KR101378698B1 - Signal control apparatus and method for distributed antenna system - Google Patents

Abstract

A signal processing method in a distributed antenna system, the method comprising: receiving a report of channel state information through a feedback channel and confirming whether a signal combining transmission is necessary using the channel state information value, and combining the signal If transmission is required, calculating the channel reliability and transmitting the calculated signal to the mobile terminal, and if the signal combination transmission is not necessary, transmitting a signal to the mobile terminal using a corresponding transmission antenna, and the signal combination transmission is required In the case where the transmitted signal and the signal-coupled transmission is not necessary, in addition to the transmitted signal, if the additional transmission is necessary, the method may include repeating the series of steps to transmit additional signals.

Signal Coupling, Channel Reliability, STBC, STBC-T

Description

SIGNAL CONTROL APPARATUS AND METHOD FOR DISTRIBUTED ANTENNA SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed antenna system in which a base station (BS) and a relay station (RS) are connected by a wired or dedicated line, and particularly, a reception signal-to-interference and noise of a mobile station (MS). Channel status information reported from MS through feedback channel in BS and RS using Space Time Block Coding (STBC) technology for the purpose of improving Signal to Interference plus Noise Ratio (SINR). The present invention relates to an apparatus and method for selectively performing additional maximum ratio transmission (MRT) signal processing on a transmission signal according to reliability of state information (CSI).

With the rapid overcoming of wireless mobile communication technology, the demand for transmitting and receiving large amounts of information at high speed is also increasing. To this end, a number of distributed antennas have recently been installed in existing cell coverage to solve shadow areas, reduce transmission power, and improve transmission efficiency compared to bandwidth. In particular, wired RS connected to a BS by an optical cable Is used as a distributed antenna, which does not require additional radio resources for transmission and reception of relay and control signals, which is advantageous for high complexity and efficient resource allocation and cooperative signal transmission between distributed antennas.

When the frequency reuse coefficient between BSs and RSs used as distributed antennas is 1, the power of interference signals increases at the coverage boundary of each distributed antenna, which results in a decrease in received signal SINR quality. As a method for mitigating or controlling the interference signal in the coverage boundary area, there is a method of receiving and combining signals transmitted by a plurality of adjacent transmission antennas cooperatively. Commonly known signal combining techniques are open and close loops, depending on whether the CSI value between the transmit and receive antennas estimated by the MS through a specific feedback channel is utilized in the processing of the BS and RS signals. Based on the signal combining technology.

Among the open loop-based signal combining techniques, a maximum ratio combination combining (MRC) scheme that maximizes the SINR when combining signals received through the receiving antennas in a method usable by an MS having a plurality of receiving antennas. Equal Gain Combining (EGC), which matches and combines phases between phases. However, when the MS has a plurality of antennas, there are disadvantages in terms of cost and implementation, as compared to having a plurality of antennas in the base station.

Unlike the open loop-based signal combining scheme, there is a closed loop based signal combining scheme that utilizes the CSI value between the transmit and receive antennas estimated by the MS through a specific feedback channel in the BS and RS signal processing. Higher received signal quality improvements can be expected over loop-based signal combining. Closed loop-based signal combining includes MRT and MRT (Maximum Ratio Transmit) and EGT (Equal Gain Transmission), which perform BS and RS signal processing similar to MRC and EGC received signal processing. Since the aforementioned open loop based signal coupling scheme and the closed loop signal coupling scheme are different from each other in the received signal processing process, when using the two types in combination, the MS should have a receiving module independent of each other. Therefore, this is inefficient in terms of size and cost in the MS implementation, and there is a disadvantage that a reduction in reception performance may be caused by using a reception module different from a signal transmission scheme.

On the other hand, unlike the signal combining method described above, by performing the same reception process on the open loop based transmission signal and the closed loop based transmission signal, a plurality of adjacent signal combining methods that can be utilized in an MS having one antenna are used. Open Loop-based Space Time Block Coding (STBC) and Closed Loop, a method of linearly combining signals received from transmit antennas through different time or frequency transmission resources to improve SINR quality of received signals Based on Space Time Block Coding with maximum ratio Transmission (STBC-T).

The STBC scheme is an open loop-based transmission scheme in which CSI values between transmit and receive antennas are not used when transmitting signals using different transmission intervals in a plurality of transmit antennas, and the STBC-T scheme uses BS CSI values between transmit and receive antennas. And an MRT signal processing process in the existing STBC signal processing process in RS.

Under the assumption that the STBC method and the STBC-T method have the same downlink as the BS and RS signal processing coefficients, the instantaneous SINR uses the CSI value, and the STBC-T, which additionally performs the MRT signal process, is always higher than the STBC value. This is known to be the same or larger, and for this reason the efficient STBC-T method is used. However, in real systems, the error between the signal processing coefficient and the downlink is caused by various factors including the Doppler effect due to the mobility of the MS and the delay of the channel feedback, which causes the performance degradation of the STBC-T. The SINR is smaller than the case used, and the efficiency decreases.

The present invention utilizes a distributed antenna system utilizing a wired RS, and adaptively selects an open loop based or closed green based cooperative signal transmission according to channel environment and signal processing coefficient accuracy in BS and RS. In particular, STBC or STBC-T as the cooperative signal transmission method, in order to use a receiver having an advantage in simplicity of its operation and implementation by always performing the same received signal processing regardless of the signal transmission method in BS and RS. It is intended to provide an apparatus and method for considering the method.

According to an aspect of the present invention, in a signal processing method in a distributed antenna system, a channel state information value is received through a feedback channel, and whether or not signal combining transmission is required using the channel state information value is determined. Checking and transmitting a signal calculated by calculating channel reliability to the mobile terminal when the combined signal transmission is required, and transmitting a signal to the mobile terminal using the corresponding transmit antenna when the combined signal transmission is not required. And transmitting additional signals by repeating the series of steps when additional transmission is required in addition to the transmitted signal when the signal-coupled transmission is required and the transmitted signal when the signal-coupled transmission is not required. It features.

According to another aspect of the present invention, in a signal processing apparatus in a distributed antenna system, a base station and a relay station for calculating a channel reliability and transmitting a signal to a mobile terminal, and a modulation scheme Irrespective of the above, it includes a mobile station which always performs the same demodulation process.

According to the present invention, in cooperative signal transmission using a transmission antenna between a base station and a relay station in a distributed antenna system, an additional signal processing technique is applied in a BS and an RS according to reliability of channel feedback information, thereby improving communication signal quality and system transmission. Expected increase in capacity. In addition, regardless of which signal combining technique is used at the transmitting end, the mobile station always performs the same demodulation process, thereby simplifying the mobile terminal implementation and its operation.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be appreciated that those skilled in the art will readily observe that certain changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims. To those of ordinary skill in the art.

As mentioned in the related art, the STBC scheme and the STBC-T scheme are methods for improving the SINR quality of the received signal by linearly combining signals received from different neighboring transmit antennas through different time or frequency transmission resources. The STBC-T method has high efficiency, but in real systems, the error between the signal processing coefficient and the downlink is caused by various factors including Doppler effect due to MS mobility and delay of channel feedback. As a cause of performance degradation of T, there was a problem in that SINR was actually smaller than when STBC was used. Therefore, in order to solve the problems mentioned in the prior art, in the present invention, a new method of adaptively selecting open-loop based or closed-loop distributed antennas according to channel environment and signal processing coefficient accuracy in BS and RS is adaptively selected. Suggest. Hereinafter, the internal configuration of the present invention will be described in detail with reference to the configuration and flow charts.

1 is a schematic diagram illustrating an example of a cellular system using a distributed antenna to which the present invention is applied. FIG. 1 illustrates an example of a distributed antenna system in which six wired RSs are connected to each BS.

1, six RSs are wired to one BS, and neighboring RSs are connected to another BS. The circled area around each RS illustrates coverage including the lowest SINR level that can be transmitted when each RS transmits the signal independently without signal coupling with another RS. The overlapped area between the coverage and the coverage is a region where signal interference is relatively high, and a region in which a large channel quality improvement is expected due to signal coupling between RSs. Multiple MSs are randomly distributed within the cell and transmit and receive signals by configuring all possible combinations of connections between RS and RS and between RS and MS.

2 is a schematic configuration diagram of a cellular system that increases transmission capacity by utilizing signal combining according to an embodiment of the present invention.

Referring to FIG. 2, as a method for applying the STBC or STBC-T signal transmission schemes to a distributed antenna system using wired RS, as shown in FIG. There is a method of cooperative operation using antennas of neighbor BSs and RSs in a system, and as shown in (b) of FIG. 2, BS and RS are independently antennas in a system having BSs and RSs having a plurality of antennas installed therein. There is a method of operating using or cooperatively using the antenna of the neighboring BS and RS. First, as shown in FIG. 2A, a cooperative transmission scheme between a BS and an RS provided with one transmitting antenna will be described as an embodiment.

In the present invention, as a cooperative transmission scheme that can be utilized in a wired RS system to improve the reception signal quality of an MS existing in overlapping areas between respective BS and RS coverages, different time or frequency transmission resources can be obtained from a plurality of adjacent transmit antennas. Consider the STBC and STBC-T signal transmission methods that linearly combine the received signals to improve the SINR quality of the received signal. Looking at the STBC and STBC-T signal transmission method in detail can be represented as follows.

First, the STBC scheme is an open loop based transmission scheme in which CSI values between the transmit and receive antennas are not utilized when transmitting signals using different transmission intervals in a plurality of transmit antennas. The method of obtaining the STBC transmission signal is shown in the following equation.

In Equation 1, each row and column of the S matrix means different antennas and different transmission intervals. When a signal transmitted by the method of Equation 1 is received by the MS through the downlink channel h, the equation for obtaining the received signal for each transmission period t and t + T is as follows.

이고 잡음 성분은

이다. MS에서는 상기 수학식 2의 수신 신호를 활용하여 CSI α, β를 추청하고, 추정된 값을 활용하여 복조과정을 수행하는 수학식을 구성하면 하기와 같다.In Equation 2, the downlink channel CSI is

And the noise component is

to be. In the MS, CSI α and β may be requested using the received signal of Equation 2, and an equation for performing a demodulation process using the estimated value is as follows.

SINR of the signal subjected to the STBC demodulation process in the MS is shown in Equation 4 below.

은 각각 잡음 신호 및 간섭 신호의 평균 전력을 의미한다. 상기에서 설명된 바와 같이 신호 결합은 특히 셀 간 경계 지역에서 주로 요구된다. 이때, 각 송수신 안테나 간 채널의 평균전력이

으로 동일한 경우 상기 수학식 4는 하기의 수학식 5로 정리될 수 있다.In Equation (4)

Denotes the average power of the noise signal and the interference signal, respectively. As described above, signal coupling is primarily required at intercell boundary regions. At this time, the average power of the channel between each transmit and receive antenna

Equation 4 can be summarized as Equation 5 below.

은 잡음 신호 및 간섭 신호 전력의 합을 채널 평균 전력으로 정규화 한 값으로 정의된다. 수학식 5를 이용하여 STBC 방식을 BS 및 RS 신호 전송에 사용할 경우 평균 대역폭 효율을 결정하면 하기의 수학식 6과 같이 나타낼 수 있다.In Equation (5)

Is defined as the normalized sum of the noise and interference signal powers to the channel average power. When the STBC scheme is used for BS and RS signal transmission using Equation 5, the average bandwidth efficiency may be determined as shown in Equation 6 below.

Next, the STBC-T method obtains an improved reception signal quality than the STBC by using an MRT signal processing process in addition to the existing STBC signal processing process in the BS and RS by using the CSI value between the transmitting and receiving antennas. It is a closed loop based signal transmission method. The method of obtaining the STBC-T transmission signal is shown in the following equation.

은 폐 루프를 통해 MS로부터 보고받은 송수신 안테나간 CSI

을 의미한다. 상기 수학식 7을 통하여 송신된 신호가 하향 링크 채널 h를 통과하여 MS에 수신되고, 각 전송 구간 t, t+T별 수신 신호를 구하는 수학식을 하기에 나타내었다.In Equation 7

CSI between transmit and receive antennas reported from MS through closed loop

. A signal transmitted through Equation 7 is received by the MS through the downlink channel h, and an equation for obtaining a received signal for each transmission period t and t + T is shown below.

Equation 8 is a component corresponding to α and β in Equation 3, and it can be seen that the received signal processing processes of STBC and STBC-T are the same in performing a demodulation process as in Equation 3. Therefore, the MS always performs the demodulation process as shown in Equation 3 regardless of the BS and RS signal processing methods.

The SINR of the signal that has undergone the STBC-T demodulation process of Equation 8 in the MS is shown in the following equation.

Using Equation 9, the average bandwidth efficiency for the STBC-T transmission method may be defined as in Equation below.

과 신호처리 계수

간 상호상관과 궤환 채널을 통한 CSI값의 신뢰도를 측정하는 파라미터를 정의하고 수학식으로 나타내면 다음과 같다.The downlink using the STBC and STBC-T signal transmission scheme described in detail above

And signal processing coefficients

Defining a parameter for measuring the reliability of the CSI value through the cross-correlation between the feedback channel and expressed by the equation as follows.

과

를 파라미터로 하여,

를 랜덤하게 생성하는 Monte-Carlo 시뮬레이션을 수행한다. 상기 파라미터 값에 따른 시뮬레이션을 통해 STBC 및 STBC-T의 SINR인 수학식 5와 수학식 7을 계산하고, 이를 통해 수학식 6과 수학식 10을 계산한다. For the determination of the conversion conditions between the STBC and STBC-T proposed in the present invention

and

With parameter as

Perform a Monte-Carlo simulation that generates randomly. Equations 5 and 7 which are SINRs of STBC and STBC-T are calculated through simulation according to the parameter value, and Equations 6 and 10 are calculated through this.

The switching conditions between the STBC and the TSBC-T signal transmission schemes as described below may be represented using the calculated values of Equations 6 and 10.

과 0부터 1범위의 값의 조합에 따라 STBC 신호 전송 방식이 더 우수한 성능을 나타내는 영역(STBC region) 및 STBC-T 신호 전송 방식이 더 우수한 성능을 나타내는 영역(STBC-T region)을 도 3에 도시하였다.By using Equation 12, the range of -20dB to 20dB

And range from 0 to 1 3 shows a region in which the STBC signal transmission scheme performs better (STBC region) and a region in which the STBC-T signal transmission scheme performs better according to a combination of values (STBC-T region).

3 is a graph divided into an STBC region and an STBC-T region according to the efficiency of a transmission scheme according to an embodiment of the present invention. STBC or STBC-T may be selectively used depending on where the combination of values calculated in FIG. 3 belongs. In FIG. 3, a cooperative transmission scheme based on reliability of channel feedback information of a distributed antenna system using a space-time block coding technique proposed by the present invention is applied to an MS existing in a region overlapping each other between coverages of each BS and RS. In addition, the average bandwidth efficiency through simulation is derived as a statistical graph and used for performance analysis.

이 -2dB인 상황을 가정하고, 수학식 11에서 정의한 CSI 신뢰도

를 0부터 1사이의 구간에서 균등 분포를 갖는 확률 변수로 발생시킨다. 수학식 12에 의해서 STBC 및 STBC-T 기법 간의 스위칭 포인트는 도 3에서 확인할 수 있는 바와 같이,

가 0.4인 값으로 결정된다. Referring to FIG. 3, for the simulation, the sum of the noise signal and the interference signal power is normalized to the average power between the transmitting antennas of two adjacent BSs or RSs and the receiving antenna of the MS.

Assume that this situation is -2dB, and the CSI reliability defined in (11)

Is generated as a random variable with an even distribution in the interval between 0 and 1. As shown in Equation 12, the switching point between the STBC and STBC-T schemes can be seen in FIG.

Is determined to be 0.4.

In particular, the MS proposed by the present invention always performs the demodulation process of Equation 3 regardless of which one of the two space-time block coding schemes is used for signal transmission using one reception antenna. Therefore, there is no need to provide hardware to perform MS independent receiving operation as many as the number of transmission signal processing methods. Therefore, there is an advantage in MS implementation in size and price, and different reception according to changes in BS and RS signal processing methods. It can also prevent the time delay caused by the operation of the module and the deterioration of the reception performance due to the misuse of the receiving module.

4 is a flowchart illustrating a signal transmission process from a BS and an RS to an MS according to an embodiment of the present invention.

값을 보고 받는다. 403단계에서 보고 받은 값들을 토대로 신호결합 전송이 필요한지를 선택한 후에 신호결합이 필요하다면 409단계로, 신호결합이 필요하지 않다면 405단계로 진행한다. 먼저 신호결합이 필요하지 않는 경우를 살펴보면, 405단계에서 k번째 송신 안테나를 찾는 수학식을 이용하여 k번째 송신 안테나를 찾은 뒤에 407단계에서 인접 BS 및 RS와의 협조적 전송 없이 k번째 송신 안테나만을 사용하여 신호를 전송하게 된다.Referring to Figure 4, first from the MS through the feedback channel in step 401

Report and receive the value. After selecting whether signal combining is necessary based on the reported values in step 403, the method proceeds to step 409 if signal combining is necessary, and proceeds to step 405 if signal combining is not necessary. First, when signal combining is not required, the k-th transmit antenna is found by using the equation for finding the k-th transmit antenna in step 405, and only the k-th transmit antenna is used in step 407 without cooperative transmission with neighboring BSs and RSs. Send a signal.

를 수학식 11을 사용하여 계산한다. 계산된 채널 신뢰도

와,

를 이용하여 두 값이 STBC 영역에 속하는지 STBC-T 영역에 속하는지를 도 3을 참조하여 판단한다. 만약 STBC 영역에 포함된다면, 413단계로 진행하여 i, j번째 송신 안테나를 사용하여 STBC 신호를 전송하고, STBC-T 영역에 포함된다면, 415단계로 진행하여 i, j번째 송신 안테나를 사용하여 STBC-T 신호를 전송한다.Next, if the signal combination is needed, the channel reliability in step 409

Is calculated using Equation 11. Calculated Channel Reliability

Wow,

It is determined by referring to FIG. 3 whether the two values belong to the STBC region or the STBC-T region using. If it is included in the STBC region, the process proceeds to step 413 to transmit the STBC signal using the i, j th transmit antennas. If it is included in the STBC-T region, the process proceeds to step 415 and the STBC uses the i, j th transmit antenna. -T Send signal.

In step 417, whether or not additional transmission is necessary is determined based on the calculated signal value when signal coupled transmission is required and the calculated signal value when signal coupled transmission is not required. This operation is performed from the beginning, and if no additional transmission is required, the transmitting end signal transmission is terminated.

5 is a graph showing the average bandwidth efficiency of each signal transmission scheme according to an embodiment of the present invention. FIG. 5 illustrates a case in which a signal is always transmitted using one antenna without cooperative transmission with neighboring BSs and RSs, and when STBC signals are always transmitted through the coordination with neighboring BSs and RSs, Each average bandwidth efficiency CDF (Cumulative Distribution Function) graph is shown for the case of STBC-T signal transmission and the case of selecting an optimal signal transmission method according to FIG. 4 which describes the algorithm proposed by the present invention.

Referring to FIG. 5, as a result of analyzing the performance of the signal transmission schemes at the 50% probability point of the CDF, STBC only, STBC-T only, and Proposed Algorithm compared to the average bandwidth efficiency when a signal is transmitted using one antenna It can be seen that the average bandwidth efficiency gains of 30.77%, 33.56% and 40.56% can be obtained, respectively.

Referring to the case of (b) of FIG. 2, when M transmit antennas are installed in each BS or RS, the STBC and STBC-T transmission methods are described as follows.

When two or more transmit antennas are installed in each BS or RS, STBC signal transmission is represented by a matrix having 2M rows. In the present invention, the case where M = 2 (a system in which two transmitting antennas are provided in each BS or RS) is represented by the following equation.

In the case of M = 2 in Equation 13, four rows are represented as a matrix, and as shown in Equation 1, each row and column of the S matrix means different antennas and different transmission intervals.

STBC-T signal transmission is also shown in the following equation, assuming that two or more transmission antennas are installed in each BS or RS and M = 2.

Equation (14) and its function are the same.

In this way, when a plurality of antennas are installed in the BS or RS, it is possible to apply the extension as if a single transmission antenna is installed.

As described above, the configuration and operation of the signal processing apparatus and method in the distributed antenna system according to the embodiment of the present invention can be made. Meanwhile, in the above description of the present invention, a specific embodiment has been described. It can be carried out without departing from the scope of. Accordingly, the scope of the present invention should not be limited by the illustrated embodiments, but should be determined by equivalents of the claims and 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 schematic structural diagram of a cellular system utilizing one or more antennas according to an embodiment of the present invention;

3 is a graph divided into the STBC region and the STBC-T region according to the efficiency of the transmission scheme according to an embodiment of the present invention

4 is a flowchart illustrating a process of transmitting a signal from a base station and a relay station to a mobile terminal according to an embodiment of the present invention.

5 is a graph showing the average bandwidth efficiency of each signal transmission scheme according to an embodiment of the present invention

Claims (9)

In the signal processing method in a distributed antenna system, Receiving and reporting channel state information values through the feedback channel, and checking whether signal combined transmission is necessary using the channel state information values; When the combined signal transmission is required, the channel reliability is calculated and the signal is transmitted to the mobile terminal using the signal transmission method selected according to the calculated reliability. If the combined signal transmission is not required, the signal is transmitted using the corresponding transmission antenna. Transmitting to the mobile terminal, And transmitting the additional signal by repeating the series of steps when additional transmission is required in addition to the transmitted signal when the signal-coupled transmission is necessary or the transmitted signal when the signal-coupled transmission is not required. Signal processing method. The method of claim 1, wherein the channel reliability is A signal processing method comprising calculating a corresponding signal using Equation 15 below.

In Equation 15, h denotes downlink and w denotes a signal processing coefficient. The method of claim 1, wherein the channel reliability is A signal processing method for selecting a signal transmission method between an open loop or a closed loop based distributed antenna according to a channel environment and accuracy of signal processing coefficients at a base station and a relay station. The method of claim 3 wherein the open loop is A signal processing method using an open loop based space-time block coding method in which channel state information between transmit / receive antennas is not utilized. 4. The closed loop of claim 3 wherein the closed loop is A signal processing method using a closed-loop based space-time block coding with maximum ratio transmission method that additionally performs a maximum efficiency transmission signal processing process using channel state information values between transmit and receive antennas. . In the signal processing apparatus in a distributed antenna system, An antenna for transmitting a signal, and configured to perform signal-coupled transmission using at least one antenna in the vicinity of the antenna, Receive the channel state information value through the feedback channel, check whether the signal-coupled transmission is necessary using the channel state information value, When the signal combined transmission is required, the channel reliability is calculated and the signal is transmitted to the mobile terminal using the signal transmission method selected according to the calculated channel reliability. When the signal combined transmission is not necessary, the signal is transmitted using the corresponding transmission antenna. To the mobile terminal, When the signal-coupled transmission is necessary or the additional signal in addition to the transmitted signal when the signal-coupled transmission is not necessary, it is configured to transmit the additional signal by repeating the series of processes. Signal processing apparatus. The method of claim 6, wherein the antenna, And at least one transmit antenna. The method of claim 6, wherein the mobile terminal And a channel state information value is obtained using the transmitted signal, and a demodulation process is performed using the channel state information value. The method of claim 6, wherein the mobile terminal Regardless of whether the base station and the relay station perform modulation in the open-loop based space-time block coding scheme or the closed loop-based space-time block coding scheme, the demodulation process is performed through Equation 16 below. Processing unit.

In Equation 16, r denotes a received signal, α and β denote CSI values, S ₀ and S ₁ denote values of 1 row and 1 column and 2 rows and 1 column of the S matrix for obtaining STBC transmission signals, respectively. Indicates noise component.

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