KR20100042027A - Method for cooperative transmission of space-time cyclic delay diversity with adaptive selection - Google Patents

Abstract

PURPOSE: A method for cooperative transmission of space-time cyclic delay diversity with an adaptive selection is provided to transmit data without any burden to an additional receiver in a situation where the number of repeaters is not regular. CONSTITUTION: At least three repeaters are divided into a first group and a second group(S210). If the number of repeaters is an even number, the repeaters are equally divided. If the number of repeaters is an odd number, the repeaters which belong to the second group are one larger than the first group. The repeaters of the first and second groups perform orthogonal space-time block coding for the received data(S220), and delays the circulation of the result codes of the orthogonal time-spatial block coding(S230).

Description

Method for cooperative transmission of space-time cyclic delay diversity with adaptive selection

The present invention relates to wireless communication, and more particularly, in an communication environment such as an ad-hoc network or a mesh network that uses orthogonal frequency division multiplexing (OFDM) and requires low power or low cost. It is about cooperative communication.

The next generation wireless system transmission technology is currently attracting attention is a multi-input input / output (Multi-Input Mutil-output: MIMO system) that can increase the transmission rate and improve the reception performance without increasing the bandwidth by using multiple antennas installed in the transceiver. However, if the size limitation of the terminal or the complexity of the hardware increases and each antenna is not sufficiently spaced apart, the reception performance is considerably degraded due to the spatial correlation between the antennas. Therefore, in order to solve this problem, researches for increasing data transmission rate and improving reception performance between terminals having one antenna have been actively discussed. Cooperative communication is a communication channel-based communication technology that improves reception performance by increasing channel capacity and reducing path loss by using a relay that relays data between a transmitter and a receiver. Recently, many studies have been conducted on cooperative communication using orthogonal space-time block codes and cyclic delay diversity. However, these two technologies have the disadvantage that the transmission rate decreases as the number of repeaters increases or the overall performance decreases.

The technical problem to be achieved by the present invention is that the number of repeaters that can help the transmitter in the cooperative communication is not constant and changes over time, so that even if the number of repeaters is not constant, it is possible to transmit without additional receiver burden. An adaptive selection method for selecting a cooperative communication scheme according to the number of repeaters is provided.

In order to solve the above technical problem, a cooperative transmission method of space-time cyclic delay diversity for adaptive selection according to the present invention comprises: dividing at least three or more repeaters into first to second groups; Performing orthogonal space-time block coding on the data respectively received by the repeaters of the first to second groups; And repeating and outputting the result codes of the orthogonal space-time block coding by the repeaters of the first to second groups, respectively.

As described above, according to the present invention, unlike conventional cooperative communication techniques, reliable communication is possible without being affected by the number of repeaters. And it can be easily applied to the existing communication system, and the optimum communication can be always performed by adaptively selecting the cooperative communication method according to the number of repeaters.

In order to achieve the above technical problem, the present invention takes advantage of the conventional cyclic delay diversity and orthogonal space-time block code scheme. When there are two repeaters, each symbol of the Alamouti code having the maximum diversity and the maximum transmission rate is transmitted as the correct symbol using the cyclic delay diversity, thereby obtaining additional benefits.

일 때, 요구되는 신호 대 잡음비를 중계기의 개수에 따라 보여주는 그래프이다.Hereinafter, an example of a cooperative transmission scheme using space-time cyclic delay diversity according to the present invention will be described in detail with reference to the accompanying drawings. 1 is a block diagram illustrating a configuration of a system to which a space-time cyclic delay diversity cooperative transmission method according to the present invention is applied. 2 is a flowchart illustrating a process of a space time circular delay diversity cooperative transmission method according to the present invention. 3 is a diagram illustrating a code design of a generalized space-time cyclic delay diversity technique, and FIG. 4 is a simplified comparison of three cooperative techniques used for adaptive selection, while FIG. When three, the bit error rate according to the transmission rate of the channel coding is a graph, Figure 6 is a graph comparing the bit error rate according to the signal-to-noise ratio of the channel between the transmitter and repeater when the number of repeaters is three , FIG. 7 and FIG. 8 are graphs comparing bit error rates according to the number of repeaters when each is 20 dB. 9 illustrates a bit error rate based on the results of FIGS. 7 and 8.

Is a graph showing the required signal-to-noise ratio according to the number of repeaters.

Reference is first made to FIG. 1. As shown in FIG. 1, in the present invention, a transmitter 110 for transmitting data, a plurality of repeaters 120 for receiving a signal transmitted from the transmitter, modulating the signal with a proposed code, and a signal transmitted from a plurality of repeaters And a receiver 130 for receiving and estimating original data from the received signal. All transmitters, repeaters and receivers have a single antenna and there is no direct path between the transmitter and receiver to better characterize the cooperative transmission.

2 and 3, a flow of a cooperative transmission method of space-time cyclic delay diversity for adaptive selection according to the present invention will be described. First, the repeaters as shown in FIG. 1 are divided into two groups I and II as shown in FIG. At this time, there should be at least three repeaters. If the number of repeaters is an even number, the split is equally divided. If the number of repeaters is an odd number, the number of repeaters is divided according to Equation 12 below so that one more repeaters belong to the second group than the first group (S210). step).

Next, the repeaters of the first to second groups perform orthogonal space-time block coding on the received data, and have the same orthogonal space-time block coded values for each group (I, II). In this case, the repeaters belonging to the first group constitute codes of the first row and the first column in the first time slot (Time t), and code of the second row and the first column in the second time slot (Time t + T) following the first time slot. And repeaters belonging to the second group constitute codes of the first row and the second column of Equation 2 in the first time slot (Time t), and codes of the second row and the second column in the second time slot (Time t + T). Configure (step S220).

,그리고 제2그룹의 경우

)를 출력하고, 나머지 중계기들은 중계기별로 상이한 지연값을 가지는 코드를 출력(제1그룹의 경우

그리고 제2그룹의 경우

)한다(S230단계).After that, as shown in FIG. 3, the repeaters of the first to second groups output cyclic delays of the result codes of the orthogonal space-time block coding, respectively, and the first repeater for each group is generated without delay (in case of the first group).

And for the second group

), And the other repeaters output codes with different delay values for each repeater (for the first group).

And for the second group

(Step S230).

For easier understanding of the process of the present invention as described above, a look through examples and generally apply. When the number of repeaters is three, the signal received from each repeater in the frequency axis is as follows.

는 송신기-중계기 채널의 주파수 응답이고,

은 평균이 0이고, 분산이

이며, 원형 대칭성 (Circular symmetric)이 있는 복소 백색 가우시안 잡음(AWGN)이다. 그리고 j는 전송되는 심볼 인덱스이고, C는 전송되는 심볼이다. 그리고 중계기에서 아래 수학식 2의 알라무티 코드를 변화하기 때문에 두 개의 심볼만 수신하게 된다.here,

Is the frequency response of the transmitter-repeater channel,

Is 0 and the variance is

And complex white Gaussian noise (AWGN) with circular symmetric. J is a symbol index to be transmitted and C is a symbol to be transmitted. And since the repeater changes the Alamouti code of Equation 2 below, only two symbols are received.

The repeater immediately estimates the transmitter's signal as follows.

는 각각의 중계기

에서 추정한 송신기의 신호를 나타낸다. 그리고 중계기에서 송신기-중계기 채널의 상황을 알고 있다고 가정한다.here

Each repeater

It shows the signal of transmitter estimated by. And it is assumed that the condition of the transmitter-relay channel in the repeater is known.

The signal detected by each repeater is coded according to Equation 4 below.

은 신호

의 순환 지연된 신호를 나타내고 아래의 식으로 구할 수 있다.Here, the horizontal axis represents time, and the vertical axis represents a signal transmitted by each repeater. And signal

Silver signal

It shows the signal of cyclic delay of and can be obtained by the following equation.

는 부반송파의 개수이고

은 그룹내에서 중계기 순서를 나타낸다. here

Is the number of subcarriers

Denotes the repeater order within the group.

Repeater 1 and repeater 2 are coded like a conventional Alamouti code, and repeater 3 sends a cyclic delay to the receiver. Here, due to the diversity gain of the cyclically delayed signal, better performance is achieved than the conventional Alamouti signal.

The receiver receives the coded signal from the repeater as shown in Equation 4, and expresses the signal in the frequency axis as follows.

는 중계기-수신기 채널의 주파수 응답이고, 채널

의 변화는 두 번의 시간 동안 동일하다고 가정한다. 그리고

는 채널의 크기이고,

는 위상이다.here

Is the frequency response of the repeater-receiver channel,

Is assumed to be the same for two times. And

Is the size of the channel,

Is phase.

In repeater 3, the cyclically delayed signal looks like a reflected wave at the receiver and increases the frequency selective characteristic of the channel. For this reason, the same symbol sent from repeater 2 and repeater 3 appears to pass through one synthesized channel and can generally be obtained as follows.

은 동일한 알라무티 코딩된 심볼의 개수이고,

는 전송 파워를 일정하게 유지시키기 위한 표준화 (normalization) 요소이며,

는 합성된 채널을 의미하는 인덱스이다. 이 합성된 채널의 증가된 주파수 선택적 특성 때문에 우리는 채널 코딩을 도입함으로써 주파수 다이버시티를 얻게 된다. 계속 해서 위의 예를 수학식 7에 대입을 하면 신호

의 합성된 채널은 다음과 같다.here

Is the number of identical Alamouti coded symbols,

Is a normalization factor to keep the transmission power constant.

Is an index representing the synthesized channel. Because of the increased frequency selective nature of this synthesized channel, we gain frequency diversity by introducing channel coding. Subsequently, substituting the above example into equation (7) gives the signal

The synthesized channel of is as follows.

So, if we write Equation 5 again:

Here, the receiver estimates the original signal as follows.

The above expression can be summarized as follows.

It can be seen that Equation 11 is the same as the decoding equation of the conventional Alamouti space-time block code. In other words, even if the number of repeaters is increased (three in this example), the space-time cyclic delay diversity technique according to the present invention has two existing receivers without any special change in the receiver using the Alamouti space-time block code. It can be seen that it can be applied. This feature can be very beneficial in compatibility with existing systems.

은 각각의 알라무티 코딩된 심볼의 개수를 나타내고 아래의 수학식 12와 같이 구한다.Reference is again made to FIG. 2. Figure 2 shows the code design of the generalized space-time cyclic delay diversity technique. In the present invention, as described above, as shown in Figure 2 determines the symbols to be transmitted in the repeater according to the number of repeaters. here

Denotes the number of each Alamouti-coded symbol and is obtained by Equation 12 below.

는 중계기의 개수를 나타낸다. 계속해서 도 2에서, 본 발명에 대해서 성능에 많은 영향을 미치는 인자인 순환 지연 요소

가 있다. 최적의 순환 지연 요소는 아래의 수학식 13과 같이 표현된다.here

Represents the number of repeaters. 2, the cyclic delay element, which is a factor that greatly affects performance for the present invention.

There is. The optimal cyclic delay element is expressed by Equation 13 below.

는 항상 0이 다. 즉

이다. 그래서 중계기가 두 개인 경우에 본 발명은 직교 시공간 블록 부호와 같다. 다른 예로 중계기가 네 개이고 FFT (Fast fourier transform) 크기가 512일 때, 다음과 같은 코드 디자인을 같게 되고, 최적의 순환 지연 요소는 256이 된다.Where the cyclic delay component of each Alamuti-coded first signal

Is always zero. In other words

to be. Thus, in the case of two repeaters, the present invention is equal to the orthogonal space-time block code. In another example, with four repeaters and a fast fourier transform (FFT) size of 512, the following code design would be equivalent, with an optimal cyclic delay factor of 256.

This optimal cyclic delay element results in a correlation between adjacent channels in the symbols of each Alamouti coding being zero or small. Therefore, the optimal performance can be obtained by selecting the optimal circulation element.

In practice, the number of repeaters that assist the transmitter in a wireless cooperative repeater system is not fixed and varies over time. However, conventional orthogonal space-time block code or cyclic delay diversity techniques were not suitable because of low throughput or low performance. Therefore, we propose an adaptive selection of three cooperative transmission techniques according to the number of repeaters for the three techniques including the present invention, and a simple comparison is summarized in FIG.

4 provides a brief comparison of the three techniques used for adaptive selection. First, the orthogonal space-time block code shows that the transmission rate decreases as the number of repeaters increases, and that a lot of quasi-static time (a constant time for a channel until all symbols are transmitted) is required. On the contrary, it can be seen that the cyclic delay diversity technique and the space-time cyclic delay diversity technique do not change the data rate, and the quasi-static time required is not long and fixed. In addition, in terms of complexity, it can be seen from FIG. 4 that the cyclic delay diversity is better because the channel estimation SISO (Single-input Single-ouput) between the repeater and the receiver is easier than the MISO (Multi-input Single-output).

5 to 9 are graphs showing performance improvement and graphs showing factors influencing performance according to the present invention. 5 through 8 represent the bit error rate, and the horizontal axis represents the signal-to-noise ratio of the signal transmitter-receiver channel. In contrast, the vertical axis of FIG. 9 represents a required signal-to-noise ratio, and the horizontal axis represents the number of repeaters. In the simulation, for fair comparison with non-cooperative communication, we assumed the sum of the total signal power and the power of each repeater's signal, and the time and frequency synchronization and channel estimation were assumed to be perfect. In addition, it is assumed that the channel experienced from each repeater to the receiver is independent. In the simulation, the FFT size is 256, the guard interval is 64, and the convolutional code is 1/3. The cyclic delay component is optimally determined according to Equation 12, and passes through a Rayleigh channel having eight passes, and a four phase shift modulation technique (QPSK) is used. Finally, each repeater has one antenna and relays it after the decoding (DF) method.

4 shows the bit error rate according to the transmission rate of channel coding when the number of repeaters is three. As the data rate increases, the performance difference between cooperative orthogonal space-time block codes and space-time cyclic delay diversity decreases. When you select a code rate of 1/4, you get approximately 0.4 dB more gain than when you select a code rate of 1/2. The reason is that the space-time cyclic delay diversity technique obtains the diversity by the frequency selective characteristic of the synthesized channel in addition to the coding gain by the channel coding.

이라고 정의 한다.

의 감소는 시스템의 성능에 상당히 나쁜 영향을 미치는 것을 볼 수 있다. 이는 중계기에서 송신기의 신호를 검출하는 과정에서 오류의 확률이 높기 때문이다. 그리고

에 따른 순환 지연 다이버시티와 직교 시공간 블록 부호의 성능차이도 다른 것을 볼 수 있다. 순환 지연 다이버시티의 성능차이가 직교 시공간 블록 부호의 성능 차이 보다 적은 것을 보게 되는데 그 이유는 중계기와 수신기 사이의 합성된 채널의 심한 페이딩에 빠질 수 있는 가능성이 직교 시공간 블록 부호의 MISO채널 보다 적기 때문이다.

이 20 dB일 때 이상적인 성능을 보이는 것을 볼 수 있고, 우리는 중계기를 선택할 때 송신기와 중계기의 채널 상태가 중요한 요소가 되는 것을 도 6을 통해서 알 수 있다. 6 shows the bit error rate according to the signal-to-noise ratio of the channel between the transmitter and the repeater when the number of repeaters is three. In the present invention, the signal-to-noise ratio of the transmitter and repeater channels is higher than the signal-to-noise ratio of the transmitter and receiver channels.

It is defined as.

It can be seen that the decrease of s significantly affects the performance of the system. This is because the probability of error is high in the process of detecting the signal of the transmitter in the repeater. And

The difference in performance between the cyclic delay diversity and the orthogonal space-time block code is also different. We see that the performance difference of cyclic delay diversity is less than the performance difference of orthogonal space-time block code, because the possibility of falling into severe fading of synthesized channel between repeater and receiver is less than that of MISO channel of orthogonal space-time block code. to be.

It can be seen that the ideal performance is shown at 20 dB, and we can see from Fig. 6 that the channel condition of the transmitter and repeater is an important factor when selecting a repeater.

이 20 dB 일 때의 협동 순환 지연 다이버시티와 직교 시공간 블록 부호와 시공간 순환 지연 다이버시티의 중계기 개수에 따른 비트 오류율은 보여준다. 쉬운 비교를 위해서 송신기와 중계기 사이의 전송 시간 지연을 고려하지 않기로 한다. 그리고 전체 전송율을 동일 하게 하기 위해서 중계기가 3, 4개 일 때 4/9의 펑처링된 (punctured) 콘볼루션 코드를 사용하고, 중계기가 5, 6개 일 때 1/2의 펑처링된 (punctured) 콘볼루션 코드를 사용한다. 중계기가 2개 일 때, 직교 시공간 블록 부호가 좋은 성능을 보이는 것을 알수 있고 다른 경우에는 시공간 순환 지연 다이버시티가 가장 좋은 성능을 보이는 것을 알수 있다. 7 and 8

The bit error rate according to the number of repeaters of cooperative cyclic delay diversity, orthogonal space-time block code and space-time cyclic delay diversity at 20 dB is shown. For ease of comparison, we do not consider the transmission time delay between the transmitter and the repeater. In order to make the total transmission rate the same, a punctured convolutional code of 4/9 is used when 3 or 4 repeaters are used, and 1/2 punctured when 5 or 6 repeaters are used. ) Use the convolution code. When there are two repeaters, we can see that the orthogonal space-time block code shows good performance, and in other cases, the space-time cyclic delay diversity shows the best performance.

일 때, 요구되는 신호 대 잡음비를 중계기의 개수에 따라 보여준다. 중계기의 개수가 증가함에 따라 다이버시티 이득이 좋아 지기 때문에 요구되는 신호 대 잡음 비가 줄어드는 것을 알수있다. 그리고 우리는 도 8을 바탕으로 중계기 개수에 따른 적응적 선택을 하게 된다. 중계기가 2개 일 때, 우리는 직교 시공간 블록 부호를 선택하게 되고, 순환 지연 다이버시티보다 2.5 dB의 이득을 얻게 된다. 하지만 다른 경우에 대해서는 시공간 순환 지연 다이버시티 기술이 가장 적은 신호 대 잡음 비를 요구하기 때문에 선택 된다.9 illustrates a bit error rate based on the results of FIGS. 7 and 8.

, The required signal-to-noise ratio is shown according to the number of repeaters. As the number of repeaters increases, the diversity gain improves, thus reducing the required signal-to-noise ratio. And we make an adaptive selection based on the number of repeaters based on FIG. When we have two repeaters, we choose an orthogonal space-time block code, which gives us 2.5 dB of gain over cyclic delay diversity. In other cases, however, the space-time cyclic delay diversity technique is chosen because it requires the least signal-to-noise ratio.

The invention can also be embodied as computer readable code on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, and also in the form of a display by a carrier wave (for example, transmission over the Internet). It includes what is implemented. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the above-described specific preferred embodiments, and the present invention belongs to the present invention without departing from the gist of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

1 is a block diagram illustrating a configuration of a system to which a space-time cyclic delay diversity cooperative transmission method according to the present invention is applied.

2 is a flowchart illustrating a process of a space time circular delay diversity cooperative transmission method according to the present invention.

3 is a diagram illustrating a code design of a generalized space-time cyclic delay diversity technique,

4 is a simplified comparison of three cooperative techniques used for adaptive selection,

5 is a graph comparing bit error rates according to transmission rates of channel coding when the number of repeaters is three.

6 is a graph comparing bit error rates according to signal-to-noise ratios of channels between a transmitter and a repeater when the number of repeaters is three.

7 and 8 are graphs comparing bit error rates according to the number of repeaters when each is 20 dB.

FIG. 9 is a graph showing the required signal-to-noise ratio according to the number of repeaters when the bit error rate is based on the results of FIGS. 76 and 8.

Claims (5)

Dividing at least three or more repeaters into first to second groups; Performing orthogonal space-time block coding on the data respectively received by the repeaters of the first to second groups; And Cyclically delaying and outputting result codes of the orthogonal space-time block coding, respectively, by the repeaters of the first to second groups; and cooperative transmission method of space-time cyclic delay diversity for adaptive selection. The method of claim 1, wherein the dividing into the first to second groups comprises: If the number of repeaters is even, divide it evenly, If the number of repeaters is an odd number, the cooperative transmission method of space-time cyclic delay diversity with adaptive selection, wherein the second group is partitioned so that one more repeaters belong to the second group. The relay of claim 1, wherein the repeaters belonging to the first group to the second group, respectively, A space-time cyclic delay diversity cooperative transmission method with adaptive selection, characterized in that each group has the same orthogonal space-time block coded values. The method of claim 3, wherein the repeaters perform orthogonal space-time block coding to generate code. Repeaters belonging to the first group constitute codes of a first row and a first column in a first time slot, codes of a second row and a first column in a second time slot following the first time slot, Repeaters belonging to the Group 2 constitute a code of the first row and the second column of Equation 2 in the first time slot, and configure the code of the second row and the second column in the second time slot. Cyclic delay diversity cooperative transmission method. The method of claim 1, wherein the step of delaying outputting The first repeater for each group outputs a code generated without a delay, the remaining repeaters output a code having a different delay value for each repeater adaptive space-time cyclic delay diversity cooperative transmission method.

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