example, a precoder codebook comprising two precoding matrices

And the possible eight cluster transmission modes for C3-AT with three C-BTSs are shown in Equation (6).

라 하고 하면, W_m,k의 첫 번째부터 n_T번째 컬럼 벡터들

은 m번째 BTS로부터 수신하는 n_T개의 데이터 스트림들에 대한 수신 가중치 벡터들이다. 가능한 클러스터 전송 모드들 중에서 AT가

를 사용할 경우, AT가 m번째 BTS의 송신 신호 벡터 X_m의 n번째 데이터 스트림의 심볼

을 다음 수학식 7과 같이 복구한다.The kth AT of the m-th BTS computes the received SINR for the _nT data streams received from the m-th BTS for all possible cluster transmission modes. The AT is calculated according to the reception algorithm of a receiver for use (n × _{R T} 3n) receives the size of the weight matrix

, The first to nth _T column vectors of W _{m, k}

Are reception weight vectors for n _T data streams received from the m < th > BTS. Of the possible cluster transmission modes, AT

, AT is the symbol of the n-th data stream of the transmission signal vector X _m of the m-th BTS

Is restored as shown in the following Equation (7).

의 SINR

은 다음 수학식 8과 같다.Recovered symbol

Of the SINR

Is expressed by the following equation (8).

개의 데이터 스트림들간의 간섭을 나타낸다.Here, the first term of the denominator in Equation (8) is simultaneously transmitted by the C-BTSs

Lt; / RTI > data streams.

을 이용하여, C-BTS 클러스터로부터 m번째 BTS의 k번째 AT간의 링크에서 다중 사용자 다이버시티 이득을 최대화하는 클러스터 전송 모드

를 다음 수학식 9와 같이 결정한다. AT is calculated

To maximize the multi-user diversity gain in the link between the kth ATs of the m-th BTS from the C-BTS cluster,

Is determined according to the following equation (9).

개의 스트림 중 SINR이 가장 큰 스트림의 SINR을 최대로 만드는 클러스터 전송 모드를 선택한다. 여기서,

,

, 그리고

는 각각 C-BTS 클러스터로부터 m번째 BTS의 k번째 AT간의 링크에서 다중 사용자 다이버시티 이득을 최대화하기 위해서 m번째 BTS와 두 개의 인접 간섭 BTS들이 동시에 사용해야 하는 프리코딩 행렬이다. 위와 같이 선택된 클러스터 전송 모드

는 m번째 BTS의 k번째 AT로의 채널 이득을 크게 하면서, 동시에 두 개의 인접한 간섭 BTS들로부터의 간섭을 최소화하는 최적의 프리코딩 행렬 조합이다. 따라서, C-BTS 클러스터에 속한 C-BTS들이 사용할 클러스터 전송 모드

를 나타내는 인덱스와 함께 클러스터 전송 모드

를 사용하여 송신할 경우, m번째 BTS의 k번째 AT에서 수신하는

데이터 스트림에 대한 SINR,

을 역방향 링크 피드백 채널을 통해 m번째 BTS로 알려준다.According to Equation (9), the mth BTS transmits and the kth AT receives

And selects the cluster transmission mode that maximizes the SINR of the stream having the largest SINR among the streams. here,

,

, And

Is a precoding matrix that must be used simultaneously by the m-th BTS and the two adjacent interfering BTSs in order to maximize the multi-user diversity gain in the link between the kth ATs of the m-th BTS from the C-BTS cluster. The cluster transfer mode selected above

Is an optimal precoding matrix combination that maximizes the channel gain to the kth AT of the mth BTS while simultaneously minimizing interference from two adjacent interfering BTSs. Therefore, when the C-BTSs belonging to the C-BTS cluster use a cluster transmission mode

With the index representing the cluster transfer mode

, It is assumed that the signal is received at the kth AT of the m < th > BTS

The SINR for the data stream,

To the m < th > BTS over the reverse link feedback channel.

를 추정한다고 가정할 수 있다. m번째 BTS와 인접한 하나의 간섭 BTS로 구성된 BTS 클러스터의 (

)개의 송신 안테나들로부터 동시에 전송된 (

) 크기의 신호 벡터 X가 m번째 BTS의 k번째 AT에 수신되는 (

) 크기의 신호 벡터 Y_m,k는 다음 수학식 10과 같다.In the case of C-SDMA for the C2-AT with two C-BTSs, the kth AT of the m-th BTS is a downlink MIMO channel matrix from one adjacent interfering BTS

. ≪ / RTI > In the BTS cluster consisting of one interfering BTS adjacent to the mth BTS,

) ≪ / RTI > transmit antennas

) Signal vector X is received at the kth AT of the m < th > BTS (

) Signal vector Y _{m, k} is given by the following equation (10).

을 결정해야 함을 보여준다. 예를 들어,

를 사용할 경우, C2-AT를 위한 클러스터 전송 모드의 개수는 클러스터에 속하는 N₀개의 BTS에서 두 개의 C-BTS를 선택하는 경우의 수에, 각 경우 별로 사용할 수 있는 프리코딩 행렬의 조합 수를 곱한

로 표현된다. 또한, N₀=3인 경우, 총 12가지의 C2-AT용 클러스터 전송 모드가 존재하게 된다. 각 링크에서 최대의 다중 사용자 다이버시티 이득을 제공하는 클러스터 전송 모드의 결정 방식은 위에서 설명된 C3-AT용 클러스터 전송 모드 결정 방식과 동일하다.Comparing Equation (10) with Equation (5) describing the signal received by the C3-AT, Equation (10) shows a cluster transmission mode that maximizes the multi-user diversity gain on the link from the cluster to the AT

. E.g,

, The number of cluster transmission modes for the C2-AT is calculated by multiplying the number of cases in which two C-BTSs are selected in N ₀ BTSs belonging to the cluster by the number of combinations of precoding matrices available for each case

Lt; / RTI > In addition, when N ₀ = 3, a total of 12 cluster transmission modes for C2-AT exist. The determination method of the cluster transmission mode that provides the maximum multi-user diversity gain in each link is the same as the above-described determination method of the cluster transmission mode for C3-AT.

Accordingly, the AT estimates the downlink channel from the BTSs belonging to the same cluster, then determines the optimal cluster transmission mode according to the number of C-BTSs capable of channel estimation, and the AT transmits the following information to the BTS through the reverse link feedback Channel.

(1) Cluster transmission mode information selected by the AT - This cluster transmission mode information includes information on how many C-BTSs transmit data for the corresponding AT, and indicates a combination of precoding matrices to be used by the C-BTSs to which data is to be transmitted Cluster transmission mode information is included. In the case where the AT estimates the downlink channel to be fed back to the base station, the base station may determine how many C-BTSs transmit the data and notify the AT to the AT. In this case, Only the combination of the matrix is transmitted.

개의 데이터 스트림들의 수신 SINR 정보② When transmitting using the selected cluster transmission mode in C-BTS,

Lt; RTI ID = 0.0 > SINR <

Next, cluster scheduling for C-SDMA according to an embodiment of the present invention will be described.

The ATs in the same cluster feedback the received SINR information by the cluster transmission mode selected by each AT and the corresponding cluster transmission mode to the BTS to which each AT belongs. The BTSs in the same cluster transmit the feedback information from the ATs to the cluster scheduler over the wired communication network. ATs belonging to the same cluster are classified into NC-AT which is a non-collaborative operation AT, C2-AT which is an AT which desires collaborative transmission between two BTSs, and collaborative transmission between three BTSs Can be divided into the desired C3-ATs. The cluster scheduler uses the cluster transmission mode selected by the ATs in the collected cluster and the received SINR information according to the selected cluster transmission mode so as to maximize the scheduling criterion, Coding matrix) and the ATs to transmit data through the selected cluster transmission mode from among all the ATs belonging to the cluster.

이다. 여기서, l은 하나의 AT를 위해 동시에 데이터를 전송하는 C-BTS의 수를 나타내며, l개의 C-BTS에 대한 전송 모드의 개수

은 N_T개의 클러스터에 속하는 BTS에서 l개의 C-BTS를 선택하는 경우의 수에, 각 경우 별로 사용할 수 있는 프리코딩 행렬의 조합 수를 곱한 것이다.

에는 하나의 C-BTS를 사용하는 NC-AT부터 N_T개의 C-BTS를 사용하는 C-AT들을 위한 클러스터 전송 모드들이 모두 포함된다. N_T=3이고 G=2라고 가정하면, 가능한 클러스터 전송 모드는 총 26 개이며, 따라서, AT에서 선택된 하나의 클러스터 전송 모드를 표현하기 위해서는 5 비트가 필요하다.If the number of precoding matrices in the precoder codebook is G and the number of BTSs included in the cluster is N _T , then the number of transmission modes available to the cluster is

to be. Where l denotes the number of C-BTSs transmitting data simultaneously for one AT, and the number of transmission modes for one C-BTS

Is obtained by multiplying the number of cases of selecting one C-BTS in a BTS belonging to N _T clusters by the number of combinations of precoding matrices usable in each case.

Includes all of the cluster transmission modes for C-ATs using NC-ATs using one C-BTS and N _T C-BTSs. Assuming N _T = 3 and G = 2, there are a total of 26 possible cluster transmission modes, so 5 bits are needed to represent one selected cluster transmission mode at the AT.

The cluster scheduler groups all ATs belonging to the cluster according to the cluster transmission mode selected by each AT. ATs belonging to the same group can share the cluster transmission mode. That is, for ATs that have selected the same cluster transmission mode, the C-BTSs can transmit data using the precoding matrix of the corresponding cluster transmission mode. Also, depending on the precoding matrix used by the C-BTS, the cluster transmission mode for C3-AT may be used as a cluster transmission mode for each BTS for NC-AT transmission or a cluster transmission mode for C2-AT .

Table 1 below illustrates the compatibility between the NC-AT cluster transmission mode, the C2-AT cluster transmission mode, and the C3-AT cluster transmission mode. Here, it is assumed that G = 2, X denotes a precoding matrix used in the NC-BTS, and any precoding matrix belonging to the precoder codebook may be used. In the first line of Table 1, the cluster transfer mode for C3-AT is compatible with the immediately preceding cluster transfer mode for C2-AT. In the second line, the cluster transfer mode for C3- Compatible with cluster transfer mode. Therefore, the cluster transmission mode for C2-AT and the cluster transmission mode for C3-AT can be used simultaneously with the cluster transmission mode for NC-AT in the first row.

The cluster scheduler performs scheduling for both NC-AT, C2-AT, and C3-AT belonging to the cluster. The cluster scheduler divides all ATs belonging to the cluster into 8 groups according to the cluster transmission mode selected by each AT based on the cluster transmission mode of the C3-AT. NC-ATs and C2-ATs also belong to the AT group that uses the cluster transmission mode for C3-AT compatible with the cluster transmission mode selected by each AT. Therefore, since the cluster transmission modes ( E 1, X , X ) in Table 1 are compatible with all of the four cluster transmission modes for the C3-AT in the third row located in the lower row, . Similarly, the transmission modes ( E 1, E 1, X ) for the C2-AT are compatible with the cluster transmission modes ( E 1, E 1, E 1) and ( E 1, E 1, E 2) It is redundantly included in the two corresponding AT groups.

라고 하면, 각 AT 그룹 별로 스케줄링이 수행된다. 각 그룹에서 사용하는 클러스터 전송 모드의 (

)개의 송신 가중치를 이용하여 데이터를 전송할, 최대 스케줄링 우선순위를 갖는 AT들을 선택한다. BTS는 다음 수학식 11과 같이 g번째 송신 모드의 n번째 송신 가중치를 이용하여 데이터를 전송할

번째 AT를 선택한다.Eight AT groups according to cluster transfer mode

, Scheduling is performed for each AT group. The cluster transfer mode used by each group (

) ≪ / RTI > transmission weights to select the ATs with the highest scheduling priority to transmit data. The BTS transmits the data using the n-th transmission weight value of the g-th transmission mode as shown in Equation (11)

Gt; AT < / RTI >

는 g번째 AT 그룹 S_g에 속하는 z번째 AT가, g번째 클러스터 전송 모드의 n번째 송신 가중치를 통해 수신 할 수 있는 SINR

을 이용하여 구한 스케줄링 우선순위이다.

는 z번째 AT가 속한 BTS를 통해 클러스터 스케줄러에 피드백 된 정보이다. 예를 들어, 데이터 전송량을 최대로 하는(max throughput) 스케줄러의 경우,

가 된다. 결론적으로 동일한 클러스터 전송 모드를 사용하는 AT들에 대해, 해당 클러스터 전송 모드의 송신 가중치 별로 스케줄링 우선순위를 최대로 하는 AT를 선택한다. 따라서, 각 AT 그룹별로 (

)개의 송신 가중치를 통해 데이터를 전송할 AT들이 선택되고, 이렇게 선택된 AT들에 의한 각 그룹별 대표 스케줄링 우선순위 pri_g가 다음 수학식 12와 같이 결정된다. 본 발명의 실시예에서는 선택된 AT들의 스케줄링 우선순위들을 합하여 해당 그룹의 스케줄링 우선순위로 설명하였으나, 그룹별 스케줄링 우선순위를 구하는 방식은 다른 방식을 사용할 수도 있다.

Th AT group belonging to the gth AT group S _g is a SINR that can be received through the nth transmission weight of the gth cluster transmission mode,

Is a scheduling priority obtained using the following equation.

Is information fed back to the cluster scheduler through the BTS to which the zth AT belongs. For example, for a scheduler that maximizes data throughput (max throughput)

. As a result, for ATs using the same cluster transmission mode, an AT that maximizes the scheduling priority is selected for each transmission weight value of the corresponding cluster transmission mode. Thus, for each AT group (

) Transmission weights, and the representative scheduling priority pri _g for each group by the selected ATs is determined as shown in the following equation (12). In the embodiment of the present invention, the scheduling priorities of the selected ATs are summed up as the scheduling priorities of the corresponding groups. However, the scheduling priorities of the groups may be calculated using another scheme.

을 수학식 13과 같이 선택한다. The cluster scheduler uses the scheduling priority for each group to determine the AT group having the largest group scheduling priority

Is selected as shown in Equation (13).

과 해당 그룹이 사용할 클러스터 전송 모드, 즉 클러스터에 속하는 BTS들이 사용할 프리코딩 행렬이 결정된다. 또한, 클러스터 스케줄러는 데이터를 전송할 AT들의 수신 SINR을 이용하여, 전송할 데이터의 MCS를 결정할 수 있다.Therefore, the AT group

And a cluster transmission mode to be used by the group, i.e., a precoding matrix to be used by the BTSs belonging to the cluster are determined. In addition, the cluster scheduler can determine the MCS of the data to be transmitted using the received SINR of the ATs to transmit data.

에 대한 정보, 해당 AT들이 사용할 클러스터 전송 모드에 대한 정보, 그리고 전송할 데이터의 MCS에 대한 정보는 유선 통신망을 통해 각 BTS로 전달된다. 각 BTS들은 선택된 AT들

에 대해, 해당 MCS 레벨의 데이터 스트림을 만들고, 선택된 클러스터 전송 모드로 프리코딩하여 클러스터 내의 C-BTS들의 송신 안테나들을 통해 전송한다. Determined by the cluster scheduler, the AT to transfer data

Information about the cluster transmission mode to be used by the ATs and information on the MCS of the data to be transmitted is transmitted to each BTS through the wired communication network. Each of the BTSs < RTI ID = 0.0 &

Generates a data stream of the corresponding MCS level, precodes the data stream in the selected cluster transmission mode, and transmits the data stream through the transmission antennas of the C-BTSs in the cluster.

에는, 선택된 클러스터 전송 모드와 호환되는 NC-AT와 C2-AT용 클러스터 전송 모드를 사용하는 AT들이 포함될 수 있다. 데이터를 전송하기 위해 선택된 NC-AT와 C2-AT들도 해당 MCS 레벨의 데이터 스트림을 만들고, 사용할 NC-AT 또는 C2-AT용 클러스터 전송 모드로 프리코딩하여, 해당 BTS들의 송신 안테나를 통해 전송한다.Determined by the cluster scheduler, the AT to transfer data

ATs that use the cluster transfer mode for NC-AT and C2-AT compatible with the selected cluster transfer mode may be included. The NC-ATs and C2-ATs selected to transmit data also generate a data stream of the corresponding MCS level, precoded in the NC-AT or C2-AT cluster transmission mode to be used, and transmitted through the transmission antennas of the corresponding BTSs .

Next, the extended cluster transmission mode selection and feedback information for increasing the multi-user diversity gain will be described.

In the C-SDMA technique according to the embodiment of the present invention, scheduling is performed on ATs that select the same cluster transmission mode or a compatible cluster transmission mode. Therefore, as the number of precoding matrices G in the precoder codebook and the number of C-BTSs belonging to the cluster become larger, the number of precoding matrix combinations that can be transmitted by the C-BTS, i.e., the number of cluster transmission modes increases. Increasing the number of cluster transmission modes reduces the number of ATs that select the same cluster transmission mode. Specifically, when the number of C-BTSs is 3 and G = 2, the number of cluster transmission modes is 8. If the number of C-BTSs is 3 and G = 1, the number of cluster transmission modes is 1. When the cluster transmission mode is 8, the ATs are scheduled to be divided into 8 groups according to the selected cluster transmission mode. On the other hand, when the cluster transmission mode is 1, all the ATs belong to one group. Therefore, . That is, when the number of transmission modes is increased, the number of ATs to be subjected to multi-user scheduling is reduced, so that the multi-user diversity gain at the system level is reduced. However, as the size of the precoder codebook, that is, G increases, detailed precoding for each link becomes possible, so that the reception SINR of each link increases. Therefore, there is a need for a method to overcome the multiuser diversity gain reduction phenomenon of the system as the size of the codebook increases while increasing the gain of each link by increasing the size of the precoder codebook.

를 사용하고, C-BTS의 개수가 3이고 AT가 속한 BTS가 프리코딩 행렬 E_m을 사용할 경우, 타 C-BTS 기지국이 사용해야 할 프리코딩 행렬 G_m,1과 G_m,2는 다음 수학식 14와 같이 결정된다. To this end, in the embodiment of the present invention, the AT selects G cluster transmission modes and feeds back the information to the BTS. This leads to an increase of the feedback information amount G times as compared with the single transmission mode selection method proposed above. AT selects a transmission mode that maximizes the multi-user diversity gain in the link between the kth ATs of the m-th BTS from the C-BTS cluster, when the BTS to which the AT belongs uses G precoding matrices in the codebook, respectively. Specifically,

And the number of C-BTSs is 3 and the BTS to which the AT belongs use the precoding matrix E _m , the precoding matrices G _{m, 1} and G _{m, 2} to be used by the other C-BTS base stations are expressed by the following equations 14 < / RTI >

을 사용하는 4가지 클러스터 전송 모드에 대해, k번째 AT가 수신하는

개의 스트림 중 SINR이 가장 큰 스트림의 SINR을 최대로 만드는 클러스터 전송 모드를 선택한다. 따라서 선택된 클러스터 전송 모드

를 나타내는 인덱스와 함께, 해당 클러스터 전송 모드를 사용하여 데이터를 송신할 경우, AT에서 수신하는

개의 데이터 스트림에 대한 SINR,

을 각각 역방향 링크 피드백 채널을 통해 m번째 BTS로 알려준다. 정리하면, AT는 BTS로 다음의 정보들을 역방향 링크 피드백 채널을 통해 전송한다.According to Equation (14), among the total 8 cluster transmission modes, the precoding matrix of the BTS to which the AT belongs

For four cluster transmission modes using the < RTI ID = 0.0 >

And selects the cluster transmission mode that maximizes the SINR of the stream having the largest SINR among the streams. Therefore,

, And when data is transmitted using the corresponding cluster transmission mode,

SINR for the data streams,

To the m < th > BTS through the reverse link feedback channel, respectively. In summary, the AT transmits the following information to the BTS over the reverse link feedback channel.

(1) Information indicating that the AT feeds back G cluster transmission modes

(2) Cluster transmission mode information selected by the AT - This transmission mode information includes information on how many C-BTSs transmit data for the corresponding AT, and indicates a combination of precoding matrices to be used by the C-BTSs to transmit data together Cluster transmission mode information is included.

개의 수신 데이터 스트림의 수신 SINR 정보③ For each of the G cluster transmission modes to be used in the C-BTS,

Lt; RTI ID = 0.0 > SINR < / RTI >

The extended cluster transmission mode selection and feedback scheme proposed in the embodiment of the present invention transmits G cluster transmission modes and corresponding reception SINR information for each AT to the cluster scheduler so that each AT allocates AT groups . Therefore, at the time of scheduling, the number of ATs included in the AT group for each cluster transmission mode increases, and the multi-user diversity gain can be increased. However, the feedback method based on the selection of the extended cluster transmission mode requires a feedback amount of G times larger than the feedback information amount required in the single cluster transmission mode selection method.

FIG. 3 and FIG. 4 illustrate operation flow of a terminal and a base station according to the C-SDMA technique according to the embodiment of the present invention.

Referring to FIG. 3, in step 301, each AT estimates a downlink MIMO channel from BTSs belonging to a cluster. Each AT is divided into a cluster transmission mode for maximizing the multi-user diversity gain in each AT link in step 302 and a cluster transmission mode for maximizing the multi-user diversity gain in step 302, based on the downlink MIMO channel estimated from the BTSs belonging to the cluster, . When using the single cluster transmission mode selection and feedback according to the embodiment of the present invention, the AT selects only one cluster transmission mode, and when using the extended cluster transmission mode selection and feedback scheme, the AT selects G cluster transmission modes . In step 303, each AT transmits information on a feedback mode (selection of a single cluster transmission mode or an extended cluster transmission mode) to be used in each AT and information on a selected cluster transmission mode The number of C-BTSs to transmit data at the same time and the corresponding cluster transmission mode), and the received SINR information of the AT according to the selected cluster transmission mode to the BTS to which the AT belongs.

Referring to FIG. 4, in operation 401, the BTS transmits information fed back from each AT to a cluster scheduler connected through a wired communication network.

개의 AT들이 선택되고, 그룹별 대표 스케줄링 우선순위가 결정된다. 404과정에서 클러스터 스케줄러는 그룹 스케줄링 우선순위를 최대로 하는 AT 그룹을 선택함으로써, 클러스터에서 데이터를 전송할 (

)개의 AT들, 해당 AT들이 사용할 클러스터 전송 모드, 그리고 해당 클러스터 전송 모드를 사용하여 전송할 데이터들의 MCS를 결정한다. 그리고 클러스터 스케줄러는 결정된 상기 정보들을 유선 통신망을 통해 클러스터 내의 각 BTS에게 전달한다.In step 402, the cluster scheduler divides the ATs that select the same cluster transmission mode or the compatible cluster transmission mode into the same AT group, and performs scheduling for each group in step 403. Data is transmitted using the corresponding cluster transmission mode for each group by the group-specific scheduling

Lt; / RTI > are selected, and the representative scheduling priority for each group is determined. In step 404, the cluster scheduler selects the AT group that maximizes the group scheduling priority to transmit data in the cluster (

) ATs, the cluster transmission mode to be used by the corresponding ATs, and the MCS of the data to be transmitted using the corresponding cluster transmission mode. The cluster scheduler transmits the determined information to each BTS in the cluster through a wired network.

개의 AT들, 해당 AT들이 사용할 클러스터 전송 모드, 그리고 해당 클러스터 전송 모드를 사용하여 전송할 데이터들의 MCS 정보를 이용하여, 해당 BTS에 속하는 AT들에 대해, 해당 MCS 레벨의 데이터 스트림을 만들고, 이를 선택된 클러스터 전송 모드로 프리코딩하여C-BTS들을 통하여 동시에 전송한다.Finally, in step 405, the BTSs in the cluster send the data from the cluster scheduler

A data stream of the corresponding MCS level is created for the ATs belonging to the corresponding BTS by using the ATs, the cluster transmission mode to be used by the ATs, and the MCS information of the data to be transmitted using the corresponding cluster transmission mode, Precoding in the transmission mode and transmitting them simultaneously through the C-BTSs.

Next, the cooperative beam forming technique will be described.

The above-described C-SDMA technique simultaneously transmits data from a plurality of BTSs belonging to the same cluster to a plurality of ATs belonging to the same cluster. The C-SDMA technique according to an embodiment of the present invention minimizes interference of other cells by BF of adjacent BTSs through collaborative beamforming (C-BF) of a plurality of BTSs belonging to the same cluster, It is possible to operate with C-BF technology that transmits data to each AT one per each.

5 and 6 are flowcharts illustrating operations of a terminal and a base station in a C-BF according to an embodiment of the present invention.

를 추정한다. m번째 BTS와 인접한 두 개의 BTS로 구성된 BTS 클러스터의

개의 송신 안테나들로부터 동시에 전송된 (3×1) 크기의 신호 벡터 X_BF가 m번째 BTS의 k번째 AT에 수신되는 신호 벡터 Y_m,k는 다음 수학식 15와 같다.In the embodiment of the present invention, C-BF for C3-AT having three C-BTSs is described. First, in step 501, the kth AT of the m-th BTS receives a downlink MIMO channel matrix from two adjacent interference BTSs

. In the BTS cluster consisting of two BTSs adjacent to the m-th BTS

The signal vector Y _{m, k} received at the kth AT of the m-th BTS from the (3 x 1) sized signal vector X _BF transmitted simultaneously from the two transmit antennas is expressed by Equation (15).

는 C-BTS 클러스터에 속한 3개의 C-BTS가 각각 f, g₁, 그리고 g₂ 가중치에 의해 BF을 했을 때, m번째 BTS의 k번째 AT에서 수신되는 (n_R×3) 크기의 하향 링크 채널 행렬을 나타낸다. 수학식 15에 따르면, C-BTS 클러스터로부터 m번째 BTS의 k번째AT간의 링크에서 수신 SINR을 최대화하는, m번째 BTS가 사용할 가중치 벡터 f와 두 개의 간섭 BTS가 각각 사용할 가중치 벡터

를 동시에 결정해야 한다. 이와 같이 수신 SINR을 최대가 되도록 각 BTS에서 사용할 가중치를 결정하면, BF에 의한 이득을 증가시키는 동시에 인접 BTS들의 BF에 의한 타 셀의 간섭을 최소화하는 최적의 가중치 조합을 결정할 수 있다. 그러나 G개의 프리코딩 행렬로 이루어진 프리코더 코드북을 사용할 경우, C-BTS의 수가 l개 일 때, C-BF을 위한 전송 모드 수가

로 상당히 크다. 따라서 선택된 클러스터 전송 모드를 피드백 하기 위해 많은 피드백 비트가 요구된다. 또한 클러스터 스케줄러에서 동일한 클러스터 전송 모드를 선택하는 AT들을 그룹화하고 이에 대해 스케줄링을 수행할 경우, 스케줄링에 의한 다중 사용자 다이버시티 이득의 감소에 따른 전송 용량이 감소된다.Where Y _{m, k} is the received signal vector of size (n _R x 1), and N _{m, k} is the noise vector of size (n _R x 1).

(N _R x 3) size downlink received from the kth AT of the m-th BTS when the three C-BTSs in the C-BTS cluster perform BF by f, g ₁ and g ₂ weights, Represents a channel matrix. According to Equation (15), the weight vector f to be used by the m-th BTS, which maximizes the reception SINR at the link between the kth ATs of the m-th BTS from the C-BTS cluster,

Should be determined at the same time. Determining the weights to be used in each BTS to maximize the reception SINR may determine an optimum weight combination that minimizes interference from other cells due to BFs of neighboring BTSs while increasing the gain by BF. However, when a precoder codebook composed of G precoding matrices is used, when the number of C-BTSs is l, the number of transmission modes for C-BF

. Therefore, many feedback bits are required to feed back the selected cluster transmission mode. Also, when grouping ATs that select the same cluster transmission mode in the cluster scheduler and performing scheduling on them, the transmission capacity due to the reduction of the multiuser diversity gain due to scheduling is reduced.

들을 각 AT에서 선택하여 AT가 속한 BTS로 피드백 한다. 클러스터 스케줄러에서는 각 AT의 신호 가중치 벡터와 주 간섭 가중치 벡터 정보를 이용하여, 데이터를 전송할 AT는 해당 AT의 신호 가중치 벡터를 사용하도록 하면서 간섭 C-BTS에서는 해당 AT의 주 간섭 가중치 벡터를 사용하지 않도록 스케줄링을 수행한다. 기지국에서 사용하는 가중치 벡터의 수가 2 이상인 경우, 피트백 비트의 수를 줄이기 위하여 복수개의 가중치를 그룹화하여 주 간섭 가중치 그룹을 피드백할수도 있다.Therefore, in the embodiment of the present invention, when the cluster transmission mode is selected, the signal weight vector f that maximizes the gain from the mth BTS to the kth AT, that is, the transmission weight vector f that the AT desires to transmit and the AT from each interfering BTS belonging to the C- The main interference weight vector which has the maximum interference amount, i.e., which is not desired to be used in each interfering C-BTS

At each AT and feeds back to the BTS to which the AT belongs. In the cluster scheduler, the signal weight vector of each AT and the main interference weight vector information are used so that the AT to transmit data uses the signal weight vector of the AT, while the interference C-BTS does not use the main interference weight vector of the corresponding AT And performs scheduling. If the number of weight vectors used in the base station is two or more, a group of the plurality of weights may be grouped to feed back the main interference weight group so as to reduce the number of pit back bits.

를 사용한다고 가정하면, 도 5의 502과정에서 m번째 BTS의 k번째 C3-AT를 위한, 신호 가중치 벡터 f와 주 간섭 가중치 벡터

를 다음 수학식 16과 같이 구한다.A precoder codebook consisting of two precoding matrices

The signal weight vector f and the main interference weight vector f for the kth C3-AT of the m < th > BTS in step 502 of FIG. 5,

As shown in the following equation (16).

은 프리코더 코드북 F의 프리코딩 행렬들의 컬럼 벡터들이다. AT는 신호 가중치 벡터 f를 m번째 BTS에서 사용하고, 두 개의 간섭 C-BTS에서 주 간섭 가중치 벡터

를 사용하지 않았을 때의, AT의 수신 SINR을 계산한다. 503과정에서 AT는 BTS로 다음의 정보들을 역방향 링크 피드백 채널을 통해 전송한다.here,

Are the column vectors of the precoding matrices of the precoder codebook F. AT uses the signal weight vector f in the m < th > BTS, and in the two interfering C-BTSs the main interference weight vector

, The reception SINR of the AT is calculated. In step 503, the AT transmits the following information to the BTS through the reverse link feedback channel.

정보(1) The selected signal weight vector f and the main interference weight vector

Information

를 사용하지 않았을 때의, AT가 수신하는 단일 데이터 스트림의 수신 SINR 정보 2) It is used in the BTS to which the selected signal weight vector f belongs, and in the two interfering C-BTSs, the main interference weight vector

Lt; RTI ID = 0.0 > SINR < / RTI > information of a single data stream received by the AT,

Referring to FIG. 6, the BTS transmits feedback information received from the AT in step 601 to the cluster scheduler. In step 602, the cluster scheduler performs scheduling for each BTS as follows. For the ATs belonging to each BTS, the scheduling priority is calculated using the received SINR of each AT that has been fed back, and the AT having the highest scheduling priority is selected to transmit data in each BTS.

In step 603, the cluster scheduler performs collision avoidance scheduling using the signal weights and the main interference weight information of the selected ATs for each BTS as follows. If the signal weights of the ATs to transmit data in one BTS coincide with the main interference weights of the other BTSs, that is, if one BTS assigns a primary interference to the ATs of the other BTSs to be used for signal transmission, The AT having a higher priority is selected from the two ATs, and the BTS to which the unselected AT belongs selects the AT having the lower priority in the scheduling priority. For the difference order AT, it is also selected to check whether the signal weights used are the primary interferences for the ATs of other selected BTSs and to transmit the data when it is not primary interference. By suppressing the collision between the beams formed by the weights used in each BTS through collision avoidance scheduling performed in the above-described cluster, it is possible to suppress transmission of other cells and improve the transmission data capacity.

In step 604, the cluster scheduler transmits MCS information of data to be transmitted using one AT to transmit data in each BTS, a beam forming weight to be used by the corresponding AT, and a corresponding beam forming weight. In step 605, the corresponding BTS is transmitted from the cluster scheduler And transmits the data to the AT according to the transmitted information.

7 and 8 are diagrams of an AT and a BTS for performing C-SDAM or beamforming according to an embodiment of the present invention, respectively. Referring to FIG. 7, the AT includes a downlink channel estimator 701, a determination unit 702, and a feedback transmission unit 703. The downlink channel estimator 701 estimates a downlink channel using the downlink sounding reference signal received from the BTS. The determination unit 702 selects a transmission mode, an SINR, a precoding matrix, or a signal weight according to an estimation result of the downlink channel estimator 701. [ The feedback transmitting unit 703 transmits the information determined by the determining unit 702 to the BTS through the reverse link feedback channel.

8, the base station system includes a BTS 810 and a cluster scheduler 820. The BTS 811 includes a feedback receiver 811 and a data transmitter 812, and the cluster scheduler 820, Includes a scheduling unit 821.

The feedback receiving unit 811 receives feedback information from the AT via the reverse link feedback channel. The scheduling unit 821 receives the feedback information received from the feedback receiving unit 811, and generates an AT, an MCS, a precoding matrix, The weights are determined. The data transmission unit 812 applies the corresponding MCS and the precoding matrix or weight to the AT according to the determination of the scheduling unit 821, and transmits the data.

According to the embodiment of the present invention, a C-SDMA technique for effectively suppressing other-cell interference by an adjacent BTS based on an SDMA technique using an existing precoder codebook in an FDD system has been proposed. Hereinafter, in order to analyze the performance of the C-SDMA technique according to the embodiment of the present invention, a conventional precoder codebook, which is scheduled according to NC-SDMA technology, i.e., BTS, in one cluster consisting of three C- The performance of the proposed SDMA technique and the proposed C-SDMA technology are compared based on the system level capacity.

개의 C3-AT들이 존재하는 하나의 클러스터에서, NC-SDMA 기술과 C-SDMA 기술을 클러스터에서의 용량을 기준으로, 프리코더 코드북 내의 프리코딩 행렬 수 G와 AT에서 피드백하는 클러스터 전송 모드의 수에 따른 성능을 비교 분석한 도면이다. 각 BTS의 송신 안테나 수 n_T은 4이고 안테나 간격이 0.5λ이며, AT의 수신 안테나 수 n_R은 4이고 안테나 간격이 0.5λ이며, 모든

개의 C-AT들은 세 개의 C-BTS들로부터 평균 SNR 10dB의 신호를 수신한다고 가정한다. FIG. 9 is a block diagram of an embodiment of the present invention, which can estimate a downlink channel from three C-BTSs

In one cluster with three C3-ATs, the number of cluster transmission modes that feed back the NC-SDMA technique and the C-SDMA technique to the number of precoding matrices G in the precoder codebook and the AT based on the capacity in the cluster And FIG. The number of transmission antennas n _T of each BTS is 4, the antenna interval is 0.5?, The number of reception antennas n _R of AT is 4, the antenna interval is 0.5?

It is assumed that the C-ATs receive signals with an average SNR of 10 dB from the three C-BTSs.

개의 C-AT들까지의 각 링크에서 MIMO 채널 계수를 10000번 발생시켜서 얻어진 클러스터의 용량을 평균하여 성능 척도로 사용하였다. 채널 계수 발생 시, BTS의 송신단에서의 AOD(angle of depature)와 AT의 수신단에서의 AOA(angle of arrival)은 (-30°,30°) 내에서 균일하게 발생시켰다. 각 링크에서 채널 발생시, 다음의 수학식 17을 이용하여 공간 상관도가 있는 MIMO 채널을 발생시켰으며, BTS의 송신단에서의 공간상관행렬 R_T와 AT의 수신단에서의 공간상관행렬 R_R는 선형 배열 안테나를 사용하며 각 스펙트럼(angular spectrum)이 AOD와 AOA를 중심으로 각각 Δ_T와 Δ_R 만큼 균일하게 분포하는 모델을 사용하여 구하였다. k번째 C-AT의 하향 링크 채널 행렬은 다음 수학식 17과 같이 구해진다.From cluster

The average capacity of clusters obtained by generating MIMO channel coefficients 10000 times in each link up to C-ATs is used as a performance measure. When the channel coefficient is generated, the AOD (angle of depature) at the transmitting end of the BTS and the AOA (angle of arrival) at the receiving end of the AT are uniformly generated within (-30 °, 30 °). The spatial correlation matrix R _T at the transmitting end of the BTS and the spatial correlation matrix R _R at the receiving end of the AT generate a linear correlation matrix M using an antenna and were determined using a model that uniformly distributed by each spectrum (angular spectrum) with each Δ _T Δ _R around the AOD and AOA. The downlink channel matrix of the k-th C-AT is obtained by Equation (17).

개의 링크들에 대해 Δ_T=5°, Δ_R=60°로 가정한다. Where H _w is a complex Gaussian matrix with no correlation (n _T × n _R ). all

Let Δ _T = 5 ° and Δ _R = 60 ° for the two links.

The precoding matrix used in FIG. 9 is expressed by Equation (18). When G = 1, F = {E ₁ , E ₂ } if F = {E ₁ } and G = 2.

In FIG. 9, it can be seen that the C-SDMA technologies show higher cluster capacity than the NC-SDMA technology. Therefore, it can be confirmed that the C-SDMA technique effectively suppresses interference of other cells and improves the system capacity. Also, it can be seen that the C-SDMA technique provides a higher cluster capacity when G = 2 than when G = 1. This is because as the size of the precoder codebook used increases, fine precoding for each link becomes possible, thereby increasing the reception SINR of each link.

비트가 요구된다. 여기서,

는 하나의 SINR을 나타내기 위해 필요한 비트 수이다. AT에서 G개의 전송 모드를 선택하고 이를 피드백하는 방식은 단일 전송 모드에서 필요한

의 G배 만큼의 피드백 비트가 요구된다. 따라서 G=2 인 경우에는 두 배의 피드백 비트가 요구된다. 그러므로 본 발명의 실시예에 따른 두 개의 피드백 방식 중에서, 시스템에서 허용되는 상향 링크 피드백 채널의 용량에 따라 최적의 피드백 방식을 선택할 수 있다.It can be seen that the method of selecting and feedbacking two cluster transmission modes at each AT provides a much higher capacity than the method of selecting and transmitting one optimal cluster transmission mode in each AT in C-SDMA. The single transmission mode feedback scheme consists of 5 bits for indicating one mode selected from the cluster transmission modes and n _T SINRs received by the AT when the selected transmission mode is used

Bit is required. here,

Is the number of bits needed to represent one SINR. The method of selecting and transmitting G transmission modes at the AT is necessary in single transmission mode

The feedback bit is required to be G times as large as the G-bit. Therefore, when G = 2, twice the feedback bit is required. Therefore, among the two feedback methods according to the embodiment of the present invention, the optimum feedback method can be selected according to the capacity of the uplink feedback channel allowed in the system.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

1 illustrates a conventional multi-antenna technique;

2 is a diagram illustrating a C-SDMA technique to which the present invention is applied.

3 is a flowchart illustrating operations of a terminal in C-SDMA according to an embodiment of the present invention.

4 is a flowchart illustrating an operation of a base station in C-SDMA according to an embodiment of the present invention;

5 is a flowchart showing operations of a terminal in C-BF according to an embodiment of the present invention;

6 is a flowchart showing the operation of a base station in a C-BF according to an embodiment of the present invention;

7 is a configuration diagram of a terminal according to an embodiment of the present invention;

8 is a configuration diagram of a base station according to an embodiment of the present invention;

개의 AT들이 존재하는 하나의 클러스터에서, NC-SDMA 기술과 C-SDMA 기술의 성능을 비교 분석한 도면.FIG. 9 is a block diagram illustrating a method for estimating a downlink channel from three C-BTSs

A comparison of the performance of NC-SDMA technology and C-SDMA technology in one cluster where there are ATs.

Claims (38)

A method for receiving downlink data in a terminal in a collaborative wireless communication system using a multiple input / output antenna, Estimating a downlink channel for each of a plurality of base stations belonging to the same cluster; Selecting a transmission mode that maximizes a signal-to-interference and noise ratio (SINR) in each of the estimated downlink channels among a plurality of transmission modes according to a combination of pre-code matrices; Feedback information on SINR when using the selected transmission mode and the selected transmission mode to at least one base station among the plurality of base stations; And receiving the downlink data from the at least one base station in the selected transmission mode. The method of claim 1, wherein the selecting of the transmission mode comprises: And selecting a transmission mode using a combination that maximizes a multi-user diversity gain among the plurality of transmission modes. 3. The method of claim 2, Wherein the transmission mode is a transmission mode using a combination of a precoding matrix maximizing a channel gain with the at least one base station and minimizing interference from base stations transmitting interference signals among the plurality of base stations. The method according to claim 1, When receiving downlink data from at least two base stations of the plurality of base stations, information on a transmission mode according to a combination of precode matrices used by the at least two base stations among the plurality of transmission modes is fed back And feeding back information indicating the number of the at least two base stations to each of the at least two base stations. 2. The method of claim 1, Selecting a transmission mode for each of the at least two base stations when receiving downlink data from at least two base stations of the plurality of base stations and transmitting information about a transmission mode selected for each of the at least two base stations To each of the at least two base stations. A method for transmitting downlink data in a base station in a collaborative wireless communication system using a multiple input / output antenna, Receiving feedback information from each of a plurality of terminals, Grouping terminal groups using the same transmission mode based on information on a transmission mode included in each received feedback information to generate terminal groups; Selecting a terminal group having a maximum priority by performing scheduling for each of the terminal groups; Determining a transmission mode to be used by terminals belonging to the selected terminal group and a modulation level of downlink data to be transmitted to terminals belonging to the selected terminal group; And transmitting the downlink data to the terminals belonging to the selected terminal group according to the determined transmission mode and the determined modulation level, Wherein the transmission mode is one of a plurality of transmission modes according to a combination of pre-code matrices, wherein each of the plurality of UEs transmits a signal-to-noise ratio (SNR) in each downlink channel estimated for each of a plurality of base stations belonging to the same cluster, to-Interference and Noise Ratio (SINR) of the downlink data is maximized. The method of claim 6, wherein the determining the transmission mode comprises: Selecting a transmission mode using a combination that maximizes a multi-user diversity gain among a plurality of transmission modes according to a combination of pre-code matrices; And determining the selected transmission mode as a transmission mode to be used by the terminals belonging to the selected terminal group. 8. The method of claim 7, wherein the determined transmission mode comprises: The UEs in the selected UE group use a combination of a precoding matrix for maximizing a channel gain with a Node B to receive downlink data and minimizing interference from Node Bs transmitting interfering signals among a plurality of Node Bs And transmitting the downlink data. 7. The method of claim 6, wherein the scheduling comprises: And determining a priority for maximizing a signal-to-interference and noise ratio (SINR) using transmission modes and transmission weights to be used by terminals belonging to the selected terminal group. 7. The method of claim 6, wherein the step of receiving the feedback information comprises: Receiving information indicating that each of the plurality of UEs feeds back information on a plurality of transmission modes and information indicating the number of base stations transmitting downlink data for each of the plurality of UEs, Downlink data transmission method. A method for receiving downlink data in a terminal in a collaborative wireless communication system using a multiple input / output antenna, Estimating a downlink channel for each of a plurality of base stations belonging to the same cluster; Determining interference weights that maximize interference to interference base stations and a signal weight of a base station that maximizes a signal-to-interference and noise ratio (SINR) in each of the downlink channels estimated; Feedbacking the determined signal weights, the determined interference weights, and information on the SINR to the base station; And receiving the downlink data according to the determined signal weights from the base station. 12. The method of claim 11, And SINR when collision between beams formed by signal weights used by the plurality of base stations is avoided. 13. The method of claim 12, Further comprising feeding back a difference between the SINR when the collision between the beams is avoided and the SINR when the collision between the beams is not avoided. 12. The method of claim 11, And grouping the signal weights of the two or more signals and feeding back the signal weights when the signal weights used by the base station are two or more. A method for transmitting downlink data in a base station in a collaborative wireless communication system using a multiple input / output antenna, Receiving feedback information from each of a plurality of terminals, Determining a scheduling priority of the plurality of UEs using a signal-to-interference and noise ratio (SINR) included in each received feedback information; Scheduling to minimize interference between base stations using the determined scheduling priority, signal weights of the base stations included in the feedback information, and interference weights of the interfering base stations; Selecting a terminal to which downlink data will be transmitted among the plurality of terminals and determining a signal weight and a modulation level to be used by the selected terminal; And transmitting the downlink data to the selected terminal according to the determined signal weight and modulation level, Wherein the signal weights are signal weights of a base station maximizing a signal-to-interference noise ratio in a downlink channel estimated for each of a plurality of base stations belonging to the same cluster, the interference weight being maximized / RTI > 16. The method of claim 15, wherein the determining the scheduling priority comprises: Calculating a transmittable data capacity for the plurality of terminals, and determining the scheduling priority according to the calculated transmittable data capacity. 17. The method of claim 16, wherein calculating the transmittable data capacity for the plurality of terminals comprises: Using the SINR of avoiding collision between beams formed from the base stations if the signal weights received from one of the plurality of terminals do not match the interference weights of the remaining ones of the plurality of terminals, Calculating a transmittable data capacity; Using the SINR when the collision between the beams formed from the base stations is not avoided when the signal weights received from one of the plurality of terminals coincide with the interference weights of the remaining ones of the plurality of terminals, And calculating a transmittable data capacity. 16. The method of claim 15, And the SINR when collision between beams formed by the signal weights is avoided by the plurality of base stations. 19. The method of claim 18, And information indicating a difference between SINR when collision between the beams is avoided and SINR when collision between the beams is not avoided. A terminal apparatus for receiving downlink data in a collaborative wireless communication system using a multiple input / output antenna, Estimating a downlink channel for each of a plurality of base stations belonging to the same cluster, and estimating a signal-to-interference ratio (SNR) in each of the estimated downlink channels among a plurality of transmission modes according to a combination of pre- A control unit for selecting a transmission mode for maximizing a Noise Ratio (SINR) A feedback transmission unit for feeding back information on the selected transmission mode and SINR when using the selected transmission mode to at least one base station among the plurality of base stations; And a receiver for receiving the downlink data from the at least one base station in the selected transmission mode. 21. The apparatus of claim 20, And selects a transmission mode using a combination that maximizes a multi-user diversity gain among the plurality of transmission modes. 22. The method of claim 21, wherein the selected transmission mode comprises: Wherein the transmission mode is a transmission mode using a combination of a precoding matrix maximizing a channel gain with the at least one base station and minimizing interference from base stations transmitting interference signals among the plurality of base stations. 21. The apparatus of claim 20, When receiving downlink data from at least two base stations of the plurality of base stations, information on a transmission mode according to a combination of precode matrices used by the at least two base stations among the plurality of transmission modes is fed back And information indicating the number of the at least two base stations is fed back to each of the at least two base stations. 21. The apparatus of claim 20, Selecting a transmission mode for each of the at least two base stations when receiving downlink data from at least two base stations of the plurality of base stations and transmitting information about a transmission mode selected for each of the at least two base stations To each of the at least two base stations. A base station apparatus for transmitting downlink data in a collaborative wireless communication system using a multi-input / output antenna, A feedback receiver for receiving feedback information from each of a plurality of terminals; Grouping terminal groups using the same transmission mode based on the information on the transmission mode included in the received feedback information, generating terminal groups, scheduling each of the generated terminal groups, A control unit for selecting a terminal group and determining a transmission mode to be used by terminals belonging to the selected terminal group and a modulation level of downlink data to be transmitted to terminals belonging to the selected terminal group; And a data transmission unit for transmitting the downlink data to terminals belonging to the selected terminal group according to the determined transmission mode and the determined modulation level, Wherein the transmission mode is one of a plurality of transmission modes according to a combination of pre-code matrices, wherein each of the plurality of UEs transmits a signal-to-noise ratio (SNR) in each downlink channel estimated for each of a plurality of base stations belonging to the same cluster, to-interference and noise ratio (SINR). 26. The apparatus of claim 25, Selects a transmission mode using a combination that maximizes a multi-user diversity gain among a plurality of transmission modes according to a combination of pre-code matrices, and determines the transmission mode to be used by terminals belonging to the selected terminal group The base station apparatus comprising: 27. The method of claim 26, wherein the determined transmission mode comprises: The UEs in the selected UE group use a combination of a precoding matrix for maximizing a channel gain with a Node B to receive downlink data and minimizing interference from Node Bs transmitting interfering signals among a plurality of Node Bs The base station apparatus comprising: 26. The apparatus of claim 25, To-interference-and-noise ratio (SINR) using a transmission mode and a transmission weight to be used by terminals belonging to the selected terminal group. The apparatus of claim 25, wherein the feedback receiver comprises: Wherein the base station receives information indicating that each of the plurality of terminals feedback information on a plurality of transmission modes and information indicating the number of base stations transmitting downlink data for each of the plurality of terminals, Device. A terminal apparatus for receiving downlink data in a collaborative wireless communication system using a multiple input / output antenna, Estimating a downlink channel for each of a plurality of base stations belonging to the same cluster and estimating a signal weight and an interference level of a base station that maximizes a signal-to-interference and noise ratio (SINR) A controller for determining interference weights that maximize interference to base stations; A feedback transmitter for feeding back the determined signal weights, the determined interference weights, and the SINR information to the base station; And a receiver for receiving the downlink data according to the determined signal weights from the base station. 31. The method of claim 30, And an SINR when collision between beams formed by signal weights used by the plurality of base stations is avoided. 32. The apparatus of claim 31, Wherein the difference value between the SINR when the collision between the beams is avoided and the SINR when the collision between the beams is not avoided is further fed back. 31. The apparatus of claim 30, And grouping the signal weights of the two or more signals when the signal weights used by the base station are two or more. A base station apparatus for transmitting downlink data in a collaborative wireless communication system using a multi-input / output antenna, A feedback receiver for receiving feedback information from each of a plurality of terminals; Determining a scheduling priority of the plurality of UEs using a signal-to-interference and noise ratio (SINR) included in the received feedback information, and transmitting the determined scheduling priority and each feedback information Scheduling to minimize interference between base stations using a signal weight of the included base station and interference weights of the interfering base stations, selecting a terminal to which downlink data is to be transmitted among the plurality of terminals, , And a data transmission unit for transmitting the downlink data to the selected terminal according to the determined signal weights and the modulation level, Wherein the signal weights are signal weights of a base station maximizing a signal-to-interference noise ratio in a downlink channel estimated for each of a plurality of base stations belonging to the same cluster, the interference weight being maximized / RTI > 35. The apparatus of claim 34, Calculates a transmittable data capacity for the plurality of terminals, and determines the scheduling priority according to the calculated transmittable data capacity. The apparatus of claim 35, Using the SINR of avoiding collision between beams formed from the base stations if the signal weights received from one of the plurality of terminals do not match the interference weights of the remaining ones of the plurality of terminals, And if the signal weights received from one of the plurality of terminals coincide with the interference weights of the remaining ones of the plurality of terminals, collision between the beams formed from the base stations is avoided And calculates the transmittable data capacity using the SINR when the SINR is smaller than a predetermined value. 35. The method of claim 34, And the SINR when collision between beams formed by signal weights is avoided by the plurality of base stations. The method of claim 37, wherein the received feedback information comprises: And information indicating a difference between an SINR when the collision between the beams is avoided and an SINR when the collision between the beams is not avoided.

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