KR20100007132A - Apparatus and method for capacity enhancement in distributed antenna system - Google Patents

Abstract

PURPOSE: An electrical transmission device for increasing capacity and a method in a distributed antenna system are provided to transmit signals between repeater stations by using transmitting antennas according to geographic location of the mobile terminal. CONSTITUTION: A base station predicts a channel state information value. The base station calculates correlation between the channel state information value received report through the feedback channel and the anticipated channel state information value. A repeater station is connected to the base station and wire. The signal is transmitted to the mobile terminal. The mobile terminal measures the received power, and the channel state information, interference and sum total of the noises signal electricity from the neighboring repeater station.

Description

APAPATUS AND METHOD FOR CAPACITY ENHANCEMENT IN DISTRIBUTED ANTENNA SYSTEM}

The present invention relates to a distributed antenna system. In particular, the channel state information is predicted by considering the time-varying characteristics of the downlink channel caused by the feedback delay between the transmitting and receiving terminals according to the geographical position of the mobile terminal and the reception power from the relay station. An apparatus and method for increasing transmission capacity by utilizing transmission signal processing.

Unlike mobile communication systems that transmit and receive data centered on voice signals in the past, current and future mobile communication systems face the need to transmit and receive large amounts of data traffic due to the development of the Internet and multimedia contents. As part of the method to meet these demands, research and development of a mobile communication system with a new structure is being actively conducted. Among them, a method of improving transmission efficiency by utilizing spatial diversity by a plurality of transmitting antennas has attracted great attention. have.

Previous studies on spatial diversity by multiple transmit antennas have focused on obtaining microscopic spatial diversity gain by using multiple antennas in one transmitter and utilizing them. In the case of completely independent characteristics and no interference by foreign cells, it is known to show effective performance in increasing transmission capacity. However, in the actual situation, it is difficult to have completely independent characteristics because many transmitting antennas are installed at a short distance, and in the multi-cell structure of a mobile communication system, its performance is very degraded at the cell boundary region due to the influence of inter-cell interference. Problem occurs. In addition, since a signal must be transmitted by using a plurality of antennas in one transmitting end, the transmission power is reduced in inversely proportional to the number of antennas, resulting in a decrease in reception power.

In order to overcome this problem, there is increasing interest in a distributed antenna system that improves transmission efficiency by utilizing spatial diversity of a plurality of geographically dispersed transmit antennas.

Cooperative signal transmission between a plurality of relay stations in a distributed antenna system utilizes EGC (Equal Gain Combining), MRC (Maximum Ratio Combining), etc., or STBC (Space Time Block Coding) transmission / reception signal in a receiver without additional transmission signal processing It can be implemented through the process. The EGC, MRC or STBC received signal processing is a method in which a mobile terminal estimates downlink channel state information and increases the signal-to-interference and noise ratio of the received signal by using the same. However, the downlink channel state information estimated by the mobile terminal is not used in the transmission signal processing process, and thus this scheme can be classified as an open loop based cooperative transmission between a plurality of relay stations.

Unlike the open loop-based signal combining method, a closed loop-based relay station can obtain additional performance gains by using downlink channel state information estimated by the mobile terminal through a specific feedback channel in transmission signal processing. There is a cooperative signal transmission scheme, and the cooperative signal transmission between multiple closed-loop based relay stations is based on the open loop-based cooperative signaling when the channel state information utilized in the transmitting end signal processing is the same as the actual downlink channel state information. Ensure higher transmission efficiency than transmission. However, in a channel in which time-varying variability exists, an error between channel state information and downlink channel state information used for transmitting signal processing due to channel feedback delay and Doppler effects due to mobility of a mobile terminal occurs. There is a problem that causes a performance deterioration factor of a cooperative signal transmission scheme between a plurality of relay stations.

The present invention utilizes the structural advantages of a distributed antenna system using a wired relay station to independently or cooperatively transmit signals between relay stations using a single or multiple transmit antennas that selectively participate in signal transmission according to the geographical location of the mobile station. An apparatus and method are provided, and an apparatus and method for maximizing a transmission capacity of a distributed antenna system by estimating channel state information in consideration of time-varying down channel in a feedback delay system are provided.

According to one aspect of the present invention, in a method for increasing transmission capacity in a distributed antenna system, a base station (B) transmits a channel state information value of a downlink and interference and noise signal power from a mobile station through a feedback channel. Reporting the sum value, predicting channel state information value to be reported using the reported downlink channel state information value through the feedback channel, and predicting channel state information value of the current downlink It is characterized in that it comprises the process of determining the signal transmission method between the relay station (Remote Station) by applying.

According to another aspect of the present invention, in the apparatus for increasing transmission capacity in a distributed antenna system, a channel state information value is predicted, and a correlation between the predicted channel state information value and the channel state information value reported through the feedback channel is calculated. Base station for determining independent signal transmission and cooperative signal transmission between relay stations, a base station connected to the base station by wire, and transmitting a signal to a mobile terminal and receiving from a neighboring relay station. And measuring a power, estimating channel state information, measuring a sum of interference signal and noise signal power, and reporting the signal to the base station through a feedback channel.

According to the present invention, by using a distributed antenna system to selectively determine the relay station to participate in independent or cooperative transmission according to the geographical position of the mobile terminal, it is possible to select a relay station for optimal transmission efficiency, and channel state information through the feedback channel. By applying the prediction technique, it is possible to improve the quality of the communication signal and the system transmission capacity to improve the performance of the closed loop based cooperative transmission.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific details such as specific components are shown, which are provided to help a more general understanding of the present invention, and the specific details may be changed or changed within the scope of the present invention. It is self-evident to those of ordinary knowledge in Esau.

First, various methods can be applied as a cooperative signal transmission method between a plurality of relay stations using a distributed antenna proposed in the present invention, but a space time block coding (STBC) method as a cooperative signal transmission method between a plurality of relay stations based on an open loop. The present invention will be described by applying a maximum ratio transmission (MRT) scheme as a cooperative signal transmission scheme between a plurality of relay stations based on a closed loop. Hereinafter, with reference to the block diagram showing the internal configuration of the present invention will be described in detail.

1 is a schematic diagram illustrating an exemplary configuration of a cellular system using a distributed antenna to which the present invention is applied. FIG. 1 illustrates a distributed antenna system in which seven relay antennas are connected to a base station by wire.

Referring to FIG. 1, seven relay stations are connected to one base station by wire to form a cell, and cells having the same structure are adjacent to each other. The area indicated by the circle of each relay station indicates the coverage including the lowest SINR (Signal to Interference Ratio) value that can be transmitted when each relay station independently transmits a signal without combining with another relay station. The overlapped area between the coverage and the coverage is an area where signal interference between the relay stations constituting the coverage is severe, and a large channel quality is expected due to cooperative signal transmission between the relay stations. As shown in FIG. 1, a plurality of mobile terminals are distributed in various locations in a cell, and each mobile terminal measures the power of a received signal from a neighboring relay station, and a channel state between a transmitting and receiving antenna between the corresponding relay station and the mobile terminal. Estimate the information value.

As shown in FIG. 1, if the number of participating relay stations is assumed to perform cooperative signal transmission between relay stations including a specific mobile terminal located in one cell, and the number of participating relay stations is included in the upper S of the received power values of the plurality of relay stations Are determined by the relay stations. When the received power values from the relay stations are expressed in the order of P1 and P2 in order of magnitude, the received SINR value in the cooperative signal transmission in which the S relay stations participate is expressed by the following equation.

는 S개의 중계국이 협조적으로 신호를 전송 시 수신 신호 전력을 의미하고,

은 신호 전송에 참여하는 S개의 중계국을 제외한 셀 내 또는 셀 외부의 중계국으로부터의 간섭 신호 및 잡음 신호 전력의 합을 의미한다. 만약, 여러 중계국으로부터 협력적 신호 전송이 아닌, 하나의 중계국으로부터 독립적 신호 전송을 수행하는 경우에 수신 SINR 값은 하기의 수학식과 같다.In Equation 1

Denotes the received signal power when S relays cooperatively transmit signals,

Denotes the sum of the power of the interference signal and the noise signal from the relay station in the cell or outside the cell except the S relay stations participating in the signal transmission. If the independent signal transmission is performed from one relay station instead of the cooperative signal transmission from several relay stations, the received SINR value is expressed by the following equation.

은 신호 전송에 참여하는 하나의 중계국을 제외한 셀 내 혹은 셀 외부 중계국으로부터의 간섭 신호 및 잡음 신호 전력의 합을 의미한다. 이하에서 설명되는 두 실시 예에서는 S의 값을 2로 가정하여 설명한다. In Equation 2, the received signal power may be represented by f1 (P1) = P1 since S is 1,

Denotes the sum of the interference signal and noise signal powers from intra-cell or out-of-cell relay stations except for one relay station participating in signal transmission. In the following exemplary embodiments, the value of S is assumed to be 2 and described.

First, the STBC scheme for cooperative signal transmission between a plurality of open loop based relay stations is a method in which channel state information values between transmit and receive antennas are not utilized when transmitting signals using different transmission intervals in a plurality of transmit antennas. The SINR of the STBC signal transmitted from the first relay station and the second relay station having the upper two power values measured by the mobile terminal is the downlink channel state information value between the first relay station and the second relay station and the mobile station, the first relay station and Through the STBC demodulation process using the sum of the interference signal and the noise signal from the relay stations in the cell or outside the cell except the second relay station can be obtained using the following equation.

In Equation 3, h1 and h2 denote downlink channel state information values between the first relay station, the second relay station, and the mobile terminal, respectively, and P1 and P2 denote power of received signals of the first relay station and the second relay station, respectively.

Next, in the MRT scheme for cooperative signal transmission between a plurality of closed loop-based relay stations, channel state information values between the transmit and receive antennas are used for transmission signal processing when signals are transmitted from the plurality of transmit antennas using the same transmission interval. That's the way. In addition to the values used for the SINR of the STBC signal, the SINR of the MRT signal is obtained by additionally using downlink channel state information between the first relay station, the second relay station, and the mobile station reported through the feedback channel. You can get it.

In Equation 4, the transmission signal processing coefficients W1 and W2 mean downlink channel state information values between the first relay station, the second relay station, and the mobile station reported through the feedback channel, respectively.

If W1 and W2 have the same value as h1 and h2, the received signal SINR value of the MRT method represented by Equation 4 is twice as large as the received signal SINR value of STBC represented by Equation 3. This has a benefit in processing a transmission signal utilizing downlink channel state information of closed loop cooperative signal transmission. However, due to the characteristics of a channel that is actually time-varying, an error may occur between signal downlink channel state information, and in this case, a processing gain of a transmission signal is reduced, and the error is greater than a specific value. In some cases, open loop cooperative signaling has a larger SINR value than closed loop cooperative signaling. Therefore, one of the two cooperative transmission schemes is selected to have a larger SINR value. The switching conditions between the open loop based and the closed loop based cooperative transmission schemes according to the present invention can be changed according to the average power values of P1 and P2, and the average received signal power values of the first relay station and the second relay station in FIG. This case is illustrated as an example.

로 정의하고, 가로축을

을 의미하는 g로 정의하여 두 파라미터에 의한 STBC 및 MRT 전송 방식 간의 전송 효율이 높은 조건을 제시한다. 상관도는 하기의 수학식을 이용하여 구할 수 있다.2 is a graph illustrating a dominant region between a closed loop and an open loop based cooperative transmission scheme according to an embodiment of the present invention. As shown in FIG. 2, the gain may be maximized by selectively selecting an open loop or a closed loop based cooperative transmission scheme according to the SINR value. In Figure 2, the vertical axis is the correlation between the signal processing coefficient W and the downlink channel state information value h

Defined by, and the horizontal axis

It is defined as g which means that the transmission efficiency condition between STBC and MRT transmission method by two parameters is suggested. Correlation can be obtained using the following equation.

Although the number of relay stations participating in the cooperative signal transmission is limited to 2, the average bandwidth efficiency can be obtained to determine the number of relay stations to participate. In the cooperative transmission scheme in which S relay stations participate, the average bandwidth efficiency can be obtained using the following equation.

Using the bandwidth efficiency of Equation 7, the number S of relay stations that a plurality of mobile terminals randomly distributed in a distributed antenna system will participate in for independent or cooperative signal transmission can be obtained using the following equation.

The transmission scheme of the distributed antenna system described above may increase transmission capacity by selecting a transmission scheme having the highest average bandwidth efficiency among independent transmission, open loop based cooperative transmission, or closed loop based cooperative transmission.

On the other hand, when the channel information has the same value, the closed-loop received signal SINR has a value twice as large as that of the open-loop received signal SINR. By considering the channel's time variability, the channel state information can be predicted to reduce the error of the system, thereby making it possible to select a closed loop based cooperative transmission. As a channel state information prediction method proposed by the present invention, a linear prediction method and a minimum mean squared error (MMSE) method will be described as an embodiment.

3 is a graph predicting a channel using a linear prediction method according to an embodiment of the present invention. In FIG. 3, the x axis represents time and the y axis represents channel state information values. In general, the channel state information has a plurality of values, but in the present invention, it is assumed that the channel state information has a real value.

, N2개의 파일럿 심볼을 이용하여 추정한 채널 상태 정보들의 평균 값인

,

과

사이의 간격인 N,

와 예측하고자 하는 채널 상태 정보

간의 거리인 M을 이용하여 미래에 전송하게 될 하향 링크 채널 정보를 1차 직선으로 모델링하고, 이를 통하여

,

,

,

등을 예측한다. 도 3에 도시된 1차 선형 예측 모델을 생성하는 방법을 설명하면, N=N1=N2=Np이고, M=1.5Np일 때, DLi의 Np개의 파일럿 심볼들을 이용하여 추정한 채널 상태 정보들의 평균값을 구하고 이를

값으로 저장한다. 또한 DLi+1의 Np개의 파일럿 심볼들을 이용하여 추정한 채널상태 정보를 평균값을 구하고 이를

값으로 저장한다. 계산된

및

는 도 3에 도시된 바와 같이, 프레임의 중간에 위치한 채널 상태 정보 값들로 활용되며, 이를 이용하여 선형 예측 모델의 기울기를 하기의 수학식을 이용하여 구할 수 있다. Referring to FIG. 3, in the linear prediction method, an average value of channel state information estimated using N1 pilot symbols is used.

, Which is an average value of channel state information estimated using N2 pilot symbols

,

and

N, the interval between

And channel state information to be predicted

Model the downlink channel information to be transmitted in the future using the distance M between the first straight line,

,

,

,

Predict the back. Referring to the method of generating the linear linear prediction model shown in FIG. 3, when N = N1 = N2 = Np and M = 1.5Np, an average value of channel state information estimated using Np pilot symbols of DLi To obtain

Save as a value. In addition, an average value of channel state information estimated using Np pilot symbols of DLi + 1 is obtained and then

Save as a value. Calculated

And

3 is used as channel state information values located in the middle of the frame, and the slope of the linear prediction model can be obtained using the following equation.

를 하기의 수학식을 이용하여 구하면 다음과 같다.Downlink channel state information at the p-th pilot position of DL i +3 using the slope of the linear prediction model calculated in Equation 9

When obtained using the following equation is as follows.

As such, when the linear prediction method is used in a mobile terminal having very low mobility or a frame structure with low feedback delay, high prediction performance can be expected.

4 is a configuration diagram to which a channel prediction method is applied using the MMSE method according to an embodiment of the present invention. 4 illustrates an embodiment of a Wiener filtering channel prediction method using the MMSE criterion that may be used as one of downlink channel state information prediction techniques. 4 is expressed as a matrix equation as follows.

와 같이 결정되며, R 및 p는 하기의 수학식을 통하여 구할 수 있다. In Equation 11, H (n) denotes a predicted channel state information value, W denotes a Wiener filter coefficient, and hd denotes a past downlink channel information value reported from a mobile terminal through a feedback channel. Wiener filter coefficient to satisfy MMSE criterion

It is determined as follows, R and p can be obtained through the following equation.

로 알려져 있고, 수학식 12에서 J0는 zero order Bessel function, fd는 도플러 주파수를 의미한다.In Equation 12, r (t) means the autocorrelation value of the downlink channel. The autocorrelation function of the Rayleigh fading channel, which is typically modeled as a wireless mobile channel,

In Equation 12, J0 denotes a zero order Bessel function and fd denotes a Doppler frequency.

As shown in FIG. 4, the MMSE method is used to predict h (n + 1) by feedback the predicted channel state information value h (n) to an input of a filter. That is, L = 2Np and a method of predicting channel state information of DLi + 3 using channel state information of DLi and DLi + 1 reported to a base station through a feedback channel will be described below.

을 예측한다. 예측된

을 활용하여 hd를 [

, hi+1,Np, hi+1,Np-1, ... , hi,2]와 같이 업데이트하고, h(n)=

을 예측한다. 이와 같은 방법을 계속 반복 수행하여 h(n)=

,

, ... ,

일 때에는 hd는 [

,

, ... , hi+1,2, hi+1,1], [

,

, ... , hi+1,3, hi+1,2], ... , [

,

, ... ,

, hi+1,Np]을 활용하여 예측이 가능하다. First, using hd = [hi + 1, Np, hi + 1, Np-1, ..., hi, 2, hi, 1] and the Wiener filter as shown in Fig. 5, h (n) =

To predict. Predicted

Take advantage of hd [

, hi + 1, Np, hi + 1, Np-1, ..., hi, 2], and h (n) =

To predict. Repeat this method over and over again, h (n) =

,

, ...,

When hd is [

,

, ..., hi + 1,2, hi + 1,1], [

,

, ..., hi + 1,3, hi + 1,2], ..., [

,

, ...,

, hi + 1, Np] can be used for prediction.

The switching condition between the closed loop based and the open loop based cooperative signal transmission method is calculated by calculating the correlation between the channel state information predicted by the channel prediction technique described above and the actual downlink channel state information reported after the feedback delay. It is used as a decision parameter. The correlation between the predicted channel state information value and the actual downlink channel state information value is determined by the following equation.

를 활용하여 폐 루프 기반과 개방 루프 기반 중 하나를 결정하게 된다. 즉 도 2에서 설명되었던 협조적 방식 전환의 두 가지 조건으로 (r,

)를 사용 하는 대신 채널 예측을 통해 도출한 (r,

)을 통하여 폐 루프 혹은 개방 루프 협조적 전송 방식을 결정할 수 있다. 채널 예측의 정확도가 높은 경우에는

대비

값이 크므로, 결과적으로 폐 루프 기반의 협조적 전송 방식이 우세한 영역이 증가하는 효과가 있으며, 이를 통하여 분산 안테나 시스템의 전체적인 전송 용량 증대 효과를 기대할 수 있다. 하기의 채널 예측 기법을 이용하여 신호 전송 방법을 선택하는 과정을 하기의 흐름도를 이용하여 나타내었다.In Equation 13, the closer the correlation value is to 1, the higher the accuracy of the channel prediction technique. Correlation between the predicted channel state information value and the actual downlink channel state information value

We then decide whether to use the closed loop base or the open loop base. In other words, two conditions of the cooperative mode switching described in FIG.

(R, derived from channel prediction, instead of using

) Can determine the closed-loop or open-loop cooperative transmission scheme. If channel prediction is high accuracy,

prepare

Since the value is large, as a result, an area in which a closed loop based cooperative transmission scheme is dominant is increased, thereby increasing the overall transmission capacity of the distributed antenna system. The process of selecting a signal transmission method using the channel prediction method described below is shown using the following flowchart.

5 is a flowchart illustrating a process of selecting a signal transmission method using a channel prediction technique according to an embodiment of the present invention.

Referring to FIG. 5, in step 501, channel state information between the relay station and the mobile station is acquired, and the value is reported to the base station through the feedback channel. In step 503, the sum of the interference signal component and the noise component signal other than the relay station participating in obtaining the channel state information value is reported to the base station through the feedback channel. In step 505, the channel state information is predicted. Here, the channel state information may be predicted using the MMSE method, the linear prediction method, or another prediction method described above. In step 507, it is determined whether there is one or more relay stations participating in obtaining the channel state information. If there is only one relay station, the process proceeds to step 517 to transmit an independent signal using only the relay station without cooperative transmission with an adjacent relay station. If the relay station is not one but many, the process proceeds to step 509 to compare the SINR value of the closed loop cooperative transmission scheme with the SINR value of the open loop cooperative transmission scheme. According to this comparison, if the open-loop based SINR value is larger, the process proceeds to step 511, and if the open-loop based cooperative signal is larger, and if the closed loop-based SINR value is larger, the process proceeds to step 513 and closes. Transmit loop-based cooperative signals. If additional transmission is needed in step 515, the flow returns to the beginning of the flowchart to perform signal transmission. If no additional transmission is required, the flowchart ends.

As described above, the channel prediction method of the present invention is applicable to any frame structure based on a pilot symbol, and uses a TDD scheme and a different frequency transmission interval using different time transmission intervals for the downlink and the uplink. It is also applicable to the FDD scheme.

는 채널 예측 방식의 정확도를 향상하기 위한 방법으로 관련 파라미터를 조절하기 위해서 사용될 수도 있다. 예를 들어, 선형 예측 방식을 사용할 경우, 상관도

에 따라서 채널 추정을 위하여 사용할 N1, N2, N, M의 크기를 적응적으로 변화시킬 수 있으며, MMSE 방식을 사용할 경우에도 상관도

에 따라서 채널 추정을 위해 사용할 필터 길이에 해당하는 L의 크기를 적응적으로 변화시킴으로써 채널 예측 성능을 향상시킬 수 있다. 하기에 채널 예측 기법을 수행하였을 경우를 일 실시 예로 나타내었다.Also, correlation

May be used to adjust related parameters in a way to improve the accuracy of the channel prediction scheme. For example, if you use linear prediction,

The size of N1, N2, N, M to be used for channel estimation can be adaptively changed.

Accordingly, the channel prediction performance can be improved by adaptively changing the size of L corresponding to the filter length to be used for channel estimation. In the following, a channel prediction technique is performed as an example.

6 is a graph illustrating bandwidth efficiency depending on whether channel state information prediction is applied according to an embodiment of the present invention. In FIG. 5, when the channel prediction is ideally performed and when the channel prediction is not performed, the performance of the MRT transmission scheme, which is one of the closed loop based cooperative transmission schemes, is illustrated as bandwidth efficiency. As shown in FIG. 5, a transmission capacity gain of about 0.25bps / Hz can be confirmed at an intermediate value.

7 is a graph illustrating a dominant region between a closed loop and an open loop based cooperative transmission scheme when the channel state information prediction technique is applied according to an embodiment of the present invention. In FIG. 6, FIG. 2 simultaneously shows a case where channel prediction is not applied.

Referring to FIG. 7, the length of the MMSE filter was set to L = 1000 and the parameters of the linear filter were set to N1 = N2 = N = 500 and M = 750 for performance evaluation. As shown in FIG. 6, when the MMSE method is used, the dominant region of the closed loop-based MRT is expanded to about r = 7 dB at ρ = 0.5, and when using the linear prediction method, it is expanded to r = 3 dB. It can be seen. That is, by applying the downlink channel state information prediction technique, the performance of the closed loop based transmission mode can be improved, and since the dominant region of the closed loop based transmission mode is enlarged, it can be seen that the transmission capacity of the overall system is increased.

As described above, the configuration and operation of a transmission capacity increasing apparatus and method in a distributed antenna system according to an embodiment of the present invention can be made. Meanwhile, in the above description of the present invention, a specific embodiment has been described. It may be practiced without departing from the scope of the invention. Therefore, the scope of the present invention should not be defined by the described embodiments, but by the claims and equivalents of the claims.

1 is a schematic diagram illustrating an exemplary configuration of a cellular system using a distributed antenna to which the present invention is applied.

2 is a graph showing a dominant region between a closed loop and an open loop based cooperative transmission scheme according to an embodiment of the present invention.

3 is a graph predicting a channel using a linear prediction method according to an embodiment of the present invention

4 is a configuration diagram to which a channel prediction method is applied using the MMSE method according to an embodiment of the present invention;

5 is a flowchart illustrating a process of selecting a signal transmission method using a channel prediction technique according to an embodiment of the present invention

6 is a graph illustrating bandwidth efficiency depending on whether channel state information prediction is applied according to an embodiment of the present invention.

7 is a graph illustrating a dominant region between a closed loop and an open loop based cooperative transmission scheme when applying channel state information prediction schemes according to an embodiment of the present invention.

Claims (10)

In the transmission capacity increasing method in a distributed antenna system, Receiving, by a base station, reporting a sum of downlink channel state information values and interference and noise signal powers from a mobile station through a feedback channel; Estimating a channel state information value to be reported using the reported downlink channel state information value through the feedback channel; And determining a signal transmission method between relay stations by applying the predicted current downlink channel state information value. The method of claim 1, wherein the reporting of the channel state information value comprises: Measuring, by the mobile terminal, received signal power from neighboring relay stations, and selecting a predetermined number of relay stations in order of receiving signal power from among the measured relay stations in order of good reception; And reporting the channel state information value of the downlink between the selected specific number of relay stations and the mobile station. The method of claim 2, wherein the sum of the interference and noise signal power is And summing the powers of interference signal components and noise signal components coming from inside or outside the cell except for the received signal powers from the selected specific number of relay stations. The method of claim 1, wherein the determining of the signal transmission method between the relay stations is performed. If the number of relay stations participating in signal transmission is one, performing independent signal transmission using only the relay station; If the number of relay stations participating in signal transmission is two or more, performing cooperative signal transmission using the participating two or more relay stations. The method of claim 4, wherein the independent signal transmission and the cooperative signal transmission And obtaining a normalized bandwidth efficiency in consideration of the number of relay stations participating in signal transmission, and determining the number of relay stations participating in the independent signal and the cooperative signal transmission using the bandwidth efficiency. The method of claim 4, wherein the cooperative signal transmission Transmission characterized in that it is divided into open loop cooperative signal transmission in which channel state information values between relay stations are not utilized for transmission signal processing, and closed loop cooperative signal transmission in which channel state information values between relay stations are used for transmission signal processing. Capacity increase method. The method of claim 1, wherein the predicting of the channel state information comprises: A method of estimating a downlink channel state information value to be reported using by using the reported downlink channel state information value and a downlink channel time change value through the feedback channel; . The method of claim 7, wherein And determining a switching condition between the closed loop based and the open loop based cooperative signal transmission method by calculating a correlation between the predicted channel state information and the actual downlink channel state information reported after the feedback delay. , The correlation is obtained by using the following equation.

In Equation 14, h denotes a value of channel state information of an actual downlink,

Means the predicted channel state information value,

Are the h and the

Means the standard deviation of. In the apparatus for increasing transmission capacity in a distributed antenna system, A base station that predicts channel state information values, calculates a correlation between the predicted channel state information values and channel state information values reported through the feedback channel, and determines independent signal transmission and cooperative signal transmission between RSs. and, A relay station connected to the base station by wire and transmitting a signal to a mobile terminal; And a mobile station for measuring received power from neighboring relay stations, estimating channel state information, measuring a sum of interference signal and noise signal power, and reporting the signal to the base station through a feedback channel. Transmission capacity increasing device. The method of claim 9, wherein the base station And selecting one of an open loop based signal burnout mode and a closed loop based signal transmission mode when selecting the cooperative signal transmission.

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