KR101386065B1 - Device for channel information feedback using mmse receiving scheme and method using the same - Google Patents

Abstract

The terminal apparatus is started. The terminal device uses a codebook storage unit for storing a codebook including a plurality of codeword vectors, and a minimum mean square error (MMSE) reception technique to signal-to-interference and noise for each of the codeword vectors. SINR calculation unit for calculating the Signal to Interference and Noise Ratio (SINR) and target code for selecting the target codeword vector fed back to the base station based on the signal-to-interference and noise ratio for each of the calculated codeword vectors And a word vector selector.

Terminal, base station, beamforming, channel information, feedback, SINR, MMSE, interference, codebook

Description

Terminal device for feeding back channel information using MMS reception method and method thereof {DEVICE FOR CHANNEL INFORMATION FEEDBACK USING MMSE RECEIVING SCHEME AND METHOD USING THE SAME}

The present invention relates to a terminal apparatus for feeding back channel information and a base station for performing beamforming by using channel information.

Recently, with the rapid development of wireless communication technology, various services such as video communication, data communication, instant messenger, movie watching, web service, and game as well as voice communication are provided as wireless communication technology. However, users are transferring large amounts of data at higher speeds and demanding higher quality services.

According to a multiple input / output communication technique for communicating using a plurality of antennas, a base station beamforms a data stream through a wireless channel formed between a base station and a plurality of antennas installed in a terminal.

However, channel information is required for the base station to perform beamforming. In general, users estimate a radio channel using a pilot signal, and feed back channel information generated based on the estimated radio channel to a base station. In this case, the channel information may include channel direction information (CDI) or channel quality information (CQI).

In addition, when there are more than two users, interference occurs between users. That is, each of the users receives not only a desired signal but also an interference signal.

At this time, if each of the users generates the channel information based on the size of the desired signal only, and feeds back the generated channel information to the base station, the base station receives the incorrect channel information due to the presence of the interference signal. In addition, the channel information generated by each of the users based solely on the size of the interference signal may not be accurate.

Accordingly, there is a need for a terminal apparatus generating channel information in consideration of interference from another user and a desired signal at the same time, and a base station performing beamforming using the channel information.

The present invention provides a terminal apparatus and a channel information generation method capable of feeding back channel information accurately indicating an actual channel by selecting a target codeword vector to be fed back using a minimum mean square error (MMSE) reception technique. .

In addition, the present invention provides a terminal device and a channel information generation method that can improve the performance of the communication system by generating channel information in consideration of interference caused by other terminal devices using the MS.

In addition, the present invention provides a base station and a beamforming method that can increase the data rate by performing beamforming based on channel information generated by the MS using the reception technique.

The terminal device according to an embodiment of the present invention uses a codebook storage unit for storing a codebook including a plurality of codeword vectors and a minimum mean square error (MMSE) receiving technique. SINR calculation unit that calculates a Signal to Interference and Noise Ratio (SINR) for each and the object fed back to the base station based on the signal-to-interference and noise ratio for each of the calculated codeword vectors A target codeword vector selection unit for selecting a codeword vector is included.

In this case, the terminal device may further include a channel information transfer unit for feeding back channel information related to the target codeword vector to the base station.

In addition, the base station according to an embodiment of the present invention is a channel information receiver for receiving the feedback channel information from a plurality of user terminal devices-the channel information is each of the user terminal devices (Minimum Mean Square Error, MMSE) Is generated based on a signal-to-interference and noise ratio for each of the codeword vectors calculated using a reception technique, and at least one target user terminal device to maximize the sum of data rates based on the channel information. It includes a user selection unit for selecting.

In addition, the method for generating channel information according to an embodiment of the present invention comprises the steps of storing a codebook including a plurality of codeword vectors, the codeword using a minimum mean square error (MMSE) receiving technique Calculating a Signal to Interference and Noise Ratio (SINR) for each of the vectors, the object being fed back to the base station based on the signal to interference and noise ratio for each of the calculated codeword vectors Selecting a codeword vector and feeding back channel information associated with the target codeword vector to the base station.

In addition, the beamforming method according to an embodiment of the present invention comprises the steps of receiving channel information fed back from a plurality of user terminal devices, the channel information of each of the user terminal devices (Minimum Mean Square Error, MMSE) Is generated based on a signal-to-interference and noise ratio for each of the codeword vectors calculated using a reception scheme, and based on the channel information, at least one target user terminal device to maximize the sum of data rates. And selecting and beamforming the data stream using at least one beamforming vector corresponding to the at least one target user terminal device.

The present invention can provide a terminal apparatus for feeding back channel information accurately indicating an actual channel by selecting a target codeword vector to be fed back using a minimum mean square error (MMSE) reception method, and a method of generating channel information. .

In addition, the present invention may provide a terminal device and a channel information generating method for improving the performance of the communication system by generating channel information considering interference caused by other terminal devices using a receiving method.

In addition, the present invention can provide a base station and a beamforming method for increasing the data rate by performing beamforming based on channel information generated using an MS receiving technique.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a base station and terminals according to an embodiment of the present invention.

Referring to FIG. 1, a plurality of antennas are installed in a base station 110, and a plurality of terminals 120, 130, and 140 are illustrated. Although one antenna is illustrated in each of the terminals 120, 130, and 140, the technical idea of the present invention may be applied to a case in which a plurality of antennas are installed in the terminals 120, 130, and 140.

In order for the base station 110 to perform beamforming or to select target terminals efficiently receiving data, channel information about a channel formed between the base station 110 and the terminals 120, 130, and 140 must be determined.

In this case, the terminals 120, 130, and 140 may estimate a channel using a pilot signal transmitted from the base station 110. The terminals 120, 130, and 140 generate channel information on the estimated channel, and feed back the generated channel information to the base station 110.

At this time, the base station 110 selects beamforming vectors based on the channel information, and beamforms the data stream using the selected beamforming vectors. In addition, the base station 110 may select target terminals of the transmission signal based on the channel information.

However, when there are a plurality of terminals 120, 130 and 140, interference occurs between the terminals 120, 130 and 140. For example, the signal received by the terminal k 130 may be represented by Equation 1 below.

: 단말 k(130)과 기지국(110) 사이에 형성된 채널,

: 단말 k(130)에 상응하는 빔포밍 벡터, 단말 k(130)에 상응하는 데이터 스트림, i: 단말 들(120, 130, 140)의 인덱스,

: 단말 k(130)에 상응하는 잡음)(

: Channel formed between the terminal k (130) and the base station (110),

: Beamforming vector corresponding to terminal k 130, data stream corresponding to terminal k 130, i: index of terminals 120, 130, 140,

: Noise corresponding to terminal k (130))

이며,

는 단말 k(130)가 아닌 다른 단말들로 인해 발생하는 간섭 신호이다. 따라서, 단말 k(130)가 원하는 신호의 크기만을 기준으로 채널 정보를 생성한다면, 단말 k(130)는 간섭 신호로 인해 오류가 있는 채널 정보를 생성할 수 있다. 결국, 오류가 있는 채널 정보를 기초로 기지국(110)이 빔포밍하거나, 대상 단말을 선택한다면 비효율적일 것이다.Referring to Equation 1, a signal desired by the terminal k 130 among the signals received by the terminal k 130 is

Lt;

Is an interference signal generated by terminals other than the terminal k 130. Accordingly, if the terminal k 130 generates channel information based only on the size of the desired signal, the terminal k 130 may generate the channel information having an error due to the interference signal. As a result, if the base station 110 beamforming or selecting a target terminal based on the error channel information, it will be inefficient.

As a result, the terminal k 130 may generate channel information in consideration of both a desired signal and an interference signal.

2 is a block diagram illustrating a terminal device according to an embodiment of the present invention.

2, the terminal device 130 according to an embodiment of the present invention includes a channel estimator 210, a codebook storage unit 220, an SINR calculator 230, and a target codeword vector selector 240. And a channel information transfer unit 250.

The channel estimator 210 estimates a channel formed between the base station and the terminal device 130 using the pilot signal transmitted from the base station. If two or more antennas are installed in the base station, the channel estimator 210 may estimate the channel in a vector format.

In addition, the codebook storage unit 220 stores a codebook including a plurality of codeword vectors. That is, the codebook includes a plurality of spatially separated codeword vectors, and in general, one codeword vector among the plurality of codeword vectors is selected as a target codeword vector.

At this time, channel information including index information of the target codeword vector is generated, and the generated channel information is fed back to the base station. In addition, channel quality information related to the signal-to-interference and noise ratio of the target codeword vector may also be fed back to the base station.

In addition, the SINR calculation unit 230 calculates a Signal to Interference and Noise Ratio (SINR) for each of the codeword vectors using a minimum mean square error (MMSE) reception technique. . In this case, the SINR calculator 230 may calculate a signal-to-interference and noise ratio using a channel value formed between the base station estimated by the channel estimator 210 and the terminal device 130.

In this case, the SINR calculator 230 may calculate a signal-to-interference and noise ratio for each of the codeword vectors in consideration of interference caused by another terminal device.

For example, the SINR calculator 230 may calculate a signal-to-interference and noise ratio for the i-th codeword vector through Equation 2 according to the MMS reception technique.

: i 번째 코드워드 벡터,

: 잡음,

: 기지국의 송신 안테나들의 개수 I: 단위 행렬,

:

와 직교하는 직교 벡터)(P: total power used by the base station, M: number of target terminals receiving data,

i-th codeword vector,

: Noise,

: Number of transmit antennas of base station I: unit matrix,

:

Orthogonal vectors orthogonal to)

는 i 번째 코드워드 벡터

와 관련된 항목(term)뿐만 아니라, 직교 벡터

와 관련된 항목을 동시에 고려하여 엠엠에스이 수신 기법에 따라 생성된다.Referring to Equation 2, the signal-to-interference and noise ratio for the i th codeword vector

Is the i th codeword vector

Orthogonal vectors as well as terms associated with them

MMS is generated according to the reception scheme in consideration of the items related to.

와 관련된 항목은 단말 장치가 원하는 신호를 의미하며, 직교 벡터

와 관련된 항목은 다른 단말 장치로 인해 발생하는 간섭 신호를 의미할 수 있다. I-th codeword vector

The item related to means a signal desired by the terminal device, and orthogonal vector

The item related to may mean an interference signal generated by another terminal device.

에 상응하는 빔포밍 벡터를 이용하여 빔 포밍하였다면,

와 관련된 항목은 단말 장치가 원하는 신호를 의미하고,

와 관련된 항목은 다른 단말 장치로 인해 발생하는 간섭 신호를 의미한다.That is, the base station for the terminal device

If beamforming is performed using a beamforming vector corresponding to

The item related to means a signal desired by the terminal device.

The item related to "interference signal" means an interference signal generated by another terminal device.

As a result, it can be seen that the signal-to-interference and noise ratio calculated according to the reception technique of the MS is considering the interference signal as well as the desired signal.

및

에 상응하는 빔포밍 벡터를 알아낼 수 있으나, 다른 단말 장치를 위해 사용된 빔포밍 벡터와 다른 단말 장치를 위해 사용된 빔포밍 벡터에 상응하는 코드워드 벡터를 알 수 없다.At this time, the terminal device based on the pre-stored codebook

And

Although the beamforming vector corresponding to the beamforming vector may be found, the codeword vector corresponding to the beamforming vector used for the other terminal device and the beamforming vector used for the other terminal device may not be known.

In general, however, the base station selects target terminals receiving data from among a plurality of terminal apparatuses such that the sum of data rates is maximum, and selects beamforming vectors corresponding to the target terminal.

에 상응하는 빔포밍 벡터를 사용하였다면, 다른 단말 장치를 위해 사용한 빔포밍 벡터는 단말 장치를 위해 사용된 벡터와 직교(또는, 거의 직교(near orthogonal))한다고 가정할 수 있다.Therefore, the base station for the terminal device

If the corresponding beamforming vector is used, it may be assumed that the beamforming vector used for the other terminal device is orthogonal (or near orthogonal) to the vector used for the terminal device.

와

가 직교한다면, 엠엠에스이 수신 기법에 따라 계산된

에 대한 신호 대 간섭 및 잡음 비는

만의 함수가 된다. 즉,

와

의 직교성이 보장되는 경우,

에 대한 신호 대 간섭 및 잡음 비는

가 변하더라도 일정하게 유지된다.In addition, the beamforming vector used for the other terminal device and the beamforming vector used for the terminal device are orthogonal to each other,

Wow

Is orthogonal, it is calculated according to the

The signal-to-interference and noise ratio for

Will be a function of In other words,

Wow

If orthogonality of is guaranteed,

The signal-to-interference and noise ratio for

Remains constant even if

및

와 직교하는

를 이용하여 엠엠에스이 수신 기법에 따른 신호 대 간섭 및 잡음 비가 계산될 수 있다. 즉, 단말 장치가 다른 단말 장치에 사용된 빔포밍 벡터와 다른 단말 장치에 사용된 빔포밍 벡터에 상응하는 코드워드 벡터를 정확히 알 수 없다고 하더라도,

와

를 이용하여 신호 대 간섭 및 잡음 비를 계산할 수 있다.therefore,

And

Orthogonal

The signal-to-interference and noise ratio according to the MMS reception technique can be calculated using. That is, even if the terminal device does not know the codeword vector corresponding to the beamforming vector used in the other terminal device and the beamforming vector used in the other terminal device correctly,

Wow

We can calculate the signal to interference and noise ratio using.

는 그람 슈미트 직교화(Gram Shmidt orthogonalization) 기법을 통하여 생성될 수 있다. 즉,

에 그람 슈미트 직교화 기법을 적용하면, 직교 벡터

가 생성될 수 있다.The orthogonal vector

Can be generated through the Gram Shmidt orthogonalization technique. In other words,

Applying Gram Schmidt Orthogonalization to Orthogonal Vectors

Can be generated.

Accordingly, the SINR calculation unit 230 generates orthogonal vectors orthogonal to each of the codeword vectors, and considers signal-to-interference for each of the codeword vectors in consideration of interference caused by another terminal device based on the generated orthogonal vectors. The noise ratio can be calculated.

In addition, the target codeword vector selector 240 selects the target codeword vector fed back to the base station based on the signal-to-interference and noise ratio for each of the calculated codeword vectors. In this case, the target codeword vector selector 240 may select a codeword vector having a maximum signal-to-interference and noise ratio as the target codeword vector.

For example, when the number of codeword vectors is N, the target codeword vector may be selected using Equation 3 below.

That is, referring to Equation 3, the target codeword vector is selected based on the signal-to-interference and noise ratio calculated for each of the codeword vectors.

In this case, channel direction information including index information n of the selected target codeword vector may be generated, and channel quality information related to signal-to-interference and noise ratio for the target codeword vector may be expressed by Equation 4 below. Can be generated.

In addition, the channel information transmitter 250 feeds back channel information related to the target codeword vector to the base station. In this case, the channel information may include channel direction information or channel quality information related to the target codeword vector.

3 is a block diagram illustrating a base station according to an embodiment of the present invention.

Referring to FIG. 3, the base station 110 according to an embodiment of the present invention includes a channel information receiver 310, a user selector 320, and a beamformer 330.

The channel information receiver 310 receives the channel information fed back from the plurality of user terminal devices. In this case, the channel information is generated on the basis of the signal-to-interference and noise ratio for each of the codeword vectors calculated by the MS receiving method in each of the user terminal devices.

In this case, since the channel information may include channel direction information or channel quality information, and is generated in consideration of desired signals and interference signals of each of the plurality of user terminal devices, the base station 110 may more efficiently use the user and the beam. You can choose the forming vector.

In addition, the user selector 320 selects a target user terminal device to which data is to be transmitted so that the sum of data rates is maximized based on the channel information. Even if there are a plurality of user terminal devices, some user terminal devices may be selected so that the sum of the data rates is maximum, and the selected user terminal devices become the target user terminal device.

In this case, the user selector 320 may select the target user terminal device using, for example, a Greedy User Selection (GUS) algorithm.

In addition, the beamformer 330 beamforms the data stream using a beamforming vector corresponding to the target user terminal device based on the channel information. In particular, a beamforming vector corresponding to the target user terminal device may be selected based on channel information (more specifically, channel direction information) fed back from the target user terminal device, and the data stream is beamed based on the selected beamforming vector. Formed.

In this case, the beamformer 330 may beamform the data stream using a zero-forced beamforming technique.

4 is a flowchart illustrating a method of generating channel information according to an embodiment of the present invention.

Referring to FIG. 4, the method for generating channel information according to an embodiment of the present invention stores a codebook including a plurality of codeword vectors (S410).

In addition, the method for generating channel information according to an embodiment of the present invention is a signal to interference and noise ratio for each of the codeword vectors using a minimum mean square error (MMSE) reception technique. Ratio, SINR) is calculated (S420).

At this time, the step of calculating the signal-to-interference and noise ratio (S420) generates orthogonal vectors orthogonal to each of the codeword vectors, and considering the interference caused by other terminal devices based on the generated orthogonal vectors Computing the signal-to-interference and noise ratio for each of the codeword vectors.

In addition, the method for generating channel information according to an embodiment of the present invention selects the target codeword vector fed back to the base station based on the signal-to-interference and noise ratio for each of the calculated codeword vectors (S430).

In this case, selecting a target codeword vector (S430) may be selecting a codeword vector having a maximum signal-to-interference and noise ratio as the target codeword vector.

In addition, the channel information generation method according to an embodiment of the present invention feeds back channel information related to the target codeword vector to the base station (S440).

5 is a flowchart illustrating a beamforming method according to an embodiment of the present invention.

Referring to FIG. 5, the beamforming method according to an embodiment of the present invention receives channel information fed back from a plurality of user terminal devices (S510).

In this case, the channel information is generated based on a signal-to-interference and noise ratio for each of the codeword vectors calculated using a minimum mean square error (MMSE) reception technique in each of the user terminal devices.

In addition, the beamforming method according to an embodiment of the present invention selects at least one target user terminal device to maximize the sum of data rates based on the channel information (S520).

In addition, the beamforming method according to an embodiment of the present invention beamforms the data stream using at least one beamforming vector corresponding to the at least one target user terminal device (S530).

Although not shown in FIGS. 4 and 5 have been described in detail with reference to FIGS. 1 to 3, a description thereof will be omitted below.

The channel information generating method and the beamforming method according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be construed as being limited to the described embodiments, but should be determined by the scope of the appended claims, as well as the appended claims.

1 is a diagram illustrating a base station and terminals according to an embodiment of the present invention.

2 is a block diagram illustrating a terminal device according to an embodiment of the present invention.

3 is a block diagram illustrating a base station according to an embodiment of the present invention.

4 is a flowchart illustrating a method of generating channel information according to an embodiment of the present invention.

5 is a flowchart illustrating a beamforming method according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

210: channel estimator

220: codebook storage unit

230: SINR calculation unit

240: target codeword vector selection unit

250: channel information transmission unit

Claims (17)

A channel estimating unit estimating a channel value formed between the base station and the terminal device using the pilot signal transmitted from the base station; A codebook storage unit for storing a codebook including a plurality of codeword vectors; An SINR calculator configured to calculate a Signal to Interference and Noise Ratio (SINR) for each of the codeword vectors using a minimum mean square error (MMSE) reception technique and the channel value; And A target codeword vector selection unit for selecting a target codeword vector fed back to the base station based on the signal-to-interference and noise ratio for each of the calculated codeword vectors Including, The SINR calculation unit And calculating the signal-to-interference and noise ratio for each of the codeword vectors in consideration of interference due to communication between the base station and another terminal device. The method according to claim 1, The SINR calculation unit Calculate, for each codeword vector of the codeword vectors, the signal-to-interference and noise ratio for each codeword vector in consideration of a term associated with each codeword vector. The item means a terminal device, characterized in that the desired signal. 3. The method of claim 2, The SINR calculation unit Generating an orthogonal vector orthogonal to each codeword vector, calculating the signal to interference and noise ratio for each codeword vector in consideration of the items associated with the orthogonal vector generated, The item related to the orthogonal vector means an interference signal generated by the other terminal device. And the signal-to-interference and noise ratio remain constant even if the orthogonal vectors change. The method of claim 3, The orthogonal vector is a terminal device, characterized in that it is generated through a Gram Shmidt orthogonalization process. The method according to claim 1, The target codeword vector selection unit And a codeword vector having the maximum signal-to-interference and noise ratio as the target codeword vector. The method according to claim 1, Channel information transfer unit for feeding back channel information related to the target codeword vector to the base station Terminal device characterized in that it further comprises. The method according to claim 6, The channel information includes channel direction information including index information of the target codeword vector or channel quality information related to the signal to interference and noise ratio for the target codeword vector. In the base station, Channel information receiver for receiving the feedback channel information from a plurality of user terminal devices-The channel information is a signal-to-interference and noise ratio for each of the codeword vectors calculated at each user terminal device of the plurality of user terminal devices The codeword vectors are generated based on a minimum mean square error (MMSE) reception scheme and a channel value formed between the base station and each user terminal device, and the channel values are calculated from the base station. Estimated using the pilot signal transmitted to each user terminal device, the signal-to-interference and noise ratio for each of the codeword vectors is calculated in consideration of the interference due to communication between the base station and the other user terminal device, The other user terminal device may include each of the plurality of user terminal devices. Other user terminal device except the user terminal device; And A user selector configured to select at least one target user terminal device to maximize the sum of data rates based on the channel information A base station comprising a. 9. The method of claim 8, A beamformer for beamforming a data stream using at least one beamforming vector corresponding to the at least one target user terminal device The base station further comprising: 10. The method of claim 9, The beam former And a base station beamforming the data stream using a zero forcing beamforming technique. 9. The method of claim 8, And the user selector selects the target user terminal device using a greedy user selection algorithm. Estimating a channel value formed between the base station and the terminal device using the pilot signal transmitted from the base station; Storing a codebook comprising a plurality of codeword vectors; Calculating a Signal to Interference and Noise Ratio (SINR) for each of the codeword vectors using a minimum mean square error (MMSE) reception technique and the channel value; Selecting a target codeword vector fed back to the base station based on the signal to interference and noise ratio for each of the calculated codeword vectors; And Feeding back channel information associated with the target codeword vector to the base station; Including, The signal-to-interference and noise ratio for each of the codeword vectors is calculated in consideration of the interference caused by the communication between the base station and the other terminal device. 13. The method of claim 12, For each codeword vector of the codeword vectors, the signal to interference and noise ratio for each codeword vector is calculated taking into account the term associated with each codeword vector, The item means a signal desired by the terminal device. Computing the signal to interference and noise ratio Generating an orthogonal vector orthogonal to each codeword vector, and calculating the signal-to-interference and noise ratio for each codeword vector in consideration of items associated with the generated orthogonal vector; The item related to the orthogonal vector means an interference signal generated by the other terminal device. And the signal-to-interference and noise ratio remain constant even if the orthogonal vectors change. 13. The method of claim 12, Selecting the target codeword vector And selecting a codeword vector having the maximum signal-to-interference and noise ratio as the target codeword vector. In the beamforming method of the base station, Receiving channel information fed back from a plurality of user terminal devices, wherein the channel information is based on a signal-to-interference and noise ratio for each of the codeword vectors calculated at each user terminal device of the plurality of user terminal devices; The codeword vectors are calculated using a minimum mean square error (MMSE) reception scheme and a channel value formed between the base station and each user terminal device, and the channel values are calculated from the base station. Estimated using a pilot signal transmitted to a terminal device, the signal-to-interference and noise ratio for each of the codeword vectors is calculated in consideration of interference due to communication between the base station and another user terminal device, the other user The terminal apparatus may include the respective user terminal apparatuses among the plurality of user terminal apparatuses. The rest of the user terminal device except for the device; Selecting at least one target user terminal device to maximize the sum of data rates based on the channel information; And Beamforming a data stream using at least one beamforming vector corresponding to the at least one target user terminal device Beamforming method comprising a. 16. The method of claim 15, Selecting the target user terminal device And selecting the target user terminal device using a greedy user selection (GUS) algorithm. A computer-readable recording medium in which a program for executing the method of any one of claims 12 to 16 is recorded.

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