KR101071803B1 - Decode-and-Forward relay system and Method for controlling the same - Google Patents

Abstract

A decode-and-forward relay system and a control method thereof are disclosed. A control method of a post-decoding relay system including a source node having M transmit antennas, a R relay node, and a destination node having L receive antennas is described above. Calculating channel power values of M × R channels formed between M transmit antennas and the R relay nodes; Selecting M minimum channel power values by selecting a minimum value among channel power values of R channels for each of the M transmit antennas; Selecting a maximum value among the M minimum channel power values and selecting one transmit antenna whose maximum value is the minimum channel power value; And transmitting, by the source node, the first signal to at least one relay node of the R relay nodes using any one of the transmit antennas. According to the present invention, a maximum diversity gain can be obtained by minimizing data loss due to transmission of channel quality information.

Post-Decode Forward, Relay, MIMO, Maximum Diversity Gain

Description

Decode-and-Forward relay system and method for controlling the same}

Embodiments of the present invention relate to a post-decoding transfer relay system and a control method thereof. More particularly, after decoding, a signal is relayed and transmitted by selecting an antenna of a source node and a target node so as to obtain a maximum diversity gain. The present invention relates to a transmission relay system and a control method thereof.

In general communication systems, transmission and reception are performed through a direct link between a fixed base station (BS) or a source node and a mobile station (MS) and a destination node. However, since the base station of the current communication system has a fixed location, it is difficult to provide a flexible communication service in a wireless environment having low flexibility, a shaded area, and a change in channel state due to a fixed wireless network. In order to overcome such drawbacks, a relay type data transfer method is applied to an existing communication system using a fixed relay node, a mobile relay node, or a general terminal (mobile station).

When using a communication system using such a relay scheme, it is possible to expand the cell service area and increase system capacity. That is, when the channel state between the source node and the target node is poor, a relay node is provided between the source node and the target node to configure a relay path through the relay node, thereby providing the target node with a better wireless channel. have. In addition, by using a relay scheme in a cell boundary region in which channel conditions are poor from a source node, a higher data channel can be provided and a cell service region can be extended.

Here, according to the role of the relay node, the relay method simply amplifies and forwards an amplify-and-forward (AF) method of amplifying and transmitting a received signal, and demodulates, decodes, and decodes the received signal at the relay node to a destination. It may be classified into a decoded-and-forward (DF) scheme.

In this case, if a plurality of antennas can be installed in both the source node, the relay node, and the destination node in the conventional post-decoding relay system, the data throughput is increased by relaying and transmitting signals using spatial multiplexing techniques. Can be improved.

If the source node, the relay node, and the destination node all have a plurality of antennas, in case of relaying and transmitting a signal according to a decoding and forwarding method, the source node may select one antenna among the plurality of transmit antennas. A signal may be transmitted to a plurality of relay nodes by using a plurality of relay nodes, and the plurality of relay nodes decode the received signal, and then re-encodes the received signal to determine one of the plurality of receiving antennas provided in the target node. Can transmit to the antenna.

In this case, with respect to the selection of the transmit and receive antennas for transmitting and receiving signals, the existing antenna selection scheme uses a channel for the source node or the destination node for the source node-relay node link (hereinafter referred to as "SR link"). It was assumed that both information and channel information about the relay node-purpose node link (hereinafter referred to as "RD link") should be known. Therefore, the source node and the destination node should exchange channel information for the S-R link and channel information for the R-D link.

Therefore, even if the channel information is represented by a signal-to-noise ratio (SNR), the number of antennas included in the source node, the relay node, and the destination node increases or the relay node participates in the signal relay. As the number increases, the data transmission efficiency is lowered.

In addition, if a decoding error occurs in the relay node due to the characteristics of the post-decoding relay system, since the generated decoding error is transmitted to the target node as it is, serious performance degradation may occur in the target node.

In order to solve this problem, a method of relaying a signal using one relay node having an optimal relay efficiency has been proposed without transmitting signals using all relay nodes in a multiple relay system. However, the above method may be a good choice when the total usage power of the relay nodes is limited, but when the total usage power increases as the number of relay nodes participating in the transmission increases, the transmission power decreases and thus the data transmission performance is reduced. Deterioration may occur.

In order to solve the problems of the prior art as described above, the present invention is to propose a post-decoding transfer relay system and its control method that can obtain the maximum diversity gain by minimizing data loss due to the transmission of channel quality information. .

According to a preferred embodiment of the present invention for achieving the above object, after decoding comprising a source node with M transmit antennas, R relay nodes, and the destination node with L receive antennas (decode) In a method of controlling a relay system (M, R, and L are integers of 2 or more), channel power values of M × R channels formed between the M transmit antennas and the R relay nodes are calculated. Making; Selecting M minimum channel power values by selecting a minimum value among channel power values of R channels for each of the M transmit antennas; Selecting a maximum value among the M minimum channel power values and selecting one transmit antenna whose maximum value is the minimum channel power value; And transmitting, by the source node, the first signal to at least one relay node of the R relay nodes by using the one of the transmission antennas.

According to another embodiment of the present invention, in a post-decoding forward relay system including a source node having M transmit antennas, an R relay node, and a destination node having L receive antennas (M, R and L are integers of 2 or more), and the source node controls a control unit to transmit the first signal to at least one relay node of the R relay nodes using any one of the M transmit antennas. And the control unit selects a minimum value among channel power values of the R channels for each of the M transmit antennas with respect to the channel power values of the M × R channels formed between the M transmit antennas and the R relay nodes. Selects M minimum channel power values, selects a maximum value from the M minimum channel power values, and sets the maximum value to the minimum value. A post-decoding transfer relay system is provided for selecting a transmit antenna having a null power value as any one of the transmit antennas.

According to the present invention, a maximum diversity gain can be obtained by minimizing data loss due to transmission of channel quality information.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals are used for like elements in describing each drawing.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, in order to facilitate the overall understanding, the same reference numerals will be used for the same means regardless of the drawing numbers.

1 is a diagram showing a state equipped with multiple antennas in a post-decoding transfer relay system according to an embodiment of the present invention.

The post decoding decoding relay system according to an embodiment of the present invention includes a source node 110, R relay nodes 120, and a destination node 130.

In this case, the source node 110 includes M transmit antennas 111 (hereinafter referred to as "first transmit antennas"), and each of the R relay nodes 120 includes m _r receive antennas 121 ( Hereinafter referred to as " second receive antenna " and transmit antenna 122 (hereinafter referred to as " second transmit antenna "), the destination node 130 has L receive antennas 131 (hereinafter " A first receiving antenna ".

The source node 110 transmits a first signal to at least one relay node of the R relay nodes using one of the first transmit antennas of the M first transmit antennas 111.

Each of the at least one relay node that receives the first signal through the second reception antenna 121 decodes the received first signal and re-encodes the first signal to generate a second signal. Thereafter, each of the at least one relay node transmits the second signal to the destination node 130 through the second transmit antenna 122.

The destination node 130 receives the second signal using at least one first receiving antenna among the L first receiving antennas.

Hereinafter, a method of selecting any one first transmitting antenna to transmit the first signal and one first receiving antenna to receive the second signal will be described in detail with reference to FIG. 2.

2 is a flowchart illustrating an overall flow of a control method of a post-decoding transfer relay system according to an exemplary embodiment of the present invention.

In FIG. 2, steps S210 to S240 are related to an operation of selecting one first transmit antenna and transmitting a first signal by a source node using the selected first transmit antenna, and step S250. Step S270 relates to selecting one first receiving antenna and receiving a second signal from the at least one relay node by the target node using the selected first receiving antenna.

First, steps S210 to S240 related to an operation of transmitting a first signal from a source node to at least one relay node are described below.

In step S210, the channel power values of the M x R channels formed between the M transmit antennas and the R relay nodes included in the source node are calculated.

That is, since R channels are formed between one first transmit antenna and R relay nodes, M × R channels are formed between M first transmit antennas and R relay nodes. Calculate the channel power values of M × R channels.

이라고 하면, t번째 제1 전송 안테나와 r번째 릴레이 노드 사이에 형성된 채널의 채널 파워 값은

와 대응된다. According to an embodiment of the present invention, the channel power value of M × R channels may correspond to the square of the magnitude (norm) value of the channel vector of the M × R channels. That is, the channel vector of the channel formed between the t th first transmit antenna among the M first transmit antennas and the r th relay node among the R relay nodes is determined.

In this case, the channel power value of the channel formed between the t th first transmit antenna and the r th relay node is

Corresponds to.

In step S220, the M minimum channel power values are selected by selecting the minimum value among the channel power values of the R channels for each of the M transmit antennas.

That is, in step S220, the minimum channel power value, that is, the minimum channel power value of each of the M first transmit antennas is selected. Therefore, M minimum channel power values are selected.

In step S230, a maximum value is selected from the M minimum channel power values, and any one transmit antenna whose minimum value is the minimum channel power value is selected.

For example, the source node has three first transmit antennas, three relay nodes exist (assuming all three relay nodes participate in relay transmission), three first transmit antennas and three Assuming that the channel power values of the nine channels formed between the relay nodes are given as shown in Table 1 below, in step S220, a value of "1" is set for the first first transmit antenna and "1" for the second first transmit antenna. A value of 4 "and a value of" 2 "for the third first transmit antenna may be selected as the minimum channel power value, respectively.

First relay node Second relay node Third relay node First first transmit antenna 3 One 4 Second primary transmission antenna 6 5 4 Third first transmit antenna 2 7 6

Subsequently, in step S230, a value of "4", which is the maximum value among "2", "4", and "1" values, is selected, and the first transmission antenna whose value of "4" is the minimum channel power value. Select the second first transmit antenna.

)과 대응되는 경우, 단계(S220) 및 단계(S230)는 아래의 수학식 1에 기초하여 수행될 수 있다. According to one embodiment of the invention, the channel power value is the square of the magnitude of the channel vector (

), Step S220 and step S230 may be performed based on Equation 1 below.

는 선택된 어느 하나의 제1 전송 안테나를 의미한다. here,

Denotes any one selected first transmit antenna.

In step S240, the source node transmits the first signal to at least one relay node of the R relay nodes by using any one selected transmit antenna.

According to an embodiment of the present invention, at least one relay node may receive a first signal transmitted from any one first transmission antenna based on a maximum ratio combining (MRC) scheme.

The maximum non-synthesis method is a signal synthesis method that extracts a single signal by synthesizing a plurality of signals received through several paths, and overlapping and synchronizing before synthesizing to obtain an optimal performance for a signal having extreme fading. The contribution is small, and the larger the signal is, the larger the contribution is.

로 표현될 수 있다. 여기서,

는 r번째 릴레이 노드에서의 수신 신호 벡터이다. In this case, the first signal received by the at least one relay node is

It can be expressed as. here,

Is the received signal vector at the r th relay node.

According to an embodiment of the present invention, steps S210 to S230 may be performed at the source node or may be performed at an apparatus outside the source node.

If the steps S210 to S230 are performed at the source node, the source node uses the first transmit antenna of one M transmit antennas to at least one relay node of the R relay nodes. It may be configured to include a control unit for controlling to transmit.

In this case, the controller selects M minimum channel power values from among M channel R channel power values for M transmit antennas, and selects M minimum channel power values with respect to M × R channel power values. A maximum value may be selected from the channel power values, and a transmission antenna having the selected maximum value as the minimum channel power value may be selected as the transmission antenna for transmitting the first signal.

On the contrary, when steps S210 to S230 are performed in a device outside of the source node, the source node receives information about channel power values of M × R channels or selected transmission antennas from the external device. Must be received.

Next, steps S250 to S270 related to the operation of transmitting the second signal from the at least one relay node to the destination node will be described below.

Here, since the relay system according to an embodiment of the present invention is based on a post-decoding transmission scheme, the at least one relay node decodes the received first signal, re-encodes the decoded signal, and then transmits it to the destination node. . That is, the second signal is a signal that is re-encoded after decoding the first signal.

In step S250, channel power values of RxL channels formed between the R relay nodes and the L first receiving antennas included in the destination node are calculated.

That is, similar to M × R channels formed between the source node and the at least one relay node, R × L channels are formed between at least one relay node of the L first receiving antennas provided in the destination node. In operation S250, channel power values of the formed R × L channels are calculated.

이라고 하면, r번째 릴레이 노드와 d번째 제1 수신 안테나 사이에 형성된 채널의 채널 파워 값은

와 대응된다.In this case, the channel power value of the R × L channels may correspond to the square of the magnitude value of the channel vector of the R × L channels. That is, the channel vector of the channel formed between the r th relay node among the R relay nodes and the d th first receiving antenna among the L first receiving antennas is determined.

In this case, the channel power value of the channel formed between the r th relay node and the d th first receiving antenna is

Corresponds to.

In operation S260, to obtain the maximum diversity gain, one of the first receiving antennas is selected among the L first receiving antennas to maximize the sum of the channel power values of the R × L channels.

)과 대응되는 경우, 단계(S260)에서는 아래의 수학식 2에 기초하여 어느 하나의 수신 안테나를 선택할 수 있다. According to one embodiment of the invention, the channel power value is the square of the magnitude of the channel vector (

In step S260, any one receiving antenna may be selected based on Equation 2 below.

는 선택된 어느 하나의 제1 수신 안테나를 의미한다. here,

Denotes any one selected first receiving antenna.

In step S270, at least one relay node transmits a second signal to any one selected first receiving antenna.

According to an embodiment of the present invention, at least one relay node may transmit a second signal to any one first receiving antenna based on a maximum ratio transmission (MRT) scheme.

로 표현될 수 있다. 여기서,

는 r번째 릴레이 노드에서 제1 신호를 디코딩한 후 재 인코딩한 신호이다. In this case, the second signal transmitted from the at least one relay node is

It can be expressed as. here,

Is a signal that is decoded after decoding the first signal at the r-th relay node.

비트의 정보 만을 적어도 하나의 릴레이 노드로 전송하게 된다. 이에 따라 목적 노드에서 적어도 하나의 릴레이 노드로 전송하는 정보의 양이 감소시켜 데이터 전송 효율을 증가시킬 수 있게 된다. According to an embodiment of the present invention, step S250 and step S260 may be performed at the destination node. In this case, since the destination node transmits only information on the selected first receiving antenna to at least one relay node,

Only bit information is transmitted to at least one relay node. Accordingly, the amount of information transmitted from the destination node to the at least one relay node can be reduced, thereby increasing data transmission efficiency.

As described above, the control method of the post-decoding transfer relay system according to an embodiment of the present invention does not select one or an optimal relay node to transfer a signal but participates in all possible relay nodes in the signal transmission. Therefore, in order to minimize error signal transmission that may occur when transmitting signals after decoding, a specific constraint on the number of antennas may be required, which may be expressed as Equation 3 below.

Here, N denotes the total number of second transmit antennas included in at least one relay node participating in the transmission, and m _r denotes the number of antennas provided in the r th relay node among the R relay nodes.

Equation 3 above shows the first transmit antenna of the source node such that the diversity gain of the SR link having the minimum diversity gain among the plurality of SR links due to the plurality of relays is not less than the maximum diversity gain that can be obtained by the RD link. It means that the number of must be determined.

Hereinafter, the system performance of the post-decoding transfer relay system according to an embodiment of the present invention will be described with reference to FIGS. 3 and 4.

3 and 4, the number of relay nodes is two, and the two relay nodes are assumed to have one and two second transmit antennas and a second receive antenna, respectively, to perform system performance measurements. 3 and 4, the number of first receiving antennas included in the destination node is 1 (L = 1) and 2 (L = 2), and the number of first transmitting antennas provided in the source node is It was set based on Equation 3 above.

에 기초하여 제1 전송 안테나 및 제1 수신 안테나를 선택하고(

는 r번째 릴레이 노드와 t번째 제1 전송 안테나간의 S-R 링크에서의 수신 SNR을,

는 r번째 릴레이 노드와 d번째 제1 수신 안테나 간의 R-D 링크에서의 수신 SNR을 각각 의미함),

은 채널 품질에 관한 정보의 전달로 인한 부가적인 데이터 손실을 반영한 것으로, 전체 데이터 전송량에 대한 채널 품질 정보 전송량의 비율을 의미한다. In addition, the "max selection" technique shown in FIGS. 3 and 4 selects the first transmit antenna and the first receive antenna such that the received SNRs of the first signal and the second signal received at the relay node and the destination node are maximized. The technique "optimal selection" refers to a technique of exchanging all information about channel quality at the source node and the destination node, and selecting a first transmit antenna and a first receive antenna based on the technique, and "proposed selection". "Method means a technique of selecting a first transmit antenna and a first receive antenna based on a control method of a post-decoding transfer relay system according to an embodiment of the present invention. Here, the "optimal selection" technique is a mathematical formula

Select a first transmit antenna and a first receive antenna based on

Is the received SNR on the SR link between the r th relay node and the t th first transmit antenna,

Denotes the received SNR on the RD link between the r th relay node and the d th first receiving antenna, respectively),

Reflects additional data loss due to transmission of information on channel quality, and means the ratio of the channel quality information transmission amount to the total data transmission amount.

First, FIG. 3 is a diagram illustrating a relationship between a signal-to-noise ratio (SNR) and an outage error probability in a case of transmitting a signal using a post-decoding transfer relay system according to an embodiment of the present invention. Set the target bit rate to 1bit / sec / Hz.

이 0.1 보다 큰 경우(즉, 채널 품질 정보 전송량이 전체 데이터 전송량의 10%를 초과하는 경우), "proposed selection" 기법이 다른 안테나 선택 기법에 비해 더 좋은 성능을 발휘함을 확인할 수 있다. 또한, "proposed selection" 기법은 전송에 참여하는 릴레이 노드의 수가 늘어남에 따라 전송 파워의 이득을 얻을 수 있으므로, 전송에 참여하는 릴레이 노드의 개수를 2개 이상으로 하는 경우, 더 좋은 성능을 발휘하게 하는

의 값은 더 작아지게 된다. Referring to Figure 3,

If this is larger than 0.1 (that is, the channel quality information transmission exceeds 10% of the total data transmission), it can be seen that the "proposed selection" technique performs better than other antenna selection techniques. In addition, the "proposed selection" technique can obtain a transmission power gain as the number of relay nodes participating in the transmission increases, so that when the number of relay nodes participating in the transmission is two or more, a better performance can be obtained. doing

The value of becomes smaller.

Next, FIG. 4 is a diagram illustrating a relationship between a signal-to-noise ratio (SNR) and a symbol error probability in the case of transmitting a signal using a post-decoding transfer relay system according to an embodiment of the present invention.

=0인 경우, "optimal selection" 기법과 "proposed selection" 기법은 동일한 오류 확률 기울기를 가지므로 최대 다이버시티를 얻고 있음을 확인 할 수 있다. 여기서, "proposed selection" 기법은 QPSK(Qudarature Phase Shift Keying) 변조 방식을 이용하여 신호를 변조하고, "optimal selection" 기법은 대부분의 QPSK심볼과

에 해당하는 비율의 16QAM 심볼을 혼합한 변조 방식을 이용하여 신호를 변조하였다. 따라서, 심볼 오류 확률 성능에서는 제안하는 기법의 성능 향상이 월등함을 확인 할 수 있다.As can be seen from Figure 4,

When = 0, the "optimal selection" technique and the "proposed selection" technique have the same error probability slope, and thus, the maximum diversity is obtained. Here, the "proposed selection" technique modulates a signal by using a QPSK (Qudarature Phase Shift Keying) modulation scheme, and the "optimal selection" technique is used with most QPSK symbols.

The signal was modulated by using a modulation method in which 16QAM symbols having a ratio corresponding to the ratio are mixed. Therefore, it can be seen that the performance improvement of the proposed scheme is superior in symbol error probability performance.

Embodiments of the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Examples of program instructions such as magneto-optical, ROM, RAM, flash memory, etc. may be executed by a computer using an interpreter as well as machine code such as produced by a compiler. Contains high-level language codes. The hardware device described above may be configured to operate as one or more software modules to perform the operations of one embodiment of the present invention, and vice versa.

As described above, the present invention has been described by specific embodiments such as specific components and the like. For those skilled in the art, various modifications and variations are possible from these descriptions. Therefore, the spirit of the present invention should not be limited to the described embodiments, and all of the equivalents or equivalents of the claims as well as the claims to be described later will belong to the scope of the present invention. .

 1 is a diagram illustrating a state equipped with multiple antennas in a post-decoding transfer relay system according to an embodiment of the present invention.

Figure 2 is a flow chart showing the overall flow of the control method of the post-decoding transfer relay system according to an embodiment of the present invention.

3 is a diagram illustrating a relationship between a signal-to-noise ratio (SNR) and an outage error probability when transmitting a signal using a post-decoding transfer relay system according to an exemplary embodiment of the present invention.

4 is a diagram illustrating a relationship between a signal-to-noise ratio (SNR) and a symbol error probability in a case of transmitting a signal using a post-decoding transfer relay system according to an embodiment of the present invention.

Claims (12)

A control method of a decode-and-forward relay system including a source node having M transmit antennas, an R relay node, and a destination node having L receive antennas (M, R, And L is an integer of 2 or more), Calculating channel power values of M × R channels formed between the M transmit antennas and the R relay nodes; Selecting M minimum channel power values by selecting a minimum value among channel power values of R channels for each of the M transmit antennas; Selecting a maximum value among the M minimum channel power values and selecting one transmit antenna whose maximum value is the minimum channel power value; And Transmitting, by the source node, a first signal to at least one relay node of the R relay nodes using the any one transmit antenna; The control method of the post-decoding transfer relay system comprising a. The method of claim 1, And a channel power value of the M × R channels corresponds to a square of a magnitude (norm) value of a channel vector of the M × R channels. The method of claim 2, Selecting the M minimum channel power values and selecting the maximum value among the M minimum channel power values The control method of the post-decoding transfer relay system, characterized in that performed according to the following equation.

here,

Is the channel vector of the channel formed between the t th transmit antenna and the r th relay node,

Denotes any one of the selected transmit antennas. The method of claim 1, The at least one relay node And receiving the first signal transmitted from any one of the transmission antennas based on a maximum ratio combining (MRC) scheme. The method of claim 1, Each of the R relay nodes includes at least one transmit antenna, The total of the M, the L, and the number of the at least one transmit antenna provided in the at least one relay node has a relationship as in the following equation.

Here, N is the total number of the at least one transmit antenna provided in the at least one relay node, m _r means the number of antennas provided in the r-th relay node of the R relay nodes, respectively. The method of claim 1, After transmitting the first signal to the at least one relay node Calculating channel power values of R × L channels respectively formed between the R relay nodes and the L receive antennas; Selecting one of the L receive antennas to maximize a sum of channel power values of the R × L channels; And The at least one relay node transmitting a second signal to any one of the receive antennas The control method of the post-decoding transfer relay system, characterized in that it further comprises. The method of claim 6, Calculation of channel power values of the R × L channels and selection of any one receiving antenna are performed at the destination node, The destination node transmits information on the at least one receiving antenna to the at least one relay node, And the at least one relay node transmits a second signal to the any one receiving antenna based on the information on the any one receiving antenna. The method of claim 6, The at least one relay node And transmitting the second signal to any one of the reception antennas based on a maximum ratio transmission (MRT) scheme. In a post-decoding relay system comprising a source node with M transmit antennas, an R node and a destination node with L receive antennas (M, R, and L are integers of 2 or more), The source node is A control unit for controlling to transmit the first signal to at least one relay node of the R relay nodes using any one of the M transmit antennas Including, The control unit With respect to channel power values of M × R channels formed between the M transmit antennas and the R relay nodes, M minimum channels are selected by selecting a minimum value among the channel power values of R channels for each of the M transmit antennas. Select the power value, Selecting a maximum value among the M minimum channel power values, And a transmission antenna having the maximum value as the minimum channel power value is selected as one of the transmission antennas. 10. The method of claim 9, And a channel power value of the M × R channels corresponds to a square of a magnitude (norm) value of the channel vector of the M × R channels. The method of claim 10, The control unit And selecting the M minimum channel power values according to the following equation, and selecting a maximum value among the M minimum channel power values.

here,

Is the channel vector of the channel formed between the t th transmit antenna and the r th relay node,

Denotes any one of the selected transmit antennas. 10. The method of claim 9, Each of the R relay nodes includes at least one transmit antenna, The sum of the number of the M, the L and the at least one transmit antenna provided in the at least one relay node has a relationship as shown in the following equation.

Where N is the total number of at least one transmit antenna provided in the at least one relay node, and m _r represents the number of antennas provided in the r th relay node among the R relay nodes.

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