KR20080028629A - Apparatus and method for receiving a signal in a mobile communication system using multiple input multiple output scheme - Google Patents

Abstract

A signal receiving device in a mobile communication system using an MIMO(Multiple Input Multiple Output) scheme and a method are provided to use a 2-stage ML(Maximum Likelihood) scheme as using a hybrid scheme for an ML scheme according to channel states when an FDFR(Full Diversity Full Rate) scheme is used in the MIMO mobile communication system, thereby minimizing operational complexity as maintaining reception performance. A selector(220) detects a selection parameter for selecting a signal detection scheme to be employed by a signal receiving device among plural signal detection schemes by using a channel matrix, compares the selection parameter with a threshold value, and selects one signal detection scheme of the plural signal detection schemes according to the compared results. A signal detector(240) detects a transmission signal in accordance with the signal detection scheme.

Description

A signal receiving apparatus and method in a mobile communication system using a multi-input multi-output method {APPARATUS AND METHOD FOR RECEIVING A SIGNAL IN A MOBILE COMMUNICATION SYSTEM USING MULTIPLE INPUT MULTIPLE OUTPUT SCHEME}

FIG. 1 is a graph illustrating BER performance in case of using a spatial multiplexing (SM) scheme and an FDFR scheme, particularly a golden code scheme, in a typical MIMO mobile communication system

2 is a diagram illustrating a signal receiving device structure of a MIMO mobile communication system according to an exemplary embodiment of the present invention.

3 is a flowchart illustrating a process of receiving a signal in a signal receiving apparatus of a MIMO mobile communication system according to an embodiment of the present invention.

4 illustrates the BER performance when the FDFR method and the hybrid method are used together in the MIMO mobile communication system, the BER performance when the FDFR method and the ML method are used together, and the BER performance when the SM method and the ML method are used together. A graph

FIG. 5 is a graph illustrating a multiplication reduction rate when a FDFR scheme and a hybrid scheme according to a modulation scheme are used together in a MIMO mobile communication system.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal receiving apparatus and method in a mobile communication system, and more particularly, to a mobile communication system using a multiple input multiple output (MIMO) scheme (hereinafter referred to as 'MIMO'). An apparatus and a method for receiving a signal in a mobile communication system.

The next generation communication system is developing into a mobile communication system for providing a service capable of high-speed, high-capacity data transmission and reception to mobile terminals (MSs). However, unlike the wired channel environment, the wireless channel environment of the mobile communication system has various factors such as multipath interference, shadowing, propagation attenuation, time-varying noise, interference, and fading. This causes an unavoidable error resulting in loss of information.

The loss of information causes severe distortion in the actual transmission signal, thereby degrading the overall performance of the mobile communication system. Accordingly, a diversity scheme is used to remove communication instability due to the fading phenomenon, and the diversity scheme includes a time diversity scheme, a frequency diversity scheme, and an antenna diversity scheme. It is classified into an antenna diversity scheme, that is, a space diversity scheme.

The antenna diversity scheme uses multiple antennas. The antenna diversity scheme includes a reception antenna diversity scheme including a plurality of reception antennas and a transmission antenna diversity scheme and a plurality of transmission antennas. It is classified into a multiple input multiple output (MIMO) method which is applied with receiving antennas and a plurality of transmitting antennas. Here, the MIMO scheme is a kind of space-time coding (STC) scheme, and the STC scheme transmits a signal encoded by a preset encoding scheme using a plurality of transmit antennas. By extending the coding scheme in the time domain to the space domain, a lower error rate is achieved.

In addition, the MIMO mobile communication system uses a full diversity full rate (FDFR) method as a signal transmission scheme. The FDFR method is an open-loop signal transmission method that does not feed back channel quality information (CQI) (hereinafter, referred to as 'CQI'), and maximizes transmission diversity and data rate simultaneously. Has the benefit of In particular, a representative example of an FDFR scheme used in a MIMO mobile communication system in which a signal transmitting apparatus uses two transmitting antennas and a signal receiving apparatus using two receiving antennas is called a golden code (Golden code). Method). Now, the Golden code method will be described.

First, the Golden code method is a method of distributing four symbols in a space-time domain through two transmission antennas during two symbol periods, and may be represented by Equation 1 below.

이다. In Equation 1, x _i (i = 1,2,3,4) represents four transmission symbols,

to be.

In the signal transmission apparatus, the symbols are transmitted in the form as shown in Equation 1 above, and when the maximum likelihood (ML) detector is used in the signal reception apparatus, Diversity gain of 4 corresponding to the product of the numbers is obtained. In the signal receiving apparatus, the received symbol vector may be represented by Equation 2 below.

는

수신 심벌 벡터를 나타내며,

는

송신 심벌 벡터를 나타내며,

는 각 엘리먼트(element)가 평균이 0인 가우시안(Gaussian) 잡음 벡터를 나타내며,

는 유효 채널 행렬로서 하기 수학식 3과 같이 나타낼 수 있다.In Equation 2,

Is

Receive symbol vector,

Is

Transmit symbol vector,

Denotes a Gaussian noise vector where each element has an average of 0,

May be expressed as Equation 3 below as an effective channel matrix.

In Equation 3, h _{i, j} represents a channel coefficient from the j th transmit antenna to the i th receive antenna. A method for detecting a received symbol vector as shown in Equation 2 as a transmission symbol using an ML detector is as shown in Equation 4 below.

=

=

의 길이가 N_T이고, 상기 변조 방식의 차수(order)가 M일 경우 집합 Ψ의 엘리먼트들은 총

개 존재한다. 따라서, 상기 수학식 4에 나타낸 바와 같은 방식을 사용하여 수신 심벌 벡터에서 송신 심벌들을 검출하기 위해서는 동시에

개의 심벌 벡터들을 비교해야만 한다. In Equation 4, Ψ represents a set of all symbol vectors corresponding to the modulation scheme used in the signal transmission apparatus, and transmit symbol vector

If the length of is N _T and the order of the modulation scheme is M, the elements of the set Ψ are total.

Dog exists. Therefore, in order to detect the transmission symbols in the received symbol vector using the scheme as shown in Equation 4 above,

Must compare two symbol vectors.

Thus, when the FDFR scheme is used, its performance can be maximized in terms of transmit diversity and data rate, but the FDFR scheme is based on the use of an ML detector. Therefore, a relatively simple structure such as zero-forcing (ZF) method or minimum mean square error (MMSE) method may be used. When the receiver is used, its gain is reduced, which will be described with reference to FIG. 1.

FIG. 1 illustrates a bit error rate (BER) when a spatial multiplexing (SM) method and an FDFR method, in particular, a golden code method, are used in a general MIMO mobile communication system. Hereinafter referred to as 'BER') is a graph showing the performance.

Referring to FIG. 1, when using a linear receiver such as a ZF receiver and an MMSE receiver, the BER performances of the FDFR scheme and the SM scheme are similar, whereas when the ML detector is used, the FDFR scheme acquires greater diversity gain than the SM scheme. It can be seen that the BER performance is excellent. Therefore, it can be seen that using the ML detector should be used when using the FDFR method.

However, as described above, in the case of the ML detector, a large number of operations are performed simultaneously to detect transmission symbols in a received symbol vector. In particular, the number of symbol vectors to be compared for the transmission symbol detection is the length of the transmission symbol vector. The computational complexity of the ML detector also increases drastically as it increases rapidly with the order of the modulation scheme. Therefore, there is a need for a receiver having a relatively low computational complexity while maintaining the gain of the FDFR scheme.

Accordingly, an object of the present invention is to provide an apparatus and method for receiving a signal when the FDFR scheme is used in a signal transmission apparatus of a MIMO mobile communication system.

Another object of the present invention is to provide a signal receiving apparatus and method for minimizing computational complexity when using the FDFR scheme in a signal transmission apparatus of a MIMO mobile communication system.

Another object of the present invention is to provide an apparatus and method for receiving a signal by selecting a signal reception method according to a channel state when the FDFR method is used in a signal transmission apparatus of a MIMO mobile communication system.

The apparatus of the present invention for achieving the above objects; A signal receiving apparatus of a mobile communication system using a multiple input multiple output scheme, comprising: detecting a selection parameter used to select a signal detection scheme to be used by the signal receiving apparatus from among a plurality of signal detection schemes using a channel matrix; A selector for comparing the selection parameter with a threshold value, and selecting one of the plurality of signal detection methods according to the comparison result, and a signal detector for detecting a transmission signal corresponding to the signal detection method; Include.

The method of the present invention for achieving the above objects; A signal receiving method in a signal receiving apparatus of a mobile communication system using a multiple input multiple output scheme, comprising: a selection parameter used to select a signal detecting scheme to be used by the signal receiving apparatus from among a plurality of signal detecting schemes using a channel matrix Detecting a signal, comparing the selection parameter with a threshold value, selecting a signal detection method among the plurality of signal detection methods according to the comparison result, and transmitting the signal corresponding to the signal detection method. Detecting a signal.

Hereinafter, with reference to the accompanying drawings in accordance with the present invention will be described in detail. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

The present invention provides a signal receiving apparatus and method in a mobile communication system (hereinafter referred to as a 'MIMO mobile communication system') using a multiple input multiple output (MIMO) scheme. Suggest. In addition, the present invention provides a signal receiving apparatus that minimizes the computational complexity when using a full diversity full rate (FDFR) method in a signal transmission apparatus of a MIMO mobile communication system; Suggest a method. The present invention also proposes an apparatus and method for receiving a signal by selecting a signal reception method according to a channel state when the FDFR method is used in a signal transmission apparatus of a MIMO mobile communication system.

In the present invention, when the FDFR method is used in the signal transmission apparatus of the MIMO mobile communication system, the signal reception apparatus selects the signal reception scheme corresponding to the channel state to receive the signal. In the present invention, the signal reception apparatus supports two signal reception methods, that is, a maximum likelihood (ML) method and a two-stage ML method, and when the channel state is relatively good, The signal is received using the two-stage ML method, and when the channel state is relatively poor, the signal is received using the ML method.

은 치환(permutaion, 이하 'permutaion'이라 칭하기로 한다)과 QR 인수 분해(factorization, 이하 'factorization'라 칭하기로 한다)를 통해 하기 수학식 5와 같이 정리할 수 있다.First, the effective channel matrix as described in Equation 3 of the prior art section.

Can be summarized as in Equation 5 through permutaion (hereinafter referred to as 'permutaion') and QR factorization (factorization, hereinafter referred to as 'factorization').

는 유니타리(unitary) 행렬을 나타내며,

이고,

이다.In Equation 5,

Represents a unitary matrix,

ego,

to be.

의 대각(diagonal) 엘리먼트들 r_i,i(i = 1,2,3,4)는 모두 양의 실수이고, 행렬

역시 유니타리 행렬이다. 상기 수학식 5로부터 종래 기술 부분 에 기재한 수학식 2의 양변에

를 곱하여 상기 수학식 2와 등가의 신호 모델을 구성할 수 있으며, 이는 하기 수학식 6에 나타낸 바와 같다.Also, the matrix

Diagonal elements of r _{i, i} (i = 1,2,3,4) are all positive real numbers

It is also a unitary matrix. On both sides of the equation (2) described in the prior art portion from the equation (5)

By multiplying to construct a signal model equivalent to the above equation (2), as shown in the following equation (6).

=

이고,

은

영(zero) 행렬을 나타내며,

이고,

이고,

이다. In Equation 6,

ego,

silver

Represents a zero matrix,

ego,

ego,

to be.

A two-stage ML scheme is proposed to reduce the amount of computation of the receiver from Equation 6, and the transmission symbol detection scheme according to the two-stage ML scheme includes three steps as follows.

로부터 수학식 6의

를 검출한다.(1) Step 1:

From Equation 6

Detect.

를

로부터 제거한다. 이 경우,

로 정리된다.(2) Step 2: Estimated in Step 1

To

Remove from in this case,

It is cleaned up.

로부터 수학식 6의

를 검출한다.(3) Step 3:

From Equation 6

Detect.

에서

로 감소하기 때문에 ML 검출기의 연산량이 크게 감소하게 된다. 일 예로, 변조 차수 M이 64이고(M = 64), 송신 심벌 벡터

의 길이가 N_T가 4일 경우(N_T = 4), 수신 심벌 벡터에서 송신 심벌들을 검출하기 위해서 동시에 비교해야하는 심벌 벡터들의 수가 64⁴ =16777216에서

으로 크게 감소하게 된다. As described above, a method of detecting a transmission symbol through three steps in block units is a two-step ML method. In the two-stage ML method, as described above, since the length of the symbol vectors of the first and third stages is 1/2 of the length of the original symbol vector, the amount of calculation of the ML detector is greatly reduced. That is, the number of comparison targets for detecting the symbol vector

in

Because of this decrease, the computation amount of ML detector is greatly reduced. As an example, the modulation order M is 64 (M = 64) and the transmission symbol vector

If the length of N _T is 4 (N _T = 4), then the number of symbol vectors to be compared at the same time to detect transmit symbols in the received symbol vector is 64 ⁴ = 16777216.

Greatly reduced.

의 대각 엘리먼트들 분포를 상기 선택 파라미터로 제안하며, 이는 하기 수학식 7에 나타낸 바와 같다.However, in the two-stage ML method, the performance deteriorates in a specific channel state. That is, when the channel state has a high spatial correlation or at least one channel state is very poor, the performance may deteriorate. Accordingly, the present invention proposes a hybrid method using a common ML method and the two-step ML method in order to overcome the occurrence of performance degradation in a specific channel state of the two-step ML method. The hybrid method is a method of selectively using the general ML method and the two-step ML method corresponding to the channel state, and in order to use the hybrid method, a selection parameter for the selection is required. In the present invention, the matrix as shown in Equation 5

The diagonal element distribution of is proposed as the selection parameter, as shown in Equation 7 below.

γ =

γ =

의 대각 엘리먼트의 최대값과 최소값의 비를 나타낸다. In Equation 7, γ is a selection parameter, and the selection parameter γ is a matrix

Represents the ratio of the maximum and minimum values of the diagonal element of.

After estimating a channel matrix in the signal receiving apparatus, QR factorization may be performed from the estimated channel matrix to detect the selection parameter γ as shown in Equation (7).

Next, a structure of a signal receiving apparatus of a MIMO mobile communication system according to an embodiment of the present invention will be described with reference to FIG. 2.

2 is a diagram illustrating a signal receiving device structure of a MIMO mobile communication system according to an embodiment of the present invention.

Referring to FIG. 2, the signal receiving apparatus includes two receiving antennas 210-1 and 210-2, a selector 220, a channel estimator 230, and a signal detector 240. The detector 240 includes a two-stage ML detector 241 and an ML detector 243.

First, a signal received through two reception antennas 210-1 and 210-2 is transmitted to the selector 220 and the channel estimator 230. The channel estimator 230 estimates a channel matrix from the signals received through the two reception antennas 210-1 and 210-2, and transmits the estimated channel matrix to the selector 220 and the signal detector 243. Output The selector 220 calculates the selection parameter γ using the channel matrix output from the channel estimator 230. The selector 220 compares the calculated selection parameter γ with a preset threshold γ ₀ to determine whether to use a two-step ML detection method or an ML detection method as a detection method for the received signal. do. Here, when the value of the selection parameter γ is less than the threshold γ ₀ , the selector 220 sends the signal received through the two reception antennas 210-1 and 210-2 to the second stage ML detector 241. When the value of the selection parameter γ is greater than or equal to the threshold γ ₀ , the selector 220 controls the ML detector 243 to receive a signal received through the two reception antennas 210-1 and 210-2. Control to be entered.

The second stage ML detector 241 inputs the signal output from the selector 220 and the channel matrix estimated by the channel estimator 230, and then detects the transmission symbol using a two stage ML scheme. Since the two-stage ML method has been described above, a detailed description thereof will be omitted. In addition, the ML detector 243 inputs the signal output from the selector 220 and the channel matrix estimated by the channel estimator 230, and then detects the transmission symbol using the ML method.

As a result, when the transmission symbol is detected in the received signal in the manner as shown in FIG. 2, the two-step ML method or the ML method is used according to the channel state. In addition, when using the ML method, the FDFR performance can be obtained as it is, thereby improving system performance.

Next, a process of receiving a signal in a signal receiving apparatus of a MIMO mobile communication system according to an embodiment of the present invention will be described with reference to FIG. 3.

3 is a flowchart illustrating a process of receiving a signal in a signal receiving apparatus of a MIMO mobile communication system according to an embodiment of the present invention.

Referring to FIG. 3, in step 311, the signal receiving apparatus estimates a channel matrix using a plurality of signals, for example, signals received through two receiving antennas, and then proceeds to step 313. In step 313, the signal receiving apparatus calculates the selection parameter γ using the estimated channel matrix, and then proceeds to step 315. In step 315, the signal receiving apparatus selects a signal detection method by comparing the calculated selection parameter γ with a threshold value γ ₀ , and proceeds to step 317. Here, the signal receiving apparatus selects a signal detection method as a two-stage ML method when the value of the selection parameter γ is less than the threshold γ ₀ as described in FIG. 2, and the value of the selection parameter γ is the threshold value. If γ _{0 or} more, the signal detection method is selected as the ML method. In step 317, the signal receiving apparatus detects and terminates a transmission symbol in the received signal according to the selected signal detection scheme.

Next, referring to FIG. 4, the bit error rate (BER) performance when the FDFR scheme and the hybrid scheme are used together in the MIMO mobile communication system, and the FDFR scheme and the ML scheme are described. The BER performance when used together and the BER performance when using the spatial multiplexing (SM) method and the ML method together will be described.

4 illustrates BER performance when the FDFR method and the hybrid method are used together in the MIMO mobile communication system, BER performance when the FDFR method and the ML method are used together, and BER performance when the SM method and the ML method are used together. It is a graph shown.

The BER performance graphs shown in FIG. 4 are used by the signal transmitter using two transmit antennas, the signal receiver using two receive antennas, and the transmit power used by each transmit antenna is the same, and is used by each transmit antenna. The modulation schemes are the same, and the BER performance graphs are assumed when the channel is an independent Rayleigh fading channel. Here, the modulation scheme is a quadrature amplitude modulation (4QAM) scheme, and it is assumed that the threshold γ ₀ used in the hybrid scheme is 2.2.

Referring to FIG. 4, the BER performance itself is best when the FDFR method and the ML method are used together, and the BER performance when the FDFR method and the hybrid method are used together is next, and the SM and ML methods are used together. The BER performance of the case is the worst. In particular, the BER performance when using the FDFR method and the hybrid method together is almost similar, since there is only about 0.2 [dB] loss at 10 ^-3 BER compared with the FDFR method and the ML method. .

As described above, when the FDFR method and the ML method are used together, the computational complexity is very high due to the ML method. However, when the FDFR method and the hybrid method are used together, the FDFR method and the ML method are used together. Although slightly degraded in terms of its BER performance, the gain in terms of its computational complexity is high.

Next, referring to FIG. 5, a comparison operation will be described for a reduction ratio of multiplication calculations when the FDFR scheme according to the modulation scheme and the hybrid scheme are used together in the MIMO mobile communication system.

FIG. 5 is a graph illustrating a multiplication reduction rate when a FDFR scheme and a hybrid scheme according to a modulation scheme are used together in a MIMO mobile communication system.

The multiplication reduction ratio performance graph shown in FIG. 5 shows that the signal transmission apparatus uses two transmission antennas, the signal reception apparatus uses two reception antennas, and the transmission power used for each transmission antenna is the same, The modulation schemes used for each antenna are the same, and the multiplication rate reduction ratio performance graphs are assuming that the channels are independent Rayleigh fading channels. Here, the modulation scheme is a 4QAM scheme, and it is assumed that the threshold γ ₀ used in the hybrid scheme is 2.2.

Referring to FIG. 5, it can be seen that as the modulation order increases, the rate of decrease of the product calculation amount increases. As described above with reference to FIGS. 4 and 5, when the FDFR method and the hybrid method are used together, the BER performance is almost similar to that when the FDFR method and the ML method are used together, but the computation amount is greatly reduced, thereby minimizing the computational complexity. ,

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention provides the advantage that the MID mobile communication system uses the two-step ML method and the ML method in a hybrid method according to the channel state, thereby minimizing the computational complexity while maintaining the reception performance. Have

Claims (10)

A signal receiving method in a signal receiving apparatus of a mobile communication system using a multiple input multiple output method, Detecting a selection parameter used to select a signal detection method to be used by the signal receiving apparatus among a plurality of signal detection methods using a channel matrix; Comparing the selection parameter with a threshold value, and selecting one of the plurality of signal detection methods according to the comparison result; Detecting a transmission signal in accordance with the signal detection method. The method of claim 1, The plurality of signal detection methods include a two-step Maximum Likelihood (ML) method and an ML method. Detecting a transmission signal in accordance with the two-step ML method; When the received signal is equal to the following Equation 8,

From Equation 8 below

Estimating process, Estimated

To

Removed from

The process of organizing with

From Equation 8 below

Signal receiving method comprising the step of detecting.

=

In Equation 8,

Indicates a transmission signal,

Represents a Unitary matrix,

ego,

Is,

ego,

silver

Represents a zero matrix,

ego,

ego,

being. The method of claim 2, The selection parameter is the matrix

The signal receiving method, characterized in that the ratio between the maximum value and the minimum value of the diagonal element of. The method of claim 2, The selection parameter is a signal receiving method, characterized in that as shown in the following equation (9).

γ = In Equation 9, γ is a selection parameter, and r _{i, i} (i = 1,2,3,4) is the matrix

Represents the diagonal element of. The method according to claim 3 or 4, Selecting a signal detection method corresponding to the comparison result; And selecting the two-stage ML method when the value of the selection parameter is less than a threshold value, and selecting the ML method when the value of the selection parameter is greater than or equal to a threshold value. In the signal receiving apparatus of a mobile communication system using a multiple input multiple output method, Detecting a selection parameter used to select a signal detection method to be used by the signal receiving apparatus among a plurality of signal detection methods using a channel matrix, comparing the selection parameter with a threshold value, and corresponding to the result of the comparison. A selector for selecting one of the signal detection methods of And a signal detector for detecting a transmission signal corresponding to the signal detection method. The method of claim 6, The plurality of signal detection methods include a two-step Maximum Likelihood (ML) method and an ML method. When the signal detection unit uses the two-step ML method, When the received signal is equal to the following equation 10,

From Equation 10 below

To estimate, Estimated

To

Removed from

To clean up,

From Equation 10 below

Signal receiving apparatus, characterized in that for detecting.

=

In Equation 10,

Indicates a transmission signal,

Represents a Unitary matrix,

ego,

Is,

ego,

silver

Represents a zero matrix,

ego,

ego,

being. The method of claim 7, wherein The selection parameter is the matrix

Signal receiving apparatus, characterized in that the ratio between the maximum value and the minimum value of the diagonal element of. The method of claim 7, wherein Wherein said selection parameter is as shown in Equation (11).

γ = In Equation 11, γ is a selection parameter, and r _{i, i} (i = 1,2,3,4) is the matrix

Represents the diagonal element of. The method according to claim 8 or 9, The selector; And selecting the two-stage ML method when the value of the selection parameter is less than a threshold value, and selecting the ML method when the value of the selection parameter is greater than or equal to a threshold value.

Images