KR101200011B1 - Method for transmitting and receiving based on vector perturbation in multiuser mimo system - Google Patents

Abstract

PURPOSE: A transmission and reception method based on vector perturbation in a multiuser multiple antenna system is provided to promote a BER(Bit Error Rate) performance by simultaneously considering of interference, a fading channel, and noise. CONSTITUTION: A transmission apparatus executes vector perturbation for a transmission target user symbol(S210). The transmission apparatus outputs the data symbol by adding the user symbol and a perturbation symbol(S220). The transmission apparatus creates the second data symbol by multiplying a first data symbol by the set first pre-coding matrix(S230). The transmission apparatus creates a third data symbol by multiplying the second data symbol by the set second pre-coding matrix(S240). The transmission apparatus transmits the created third data symbol(S250). [Reference numerals] (AA) Start; (BB) End; (S210) Pertubation symbol is created by executing a vector pertubation for a user symbol; (S220) A first data symbol is outputted by summing a user symbol and a pertubation symbol; (S230) A second data symbol is created by multiplying a first data symbol by the set first pre-coding matrix; (S240) A third data symbol is created by multiplying a second data symbol by the set second pre-coding matrix; (S250) A third data symbol is transmitted through a plurality of transmission antennas

Description

METHODO FOR TRANSMITTING AND RECEIVING BASED ON VECTOR PERTURBATION IN MULTIUSER MIMO SYSTEM}

The present invention relates to a multi-user multi-antenna system, in particular, a process of separating data streams to each antenna and removing interference between users in consideration of the degree of distortion caused by interference between each user signal, fading channel, and noise. A vector perturbation based transmission method and reception method in a multi-user multi-antenna system for performing precoding.

The multi-user multi-antenna system is a system for transmitting and receiving signals of each user simultaneously toward a plurality of users in a transmitter having a plurality of antennas. Since the signals of all users are transmitted using the same time, the same frequency, the same space, and the antenna, the receiving end acts as interference between each other, which causes a problem that the reception performance of the entire system is degraded.

In order to remove such interference from the receiver, a signal processing process including a very complicated calculation process is required, and such a receiving process is a great burden for a receiving terminal such as a mobile phone in a general system. For this reason, many techniques for precoder that transmits a signal after preprocessing the transmission signal to remove interference have been studied. Vector perturbation is one of the well-known precoding techniques.

Most existing precoding schemes are designed with the goal of lowering this value when the error rate at each receiver is calculated using the signal transmitted through preprocessing. This precoding method, represented by Zero Forcing-Beamforming (ZF-BF) and Minimum Mean Square Error-Beamforming (MMSE-BF), uses a channel between the transmitter and the receiver to multiply the signal to be transmitted by the inverse of the channel, By transmitting the symbol, it is designed to simultaneously remove the distortion of the channel and the interference between the symbols at the receiving end.

On the other hand, the precoding method represented by block diagonalization (BD) is divided into a part of removing interference between signals of each user and a part of removing interference between signals of each user when each user has multiple antennas. Coders are designed and there are many precoding methods designed for similar purposes.

When designing the matrix constituting the precoding, various types of precoder may exist according to the criteria to be considered, and thus, the reception performance and the performance of the entire system are determined. It is important.

If each user has multiple antennas, the existing vector perturbation scheme is designed with ZF criterion to completely eliminate interference between adjacent users. However, considering the interference between adjacent users, designing with MMSE criterion can further reduce the power scaling factor.

Therefore, to solve the problems of the prior art, an object of the present invention is to separate the data stream to each antenna in consideration of the interference between each user signal and the degree of distortion by the fading channel, noise and interference between users The present invention provides a vector perturbation-based transmission method and a reception method in a multi-user multi-antenna system that can perform precoding, which is performed by a removing process.

However, the objects of the present invention are not limited to those mentioned above, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above objects, in the multi-user multi-antenna system according to an aspect of the present invention, a vector perturbation based transmission method may include: performing permutation of a user symbol to be transmitted to generate a perturbation symbol; Adding the user symbol and the perturbation symbol to output a first data symbol; Generating a second data symbol by multiplying the first data symbol by a preset first precoding matrix; Generating a third data symbol by multiplying the second data symbol by a preset second precoding matrix; And transmitting the generated third data symbol through a plurality of transmit antennas.

에 의하여 구하고, 여기서, β는 power normalization 값을 의미하고, K는 전체 사용자 수를 의미하며, P_T는 송신 전력을 의미하며, H_k는 각 사용자의 채널을 의미하며, W_j는 제2 프리코딩 행렬을 의미하며, N_r은 모든 사용자의 안테나 개수의 합을 의미하며,

은 AWGN 잡음의 variance를 의미하며,

는 N_t×N_t identity matrix를 의미하며, d_j[n]는 벡터 퍼터베이션을 수행한 후의 j번재 사용자의 심볼을 의미하는 것을 특징으로 한다.Preferably, the first precoding matrix F _j is

Where β is the power normalization value, K is the total number of users, P _T is the transmit power, H _k is the channel of each user, and W _j is the second free The coding matrix, N _r is the sum of the number of antennas of all users,

Is the variance of AWGN noise,

Denotes an N _t × N _t identity matrix, and d _j [n] denotes a symbol of a user j after performing vector permutation.

에 의해 구하는 것을 특징으로 한다.Preferably, β is the equation

It is characterized by obtaining by.

Preferably, the perturbation symbol is obtained using a sphere encoder algorithm such that β is minimized.

Preferably, the first precoding matrix is designed such that the sum of MSEs of the plurality of user terminals is minimum.

을 만족하고 대각행렬

의 각 원소는

을 만족하는 경우, 상기 대각행렬

의 가장 큰 순서대로 N_{r ,j}개의 원소에 해당하는 U의 N_r,j개의 열벡터이고, 여기서,

는 사용자 j를 제외한 다른 사용자의 채널로 구성된 행렬을 의미하고, H_k는 각 사용자의 채널을 의미하며,

은 AWGN 잡음의 variance를 의미하며,

는 N_t×N_t identity matrix를 의미하는 것을 특징으로 한다.
Preferably, the second precoding matrix W _j is

Satisfying the diagonal matrix

Each element of

When satisfying the diagonal matrix

Where N _{r, j} column vectors of U corresponding to N _{r , j} elements in the largest order of,

Denotes a matrix composed of channels of other users except for user j, and H _k denotes a channel of each user.

Is the variance of AWGN noise,

Denotes an N _t × N _t identity matrix.

In a multi-user multi-antenna system according to another aspect of the present invention, a vector perturbation based receiving method includes receiving data symbols transmitted from a transmitter via a plurality of receiving antennas; Adding a noise symbol to the received data symbol and outputting an estimated data symbol; And receiving the estimated data symbol, performing a modulo operation on the received estimated data symbol, and generating an estimated user symbol as a result of the modulated operation.

In this way, the present invention performs a precoding consisting of the process of separating the data stream to each antenna and removing the interference between users in consideration of the degree of distortion by the interference, fading channel, noise between each user signal, This has the effect of improving BER performance.

1 is a diagram illustrating a vector permutation based multi-user multi-antenna system according to an embodiment of the present invention.
2 is a diagram illustrating a vector perturbation based transmission method in a multi-user multi-antenna system according to an embodiment of the present invention.
3 is a diagram illustrating a vector perturbation based receiving method in a multi-user multi-antenna system according to an embodiment of the present invention.
4 is a diagram showing a simulation result of BER performance according to an embodiment of the present invention.

Hereinafter, with reference to Figures 1 to 4 attached to the vector perturbation based transmission method and reception method in a multi-user multi-antenna system according to an embodiment of the present invention. It will be described in detail focusing on the parts necessary to understand the operation and action according to the present invention. Like reference numerals in the drawings denote like elements throughout the specification. In addition, in describing the present invention, when it is determined that a detailed description of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted.

According to the present invention, a method for performing precoding consisting of a process of separating a data stream to each antenna and a process of removing interference between users in consideration of the degree of distortion caused by interference, fading channels, and noise between user signals is performed. Suggest.

1 is a diagram illustrating a vector permutation based multi-user multi-antenna system according to an embodiment of the present invention.

As shown in FIG. 1, the vector permutation based multi-user multi-antenna system according to the present invention may include a base station 100, a user terminal 200, and the like.

The base station 100 simultaneously transmits a transmission signal or a transmission symbol to be transmitted to each of a plurality of users, and performs vector perturation-based precoding, which is distorted by interference, fading channel, and noise between each user signal. In consideration of this, a process of separating a data stream to each antenna and a process of removing interference between users may be transmitted to the plurality of user terminals 200.

Each user terminal 200 may restore the original transmission symbol transmitted from the base station 100 by removing the perturbation vector from the signal received through the modulo operation.

FIG. 2 is a diagram illustrating a vector perturbation based transmission method in the multi-user multi-antenna system shown in FIG. 1.

As shown in FIG. 2, a transmitter for a vector permutation-based multi-user multi-antenna system according to the present invention receives user symbols u ₁ ,..., U _K to be transmitted, and receives the received user symbols u _1. As a result of performing vector permutation on,..., u _K , the permutation symbols P ₁ ,..., P _K may be generated (S210).

Next, the transmitter receives the user symbols u ₁ , ..., u _K and the perturbation symbols P ₁ , ..., P _K, and receives the received user symbols u ₁ , ..., u _K and the perturbation symbol. Each of P ₁ ,..., And P _K is added, and as a result of the addition, the data stream or the first data symbols d ₁ ,..., And D _K may be output (S220).

Next to, the transmitter removes the first data symbols d _1, ..., the first data symbols d _1, ..., interference will occur between each of the antennas to the user who receives the _K d _K d, the input A second data symbol s ₁ ,..., S _K may be generated by multiplying the _first precoding matrix F ₁ ,..., F _K (S230).

와 사용자 j를 목적으로 하는 신호 d_j의 MSE(mean square error)가 최소가 되도록 설계한다. 그리고 사용자 j를 위한 신호 d_j가 다른 사용자 k (k≠j) 에게 비치는 간섭 성분도 최소가 되도록 설계한다.In this case, the first precoding matrix is a signal received by user j.

And it is designed such that the signal d _j to the user j for the purpose is the minimum MSE (mean square error). In addition, the interference component of the signal d _j for the user j to the other user k (k ≠ j) is also designed to be minimum.

The MSE of the user j may be expressed as in Equation 1 below.

[Equation 1]

는 Euclidean 2-norm의 제곱을 의미한다.Here, s _j denotes a symbol after performing the first precoding, d _j denotes a symbol of the user j after performing vector perturbation, n _j denotes noise of the receiver, and u _j denotes j means user symbol, β means power normalization value, K means total number of users,

Is the square of Euclidean 2-norm.

는

를 나타낸 것으로 H_j는 사용자 j로의 채널을 나타낸다. W는 [W₁, ..., W_K]로 W_j는 SLNR (signal to leakage plus noise ratio)을 최대화하기 위한 프리코더로 인접 사용자간의 간섭을 줄여준다. 제안된 SLNR 기반의 프리코딩 기법은 각 사용자의 안테나 간의 간섭을 분리하기 위해 각 사용자는 별도의 수신 필터를 사용한다. 이를 위해서는 각 수신단은 프리코딩 행렬 W_j를 알아야 한다. 각 사용자가 W_j를 알기 위해서는 송신단이 각 사용자에게 W_j를 보내거나 별도의 채널 추정 기간이 필요하다. 통신 시스템 환경에서 이러한 과정은 많은 자원을 낭비하게 되므로 각 사용자가 수신 필터를 사용하는 대신 송신단에서 채널 정보를 바탕으로 선 등화과정을 미리 해준다면 각 사용자가 W_j를 알기위한 별도의 프로세스 과정은 사라지게 되고, 더불어 수신 필터가 필요하지 않게 되므로 수신단의 복잡도는 감소되게 된다. 따라서 프리코딩 행렬 F₁, ..., F_K를 사용함으로써 각 사용자의 인접 안테나 간의 간섭을 줄여주게 된다. 하지만 새로운 프리코딩 행렬을 추가하고 BER (bit-error-rate) 성능을 높이기 위해 벡터 퍼터베이션을 사용하게 되면 이로 인해 제안된 W_j는 더 이상 SLNR이 최대가 되도록 설계되지 않는다. 따라서 잔재하는 간섭성분을 더욱 줄여주기 위한 별도의 프로세싱을 해준다. 이 과정이 위 MSE_j 식의 두 번째 항인

에 해당된다.The first term in the equation

The

Where H _j represents the channel to user j. W is [W ₁ , ..., W _K ] and W _j is a precoder to maximize signal to leakage plus noise ratio (SLNR), reducing interference between adjacent users. In the proposed SLNR-based precoding scheme, each user uses a separate receive filter to separate interference between antennas of each user. To this end, each receiver must know the precoding matrix W _j . In order for each user to know W _j , the transmitter sends W _j to each user or requires a separate channel estimation period. In a communication system environment, this process wastes a lot of resources. If each user pre-qualifies the channel prioritization based on channel information instead of using a receive filter, the separate process for each user to know W _j disappears. In addition, since the reception filter is not required, the complexity of the receiving end is reduced. Therefore, by using the precoding matrices F ₁ , ..., F _K , interference between adjacent antennas of each user is reduced. However, when we add a new precoding matrix and use vector perturbation to improve bit-error-rate (BER) performance, the proposed W _j is no longer designed to maximize SLNR. Therefore, separate processing is performed to further reduce residual interference. This course is MSE _j The second term of the equation

Corresponds to

Therefore, the precoding matrices F ₁ , ..., F _K are designed such that the sum of MSE _j of each user is minimized, and a criteria for optimizing can be given by Equation 2 below.

&Quot; (2) "

Here, P _T may represent transmit power. The precoding matrices F _j (j = 1, ..., K) and β satisfying Equation 2 may be expressed as in Equations 3 to 4 below.

&Quot; (3) "

를 의미하며,

은 AWGN 잡음의 variance를 의미하며,

는 N_t×N_t identity matrix를 의미한다.Here, β means power normalization value, K means total number of users, P _T means transmit power, H _k means channel of each user, and W _j means second precoding channel. N _r is the sum of the antenna numbers of all users. If the number of antennas of each user is N _{r , j} , N _r is

Means,

Is the variance of AWGN noise,

Denotes an N _t × N _t identity matrix.

&Quot; (4) "

Therefore, the perturbation vector P _j (j = 1, ..., K) is designed such that β is minimum. P _j at which β becomes the minimum can be obtained using, for example, a sphere encoder algorithm.

Next, the transmitter is the second data symbols s _1, ..., the second data symbols being received in input to s _K s _1, ..., a second precoding matrix W to s _K for removing interference between users By multiplying may generate a third data symbol to be transmitted (S240).

In this case, the second precoding matrix W is [W ₁ , ..., W _K ] and W _j is a precoder for maximizing SLNR, and the following Equation 5 is designed to be the maximum.

[Equation 5]

를 재구성하면 다음의 [수학식 6]과 같이 나타낼 수 있다.W _j maximizing [Equation 5] is an eigenspace pair

Reconstructing can be expressed as Equation 6 below.

&Quot; (6) "

는 사용자 j를 제외한 다른 사용자의 채널로 구성된 행렬을 의미한다.here,

Denotes a matrix composed of channels of users other than the user j.

라 하면 eigenvalue

에 해당하는 eigenvector가 W_j가 될 수 있다. 즉, U의 N_{r ,j}개의 열벡터가 W_j 값이 될 수 있다.Where eigenvalue is

Eigenvalue

The corresponding eigenvector may be W _j . That is, N _{r , j} column vectors of U are W _j Lt; / RTI >

의 각 원소는

을 만족하는 경우, 대각행렬

의 원소들

중 가장 큰 순서대로 N_{r ,j}개의 원소에 해당하는 U의 N_{r ,j}개의 열벡터를 나타낼 수 있다.
In other words, the second precoding matrix W _j satisfies Equation 6 above and is diagonal.

Each element of

If satisfying the diagonal matrix

Elements of

N _{r , j} column vectors of U corresponding to N _{r , j} elements may be represented in the largest order.

Next, the transmitter may transmit the generated third data symbol through a transmission antenna (S250). For example, the third data symbol T may be represented as Equation T = W * (s ₁ ,..., S _K ).

FIG. 3 is a diagram illustrating a vector perturbation based receiving method in the multi-user multi-antenna system shown in FIG. 1.

As shown in FIG. 3, a receiver for a vector permutation based multi-user multi-antenna system according to the present invention may receive data symbols transmitted from a transmitter, respectively (S310).

, ...,

를 출력할 수 있다(S320).Next, the receiver receives the received data symbols and adds the noise symbols n ₁ ,..., N _k to the received data symbols, and adds the estimated data symbols to the received data symbols.

, ...,

Can be output (S320).

, ...,

을 입력받고 퍼터베이션 벡터를 제거하기 위하여 입력받은 추정 데이터 심볼 d₁, ..., d_k에 대한 모듈로 연산을 수행하여 그 수행한 결과로 추정 사용자 심볼 u₁, ..., u_k를 생성할 수 있다(S330).
Next, the receiver is estimated data symbol

, ...,

And modulo operation on the estimated data symbols d ₁ , ..., d _k in order to remove the perturbation vector, and the estimated user symbols u ₁ , ..., u _k Can be generated (S330).

4 is a diagram illustrating a simulation result of BER performance according to an embodiment of the present invention.

As shown in FIG. 4, the precoding scheme according to the present invention can provide improved BER performance because simultaneously considering two factors in which a transmission signal may be distorted.

Meanwhile, the above-described embodiments of the present invention can be realized in a general-purpose digital computer that can be created as a program that can be executed by a computer and operates the program using a computer-readable recording medium. The computer-readable recording medium includes a storage medium such as a magnetic storage medium (e.g., ROM, floppy disk, hard disk, etc.), optical reading medium (e.g., CD ROM,

The embodiments described above are just an example, and various modifications and variations may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas falling within the scope of the same shall be construed as falling within the scope of the present invention.

Claims (7)

Generating a permutation symbol by performing vector permutation on a user symbol to be transmitted;
Adding the user symbol and the perturbation symbol to output a first data symbol;
Generating a second data symbol by multiplying the first data symbol by a preset first precoding matrix;
Generating a third data symbol by multiplying the second data symbol by a preset second precoding matrix; And
Transmitting the generated third data symbol through a plurality of transmit antennas;
Wherein the first precoding matrix F _j is expressed as:

Where β is the power normalization value, K is the total number of users, P _T is the transmit power, H _k is the channel of each user, and W _j is the second free The coding matrix, N _r is the sum of the number of antennas of all users,

Is the variance of AWGN noise,

Denotes the N _t × N _t identity matrix, and d _j [n] denotes the symbol of user j after performing vector perturbation.
Β is the equation

Obtained by
The perturbation symbol is obtained by using a sphere encoder algorithm so that the β is the minimum vector perturbation based transmission method in a multi-user multi-antenna system. delete delete delete The method according to claim 1,
The first precoding matrix,
A vector perturbation based transmission method in a multi-user multi-antenna system, characterized in that the sum of MSEs of a plurality of user terminals is minimized. The method according to claim 1,
The second precoding matrix W _j is
Equation

Satisfying the diagonal matrix

Each element of

When satisfying the diagonal matrix

N _{r , j} column vectors of U corresponding to N _{r , j} elements in the largest order of,

Denotes a matrix composed of channels of other users except for user j, and H _k denotes a channel of each user.

Is the variance of AWGN noise,

A vector perturbation based transmission method in a multi-user multi-antenna system, characterized in that N _t × N _t identity matrix. delete

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