KR100939919B1 - Method and Apparatus of Successive interference cancellation for Wireless communication system - Google Patents

Abstract

A method and apparatus for sequential interference cancellation reception in a wireless communication system is disclosed. A method of detecting a transmission signal for a sequential interference cancellation reception method includes receiving a transmission signal transmitted from M antennas, calculating a residual error value for each of the received transmission signals, and calculating the calculated residual error value. Determining a detection order of the transmission signal according to the method.

Multiple-Input Multiple-Output (MIMO), V-BLAST, MMSE

Description

Method and apparatus for receiving sequential interference cancellation in wireless communication system {Method and Apparatus of Successive interference cancellation for Wireless communication system}

The present invention relates to sequential interference cancellation in a wireless communication system that performs multiple transmission multiple reception, and more particularly, to a method and apparatus for sequential interference cancellation for determining a detection order of received data streams in advance and removing the sequential interference according to the determined detection order. It is about.

The present invention is derived from research conducted as part of the IT growth engine technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. [Task Management Number: 2006-S-001-02, Title: Adaptive Wireless Access for 4th Generation Mobile Communications] And transmission technology development].

In general, wireless channel environments exhibit low reliability due to multipath interference, shadowing, propagation short circuits, time-varying noise, and interference.

Many techniques have been developed to solve the low reliability problem of the wireless channel environment.

In particular, a multiple-input multiple-output system for separating signals using different fading information for multipath signals is independent of each other using multiple antennas at the transmitter or receiver, or both. Diversity is obtained by an in fading signal.

In the multi-transmission multiple-receiving system, a conventional technique for obtaining high frequency efficiency is 'V-BLAST (V-BLAST: Vertical Bell Lab LAyered Space Time)' proposed by 'Bell Lab'.

The V-BLAST detects a data symbol having a good channel state first, and then repeats the process of removing the influence of the detected symbol.

However, V-BLAST described above has a problem that the complexity of the system is increased because the calculation amount for data stream detection is very large as O (M ⁴ ) (M is the number of transmit antennas).

In addition, a method using QR decomposition and a square-root algorithm has been proposed to solve the problems of the V-BLAST scheme. It improves the complexity of the system by reducing the amount of computation for data stream detection to O (M ³ ) using QR decomposition and square-root algorithm.

In addition, a number of studies have been conducted to obtain high frequency efficiency in a multi-transmission multi-receiving system, but there is no proposal for a sequential interference cancellation reception method suitable for an actual wireless channel environment.

Therefore, the present invention has lowered the complexity of the V-BLAST detector from O (M ⁴ ) to O (M ³ ), but the actual number of realistic transmission antennas is limited. In this case, the complexity improvement is only about two times. Accordingly, an aspect of the present invention is to provide a sequential interference cancellation reception method and apparatus capable of lowering the complexity of a V-BLAST detector by more than twice as much as the prior art by using Cholesky decomposition.

In addition, the present invention is to provide a method for determining the detection order of the transmission symbol vector that can reduce the complexity of the V-BLAST detector.

In addition, the present invention is to provide an equalization coefficient determination method that can reduce the complexity of the V-BLAST detector.

An embodiment of the present invention includes the steps of receiving transmission signals transmitted from M antennas, determining a detection order of transmission signals according to residual error values of the received transmission signals, and determining a first detection order according to the determined detection order. Selecting a transmission signal, calculating a nulling vector for the first transmission signal by a Coleskey algorithm, and removing interference of a transmission signal other than the first transmission signal from the reception signal using the calculated nulling vector; It provides a sequential interference cancellation method comprising the step.

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In addition, another embodiment of the present invention is a detection order determiner for determining the detection order of the first transmission signal and the second transmission signal transmitted from a plurality of antennas based on the residual error value, and the first corresponding to the first transmission signal; A first filter unit which removes interference of transmission signals other than the first transmission signal from the reception signal by using a first filter coefficient, and decoding the reception signal from which interference of transmission signals other than the first transmission signal is removed A first decoder, a first remover that removes the first transmission signal from the received signal by using the decoded received signal, and the first transmission by using a second filter coefficient corresponding to the second transmission signal. A second filter unit which removes interference of transmission signals other than the second transmission signal from the received signal from which the signal has been removed, and the reception signal from which interference of transmission signals other than the second transmission signal are removed are recovered. Calling provides a sequential interference cancellation device including a second decoder.

According to the present invention, it is possible to provide a sequential interference cancellation reception method and apparatus which can reduce the complexity of the V-BLAST detector by more than two times using the Cholesky decomposition.

In addition, according to the present invention, it is possible to provide a method for determining the order of detection of a transmission symbol vector that can reduce the complexity of the V-BLAST detector.

In addition, the present invention can propose an equalization coefficient determination method that can lower the complexity of the V-BLAST detector.

 Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In describing the present invention, when it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. Terminology used herein is a term used to properly express a preferred embodiment of the present invention, which may vary according to a user, an operator's intention, or a custom in the field to which the present invention belongs. Therefore, the definitions of the terms should be made based on the contents throughout the specification.

1 shows a schematic configuration of a multiplex transmission multiple reception system.

As shown in FIG. 1, in a multi-antenna system including M transmit antennas 109, 111, and 113 and N receive antennas 121, 123, and 125, a transmitter includes a multiplexer 101 and an IFFT ( Inverse Fast Fourier Transforms (103, 105, 107).

The receiver includes a fast fourier transform (FFT) 127, 129, 131 and a signal detector 133.

First, in the transmitter, the multiplexer 101 multiplexes and outputs the data stream to be transmitted to the receiver by the same number as the number of transmit antennas 109, 111, and 113. The IFFTs 103, 105, and 107 exist for each of the transmit antennas 109, 111, and 113, and perform inverse fast Fourier transform on an output signal of the multiplexer 101 to transmit the inverse fast Fourier transforms. Send through).

Next, the receiver receives a signal for each antenna 121, 123, and 125 from the transmitter, and performs fast Fourier transform in the FFTs 127, 129, and 131 that exist for each of the reception antennas 121, 123, and 125. do. The signal detector 133 performs a predetermined process on the fast Fourier transformed data stream in the FFTs 127, 129, and 131.

In this case, the N-dimensional received signal may be represented by Equation 1 below.

[Equation 1]

는

채널 행렬이고,

는 송신 신호 벡터이고, n은 백색 가우시안 잡음이다. In Equation 1,

Is

Channel matrix,

Is the transmit signal vector and n is the white Gaussian noise.

이고,

으로 수신 안테나 당 신호대 잡음비는

가 된다. In addition, the energy of the transmission signal vector

ego,

The signal-to-noise ratio per receive antenna is

Becomes

The received signal after removing interference due to another data stream of the i-th sequence of the V-BLAST sequential interference cancellation method is expressed by Equation 2 below.

In the following description, (-) ^T means a transpose function and (-) ^H means a conjugated complex function.

[Equation 2]

이고,

이다.In Equation 2,

ego,

to be.

A nulling vector for the interference canceled signal as shown in Equation 2 can be expressed as Equation 3 below.

[Equation 3]

는

의 열벡터이고,

는 V-BLAST 순차간섭 제거 수신 방법에 따른 i 번째 순차의 감소된 오차 공분산(error covariance)을 나타낸다. In Equation 3,

Is

Is the column vector of,

Denotes a reduced error covariance of the i-th sequence according to the V-BLAST sequential interference cancellation method.

Equation 3 may be an equalization coefficient for filtering a minimum mean square error (MMSE).

In the V-BLAST method, a method of determining the transmission signal index for determining the detection order for the M transmission signals is expressed by Equation 4 below.

[Equation 4]

는 행렬 A의 ij 번째 요소를 의미한다.In Equation 4,

Denotes the ij th element of the matrix A.

Referring to Equation 4, V-BLAST preferentially detects a signal having the smallest estimated error variance (signal having the smallest error probability) in every sequence. As described above, this detection method has a disadvantage in that the amount of computation is very large.

2 shows a configuration of an apparatus for sequential interference cancellation according to an embodiment of the present invention.

Referring to FIG. 2, the apparatus for sequential interference cancellation includes a detection order determiner 201 that determines a detection order of transmission signals transmitted from M antennas based on a residual error value, and a transmission signal x ₁ corresponding to the determined detection order. A first filter unit 202 for removing interference of a transmission signal other than the transmission signal x ₁ from the received signal by using a first filter coefficient w _{1 for?} ) Other than the transmission signal x ₁ A first decoding unit 203 which decodes the received signal y ₁ from which the interference of other transmission signals is removed, and removing the transmitted signal x ₁ from the received signal y by using the decoded signal. 1 remover 204, from the received signal from which the transmission signal x ₁ has been removed using the second filter coefficient w ₂ corresponding to the transmission signal x ₂ corresponding to the next detection order. x ₂₎ a second filter unit 205 and the transmission to eliminate the interference from other transmission signals other than No. (x ₂₎ and a second decoding unit 206 for decoding the received signal (y ₂₎ interfere with the removal of the other transmission signals other than.

If the number of transmitting antennas M is 3 or more, the sequential interference eliminating apparatus removes the x ₁ and x ₂ from the received signal y and detects a transmission signal other than the x ₁ and x _2. The decoding block 207 is further included.

In this case, the third decoding block 207 includes a second remover 208, a first remover 209, a third filter unit 210, and a third decoder 211. Since each of these functions 207 to 211 performs the same functions as the first eliminator 204, the second filter unit 210 and the second decoding unit 206, the detailed description of these functions will be described. Omit.

As described above, compared to the V-BLAST method, the sequential interference cancellation apparatus according to the embodiment of the present invention has a different detection order of the transmission signal, and an equalization coefficient (MMSE filter coefficient) for interference nulling It can be seen that there is a difference.

The detection order determiner 201 determines the detection order of the transmission symbol vectors according to the method shown in FIG.

3 illustrates a signal detection order determination method of a multi-antenna system according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the method of determining a signal detection order may include receiving transmission signals transmitted from M antennas (S301), calculating residual error values for each of the received transmission signals (S302), and calculating the residuals. Determining the detection order of the transmission signal according to the error value (S303).

That is, the transmission signal detection method according to an embodiment of the present invention is represented by Equation 5 below.

[Equation 5]

는 임의로 선택될 수 있는 설계상수(weighting factor) 이고,

는 다른 신호(

)의 간섭이 완벽하게 제거되었을 때의 전송신호 x_m의 추정 오차 공분산 (estimation error covariance)으로써 하기 수학식 6과 같이 나타낼 수 있다.In Equation 5,

Is a weighting factor that can be chosen arbitrarily,

Is another signal (

) Can be expressed as Equation 6 below as an estimation error covariance of the transmission signal x _m when the interference of?) Is completely removed.

[Equation 6]

은 다른 모든 간섭이 완벽하게 제거된 후에도 줄일 수 없는 x_m의 MMSE 추정치의 오차 공분산을 의미한다. 따라서, 순차 간섭제거의 초기에 이러한 줄일 수 없는 (irreducible) 추정 오차가 큰 신호를 오류없이 제거할 수 있다면 남은 신호들은 줄일 수 없는 추정 오차가 상대적으로 적으므로 전체 신호의 추정 오차 공분산의 합을 줄일 수 있다. 따라서, 수학식 5는 줄일 수 없는 추정 오차가 큰 신호가 설계상수에 따라 가능한 빠른 순차에서 제거가 되어 전체 신호의 추정 오차의 합이 적도록 하여 수신 비트 오류율을 낮추는 작용을 한다. The estimation error

Denotes the error covariance of the MMSE estimate of x _{m that} cannot be reduced after all other interference has been completely removed. Therefore, if a signal having such a large irreducible estimation error can be removed without error at the beginning of sequential interference cancellation, the remaining signals have relatively small estimation errors that cannot be reduced, thereby reducing the sum of the estimated error covariance of the entire signal. Can be. Therefore, Equation 5 serves to lower the received bit error rate by eliminating the signal having a large estimated error that cannot be reduced in the sequential order as quickly as possible according to the design constant so that the sum of the estimated errors of the entire signal is small.

Referring to Equation 5, it can be seen that the embodiment of the present invention can determine the detection order for all M transmission signals in advance, unlike V-BLAST, which determines the sequence separately for each sequence.

In addition, Equation 5 can reduce the amount of calculation as described below because the detection order is predetermined while exhibiting similar performance to the conventional V-BLAST arrangement in Equation 4.

The difference between the present invention and V-BLAST can be better understood through the following examples.

,

,

및

이라 가정한다. For example, M = 2,

,

,

And

Assume that

가 1인 경우 본 발명의 실시예에 따르면 수학식 5에 의하여 x₂을 첫 번째 검출된 신호로 결정함을 알 수 있다.In this example, despite the minimum error covariance of x _{2 in} the entire sequence, the V-BLAST scheme will select x ₁ as the first detected transmission signal by Equation 4 above. But,

In the case of 1, it can be seen that x ₂ is determined as the first detected signal according to Equation 5 according to the embodiment of the present invention.

The filter units 202, 205, and 210 may calculate MMSE filter coefficients according to the method illustrated in FIG. 4.

4 illustrates a method of determining MMSE filter coefficients according to an embodiment of the present invention.

Referring to FIG. 4, factoring the error covariance matrix of the i th transmission signal among the M transmission signals by the Coleskey algorithm (S401 to S403), and nulling by the Coleskey factor of the factored error covariance matrix. Computing a vector (S404, S405) and determining an equalization coefficient for the i-th transmission signal using the calculated nulling vector (S406).

The filter units 202, 205, and 210 determine the coefficients of the MMSE filter using Cholesky decomposition, which will be described later.

First, the error covariance matrix may be factored in Coleskey as shown in Equation 7 below.

[Equation 7]

는 양의 대각 엘리먼트를 갖는 하위 삼각 행렬(unique lower triangular matrix)로써,

의 콜레스키 인수(factor)를 나타낸다.In Equation 7,

Is a unique lower triangular matrix with positive diagonal elements,

Represents the Cholesky factor of.

의 콜레스키 인수분해는 하기 수학식 8과 같이 나타낼 수 있다.Meanwhile,

Cholesky factorization of can be expressed by Equation 8 below.

[Equation 8]

은

의 콜레스키 인수를 나타낸다. In Equation 8

silver

Represents the Coleskey argument of.

When the inverses of both sides of Equation 8 are obtained, Equation 9 can be expressed as follows.

[Equation 9]

는 UL 인수분해에 의한 상위(upper) 삼각 행렬을 나타낸다. In Equation 9,

Denotes an upper triangular matrix by UL factorization.

Accordingly, the MMSE filter coefficients may be expressed as in Equation 10 using Equation 7.

[Equation 10]

이 성립하고

및

이다. In Equation 10,

This holds true

And

to be.

는 하기 수학식 11과 같이 나타낼 수 있다.At this time, the Coleskey factor by the equation (5)

Can be expressed as in Equation 11 below.

[Equation 11]

Using the equations (10) and (11), the MMSE filter coefficients can be obtained.

Thus, it can be seen that the filter coefficient calculation method described above can reduce the complexity compared to the prior art.

For reference, Equation 11 may be verified by the Coleskey algorithm.

Referring to FIG. 4, an embodiment of the present invention obtains MMSE filter coefficients using Equations 3 to 11, and detects a transmission signal according to a detection order.

As described above, the sequential interference cancellation according to the embodiment of the present invention can be summarized as follows.

First, the detection order determiner 201 determines a detection order of a transmission signal according to a residual error value of the received transmission signal.

)를 콜레스키 알고리즘에 의하여 계산한다.Next, the first filter unit 202 selects a first transmission signal in accordance with the determined detection order, and selects a nulling vector for the first transmission signal.

) Is calculated by the Coleskey algorithm.

The first remover 204 may remove interference of a transmission signal other than the first transmission signal from the received signal by using the calculated nulling vector.

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 limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

1 shows a schematic configuration of a multiplex transmission multiple reception system.

2 shows a configuration of an apparatus for sequential interference cancellation according to an embodiment of the present invention.

3 illustrates a signal detection order determination method of a multi-antenna system according to an exemplary embodiment of the present invention.

4 illustrates a method of determining MMSE filter coefficients according to an embodiment of the present invention.

Claims (11)

A detection order determiner that determines a detection order of the first transmission signal and the second transmission signal transmitted from the plurality of antennas based on the residual error value; A first filter unit which removes interference of a transmission signal other than the first transmission signal from the received signal by using a first filter coefficient corresponding to the first transmission signal; A first decoder to decode a received signal from which interference of other transmission signals other than the first transmission signal is removed; A first remover which removes the first transmission signal from the received signal by using the decoded received signal; A second filter unit which removes interference of transmission signals other than the second transmission signal from the reception signal from which the first transmission signal is removed using a second filter coefficient corresponding to the second transmission signal; And And a second decoder to decode a received signal from which interference of other transmission signals other than the second transmission signal is removed. The method of claim 1, The residual error value for the first transmission signal is smaller than the residual error value for the second transmission signal. The method of claim 1, And the first filter coefficient and the second filter coefficient are determined by a Coleskey factor and a nulling vector. The method of claim 3, wherein And the Coleskey factor is a lower triangular matrix with positive diagonal elements. The method of claim 3, wherein And the nulling vector is calculated by [element of first row and column of Cholesky factor] and [conjugated complex function of first column of Cholesky factor]. The method of claim 1, And a third filter unit for removing the first transmission signal and the second transmission signal from the received signal and detecting a transmission signal other than the first transmission signal and the second transmission signal. . The method of claim 1, Detection order of the first transmission signal and the second transmission signal, And a transmission signal having a smaller residual error value is detected in order of transmission signals having the largest residual error value. Receiving transmission signals transmitted from the M antennas; Determining a detection order of a transmission signal according to a residual error value of the received transmission signal; Selecting a first transmission signal according to the determined detection order and calculating a nulling vector for the first transmission signal by a Coleskey algorithm; And And removing interference of a transmission signal other than the first transmission signal from the received signal by using the calculated nulling vector. The method of claim 8, Decoding the interference-received received signal; And removing the interference caused by the first transmission signal from the received signal by using the decoded signal. The method of claim 8, Determining the detection order of the transmission signal, Calculate a residual error value for each of the transmission signals, And detecting the transmission signal having the smallest residual error value in order of the transmission signal having the largest residual error value. The method of claim 8, The nulling vector is calculated by [element of the first row and column of the Coleskey argument] and [conjugate complex function for the first column of the Coleskey argument].

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