KR100995270B1 - Iterative channel euqualization device based on est in mimo system - Google Patents

Abstract

An iterative channel equalizer based on EST in a MIMO system is disclosed. The disclosed apparatus includes a plurality of receive antennas; A plurality of equalization modules coupled to each receive antenna; And a channel estimator for estimating channel information, wherein each of the plurality of equalization modules receives a space-time encoded signal from a transmitter to perform channel equalization using channel information estimated by the channel estimator and distortion power in a previous iteration. An equalizer to perform, the distortion power is a sum of noise and interference power, an IEST unit performing EST inverse transform on the output signal of the channel equalizer, a determination unit determining a symbol level of the output signal of the IEST unit, An inter-symbol interference canceller that removes the inter-symbol interference component in the next iteration through feedback using the signal determined in the judging unit and the intra-symbol interference component in the next iteration through feedback using the signal determined in the judging unit An intra symbol interference canceller for removing the inter symbol interference canceller and an intra symbol Interference canceller is designed to maximize the signal compared to interference and noise. According to the disclosed apparatus, it is possible to obtain maximum diversity gain and maximum transmission efficiency in a MIMO system while performing repetitive channel equalization based on EST.

Description

Iterative Channel Euqualization Device Based on EST in MIMO System}

The present invention relates to a channel equalizer in a communication system, and more particularly, to an iterative channel equalizer based on an EST for obtaining maximum diversity gain and maximum transmission efficiency in a MIMO system.

In general, wireless channel environments, unlike wired channel environments, are inevitable errors due to various factors such as multipath interference, shadowing, propagation attenuation, time varying noise, and fading. Occurs and information is lost.

Diversity techniques are used to mitigate multipath fading in a wireless communication system, for example, time diversity, frequency diversity, and antenna diversity.

The dual antenna diversity scheme uses multiple antennas. The antenna diversity scheme includes a receive antenna diversity scheme using a plurality of receive antennas and a transmit antenna diversity scheme using a plurality of transmit antennas. And a Multiple Input Multiple Output (MIMO) scheme using a plurality of transmit antennas and a plurality of receive antennas.

Here, the MIMO scheme is a kind of space-time coding (STC) scheme, and the space-time coding scheme encodes transmission data in a predetermined manner and transmits the data using a plurality of transmission antennas, thereby providing a time domain. The diversity effect at can be extended to the space domain to achieve a lower error rate.

In addition, as the demand for high-speed data transmission in a wireless communication service increases, the demand for a full diversity full rate (FDFR) code that can obtain maximum diversity gain while obtaining maximum transmission efficiency using multiple antennas also increases. Doing.

Typical FDFR codes are known as Golden Code and Threaded Algebraic Space Time (TAST) codes. The golden code has the best performance in the MIMO system with two transmit / receive antennas among the known FDFR codes.

However, there is a problem in that Golden code can apply only two transmit / receive antennas to a MIMO system, and a TAST code is developed as a code for obtaining FDFR in a MIMO system having three or more transmit / receive antennas.

The TAST code can obtain the FDFR regardless of the number of transmit / receive antennas, but to obtain the FDFR, an ML (Maximum Likelihood) decoder must be used. Therefore, the complexity increases exponentially as the number of transmit / receive antennas increases.

On the other hand, iterative equalization technique based on EST (Energy Spreading Transform) has been proposed as an iterative equalization technique that can maintain the performance without increasing the complexity in the channel equalization technique. EST is a method of distributing each symbol energy at different frequencies and times, and EST enables repeated signal detection.

However, the proposed EST-based equalization technique has been applied in single input single output (SISO) systems with one transmit / receive antenna. If the number of transmit / receive antennas is multiple, not only channel equalization can be achieved by the EST-based equalization method, but also FDFR cannot be obtained. Therefore, channel equalization technique based on EST that can simultaneously obtain FDFR while sufficient channel equalization is achieved is required.

In order to solve the problems of the prior art as described above, the present invention proposes an iterative channel equalization apparatus based on EST applicable to a MIMO system.

Another object of the present invention is to provide an iterative channel equalizer based on EST for obtaining maximum diversity gain and maximum transmission efficiency in a MIMO system.

Other objects of the present invention will be readily apparent to those skilled in the art through the following examples.

In order to achieve the above object, according to an aspect of the present invention, a plurality of receiving antenna; A plurality of equalization modules coupled to each receive antenna; And a channel estimator for estimating channel information, wherein each of the plurality of equalization modules receives a space-time encoded signal from a transmitter to perform channel equalization using channel information estimated by the channel estimator and distortion power in a previous iteration. An equalizer to perform, the distortion power is a sum of noise and interference power, an IEST unit performing EST inverse transform on the output signal of the channel equalizer, a determination unit determining a symbol level of the output signal of the IEST unit, An inter-symbol interference canceller that removes the inter-symbol interference component in the next iteration through feedback using the signal determined in the judging unit and the intra-symbol interference component in the next iteration through feedback using the signal determined in the judging unit An intra symbol interference canceller for removing the inter symbol interference canceller and an intra symbol The interference canceller is provided with an EST-based iterative channel equalizer in a MIMO system designed to maximize signal-to-signal interference and noise.

Preferably, the determination section performs symbol level determination by soft decision.

The equalization module is provided at the rear end of the determining unit and performs a EST conversion on the delay signal for delaying the symbol determined by the determining unit by a predetermined time interval and the signal converted inversely by the IEST unit with respect to the output signal of the delay unit. The apparatus may further include an EST unit configured to provide an EST converted signal to the inter symbol interference canceller and the intra symbol interference canceller.

The inter-symbol interference canceller and the intra-symbol interference canceller use the output of the equalizer to predict the interference to noise and the noise ratio.

The signal-to-interference and noise ratio predicted by using the output of the equalizer can be estimated by the following equation.

와,

,

,

는 각각 신호의 파워와 인터 심볼 간섭의 파워, 인트라 심볼 간섭의 파워 및 잡음의 파워를 의미함. In the above equation, (i) means the i-th iteration

Wow,

,

,

Are power of signal and power of inter symbol interference, power of intra symbol interference and power of noise, respectively.

The space-time coded signal may be a space-time coded signal by using a layered time space coding scheme.

The equalizer may perform channel equalization by a time response as in the following equation.

는 정규화 파라미터이고

은 안테나에서의 잡음 파워,

은

번째 송신 신호에 대한 채널의 응답이며,

은

번째 신호에 대한 이전 반복에서의 왜곡 파워이고, n은 채널 매트릭스에서의 컬럼을 의미하고, I는 아이덴터티 행렬을 의미함. In the above equation,

Is a normalization parameter

Is the noise power at the antenna,

silver

Response of the channel to the first transmission signal,

silver

The distortion power at the previous iteration for the first signal, n denotes the column in the channel matrix, and I denotes the identity matrix.

The distortion power in the previous iteration is obtained by the following equation using the output signal of the determination unit.

The inter symbol interference canceller and the intra symbol interference canceller perform interference cancellation using a block diagonal matrix and estimated channel information on the equalizer output.

The time response of the inter symbol interference canceller and the intra symbol interference canceller may be set as in the following equation.

인 경우가 인터 심볼 간섭 제거기의 시간 응답이고,

인 경우가 인트라 심볼 간섭 제거기의 시간 응답이며,

로 정의되며, H_j는 추정된 채널 정보이고,

는 등화기 출력의 블록 대각(Diagonal) 행렬이며, m(

)는 대각(Diagonal) 행렬

의 대각 엘리먼트들의 평균값임. In the above equation,

Is the time response of the inter symbol interference canceller,

Is the time response of the intra symbol interference canceller,

H _j is estimated channel information,

Is the block diagonal matrix of the equalizer output, where m (

) Is a diagonal matrix

≪ / RTI >

According to another aspect of the invention, a plurality of receiving antennas; A channel estimator for estimating channel information; And a transmission signal obtained by space-time encoding the EST-converted signal combined with each of the receiving antennas, performing channel equalization using the channel information estimated by the channel estimator and the distortion power in the previous iteration, and interfering with the signal through feedback. And a plurality of equalization modules for canceling inter symbol interference and intra symbol interference in the next iteration so that the noise ratio is maximized.

According to the present invention, it is possible to obtain the maximum diversity gain and the maximum transmission efficiency in a MIMO system while performing repetitive channel equalization based on EST.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the EST-based iterative channel equalizer in the MIMO system.

Before describing the channel equalizer according to the present invention, an energy spreading transform (EST) will be described.

1 is a view for explaining the principle of the EST conversion applied to the present invention.

EST is a transformation that disperses the energy of each symbol at different frequencies and at different times. The purpose of dispersion in the frequency domain is to take advantage of frequency diversity. The determination of the symbol is made by the total energy transmitted over the entire bandwidth.

By variance in the time domain, the energy of erroneously determined symbols is distributed to other time bands.

가 잘못 검출된 심볼이고, 시간 도메인 필터가 세 개의 탭 {

}을 가지고 있다고 가정한다. 타임 도메인에서의 분산이 없을 경우, 잘못 검출된 심볼

는

및

의 검출에도 영향을 미친다. Referring to Figure 1

Is an incorrectly detected symbol and the time domain filter has three tabs {

} Assume you have Incorrectly detected symbol if there is no variance in time domain

Is

And

It also affects the detection of.

및

이 중요한 요소일 경우,

에 대한 잘못된 판정은

및

의 검출에 더 큰 간섭을 일으키게 된다. 반면에, 시간 도메인에 대한 분산이 이 루어질 경우 잘못 검출된 심볼 에너지는 블록 전체로 분산된다. EST에 의한 분산은 블록의 모든 심볼의 검출에 영향을 미치지만, 도 1의 (b)에 도시된 바와 같이 시간 도메인 필터에서 포착되는 심볼 에러 에너지는 블록 사이즈 N에 비례해서 줄어들게 된다. 따라서 심볼에 대한 판정 에러가 발생할 확률은 EST를 사용하지 않는 경우에 비해 줄어들게 된다.if

And

Is an important factor,

False verdict against

And

Will cause greater interference in the detection of. On the other hand, if variance is made for the time domain, the erroneously detected symbol energy is distributed throughout the block. The variance due to EST affects the detection of all symbols in the block, but the symbol error energy captured in the time domain filter is reduced in proportion to the block size N, as shown in Fig. 1 (b). Therefore, the probability of occurrence of a decision error for a symbol is reduced compared to the case of not using EST.

Hereinafter, a transmitter and channel equalization apparatus for achieving maximum diversity gain and maximum transmission efficiency and effectively eliminating interference while a system using such an EST transformation can be used in a MIMO environment will be described.

2 is a diagram illustrating a configuration of a transmitter for providing a signal to an iterative channel equalizer based on EST for obtaining maximum diversity gain and maximum transmission efficiency in a MIMO system according to an embodiment of the present invention.

Referring to FIG. 2, a transmitter for providing a signal to a channel equalizer according to an embodiment of the present invention may include an EST unit 200 and a space-time encoder 210.

The transmitting end is a transmitting end of the MIMO system for transmitting signals through a plurality of antennas, the EST unit 200 is provided corresponding to each antenna provided in the transmitting end, the number of the EST unit 200 is equal to the number of antennas of the transmitting end. .

The EST unit 200 converts the energy of each symbol in a transmission signal at different frequencies and at different times. For more detailed information on EST conversion, see the article “Novel iterative equalization based on energy spreading spectrum, proc. of 2004 IEEE International Conf. on commun., Pasir, France, June 2004 / IEEE Trans. Signal Processing, vol 43, no. 1, pp. 190-203, January 2006 ".

The space-time encoder 210 outputs the space-time encoded signals obtained by the EST unit 200 according to a predetermined encoding matrix, and the space-time coded signals are transmitted to the receiver through a plurality of antennas.

According to a preferred embodiment of the present invention, the space-time encoder 210 may perform space-time encoding by a layered space time coding method of performing space-time incubation for each layer.

The space-time encoder 210 may output the final transmission signal by encoding the transmission signal EST-converted by Equation 1 below.

}는 대각(diagonal) 엘리먼트에

이 들어가 있는 정사각형 행렬을 의미하며, N_T는 송신 안테나의 개수를 의미한다. In Equation 1 above, J is a space-time coding matrix and diag {

} For the diagonal element

This means a square matrix that contains, N _T means the number of transmit antennas.

3 is a diagram illustrating a configuration of an iterative channel equalizer based on EST in a MIMO system according to an embodiment of the present invention.

Referring to FIG. 3, an iterative channel equalizer based on EST in a MIMO system according to an embodiment of the present invention includes a plurality of equalization modules 351 and 352, and each equalization module includes an equalizer 300 and an IEST. The unit 302, the determiner 304, the delay unit 306, the EST unit 308, the inter symbol interference canceller 310, and the intra symbol interference canceller 312 and the channel estimator 314 may be included. .

As shown in FIG. 3, the equalization modules 351 and 352 are provided for each reception antenna, and N _T equalization modules are provided for a total of N _T reception antennas.

The transmission signal encoded by the space-time encoder 210 is received by a receiving antenna through a channel, and the equalizer 300 connected to each receiving antenna performs channel equalization on a stream received from the connected antenna.

Each equalizer 300 performs iterative equalization in consideration of inter-symbol interference and intra-symbol interference by obtaining information on the current channel through the channel estimator 314 and measuring the distortion power in the previous iteration.

Here, inter symbol interference means interference caused by another symbol of a stream belonging to the same layer in a space-time encoded signal, and intra symbol interference means interference caused by a symbol belonging to another layer.

로 정의한다. Where the distortion power is the sum of the noise and interference power, and the distortion power from the previous iteration ((i-1) th iteration)

.

According to a preferred embodiment of the present invention, each equalizer 300 performs iterative channel equalization using the channel response and the sum of the distortion powers in the previous iteration for each transmitted signal.

If the time response of the equalizer 300 according to an embodiment of the present invention is expressed by Equation 2, it may be expressed as Equation 2 below.

는 정규화 파라미터이고

은 안테나에서의 잡음 파워,

은

번째 송신 신호에 대한 채널의 응답이며,

은

번째 신호에 대한 이전 반복에서의 왜곡 파워이고, n은 채널 매트릭스에서의 컬럼을 의미하며, I는 아이덴터티 행렬을 의미한다. In Equation 2 above,

Is a normalization parameter

Is the noise power at the antenna,

silver

Response of the channel to the first transmission signal,

silver

The distortion power at the previous iteration for the first signal, n denotes a column in the channel matrix, and I denotes an identity matrix.

The IEST unit 302 performs an EST inverse transform on the EST converted signal at the transmitter, and refers to a recovery operation for distributed symbol energy. The EST inverse transform in the IEST unit 302 is performed in advance in the determination unit 304 for symbol level determination of the received signal.

The signal inversely converted by the IEST unit 302 is input to the determination unit 304, and the determination unit 304 performs symbol level determination. According to a preferred embodiment of the present invention, the determination unit 304 performs the determination on the symbol level by the soft decision. The soft decision method is more desirable to prevent error propagation at low signal-to-noise ratios.

The delay unit 306 delays the symbol determined by the determination unit 304 by a predetermined time interval. The EST unit 314 converts the delayed symbols to the delayed symbols for inter symbol interference cancellation in the inter symbol interference canceller 310 and intra symbol interference cancellation in the intra symbol interference canceller 312. Do this.

As shown in Fig. 3, the channel equalizer of the present invention has a repetitive equalization structure. The inter symbol interference canceller 310 and the intra symbol interference canceller 312 remove the inter symbol interference component for the output signal of the equalizer 300 at the next iteration, and the removal of the inter symbol interference component at this next iteration is Iteratively reduces the inter symbol interference component gradually.

Intra symbol interference canceller 312 removes the intra symbol interference component for the output signal of the equalizer at the next iteration, and the removal of the intra symbol interference component at this next iteration is repeated to gradually reduce the intra component interference component. I'm going. Detailed time response and operation of the inter symbol interference canceller 310 and the intra symbol interference canceller 312 will be described in detail later.

As shown in FIG. 3, the present invention provides a MIMO based channel equalization apparatus based on a conventional EST to remove inter-symbol interference and intra-symbol interference generated in a MIMO system based on an EST that obtains a maximum diversity gain and a maximum data rate. System, and thus, inter-symbol interference canceller and intra-symbol interference canceller operate as a feedback filter in order to effectively remove inter-symbol interference and intra-symbol interference that would otherwise occur.

According to a preferred embodiment of the present invention, the elimination of inter symbol interference and intra symbol interference is designed to maximize signal to interference and noise ratio.

The signal-to-interference and noise ratio of the receiver may be represented by a symbol error rate (SER) as shown in Equation 3 below.

In Equation 3 above, Q means Q-function.

In addition, the inter symbol interference canceller 310 and the intra symbol interference canceller 312 applied to the present invention use the equalizer 300 to perform filtering based on the distortion power of the channel and the previous iteration. It is designed to predict the signal-to-interference and noise ratio of and to maximize the predicted signal-to-interference and noise ratio.

The signal to interference and noise ratio in each iteration predicted using the equalizer 202 may be expressed as Equation 4 below.

와,

,

,

는 각각

번째 신호의 파워와 인터 심볼 간섭의 파워, 인트 라 심볼 간섭의 파워, 잡음의 파워를 의미한다. 각각의 파워는 신호 파워 측정기, 인터 심볼 간섭 파워 측정기, 인트라 심볼 간섭 파워 측정기 및 잡음 파워 측정기를 통해 측정될 수 있다.In Equation 4, (i) refers to the i iteration

Wow,

,

,

Respectively

The power of the first signal, the power of inter symbol interference, the power of intra symbol interference, and the power of noise. Each power may be measured via a signal power meter, an inter symbol interference power meter, an intra symbol interference power meter, and a noise power meter.

The power of the signal, the power of the inter-symbol interference, the power of the intra-symbol interference, and the power of the noise can be expressed by Equation 5, Equation 6, Equation 7 and Equation 8, respectively.

이 필요하다. According to the above-described equations, in order to predict the signal-to-interference and noise ratio in the current iteration, the distortion power in the (i-1) th iteration due to the operation of the iterative equalizer using the output of the equalizer and the soft decision

This is necessary.

를 분석하여 신호 대비 간섭 및 잡음비를 추정한다. (i-1)번째 반복에서의 왜곡 파워인

는 연성 판정으로 나온 수신 신호

를 이용하여 다음의 수학식 9와 같이 구할 수 있다.According to a preferred embodiment of the present invention

Analyze the signal to estimate the interference and noise ratio. distortion power at the (i-1) th iteration

Is the received signal from the soft decision

By using the equation (9) can be obtained.

The inter symbol interference canceller and the intra symbol interference canceller perform interference cancellation using the block diagonal matrix and the estimated channel information on the equalizer output, and using the equation 2, the inter symbol interference canceller and the intra symbol interference canceller are used. Can be set as shown in the following Equation (10).

일 경우가 인터 심볼 간섭 제거기의 시간 응답이다. 여기서,

과

가 동일하다는 것은 레이어드 타임 스페이스 코딩을 이용하는 시공간 부호화기에서 동일한 레이어에 대한 시공간 부호화 신호라는 것을 의미한다. In Equation 10 above, in the above equation

One case is the time response of the inter symbol interference canceller. here,

and

The same means that is a space-time coded signal for the same layer in the space-time coder using layered time-space coding.

일 경우가 인트라 심볼 간섭 제거기의 시간 응답이고,

과

가 동일하지 않다는 것은 레이어드 타임 스페이스 코딩을 이용하는 시공간 부호화기에서 서로 다른 레이어에 대한 시공간 부호화 신호라는 의미이다. Also, in the above equation

Is the time response of the intra symbol interference canceller,

and

That is not the same means that is a space-time coded signal for different layers in the space-time coder using layered time-space coding.

는 다음의 수학식 11과 같이 표현될 수 있다. On the other hand, of the equation (10)

May be expressed as Equation 11 below.

는

번째 신호에 대한 등화기 출력의 블록 대 각(Diagonal) 행렬이며, 이는 다음의 수학식 12와 같이 표현될 수 있다. In Equation 11 above

Is

A block diagonal matrix of the equalizer output for the first signal, which may be expressed as in Equation 12 below.

)는 대각 행렬

의 대각 엘리먼트들의 평균값이며, 이는 다음의 수학식 13과 같이 표현될 수 있다. In addition, m (

) Is a diagonal matrix

It is an average value of diagonal elements of, which may be expressed as Equation 13 below.

1 is a view for explaining the principle of the EST conversion applied to the present invention.

2 is a diagram illustrating a configuration of a transmitter for providing a signal to an iterative channel equalizer based on an EST for obtaining maximum diversity gain and maximum transmission efficiency in a MIMO system according to an embodiment of the present invention.

3 is a diagram illustrating a configuration of an iterative channel equalizer based on EST in a MIMO system according to an embodiment of the present invention.

Claims (12)

A plurality of receive antennas; A plurality of equalization modules coupled to each receive antenna; And A channel estimator for estimating channel information, Each of the plurality of equalization modules, An equalizer which receives a space-time encoded signal from a transmitter and performs channel equalization using the channel information estimated by the channel estimator and the distortion power in a previous iteration, wherein the distortion power is a sum of noise and interference power; An IEST unit performing EST inverse conversion on the output signal of the channel equalizer, A judging section for judging a symbol level of the output signal of the IEST section, An inter-symbol interference canceller for removing the inter-symbol interference component in the next iteration through feedback using the signal determined by the determination unit; An intra symbol interference canceller for removing an intra symbol interference component at a next iteration through feedback using the signal determined by the determination unit, Wherein the inter-symbol interference canceller and the intra-symbol interference canceller are designed to maximize signal-to-interference and noise. The method of claim 1, And the determining unit performs symbol level determination by a soft decision. The method of claim 1, The equalization module, A delay unit for delaying a symbol determined by the determination unit by a predetermined time interval and a EST-converted signal which is inversely converted by the IEST unit with respect to an output signal of the delay unit; And an EST unit providing an EST-converted signal to the intra symbol interference canceller. The method of claim 1, The inter symbol interference canceller and the intra symbol interference canceller predict the interference and the noise ratio to the signal using the output of the equalizer. The method of claim 4, wherein Wherein the signal to interference and noise ratio predicted using the output of the equalizer is predicted according to the following equation: < RTI ID = 0.0 > EST < / RTI >

In the above equation, (i) means the i-th iteration

Wow,

,

,

Are power of signal and power of inter symbol interference, power of intra symbol interference and power of noise, respectively. The method of claim 1, Wherein the space-time coded signal is a space-time coded signal according to a layered time-space coding scheme. The method of claim 6, The equalizer is an iterative channel equalizer based on EST in the MIMO system, characterized in that for performing the channel equalization by the time response as shown in the following equation.

In the above equation,

Is a normalization parameter

Is the noise power at the antenna,

silver

Response of the channel to the first transmission signal,

silver

The distortion power at the previous iteration for the first signal, n denotes the column in the channel matrix, and I denotes the identity matrix. The method of claim 7, wherein The repetitive channel equalizer of the EST in the MIMO system, characterized in that the distortion power in the previous iteration is calculated using the output signal of the determination unit as shown in the following equation.

The method of claim 7, wherein An inter symbol interference canceller and an intra symbol interference canceller perform interference cancellation using a block diagonal matrix of the equalizer output and estimated channel information, and the EST-based iterative channel equalizer in the MIMO system. 10. The method of claim 9, Wherein the time response of the inter-symbol interference canceller and the intra-symbol interference canceller is set according to the following equation: < RTI ID = 0.0 > E < / RTI >

In the above equation,

Is the time response of the inter symbol interference canceller,

Is the time response of the intra symbol interference canceller,

H _j is estimated channel information,

Is the block diagonal matrix of the equalizer output, and m (

) Is a diagonal matrix

Average of the diagonal elements of. A plurality of receive antennas; A channel estimator for estimating channel information; And Receives a transmission signal obtained by space-time encoding the EST-converted signal coupled to each of the receiving antennas, performs channel equalization using the channel information estimated by the channel estimator, and the distortion power in the previous iteration, and provides an interference and And a plurality of equalization modules for canceling inter symbol interference and intra symbol interference in the next iteration such that the noise ratio is maximized. The method of claim 11, Each of the plurality of equalization modules, An equalizer which receives the transmission signal and performs channel equalization using the estimated channel information and the distortion power from a previous iteration; An IEST unit performing inverse EST conversion on the output signal of the equalizer, A judging section for judging a symbol level of the output signal of the IEST section, An inter-symbol interference canceller for removing the inter-symbol interference component in the next iteration through feedback using the signal determined by the determination unit; And an intra symbol interference canceller which removes an intra symbol interference component in a next iteration through feedback using the signal determined by the determination unit.

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