KR101054177B1 - Hybrid Cyclic Delay Diversity Cooperative Communication System Using ODFM and Method thereof - Google Patents

Abstract

The present invention relates to a hybrid cyclic delay diversity cooperative communication system using OFDM and a method thereof. In the hybrid cyclic delay diversity cooperative communication system using OFDM according to the present invention, a transmitter for transmitting a signal based on an orthogonal frequency multiplexing scheme (OFDM) is grouped into a plurality of groups, and cyclically delays a signal received from each group. A plurality of repeaters to transmit, and a receiver for receiving the signals transmitted from the plurality of repeaters through a plurality of antennas, respectively, and estimates the original signal. As described above, according to the present invention, in the cooperative communication method, diversity and multiplexing gain can be simultaneously obtained to perform reliable communication at a high data rate. And it is applicable to the previously installed cooperative communication system, it is not affected by the number of repeaters and according to the number of repeaters can perform optimal communication without the need for additional structural changes in the receiver.

OFDM, Hybrid, Cooperative Communications, Repeaters, Diversity

Description

Hybrid Using OFDM cyclic delay diversity, cooperative communications system and method {HYBRID CYCLIC DELAY DIVERSITY COOPERATIVE COMMUNICATION SYSTEM USING ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING AND METHOD THEREOF}

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

Multi-Input Mutil-output (MIMO system), a next-generation wireless system transmission technology, uses multiple antennas installed at the transceiver to increase transmission rate and improve reception performance without increasing bandwidth. However, due to terminal size or cost limitation, it is difficult to support multiple antennas in most actual wireless communications. Therefore, in order to solve this problem, researches for improving data transmission rate and improving reception performance by making a virtual multi-input / output system in cooperation with each other having a single antenna have been actively discussed.

In cooperative communication, various multiple input / output (MIMO) technologies can be applied to obtain cooperative diversity or multiplexing gain. For high throughput and reliable transmission in cooperative communication, a hybrid STBC transmission technique that can simultaneously obtain the diversity and multiplexing gains can be applied. However, as the number of cooperative repeaters increases, the technology reduces the data rate, requires structural changes in the receiver, and requires complex decoding. In addition, since each repeater requires a specific orthogonal space-time block code design, the repeater cannot apply this technique unless the repeater is equipped with the corresponding encoder.

Therefore, the technical problem to be achieved by the present invention is that it is not necessary to attach a specific encoder to the repeater in a cooperative communication system using OFDM, and reliable transmission that can arbitrarily select the number of repeaters without any additional structural change at the receiving end regardless of the number of repeaters. It is to provide a cooperative communication technique and method for ensuring the security.

A hybrid cyclic delay diversity cooperative communication system using OFDM according to an embodiment of the present invention for achieving the technical problem, the transmitter for transmitting a signal based on the orthogonal frequency multiplexing (OFDM), grouped into a plurality of groups, And a plurality of repeaters for cyclically delaying the signals received from each group, and a receiver for receiving the signals transmitted from the plurality of repeaters through a plurality of antennas, respectively, and estimating the original signal.

The plurality of repeaters may cyclically delay a signal received from each group by using the following equation.

는 시간 t일때 l 번째 중계기에서 순환 지연된 신호이고,

는 각 그룹의 l 번째 중계기의 순환지연 길이이며,

는 부반송파의 개수를 나타내고 k는 부반송파의 인덱스를 나타낸다. here,

Is the cyclically delayed signal at the l th repeater at time t,

Is the cyclic delay length of the l th repeater in each group,

Denotes the number of subcarriers and k denotes the index of the subcarriers.

The cyclic delay length can be expressed by the following equation.

Where L represents the number of repeaters belonging to each group.

Repeaters included in the same group may transmit a signal to the receiver through a channel shown in the following equation.

Where n is the antenna index of the receiver.

The plurality of repeaters may be grouped by the following equation.

과

은 각 그룹에서 그룹핑된 중계기의 개수를 나타낸다. Where M represents the total number of repeaters,

and

Represents the number of repeaters grouped in each group.

The transmitter and repeater may have a single antenna.

In the hybrid cyclic delay diversity cooperative communication method using OFDM according to an embodiment of the present invention, a plurality of repeaters are grouped into a plurality of groups, and the repeaters included in each group are signals based on an orthogonal frequency multiplexing scheme (OFDM). Receiving from the transmitter, the repeater included in each group includes the step of cyclically delaying the signal received in each group, and transmitting the cyclically delayed signal to a plurality of antennas provided in the receiver, respectively.

As described above, according to the present invention, in the cooperative communication method, diversity and multiplexing gain can be simultaneously obtained to perform reliable communication at a high data rate. And it is not necessary to install a specific encoder in the repeater, it is applicable to the previously installed cooperative communication system, it is not affected by the number of repeaters, and according to the number of repeaters to perform optimal communication without the need for additional structural changes in the receiver Can be.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

1 is a diagram illustrating a cooperative communication system using OFDM according to an embodiment of the present invention, and FIG. 2 is an exemplary diagram of a hybrid CDD cooperative communication system using OFDM according to FIG. 1.

As shown in FIG. 1, a cooperative communication system using OFDM includes a transmitter for transmitting data (Source, denoted by “S” in FIG. 1), and a plurality of signals that are transmitted from a transmitter, modulated by a proposed code, and transmitted. A repeater (relay, denoted as "R ₁ , R ₂ ,..., R _M " in FIG. 1), and a receiver receiver that receives signals transmitted from a plurality of repeaters and estimates original data from the received signals ( Destination, denoted by "D" in FIG. 1).

The transmitter and repeater have a single antenna, and the receiver has two antennas for multiplexing gain.

For convenience of explanation, it is assumed that there is no direct path between the transmitter and the receiver to better characterize the cooperative communication.

)을 6개의 중계기(R₁, R₂, R₃, R₄, R₅, R₆)를 통하여 전송한다. In FIG. 2, the number of repeaters is assumed to be 6 for convenience of description. When the number of repeaters is six, the 6 × 2 hybrid cyclic delay diversity (Hybrid CDD) cooperative communication system uses two transmission symbols (

) Is transmitted through six repeaters (R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ ).

According to an embodiment of the present invention, the repeaters are divided into two groups. Therefore, it is assumed that three repeaters R ₁ , R ₂ , and R ₃ correspond to the first group among the six repeaters, and three repeaters R ₄ , R ₅ , and R ₆ correspond to the second group. .

Therefore, each group transmits one symbol using three repeaters using a 3 × 1 cyclic delay diversity scheme.

In six repeaters, the received signal is designed in the following code.

는 각 그룹의 l 번째 중계기의 순환지연 길이를 나타낸다. 가로축은 각각의 중계기가 송신하는 신호를 나타내며, 모든 신호는 동시에 송신된다. 그리고 신호

는 신호

의 순환 지연된 신호를 시간 축에서 표현한 것이고 시간 t일때 l 번째 중계기에서 순환 지연된 신호는 아래와 같이 나타낸다.here

Denotes the cyclic delay length of the l th repeater of each group. The horizontal axis represents the signal transmitted by each repeater, and all signals are transmitted simultaneously. And signal

Signal

The cyclically delayed signal of is expressed on the time axis. At time t, the cyclically delayed signal in the lth repeater is expressed as follows.

는 부반송파의 개수를 나타내고 k는 부반송파의 인덱스이다. here

Is the number of subcarriers and k is the index of subcarriers.

을 순환 지연시켜 수신기(D)로 전송하고, 제2 그룹에 속한 중계기(R₁, R₂, R₃)는 신호

를 수신기(D)로 전송한다. 여기서 순환 지연된 각 신호들은 다이버시티 이득을 획득하므로 보다 신뢰성 있는 전송을 할 수 있게 한다.As shown in equations (1) and (2), the repeaters belonging to the first group (R ₁ , R ₂ , R ₃ ) are signals

Cyclic delay is transmitted to the receiver (D), and the repeaters belonging to the second group (R ₁ , R ₂ , R ₃ )

Is transmitted to the receiver (D). In this case, the cyclically delayed signals acquire diversity gain, thereby enabling more reliable transmission.

In the present invention, the selection of the cyclic delay has a great effect on performance. To select an optimal cyclic delay value, the following equation is used.

는 항상 0이다

. Where L represents the number of repeaters belonging to each group. And the cyclic delay component of the first signal in each group

Is always 0

.

The receiver receives two signals coded as shown in Equation 1 from six repeaters in two antennas. The signal is expressed on the frequency axis as follows.

은 n번째 안테나가 받는 신호를 나타내며,

는 i번째 중계기에서 n번째 수신 안테나 사이의 채널의 주파수 응답이다.

은 평균이 0이고, 분산이

이며, 원형 대칭성 (Circular symmetric)이 있는 복소 백색 가우시안 잡음(AWGN)이다.here

Represents the signal received by the nth antenna,

Is the frequency response of the channel between the nth receive antenna in the i th repeater.

Is 0 and the variance is

And complex white Gaussian noise (AWGN) with circular symmetric.

In each group, one signal is sent to the receiver as a cyclically delayed signal from three repeaters, which look like a reflected wave at the receiver and increase the frequency selective characteristics of the channel. For this reason, the same symbol sent from three repeaters included in the same group appears to pass through one synthesized channel, and can be obtained as follows.

는 전송 파워를 일정하게 유지시키기 위한 표준화(normalization) 요소이며, n은 수신기의 안테나 인덱스이다. Where L is the number of repeaters transmitting the same symbol belonging to each group,

Is a normalization factor for keeping the transmission power constant, and n is the antenna index of the receiver.

Because of the increased frequency selective nature of the synthesized channel, frequency diversity is obtained in the embodiment of the present invention by introducing channel coding.

의 채널은 각각 다음과 같다. Applying Equation 4 to Equation 5 signal transmitted by the repeater

The channels of are as follows.

Therefore, if you write Equation 4 again.

Where the above equation can be transformed into the matrix vector notation:

Equation 8 is the same as 2 × 2 vertical blast (Vertical-BLAST (Bell Labs Layered Space Time), hereinafter referred to as 'V-BLSAT'), and can be represented by a spatial division multiple (SDM) method. have.

In the embodiment of the present invention, even if the number of repeaters is increased, the receiver has a 2x2 V-BLAST type receiver structure in which two symbols are simultaneously transmitted to two receiving antennas regardless of the number of repeaters. Cyclic delay diversity technology transforms a multiple input single output channel (MISO) into the form of a single input single output (SISO).

In the embodiment of the present invention, various V-BLAST decoding algorithms are applied to Equation 8 for signal detection. For example, the zero-forcing method in which noise is not considered is shown in Equation 9.

According to an embodiment of the present invention, as shown in Figure 1 determines the symbols to be transmitted in the repeater according to the number of repeaters. Several repeaters are divided into two groups according to the number, and two symbols are transmitted simultaneously through the repeaters of each group.

개의 중계기를 이용하는 그룹 하나와

개의 중계기를 이용하는 또 다른 그룹으로 두 개의 그룹으로 나눌 수 있다.In the exemplary embodiment of the present invention, the six repeaters have been divided into two groups of three, but the plurality of repeaters is represented by Equation 10.

One group using four repeaters

Another group using two repeaters can be divided into two groups.

Where M represents the total number of repeaters. The general code design of the hybrid CDD cooperative communication scheme of repeaters divided into two groups is as follows.

In practice, the number of repeaters that assist the transmitter in a wireless cooperative repeater system is not fixed and varies over time. Since the number of repeaters participating in cooperative communication affects the overall system performance, the present invention obtains a high diversity gain as the number of available repeaters increases. However, as the number of repeaters varies, no additional structure modification is required at the receiving end. In addition, as the number of antennas in the receiver increases, an additional multiplexing gain can be obtained, thereby increasing the data rate as the number of antennas in the receiver increases.

Table 1 shows a simple comparison between the hybrid STBC cooperative technique, which is a conventional cooperative transmission technique, which can simultaneously obtain multiplexing and diversity gain, and the present hybrid CDD cooperative technique.

First, the hybrid STBC cooperative communication method has a low transmission rate as the number of repeaters increases, and requires a lot of quasi-static time (required quasi stationary time required for the channel to remain constant until all symbols are transmitted). Also, as the number of repeaters changes, the structure of the receiver changes and the decoding complexity of the receiver increases.

On the other hand, in the hybrid CDD cooperative communication method, even if the number of repeaters increases, the data rate does not change and the quasi-static time required is short. In addition, the structure at the receiver does not change, and the complexity is simple compared to the hybrid STBC cooperative communication method. The decoding complexity in the receiver is compared only with the required number of multiplication, and the following Equation 12 is used.

은 송신기가 전송한 심볼의 개수이고

는 준정적 시간이 지난 이후에 수신기가 수신한 총 심볼의 개수이다. 하나의 복소수 곱하기 연산은 4개의 곱셈으로 표현된다.here

Is the number of symbols sent by the transmitter

Is the total number of symbols received by the receiver after the quasi-static time. One complex multiply operation is represented by four multiplications.

Hereinafter, the performance improvement of the hybrid CDD cooperative communication method according to an embodiment of the present invention will be described with reference to FIGS. 3 and 4. 3 and 4 are graphs of the results for the simulations, where the vertical axis represents the bit error rate and the horizontal axis represents the signal-to-noise ratio (SNR) of the signal transmitter-receiver channel.

In the simulation, for the fair comparison with non-cooperative communication, the total signal power and each repeater signal power are equal, the time and frequency synchronization and channel estimation are perfect and each channel is assumed to be independent of each other. It is also assumed that the channels traveling from each repeater to the receiver are independent.

Using the four-phase shift keying technique (QPSK), the FFT size is 512, the guard interval is 128, and the convolutional code with the constraint length of 7 and the transmission rate is 1/3. use. It passes through the Rayleigh channel with eight passes, with each repeater and transmitter having one antenna and the receiver having two antennas. The repeater also relays after decryption in the Hall of Fame (DF) method. The cyclic delay element is optimally determined according to the equation (3).

3 is a graph showing a bit error rate according to the number of repeaters in a hybrid CDD cooperative communication system according to an embodiment of the present invention. Here, in order to more clearly show the performance improvement according to the increase in the number of repeaters, it is assumed that the signal-to-noise ratio of the transmitter and repeater channels (S-R) is 10dB higher than the signal-to-noise ratio of the repeater and receiver channels (R-D). This is because the probability of an error in the process of detecting the transmitter signal in the repeater significantly affects the performance of the system. Therefore, the effect of the number of repeaters cannot be accurately seen. Diversity gain is affected by the number of repeaters, so the Hybrid CDD cooperative technique shows that the system performance improves considerably as the number of repeaters used increases. Therefore, if better performance is required, more repeaters can improve performance.

4 is a graph showing bit error rates of the hybrid CDD cooperative communication method, the hybrid STBC cooperative communication method, and the V-BLAST communication method when the number of repeaters is six. Here, it is assumed that the signal-to-noise ratio of the transmitter and repeater channels (S-R) is the same as the signal-to-noise ratio of the repeater and receiver channels (R-D). In addition, in order to make the total data rate the same as the hybrid CDD cooperative communication method according to an embodiment of the present invention, the hybrid STBC cooperative communication method uses a punctured convolution code of 9/10.

The two hybrid techniques show better performance than the V-BLAST technique because additional diversity gain can be obtained over the existing V-BLAST technique. In the low SNR, the conventional hybrid STBC cooperative technique shows slightly better performance, but the hybrid CDD cooperative communication method according to the embodiment of the present invention narrows the performance difference with the hybrid STBC cooperative communication method as the SNR value increases.

At about 24dB, the hybrid CDD cooperative communication method according to the embodiment of the present invention catches up with the performance of the hybrid STBC cooperative communication method, and at high SNR, the hybrid CDD cooperative communication method has better performance.

The simulation result shown in FIG. 4 also shows the performance when no coding is performed in the hybrid CDD cooperative communication method and the basic V-BLAST method according to the embodiment of the present invention. Since the space-time cyclic delay diversity technique can obtain diversity gain when using channel coding, it can be seen that the hybrid CDD cooperative communication method also cannot obtain additional diversity gain without channel coding.

Hereinafter, the complexity improvement of the hybrid CDD cooperative communication method according to the embodiment of the present invention will be described with reference to FIG. 5.

5 is a graph illustrating the complexity of the hybrid CDD cooperative communication method and the hybrid STBC cooperative communication method according to the prior art according to the number of repeaters. 5 is a result graph for the simulation, where the vertical axis is the number of multiplication operations per symbol representing complexity, and the horizontal axis is the number of repeaters.

As can be seen from the simulation, when the number of repeaters used for transmission is 4 and 6, the hybrid CDD cooperative technique of the present invention can reduce the complexity by 73% and 93%, respectively, compared with the conventional hybrid STBC cooperative technique. In addition, as the number of repeaters increases, the hybrid STBC cooperative technique requires a more complex receiver structure, and the number of multiplication operations per symbol increases, but the hybrid CDD cooperative technique has complexity at the same receiver regardless of the increase in the number of repeaters. Therefore, the hybrid CDD cooperative technique of the present invention exhibits its advantages over conventional techniques as more repeaters are used.

As described above, according to the embodiment of the present invention, in the cooperative communication method, diversity and multiplexing gain can be simultaneously obtained to perform reliable communication at a high data rate. And it is applicable to the previously installed cooperative communication system, it is not affected by the number of repeaters and according to the number of repeaters can perform optimal communication without the need for additional structural changes in the receiver.

On the other hand, the cooperative communication method using the above-described OFDM, is implemented as a computer-readable code / instructions (instructions) / program. For example, the method may be implemented in a general-purpose digital computer for operating the code / instructions / program using a computer-readable recording medium. The computer-readable recording media may include magnetic storage media (ex, ROM, floppy disk, hard disk, magnetic tape, etc.), optical reading media (ex, CD-ROM, DVD, etc.) and carrier waves (ex, transmission via the Internet). Storage media, and the like. In addition, embodiments of the present invention may be implemented as a medium (s) containing computer readable code, such that a plurality of computer systems connected via a network can be distributed and processing operations. It is obvious that the functional programs, codes and code segments realized by the method of the present invention can be easily inferred by programmers in the technical field to which the present invention belongs.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 is a diagram illustrating a cooperative communication system using OFDM according to an embodiment of the present invention.

2 is an exemplary diagram of a hybrid CDD cooperative communication system using OFDM according to FIG. 1.

3 is a graph showing a bit error rate according to the number of repeaters in a hybrid CDD cooperative communication system according to an embodiment of the present invention.

4 is a graph showing bit error rates of the hybrid CDD cooperative communication method, the hybrid STBC cooperative communication method, and the V-BLAST communication method when the number of repeaters is six.

5 is a graph illustrating the complexity of the hybrid CDD cooperative communication method and the hybrid STBC cooperative communication method according to the prior art according to the number of repeaters.

Claims (10)

In a hybrid cyclic delay diversity cooperative communication system using OFDM, A transmitter for transmitting a signal based on an orthogonal frequency multiple division scheme (OFDM), A plurality of repeaters which are grouped into a plurality of groups and cyclically delay and transmit the signals received from each group; and It includes a receiver for receiving the signals transmitted from the plurality of repeaters through a plurality of antennas to estimate the original signal, respectively, And said transmitter and repeater have a single antenna. The method of claim 1, The plurality of repeaters, Hybrid cyclic delay diversity cooperative communication system for cyclically delaying the signals received from each group using the following equation:

here,

Is a signal that is cyclically delayed at the l th repeater at time t,

Is the cyclic delay length of the l th repeater in each group,

Denotes the number of subcarriers and k denotes the index of the subcarriers. The method of claim 2, The cyclic delay length is a hybrid cyclic delay diversity cooperative communication system represented by the following equation:

Where L represents the number of repeaters belonging to each group. The method of claim 3, wherein A hybrid cyclic delay diversity cooperative communication system for transmitting a signal to the receiver through a channel represented by the following equation:

Where n is the antenna index of the receiver. 5. The method of claim 4, Hybrid repeater delay diversity cooperative communication system wherein the plurality of repeaters are grouped by the following equation:

Where M represents the total number of repeaters,

and

Represents the number of repeaters grouped in each group. delete In the hybrid cyclic delay diversity cooperative communication method using OFDM, A plurality of repeaters are grouped into a plurality of groups, the repeater included in each group receives a signal based on an orthogonal frequency multiple division scheme (OFDM) from the transmitter, The repeater included in each group cyclically delays a signal received from each group, and Transmitting the cyclically delayed signals to a plurality of antennas provided in a receiver, respectively. And said transmitter and repeater have a single antenna. The method of claim 7, wherein The plurality of repeaters, Hybrid cyclic delay diversity cooperative communication method for cyclically delaying the signals received from each group using the following equation:

here,

Is a signal that is cyclically delayed at the l th repeater at time t,

Is the cyclic delay length of the l th repeater in each group,

Denotes the number of subcarriers and k denotes the index of the subcarriers. The method of claim 8, The cyclic delay length is a hybrid cyclic delay diversity cooperative communication method represented by the following equation:

Where L represents the number of repeaters belonging to each group. 10. The method of claim 9, Hybrid cyclic delay diversity cooperative communication method for transmitting a signal to the receiver through the channel represented by the following equation in the same group:

Where n is the antenna index of the receiver.

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