KR101742503B1 - Codebook for multiple-user multiple input multiple output communication and communication device of using the codebook - Google Patents

Abstract

In multi-user MIMO communications, each of the receivers can use a different channel codebook, and the transmitter determines beamforming vectors using a beamforming codebook corresponding to each of the receivers.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a codebook for multi-user multi-input / output communication, and a communication device using the codebook. [0002]

The following embodiments relate to a codebook for multi-user multi-input / output communication and a communication device using the codebook.

2. Description of the Related Art In recent years, various studies have been conducted to provide various multimedia services including voice service and support high-quality and high-speed data transmission in a wireless communication environment. In particular, a technology for a multi-input multi-output (MIMO) communication system using a plurality of channels in a spatial domain is rapidly developing.

In a MIMO communication system, a base station and terminals use a codebook to appropriately cope with a channel environment. The specific space can be quantized into a plurality of codewords according to a certain criterion, and the generated plurality of codewords can be stored as a codebook in the base station and the terminals. This codebook can be used by base stations and terminals to share channel information, and can also be used to determine beamforming vectors.

The communication method of a transmitter for multi-user MIMO communication according to an embodiment of the present invention includes: maintaining a memory in which a first channel codebook corresponding to a first receiver and a second channel codebook corresponding to a second receiver are stored; Information on a first preferred code word among codewords included in the first channel codebook from the first receiver and information on a second preferred codeword among codewords included in the second channel codebook from the second receiver Receiving information; And determining a first beamforming vector for the first receiver and a second beamforming vector for the second receiver based on the first preferred codeword and the second preferred codeword. Here, the first channel codebook and the second channel codebook are different from each other.

Wherein the information about the first preferred codeword is related to the covariance of the first channel between the transmitter and the first receiver and the information about the second preferred codeword is related to the covariance of the first preferred codeword between the transmitter and the second receiver May be related to the covariance of the second channel.

Wherein the code words contained in one channel codebook are M _t M _r1 x defined by the vector basis of which the grass maenian line packing codebook for one-dimensional, the second codewords contained in the two-channel codebook are M _t M _r2 x 1 Dimensional Grass Line Packing Code, wherein M _r1 is the number of receive antennas of the first receiver, M _r2 is the number of receive antennas of the second receiver, and M _t is the number of transmit antennas of the transmitter May be the number of transmit antennas.

The vectors in the M _t M _r 1 x 1-dimensional Grassmannian line packing codebook are transformed into matrices of dimension M _t x M _r1 , and each of the codewords included in the first channel codebook is transformed into M _t x M _r1 dimension Wherein the vectors in the M _t M _r2 x 1 dimensional Grassmannan line packing codebook are transformed into Matrixes of M _t x M _r2 dimensions and the code words contained in the second channel codebook May be defined by each of the M _t x M _r2 dimensional matrices.

Wherein determining the first beamforming vector for the first receiver and the second beamforming vector for the second receiver determines the first beamforming vector using a first beamforming codebook for the first receiver , And determining the second beamforming vector using the second beamforming codebook for the second receiver different from the first beamforming codebook.

The minimum distance between the first beamforming codewords included in the first beamforming codebook and the minimum distance between the second beamforming codewords included in the second beamforming codebook may be equal to each other.

Wherein determining the first beamforming vector for the first receiver and the second beamforming vector for the second receiver is based on the assumption that the first receiver and the second receiver are each a zero forcing linear receiver, Calculating a sum rate for the receiver and the second receiver; And selecting a first beamforming vector for the first receiver and a second beamforming vector for the second receiver based on a sum rate for the first receiver and the second receiver.

Wherein each of the first beamforming codebook and the second beamforming codebook may be designed such that a correlation between the first beamforming codewords and the second beamforming codewords is minimal.

Wherein the first beamforming codebook is generated by inner producting each of the codewords contained in a first unitary rotation matrix and a predefined basic codebook and the second beamforming codebook is generated by an inner product of the first unitary rotation matrix By a second unitary rotation matrix and an inner product of each of the codewords contained in the predefined basic codebook.

The method of communication of the transmitter may further comprise providing information about the first unitary rotation matrix to the first receiver and providing information about the second unitary rotation matrix to the second receiver .

Wherein the communication method of the transmitter is based on an inner product between the first beamforming vector and a Hermitian of the first beamforming vector and an inner product between the second beamforming vector and a Hermitian of the second beamforming vector. calculating statistics; And providing information about the interference statistics to the first receiver and the second receiver.

A communication method of a second receiver for a multi-user MIMO communication system including a transmitter, a first receiver, and a second receiver according to an embodiment of the present invention includes a first channel codebook corresponding to a first receiver, Maintaining a memory in which a second channel codebook corresponding to the receiver is stored; Calculating a covariance of a second channel between the transmitter and the second receiver; Selecting a second one of the codewords included in the second channel codebook based on the covariance of the second channel; Providing information on the second preferred codeword to the transmitter; If the transmitter uses a second beamforming vector based on the second preferred codeword, determining the second beamforming vector; And calculating a received combining vector according to the second beamforming vector and the second channel.

Wherein the communication method of the receiver further comprises calculating an effective channel between the transmitter and the second receiver using a dedicated pilot for the second receiver transmitted from the transmitter, The step of grasping the vector may be the step of grasping the second beamforming vector based on the effective channel.

Wherein the transmitter uses the first beamforming codebook for the first receiver to determine the first beamforming vector and the second beamforming codebook for the second receiver is different from the first beamforming codebook, Wherein the second beamforming codebook is generated by using an inner product of each of the code words included in the unitary rotation matrix and a predefined basic codebook, Receiving information about a unitary rotation matrix from the transmitter, wherein the step of grasping the second beamforming vector grasps the second beamforming vector using information about the unitary rotation matrix Step.

The method of communication of claim 1, wherein the communication method of the receiver comprises: interference statistics from the transmitter, the interference statistics including an inner product between a first beamforming vector for the first receiver and a Hermitian of the first beamforming vector, Wherein the step of receiving information on the received combine vector based on an inner product between a received beamforming vector and a Hermitian of the second beamforming vector, And calculating the inning vector.

1 is a diagram illustrating a closed loop multiuser multi-input / output communication system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a transmitter having M _t transmission antennas and a receiver having M _r reception antennas. Referring to FIG.
FIG. 3 is a diagram showing a matrix in the M _t M _r x 1 -dimensional matrix and a matrix in the M _t x M _r dimension generated based on the vector.
FIG. 4 shows an example in which codewords included in one codebook and codewords included in each of the other codebooks have little correlation.
5 is a flowchart illustrating a communication method of a transmitter and a receiver i in a multi-user MIMO communication system according to an embodiment of the present invention.
6 is a block diagram illustrating a transmitter according to an embodiment of the present invention.
7 is a block diagram illustrating a receiver in accordance with an embodiment of the present invention.

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

1 is a diagram illustrating a closed loop multiuser multi-input / output communication system according to an embodiment of the present invention.

Referring to FIG. 1, a closed loop multi-user MIMO communication system includes a base station 110 and users' terminals 120, 130, and 140. Embodiments of the present invention can be applied to the uplink, but for convenience of description, the downlink case will be mainly described below. The term 'closed loop' means that the UEs 120, 130 and 140 feed back feedback information including channel information to the BS 110 and the BS 110 performs beamforming using feedback information. do.

A plurality of antennas are installed in the base station 110, and one or a plurality of antennas may be installed in each of the users' terminals 120, 130, and 140. Channels are formed between the base station 110 and users' terminals 120, 130, and 140, and signals are transmitted / received through each of the channels.

When the channel between the base station 110 and the user k is _Hk , the base station 110 transmits a common pilot so that the terminal of the user k can estimate the channel _Hk . At this time, the base station 110, information relating to the terminal of the user k determines the preferred code words of the code words included in the after estimating the channel H _k, the codebook based on the channel H _k, the preferred code words Feedback. The base station 110 determines the beamforming vector for the user k's terminal used to beamform the data streams S ₁ , S _N based on the information about the preferred codeword.

According to embodiments of the present invention, a base station may transmit a dedicated pilot for a terminal of user k and a terminal of user k may transmit an effective channel H _k w _k Can be estimated. Where w _k is a beamforming vector for the user k's terminal. In addition, the base station 110 according to the embodiments of the present invention can use a codebook for grasping information (channel information) about the channel H _k , as well as a codebook in which candidates of a beamforming vector are stored . When a codebook in which candidates of a beamforming vector are stored is used, the base station 110 may select any one of the candidates of the beamforming vector as a beamforming vector.

FIG. 2 is a diagram illustrating a transmitter having M _t transmission antennas and a receiver having M _r reception antennas. Referring to FIG.

Referring to FIG. 2, transmitter 1 210 includes M _t transmit antennas, and each of receivers 220, 230, and 240 includes M _r receive antennas. Here, it is assumed that the number of receivers 220, 230, and 240 is K. Transmitter 1 210 may be a base station, a repeater, or the like in the downlink, and may be a terminal in the uplink. Similarly, each of receivers 220, 230, and 240 may be a terminal on the downlink and may be a base station or repeater in the uplink.

In the following, when M _r is greater than or equal to M _t, and M _r if M is less than _t will be described embodiments of the present invention for each.

M _r M is M _t Greater than or equal to

In the case where each of the transmitter and the receiver uses a channel codebook having a limited size to share channel information, a transmitter may be referred to as partial channel information (partial channel state information) from each of the receivers Can be obtained. And, assuming that the transmission power for each of the receivers is the same, each of the receivers is assigned a transmission power of P / K. P represents the total transmission power. At this time, the received signal vector in a receiver i y _i can be expressed as Equation (1).

[Equation 1]

이고, C^{Mr x Mt}는 M_r x M_t 차원의 컴플렉스 공간을 나타낸다.

는 수신기 i를 위한 빔포밍 벡터를 나타내며,

는 규준화된 노이즈 벡터를 나타낸다.

의 엔트리들은 표준 정규 분포

에 따라 identically independent distributed하다. 그리고,

는 전송 심볼을 나타내며, 전송 심볼의 에너지는

이며,

는 신호 대 잡음 비(SNR)이다.here,

And C ^{Mr x Mt} represents the complex space of dimension M _r x M _t .

Denotes a beamforming vector for receiver i,

Represents a normalized noise vector.

The entries of the standard normal distribution

It is identically independent distributed according to. And,

Represents the transmission symbol, and the energy of the transmission symbol is

Lt;

Is the signal-to-noise ratio (SNR).

를 계산할 수 있다. 여기서, H_i ^*는 H_i의 허미시안을 나타내며,

는 H_i의 프로비니어스 놈의 제곱(square)을 의미한다.Receiver i may be using the common pilot transmitted from the transmitter to estimate the channel H _i between the receiver i and the transmitter. When modeled as a received signal vector y _i at receiver i and the equation (1), the receiver i can calculate the covariance of _i ^* H _i H H _i of the channel. In addition, receiver i

Can be calculated. Here, H _i ^* represents the Hermitian of H _i ,

Is the square of the probabilistic norm of H _i .

를 이용하여

에 대응하는 선호 코드워드를 선택할 수 있다. 여기서,

는 하기 수학식 2와 같이 N1 개의 코드워드들을 포함한다.
Receiver i is a channel codebook of size N1

Using

Can be selected. here,

N1 < / RTI > codewords as shown in Equation (2).

&Quot; (2) "

에 포함되는 코드워드들 중 선호 코드워드는 하기 수학식 3을 통하여 선택될 수 있다.
here,

The preferred codeword among the codewords included in the first codeword may be selected through Equation (3).

&Quot; (3) "

이고, 수신기들 각각은 서로 다른 채널 코드북

를 갖는다. 예를 들어, 수신기 1은 채널 코드북 g⁽¹⁾, 수신기 2는 채널 코드북 g⁽²⁾를 갖는다. 그리고, 코드워드들 각각

는 하기 수학식 4를 통해 알 수 있는 바와 같이, M_tM_r x 1 차원의 그래스매니안 라인 팩킹 코드북에 있는 벡터들을 기초로 생성될 수 있다.
here,

, And each of the receivers has a different channel codebook

. For example, receiver 1 has channel codebook g ⁽¹⁾ and receiver 2 has channel codebook g ⁽²⁾ . Then, each of the codewords

Can be generated based on the vectors in the Grt-millimax line-packing codebook of M _t M _r x 1, as can be seen from the following equation (4).

&Quot; (4) "

는 그래스매니안 라인 팩킹 코드북

에 있는 벡터이다. 함수

는 벡터

를

차원의 매트릭스로 변환한다. 특히, 함수

는 벡터

의 원소들을 컬럼별로(columnwisely) 쌓음(stacking)으로써

차원의 매트릭스를 생성할 수 있다.

는 A x B 차원의 오쏘노말(orthonormal) 매트릭스 스페이스를 나타낸다.
here,

Grassmanian Line Packing Codebook

In the vector. function

Vector

To

Dimensional matrix. In particular,

Vector

By columnwisely stacking the elements of

You can create a matrix of dimensions.

Represents an orthonormal matrix space of A x B dimension.

FIG. 3 is a diagram showing a matrix in the M _t M _r x 1 -dimensional matrix and a matrix in the M _t x M _r dimension generated based on the vector.

Referring to FIG. 3, the dimension of the vector 310 is M _t M _r x 1, and the dimension of the matrix 320 is M _t x M _r . M _t is 2, and M _r is 4.

의 원소이며, 매트릭스(320)은 벡터(310)의 원소들을 컬럼별로(columnwisely) 쌓음(stacking)으로써 생성된다.
The vector 310 may be represented by M _t M _r x 1-dimensional Grassmannian line packing codebook

And the matrix 320 is generated by columnwisely stacking the elements of the vector 310. [

를 추정하고, 복조 시간에서 전용 파일럿을 이용하여 에러 없이

의 실효 채널

를 추정한다고 가정한다. 여기서,

는 수신기 i를 위해 송신기에 의해 사용되는 빔포밍 벡터를 나타내며,

는 N2 사이즈의 빔포밍 코드북으로부터 선택된다. 이 때, 제로포싱 선형 컴바이너는 하기 수학식 5와 같이 나타낼 수 있다.
Assuming that receivers use a zero-forcing linear combination technique, and that receiver I uses a common pilot at measurement time

, And using a dedicated pilot in the demodulation time without error

Effective channel

. here,

Represents the beamforming vector used by the transmitter for receiver i,

Is selected from N2 sized beam-forming codebooks. In this case, the zero-forcing linear combiner can be expressed by the following equation (5).

&Quot; (5) "

라고 가정한다. 여기서, n_i는 수신기 i를 위한 빔포밍 코드북에서 수신기 i를 위한 빔포밍 벡터의 인덱스를 나타낸다. 전용 파일럿이 사용되는 경우, 수신기 i는 실효 채널을 추정함으로써,

를 파악할 수 있지만, 전용 파일럿이 사용되지 않는 경우, 송신기는 다운링크에서

를 수신기 i로 알려줄 수 있다.Here, a beamforming vector for the receiver i is selected so that the beamforming vector for the receiver i can be distinguished from other receivers

. Where n _i represents the index of the beamforming vector for receiver i in the beamforming codebook for receiver i. If a dedicated pilot is used, receiver i estimates the effective channel,

, But if the dedicated pilot is not used,

To receiver i.

라고 한다면, 수신기들 각각은

를 송신기로 피드백한다. 여기서,

은 채널 코드북

에서 l 번째 코드워드를 의미한다. 송신기가 적절한 스케쥴링을 수행할 수 있도록 송신기들 각각은

를 피드백한다.The preferred codeword of each of the receivers

, Each of the receivers

To the transmitter. here,

Channel codebook

≪ / RTI > To enable the transmitter to perform the proper scheduling, each of the transmitters

.

"로 나타낼 수 있다. 그리고, 수신기들 각각에 대응하는 빔포밍 코드북은 그래스매니안 라인 팩킹 코드북일 수 있다. 즉, 수신기 1 내지 수신기 K의 빔포밍 코드북은 하기 수학식 6과 같이 나타낼 수 있다.The transmitter generates K beamforming vectors for receivers based on the preferred codewords of each of the receivers. At this time, each of the receivers may have a different beam-forming codebook, and the transmitter selects K beam-forming vectors from the beam-forming codebook corresponding to each of the receivers. The beamforming vectors selected by the transmitter are "

The beamforming codebook corresponding to each of the receivers may be a Grassmanian line packing codebook. That is, the beamforming codebook of the receiver 1 to the receiver K may be expressed by Equation (6).

&Quot; (6) "

는 수신기 i를 위한 빔포밍 코드북을 나타내며, N2는

의 사이즈이다. 이러한 빔포밍 코드북들은 수신기들마다 서로 다르게 디자인되지만, 거의 그래스매니안 매니폴드(manifold) 내에서 동일한 '최소 거리(minimum distance)' 특성을 가질 수 있다. '최소 거리'는

에 포함된 코드워드들 사이의 거리들 중에서 가장 작은 거리를 의미한다.here,

Denotes a beamforming codebook for receiver i, N2 denotes

. Although these beamforming codebooks are designed differently for each receiver, they may have the same 'minimum distance' characteristic in almost the grating manifold manifold. The "minimum distance"

Quot; means the smallest distance among the codewords included in the codewords.

When each of the receivers performs a zero-forcing linear combination, the transmitter may select K beamforming vectors using Equation (7).

&Quot; (7) "

Referring to Equation (7), the transmitter selects K beamforming vectors such that the sum rate to the receivers is maximized.

The average transmission rate of the transmitter can be expressed by Equation (8).

&Quot; (8) "

In the broadcast channel, the sum rate is limited due to high interference between receivers in the high SNR region. It may be more efficient to suppress the interference power than to increase the desired signal power of each of the receivers only in this high SNR region. An efficient beamforming codebook design method requires increasing the sum of the transmission rates by reducing the interference power between receivers. As one possible method for an efficient beamforming codebook design, interference limited beamforming codebooks are described below.

The transmission rate sum formula with perfect channel information can be expressed by Equation (9).

&Quot; (9) "

The transmission rate sum of Equation (9) is lower bounded by Equation (10).

&Quot; (10) "

에 대하여

가 취해진다.

에 대하여

가 취해지면, 하기 수학식 11을 나타낼 수 있다.
Assuming interference is limited,

about

Lt; / RTI >

about

The following expression (11) can be obtained.

&Quot; (11) "

Referring to Equation (11), the codebook design criterion in the high SNR region means that the sum rate is dominated by the separation characteristic among the codebooks of other receivers in a unit sphere . In other words, the transmission rate sum in the high SNR region is greatly influenced by the separation characteristics between the codebooks of other receivers.

Each of the K receivers has one preferred codeword. All possible permutations of the indices of the preferred codewords can be defined as: < EMI ID = 12.0 >

&Quot; (12) "

는 K 튜플(tuple) 벡터이며, K 튜플 벡터의 엘리먼트들은 선호 코드워드들의 인덱스들이다. 빔포밍 코드북 설계 목표 함수는 하기 수학식 13과 같이 나타낼 수 있다.
here,

Is a K tuple vector, and the elements of the K tuple vector are the indices of the preferred codewords. The beamforming codebook design target function can be expressed by Equation (13).

&Quot; (13) "

이고, 다른 빔포밍 코드북들이

(

)인 경우,

는

의 기울어진(tilted) 버전이거나,

의 회전된 버전일 수 있다. 그리고,

및

는 단위 구 내에 위치하며, 동일한 최소 거리 특성을 최대한 갖는 것이 효율적일 수 있다.
The target function of Equation (13) implies that the beamforming codebook should be designed such that the correlation between the codewords of the beamforming codebook for other receivers is minimized. An intuitively given beam-forming codebook

, And the other beam-forming codebooks

(

),

The

Or a tilted version of < RTI ID = 0.0 >

Lt; / RTI > And,

And

Is located within the unit sphere, and it may be efficient to have the same minimum distance characteristic as much as possible.

FIG. 4 shows an example in which codewords included in one codebook and codewords included in each of the other codebooks have little correlation.

Each of the sphere 410, sphere 420, and sphere 430 in FIG. 4 refers to a space including codewords. The codewords included in phrase 410, the codewords contained in phrase 420, and the codewords contained in phrase 430 are orthogonal and thus have a zero correlation.

As shown in FIG. 4, when the codewords of the codebook corresponding to the specific receiver and the codewords of the codewords corresponding to other receivers are orthogonal, the optimal codebooks of Equation (13) can be designed.

를 가정하는 경우, K 개의 수신기들을 위한 코드북은 하기 수학식 14와 같이 설계될 수 있다.
It may be very difficult to optimize Equation (13) for any beam-forming codebooks. At this time, embodiments of the present invention can provide a systematic beam-forming codebook design approach. Mt-dimensional Grassmanian Line Packing Codebook

, The codebook for the K receivers can be designed as: < EMI ID = 14.0 >

&Quot; (14) "

는 수신기 i를 위한 Mt 차원의 유니터리 회전 매트릭스를 의미한다. 주어진 베이스 코드북

에 대하여, 유니터리 회전 매트릭스

는 상기 수학식 13을 통하여 최적화될 수 있다.here,

Means a unitary rotation matrix of Mt dimensions for receiver i. Given base codebook

, The unitary rotation matrix

Can be optimized through Equation (13).

과 회전 매트릭스의 후보들을 포함하는

를 미리 저장할 수 있고, 수신기들이 송신기에 의해 서빙되기 위하여 셀로 접속할 때마다, 송신기는 회전 매트릭스의 Ui의 인덱스를 수신기들로 피드포워드할 수 있다. 이러한 경우, 수신기들은 회전 매트릭스 Ui를 이용하여 기본 코드북

을 회전함으로써 코드북 구조(configuration)를 쉽게 변경할 수 있다. 특히, 전용 파일럿이 사용될 수 있다면, 수신기들은 Ui 및

를 알 필요가 없다.The above-described systematic beam-forming codebook structure can be an efficient structure. In particular,

And candidates of the rotation matrix

And whenever the receivers connect to the cell to be served by the transmitter, the transmitter can feed-forward the index of the Ui of the rotation matrix to the receivers. In this case, the receivers use the rotation matrix Ui to generate the basic codebook

It is easy to change the codebook configuration. In particular, if a dedicated pilot can be used,

.

To improve the overall performance, it is assumed that a feed-forward link from the transmitter to each of the receivers is available. Through this feed forward link, the transmitter can broadcast information on interference statistics to all receivers.

At this time, the interference statistics can be expressed by the following equation (15).

&Quot; (15) "

를 설계하는 데에 도움을 준다. 최적의 컴바이닝 벡터

는 하기 수학식 16과 같이 나타낼 수 있다.
Assuming that the interference-limited beamforming codebook is used as in Equation (14), the interference statistics in Equation (15)

It helps to design. Optimal Combining Vector

Can be expressed by the following equation (16).

&Quot; (16) "

는 하기 수학식 17을 기초로 계산될 수 있다.
here,

Can be calculated based on the following equation (17).

&Quot; (17) "

Each of the receivers can design the optimal combiner shown in Equation (16). In addition, K beamforming vectors maximizing the sum of the transmission rates can be obtained based on the partial channel information fed back from each of the receivers.

&Quot; (18) "

와 같이 특이값 분해가 수행되는 경우,

는 우측 특이 매트릭스(right singular 매트릭스)이고,

는 대각 특이 값(diagonal singular value)이다.here,

When the singular value decomposition is performed,

Is a right singular matrix,

Is a diagonal singular value.

(

)을 기초로, 송신기는 수신기들로 데이터 스트림을 송신할 수 있다. 이 때, 실제의 전송률 합은 하기 수학식 19와 같이 나타낼 수 있다.
Beamforming vectors

(

), The transmitter may transmit the data stream to the receivers. At this time, the actual transmission rate sum can be expressed by the following equation (19).

&Quot; (19) "

In the above, the case where M _r is equal to or greater than M _t is described. Hereinafter, the case where M _r is smaller than M _t will be described.

M _r This M _t Less than

When M _t is larger than M _r , the received signal vector of the receiver i can be expressed by Equation (20).

&Quot; (20) "

이고, C^{Mr x Mt}는 M_r x M_t 차원의 컴플렉스 공간을 나타낸다.

는 수신기 i를 위한 빔포밍 벡터를 나타내며,

는 규준화된 노이즈 벡터를 나타낸다.

의 엔트리들은 표준 정규 분포

에 따라 identically independent distributed하다. 그리고,

는 전송 심볼을 나타내며, 전송 심볼의 에너지는

이며,

는 신호 대 잡음 비(SNR)이다.here,

And C ^{Mr x Mt} represents the complex space of dimension M _r x M _t .

Denotes a beamforming vector for receiver i,

Represents a normalized noise vector.

The entries of the standard normal distribution

It is identically independent distributed according to. And,

Represents the transmission symbol, and the energy of the transmission symbol is

Lt;

Is the signal-to-noise ratio (SNR).

는 사이즈 N2의 빔포밍 코드북으로부터 선택된 빔포밍 벡터라고 가정한다. 이 때, 최소 자승 결합(least square combining) 기법에 따른 컴바이너는 하기 수학식 21과 같이 나타낼 수 있다.
It is assumed that receivers use a least square combining technique. And,

Is a beamforming vector selected from a beamforming codebook of size N2. In this case, the combiner according to the least square combining technique can be expressed by Equation (21).

&Quot; (21) "

라고 가정한다. 여기서, n_i는 수신기 i를 위한 빔포밍 코드북에서 수신기 i를 위한 빔포밍 벡터의 인덱스를 나타낸다. 전용 파일럿이 사용되는 경우, 수신기 i는 실효 채널을 추정함으로써,

를 파악할 수 있지만, 전용 파일럿이 사용되지 않는 경우, 송신기는 다운링크에서

를 수신기 i로 알려줄 수 있다.To distinguish the beamforming vector for receiver i from the other receivers, we use a beamforming vector for receiver i

. Where n _i represents the index of the beamforming vector for receiver i in the beamforming codebook for receiver i. If a dedicated pilot is used, receiver i estimates the effective channel,

, But if the dedicated pilot is not used,

To receiver i.

The transmission rate sum formula with perfect channel information can be expressed by Equation (22).

&Quot; (22) "

는

의 row 서브스페이스를 나타내며, U_j는

이고,

이며,

이다. 상기 수학식 22의 전송률 합은 하기 수학식 23에 의해 하한된다(lower bounded).
here,

The

Of the row represents the subspace, U _j is

ego,

Lt;

to be. The transmission rate sum of Equation (22) is lower bounded by Equation (23).

&Quot; (23) "

에 대하여

가 취해진다.

에 대하여

가 취해지면, 하기 수학식 24를 나타낼 수 있다.
Considering again the interference suppression,

about

Lt; / RTI >

about

The following equation (24) can be obtained.

&Quot; (24) "

를 양자화한다.By analyzing Equation 24, the following embodiments can be proposed. That is, the receiver i uses a channel codebook of N1 size

Lt; / RTI >

At this time, the channel codebook for the receiver i can be expressed by Equation (25).

&Quot; (25) "

Here, the codewords included in the channel codebook for receiver i may be generated based on Equation (26).

&Quot; (26) "

를 갖고, 각각의 채널 코드북은 그래스매니안 라인 팩킹 코드북이라고 가정한다. 수신기들 각각의 선호 코드워드를

라고 한다면, 수신기들 각각은

를 송신기로 피드백한다.

은 채널 코드북

에서 l 번째 코드워드를 의미한다. 송신기가 적절한 스케쥴링을 수행할 수 있도록 송신기들 각각은

를 피드백한다.In addition, each of the receivers has a different channel codebook

, And each channel codebook is a Grassman's line packing codebook. The preferred codeword of each of the receivers

, Each of the receivers

To the transmitter.

Channel codebook

≪ / RTI > To enable the transmitter to perform the proper scheduling, each of the transmitters

.

로 나타낼 수 있다. 그리고, 수신기들 각각에 대응하는 빔포밍 코드북은 그래스매니안 라인 팩킹 코드북일 수 있다. 즉, 수신기 1 내지 수신기 K의 빔포밍 코드북은 하기 수학식 27과 같이 나타낼 수 있다.
The transmitter generates K beamforming vectors for receivers based on the preferred codewords of each of the receivers. At this time, each of the receivers may have a different beam-forming codebook, and the transmitter selects K beam-forming vectors from the beam-forming codebook corresponding to each of the receivers. The beamforming vectors selected by the transmitter are

. And, the beamforming codebook corresponding to each of the receivers may be a Grassmanian line packing codebook. That is, the beamforming codebook of the receiver 1 to the receiver K can be expressed by the following equation (27).

&Quot; (27) "

은 수신기 i를 위한 빔포밍 코드북을 나타내며, N2는

의 사이즈이다. LSC를 사용하는 수신기 i의 신호 파워를 최대화하는 빔포밍 방향은 서브스페이스

위에 있어야 한다. 따라서,

는 서브스페이스

위에 있어야 하며, 송신기에서의 K 개의 빔포밍 벡터들

는

와 함께 계산되는 전송률 합을 최대화하도록 결정되어야 한다는 두 가지 제한(constrain)을 제안할 수 있다.Here, the beam forming codebook

Denotes a beamforming codebook for receiver i, N2 denotes

. The beam-forming direction that maximizes the signal power of the receiver i using the LSC is the subspace

Should be on. therefore,

Subspace

And the K beamforming vectors at the transmitter

The

And that the sum of the transmission rates computed with < RTI ID = 0.0 > T, < / RTI >

와 관련하여,

이 N1 개 존재하며,

는

(j=1, 2, 3, . . , N1)과 관련된다. 송신기가 수신기들 각각으로부터

를 얻은 이후에, 송신기는 K 개의 빔포밍 벡터들을 선택한다. 특히, 송신기는 하기 수학식 28을 이용하여 K 개의 빔포밍 벡터들을 선택할 수 있다.
Subspace codebook allocated to receiver i

In connection with this,

Lt; RTI ID = 0.0 > N1 &

The

(j = 1, 2, 3, ..., N1). From the transmitter

, The transmitter selects the K beamforming vectors. In particular, the transmitter may select K beamforming vectors using Equation (28).

&Quot; (28) "

는

안에 있어야 하는 제한, 채널 서브스페이스 양자화를 가지고, 아래에서 설명하는 것과 같이 코드북 디자인 제한을 얻을 수 있다.
The following describes how the beam-forming codebook is designed. Equation 24 provides a design criterion for the beamforming codebook in the interference limited region.

The

With channel subspace quantization, the codebook design constraint can be obtained as described below.

The possible permutations of the indices of the preferred codewords from the K receivers may be expressed as: < EMI ID = 29.0 >

&Quot; (29) "

는 K 튜플 벡터이며, K 튜플 벡터의 엘리먼트들은 선호 코드워드들의 인덱스들이다. 빔포밍 코드북 설계 목표 함수는 하기 수학식 30과 같이 나타낼 수 있다.
here,

Is a K tuple vector, and the elements of a K tuple vector are indices of preferred codewords. The beamforming codebook design target function can be expressed by Equation (30).

&Quot; (30) "

The beamforming codebook design objective function means that the beamforming codebook associated with the quantized channel subspace of receiver i should be designed such that the correlation between codewords from other receivers is minimized.

To improve the overall performance, it is assumed that a feed-forward link from the transmitter to each of the receivers is available. Through this feed forward link, the transmitter can broadcast information on interference statistics to all receivers.

At this time, the interference statistics can be expressed by the following equation (31).

&Quot; (31) "

를 설계하는 데에 도움을 준다. 최적의 컴바이닝 벡터

는 하기 수학식 32과 같이 나타낼 수 있다.
The interference statistic of Equation (31) indicates that the receiver i is the optimal combining vector

It helps to design. Optimal Combining Vector

Can be expressed by the following equation (32).

(32)

는 하기 수학식 33을 기초로 계산될 수 있다.
here,

Can be calculated based on the following equation (33).

&Quot; (33) "

The transmitter may select K beamforming vectors that can maximize the rate sum based on the quantized channel matrix from each of the receivers using Equations 32 and 33 above. In particular, the transmitter may use the following equation (34).

&Quot; (34) "

5 is a flowchart illustrating a communication method of a transmitter and a receiver i in a multi-user MIMO communication system according to an embodiment of the present invention.

를 추정한다.First, referring to FIG. 5, embodiments of the present invention will be described when M _r is equal to or greater than M _t . Referring to FIG. 5, the transmitter transmits a common pilot. Each of the plurality of receivers estimates a channel, and receiver i, which is one of a plurality of receivers,

.

를 이용하여 추정된 채널

에 대응하는 선호 코드워드

를 선택한다. 보다 구체적으로, 수신기 i는 상기 수학식 3을 이용하여

를 선택할 수 있다.Each of the receivers has a different channel codebook. Receiver i < / RTI >

Lt; RTI ID = 0.0 >

The preferred code word < RTI ID = 0.0 >

. More specifically, receiver i uses Equation 3 above

Can be selected.

가 선택되면, 수신기 i는

의 인덱스를 송신기로 피드백한다. 마찬가지로, 송신기에 의해 서빙되기 위하여 셀에 접속한 모든 수신기들 각각은 해당 선호 코드워드의 인덱스를 송신기로 피드백한다. 또한, 위에서 설명한 바와 같이,

도 피드백된다.

Is selected, receiver i

To the transmitter. Likewise, all of the receivers connected to the cell to be served by the transmitter feed back the index of the corresponding preferred codeword to the transmitter. In addition, as described above,

Is also fed back.

The transmitter selects K beamforming vectors based on the feedback index from each of the receivers. That is, the transmitter selects K beamforming vectors from the beamforming codebook corresponding to each of the receivers described in Equation (6).

의 인덱스를 수신함으로써,

를 파악할 수 있다. 뿐만 아니라, 송신기가 전용 파일럿을 사용할 수 있는 경우, 수신기들은 해당 실효 채널을 파악함으로써, 해당 빔포밍 벡터를 파악할 수 있다.If the transmitter is able to use the feedforward link, information about the selected beamforming vector may be feed forwarded. For example, receiver i

By receiving an index of < RTI ID =

. In addition, when the transmitter can use the dedicated pilot, the receivers can grasp the corresponding beamforming vector by grasping the corresponding effective channel.

If the transmitter uses beamforming codebooks such as Equation (14) above, the transmitter may feed forward information about the rotation matrix and feed forward information about the interference statistics.

The above-described steps can be applied well even when M _r is smaller than M _t , so a detailed description will be omitted.

6 is a block diagram illustrating a transmitter according to an embodiment of the present invention.

Referring to FIG. 6, a transmitter for multi-user MIMO communication includes a memory 610, a receiver 720, a processor 730, and a transmitter 740.

In the memory 610, a channel codebook and a beamforming codebook corresponding to each of the receivers are stored, and further candidates of the rotation matrix, base codebook can be further stored.

According to the control of the processor 630, the transmitting unit 640 transmits a common pilot, and after each of the receivers estimates the channel, partial channel information (information on the preferred codeword) and channel quality information do. At this time, since the channel codebook corresponding to each of the receivers is different from each other, the transmitter must refer to the corresponding channel codebook to grasp the partial channel information of each of the receivers.

That is, the receiver 620 receives the information on the preferred codeword from each of the receivers, and the processor 630 refers to the channel codebook of each of the receivers previously stored in the memory 610, I understand.

Once the preferred codewords of each of the receivers are grasped, the processor 630 determines K (number of receivers) from the beamforming codebook of each of the receivers previously stored in the memory 610 based on the preferred codeword of each of the receivers Beamforming vectors.

Once the beamforming vectors are determined, the processor 630 may generate information about the beamforming vectors, information about the interference statistics, information about the rotation matrix corresponding to each of the receivers, etc., if a feedforward link is available have.

Transmit unit 640 transmits the precoded data stream to receivers using beamforming vectors. At this time, the transmitting unit 640 may selectively transmit information on beamforming vectors, information on interference statistics, information on a rotation matrix corresponding to each of the receivers, and the like. In addition, when a dedicated pilot can be used, the transmitter 640 may also transmit a dedicated pilot.

The transmitter shown in FIG. 6 can be applied to all of the descriptions shown in FIG. 1 to FIG. 5, and thus a detailed description thereof will be omitted.

7 is a block diagram illustrating a receiver in accordance with an embodiment of the present invention.

7, a receiver for multi-user MIMO communication includes a memory 710, a channel estimator 720, a receiver 730, a processor 740, and a transmitter 740.

In the memory 610, a channel codebook and a beam-forming codebook corresponding to the receiver are stored, and further candidates of the rotation matrix, base codebook can be further stored.

When a common pilot is transmitted from the transmitter, the received common pilot is provided from the receiver 730 to the channel estimator 720. The channel estimator 720 estimates the channel between the receiver and the transmitter.

Processor 740 selects the preferred codeword from the channel codebook pre-stored in memory 610 based on the estimated channel. Information on the preferred codeword is fed back via the transmitting unit 740. [

If the transmitter precodes the data stream using the beamforming vector after determining the beamforming vector corresponding to that receiver, the received data stream is processed by the processor 740. At this time, the processor 740 may be configured to optimize the optimal channel estimate based on the information about the beamforming vectors fed-forward from the transmitter, the information about the interference statistics, the information about the rotation matrix, or the effective channel estimated based on the dedicated pilot from the transmitter You can design combiners. The received data stream is processed according to the optimal combiner.

1 to 5 may be applied to the receiver shown in FIG. 7, so that a detailed description thereof will be omitted.

The above-described methods may be implemented in the form of program instructions that can be executed through various computer means and recorded in 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 configured 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.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. This is possible.

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

110: base station

Claims (15)

A communication method of a transmitter for multi-user multi-input / output communication,
Maintaining a memory in which a first channel codebook corresponding to a first receiver and a second channel codebook corresponding to a second receiver are stored;
Information on a first preferred code word among codewords included in the first channel codebook from the first receiver and information on a second preferred codeword among codewords included in the second channel codebook from the second receiver Receiving information; And
Determining a first beamforming vector using a first beamforming codebook for the first receiver based on the first preferred code word and the second preferred code word, Determining a second beamforming vector using a second beamforming codebook for the receiver,
Lt; / RTI >
The first channel codebook and the second channel codebook are different from each other,
The first beamforming codebook is generated by inner producting each of the code words included in the first unitary rotation matrix and the predefined basic codebook,
Wherein the second beamforming codebook is generated by inner producting each of a second unitary rotation matrix different from the first unitary rotation matrix and code words included in the predefined basic codebook,
Wherein the first channel codebook is different from the first beamforming codebook and the second channel codebook is different from the second beamforming codebook,
A communication method of a transmitter for multiuser multi - input / output communication.

The method according to claim 1,
Wherein the information about the first preferred codeword is related to the covariance of the first channel between the transmitter and the first receiver and the information about the second preferred codeword is related to the covariance of the first preferred codeword between the transmitter and the second receiver Wherein the first channel is associated with a covariance of a second channel.

The method according to claim 1,
Wherein the code words contained in one channel code book are defined on the basis of the vectors in the codebook of the packing line grass maenian dimension _r1 x M _t M 1,
Wherein the code words contained in the two-channel codebooks are defined on the basis of the vector in the grass maenian packing line code of dimension M _t M x _r2 1,
_Wherein M _r1 is the number of receive antennas of the first receiver, M _r2 is the number of receive antennas of the second receiver, and M _t is the number of transmit antennas of the transmitter. .

The method of claim 3,
The vectors in the M _t M _r 1 x 1-dimensional Grassmannian line packing codebook are transformed into matrices of dimension M _t x M _r1 , and each of the codewords included in the first channel codebook is transformed into M _t x M _r1 dimension Lt; / RTI > defined by each of the matrices of <
Wherein the vectors in the M _t M _r2 x 1 dimensional grasping line packing codebook are transformed into matrices of dimension M _t x M _r2 , and each of the codewords contained in the second channel codebook is transformed into M _t x M _r2 dimension Wherein the first and second matrices are defined by respective ones of the matrices.

delete The method according to claim 1,
Wherein the minimum distance between the first beamforming code words included in the first beamforming codebook and the minimum distance between the second beamforming code words included in the second beamforming codebook are the same for multi- A method of communication of a transmitter.

The method according to claim 1,
Wherein determining a first beamforming vector for the first receiver and a second beamforming vector for the second receiver comprises:
Calculating a sum rate for the first receiver and the second receiver, assuming that the first receiver and the second receiver are each a zero-forcing linear receiver; And
Selecting a first beamforming vector for the first receiver and a second beamforming vector for the second receiver based on a sum rate for the first receiver and the second receiver
And a transmitter for transmitting the multi-user multi-input / multi-output communication.

The method according to claim 6,
The first beamforming codebook and the second beamforming codebook, respectively,
Wherein the correlation between the first beamforming codewords and the second beamforming codewords is minimized. ≪ Desc / Clms Page number 20 >

delete The method according to claim 1,
Providing information about the first unitary rotation matrix to the first receiver and providing information about the second unitary rotation matrix to the second receiver
Further comprising the steps of: receiving a message from the transmitter;

The method according to claim 1,
Calculating interference statistics based on an inner product between the first beamforming vector and a Hermitian of the first beamforming vector and an inner product between the second beamforming vector and a Hermitian of the second beamforming vector step; And
1 'providing information on the interference statistics to the first receiver and the second receiver
Further comprising the steps of: receiving a message from the transmitter;

A communication method of a second receiver for a multi-user MIMO communication system including a transmitter, a first receiver and a second receiver,
Maintaining a memory in which a second channel codebook corresponding to a second receiver distinct from a first channel codebook corresponding to a first receiver is stored;
Calculating a covariance of a second channel between the transmitter and the second receiver;
Selecting a second one of the codewords included in the second channel codebook based on the covariance of the second channel;
Providing information on the second preferred codeword to the transmitter;
Wherein the transmitter uses a first beamforming codebook for the first receiver to determine a first beamforming vector and a second beamforming codebook for the second receiver different from the first beamforming codebook, And when the second beamforming codebook is generated by inner product of each of the code words included in the unitary rotation matrix and the predefined basic codebook, information about the unitary rotation matrix From the transmitter;
If the transmitter uses the second beamforming vector based on the second preferred codeword, grasping the second beamforming vector using information about the unitary rotation matrix; And
Calculating a received combine- tion vector according to the second beamforming vector and the second channel,
Lt; / RTI >
Wherein the first channel codebook is different from the first beamforming codebook and the second channel codebook is different from the second beamforming codebook,
A communication method of a second receiver for multiuser multi input / output communication.
13. The method of claim 12,
Calculating an effective channel between the transmitter and the second receiver using a dedicated pilot for the second receiver transmitted from the transmitter
Further comprising:
The step of grasping the second beamforming vector
And grasping the second beamforming vector based on the effective channel.

delete 13. The method of claim 12,
Interference statistics from the transmitter, the interference statistics comprising an inner product between the first beamforming vector for the first receiver and the Hermitian of the first beamforming vector, and the second beamforming vector and the second beamforming < RTI ID = 0.0 > Calculating information based on an inner product between the Hermitian cube of the vector
Further comprising:
The step of calculating the received combining vector
And calculating the reception combining vector based on the interference statistics.

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