KR102396405B1 - Two-way Relay System and Method using Space Frequency Block Coding with Physical Network Coding - Google Patents

Abstract

The present invention applies physical network coding (PNC) and a two-step bidirectional transmission method in which user terminals transmit and receive simultaneously using SFBC technology, making it difficult to obtain a feedback path or reliable channel reversibility The present invention relates to a bidirectional relay station system and method capable of obtaining both the temporal efficiency of PNC and the diversity gain of SFBC even in a situation where it is difficult to obtain channel information because it is not established to a satisfactory level.

Description

Two-way Relay System and Method using Space Frequency Block Coding with Physical Network Coding

The present invention relates to a bidirectional relay station system and method, and more particularly, to a bidirectional relay station system and method using spatial frequency block coding and physical network coding.

In the conventional relay station system, in order for two user terminals U _A and U _B to exchange information with each other using the relay station R, as shown in FIG. 1 , a total of four data transmission processes are required.

In order to reduce the number of such four transmission processes, a bidirectional relay station system using network coding is in the spotlight. In this method, as shown in FIG. 2, in the first multiple access (MA) process, U _A and U _B transmit respective information to the relay station R at the same time, and the relay station R receives it and Apply network coding. And, in the second BC (Broadcast) process, the relay station (R) transmits the data generated through network coding in this way to U _A and U _B at the same time. U _A and U _B can obtain each other's information by removing the information they have transmitted from the received information.

In this case, the network coding method applied by the relay station R includes analog network coding (ANC) and physical network coding (PNC). In the case of ANC, the relay station (R) generates network coding information to be transmitted in the BC process by adjusting the amount of power of the signal received from both sides. XOR) is used to generate network coding information to be transmitted in the BC process. However, ANC has disadvantages such as a constraint that user terminals need channel information between the relay station R and the other user terminal as well as channel information between itself and the relay station R, and a noise enhancement phenomenon. On the other hand, in PNC, user terminals only need to know channel information between themselves and the relay station R, and since the relay station R decodes the signal, there is no noise enhancement.

In a two-way relay communication system to which physical network coding (PNC) is applied having such an advantage, when a relay station R having two antennas is considered, if the relay station R transmits the channel information between itself and the two user terminals, the channel reversibility ( If it can be obtained through channel reciprocity or a feedback path, a beam from which the diversity gain of the user terminal can be derived may be formed. However, there is a problem in that the relay station R cannot form a meaningful beam in a situation in which it is difficult to acquire a feedback path or to acquire channel information because channel reversibility is not established at a reliable level.

Accordingly, the present invention has been devised to solve the above problems, and an object of the present invention is to use a plurality of frequency subcarriers such as OFDM (Orthogonal Frequency Division Multiplexing) in a bidirectional relay station communication system to which physical network coding (PNC) is applied. When relaying signal transmission between user terminals, space frequency block coding (SFBC) is applied using the quasi-statistical property that the channels between adjacent subcarriers are similar, so that user terminals and the relay station communicate with each other in advance. An object of the present invention is to provide a bidirectional relay station system and method in which a user terminal can form a beam from which a diversity gain can be derived using spatial frequency block coding (SFBC) even when channel information is not known.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

First, to summarize the features of the present invention, a signal relay method in a bidirectional relay station apparatus according to an aspect of the present invention for achieving the above object is a multi-channel method for receiving signals transmitted by a plurality of user terminals simultaneously using a multi-frequency subcarrier. connection step; extracting the transmission target signals transmitted by the plurality of user terminals from the received signals, and encoding the transmission target signals according to a physical network coding scheme; and a broadcasting step of simultaneously transmitting the coded signals to the plurality of user terminals using a multi-frequency subcarrier, wherein a corresponding transmission target signal is exchanged between the plurality of user terminals by transmitting the coded signals. characterized in that

In the signal relay method, the plurality of user terminals by a two-step bidirectional transmission method of simultaneously receiving the transmission target signals from the plurality of user terminals and simultaneously transmitting the coded signals to the plurality of user terminals It is characterized in that the information exchange between the two is completed.

The signal relay method is characterized in that it improves the diversity gain according to the spatial frequency block coding scheme using the multi-frequency subcarriers and at the same time improves the temporal efficiency according to the physical network coding scheme.

과

)을 전송하고 동시에 제2주파수 대역의 부반송파를 이용해

를 전송하는(*는 공액 복소수) 단계를 포함하고, 상기 복수의 사용자 단말들은 각각 상기 브로드캐스트된 신호를 수신하여 단일(unitary) 행렬을 이용해

과

을 획득하고

과

로부터 자기 간섭 제거를 통해 상대방의 전송 대상 신호를 획득하는 것을 특징으로 한다.In the broadcasting step, the coded signals (

class

) and at the same time using the subcarrier of the second frequency band

transmitting (* is a conjugated complex number), wherein the plurality of user terminals each receive the broadcast signal and use a unitary matrix

class

to acquire

class

It is characterized in that the transmission target signal of the other party is obtained through self-interference cancellation from the

In addition, a bidirectional relay station apparatus according to another aspect of the present invention includes: a receiving unit for receiving signals transmitted by a plurality of user terminals simultaneously using multi-frequency subcarriers; a coding unit for extracting transmission target signals transmitted by the plurality of user terminals from the received signals, and encoding the transmission target signals according to a physical network coding scheme; and a transmitter for simultaneously broadcasting the coded signals to the plurality of user terminals using a multi-frequency subcarrier, wherein the exchange of the corresponding transmission target signal is made between the plurality of user terminals by transmitting the coded signals. characterized.

The two-way relay station apparatus simultaneously receives the transmission target signals from the plurality of user terminals and simultaneously transmits the coded signals to the plurality of user terminals by a two-step bidirectional transmission method. It is characterized in that the information exchange between the two is completed.

The bidirectional relay station apparatus is characterized in that it improves the diversity gain according to the spatial frequency block coding scheme using the multi-frequency subcarriers and at the same time improves the temporal efficiency according to the physical network coding scheme.

과

)을 전송하고 동시에 제2주파수 대역의 부반송파를 이용해

를 전송하며(*는 공액 복소수), 상기 복수의 사용자 단말들은 각각 상기 브로드캐스트된 신호를 수신하여 단일(unitary) 행렬을 이용해

과

을 획득하고

과

로부터 자기 간섭 제거를 통해 상대방의 전송 대상 신호를 획득하는 것을 특징으로 한다.The transmitting unit, using the subcarrier of the first frequency band, the coded signals (

class

) and at the same time using the subcarrier of the second frequency band

(* is a conjugated complex number), and each of the plurality of user terminals receives the broadcast signal and uses a unitary matrix.

class

to obtain

class

It is characterized in that the transmission target signal of the other party is obtained through self-interference cancellation from the

According to the bidirectional relay station system and method according to the present invention, only unidirectional is considered in the relay station system to which the existing spatial frequency block coding (SFBC) technology is applied. By applying a two-step bidirectional transmission method in which user terminals transmit and receive simultaneously using There is an effect that both the efficiency and the diversity gain of SFBC can be obtained.

1 is a diagram for describing a process in which two user terminals at both ends exchange information with each other using a relay station in a conventional relay station system.
2 is a diagram for explaining an information exchange process in a bidirectional relay station system using general network coding.
3 is a diagram for explaining a bidirectional relay station system according to an embodiment of the present invention.
4 is a flowchart for explaining the operation of a bidirectional relay station system according to an embodiment of the present invention.
5 is a diagram for explaining an example of a method of implementing a bidirectional relay station system according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same components are given the same reference numerals as much as possible even though they are indicated on different drawings. In addition, in describing the embodiment of the present invention, if it is determined that a detailed description of a related known configuration or function interferes with the understanding of the embodiment of the present invention, the detailed description thereof will be omitted.

In describing the components of the embodiment of the present invention, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only for distinguishing the component from other components, and the essence, order, or order of the component is not limited by the term. In addition, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

3 is a diagram for explaining a bidirectional relay station system (or device) 100 according to an embodiment of the present invention. For description of the operation of the bidirectional relay station system 100 according to an embodiment of the present invention, reference is made to the flowchart of FIG. 4 .

Referring to FIG. 4 , the bidirectional relay station system 100 according to an embodiment of the present invention includes two or more antennas 10 and 20 , a receiving unit 110 , a coding unit 120 , and a transmitting unit 130 . do. Such components of the bidirectional relay station system 100 of the present invention may be implemented by hardware, software, or a combination thereof. Here, it is assumed that there are two antennas 10 and 20 for signal transmission and reception, but the present invention is not limited thereto, and a larger number of antennas may be used for transmission of two or more multi-frequency subcarriers such as OFDM.

First, the functions of the components of the bidirectional relay station system 100 will be briefly described.

The receiver 110 receives signals transmitted by a plurality of user terminals (eg, two user terminals) simultaneously using multi-frequency subcarriers through the antennas 10 and 20 . The coding unit 120 extracts transmission target signals transmitted by the plurality of user terminals from the signals received by the receiving unit 110 and codes the corresponding transmission target signals according to a physical network coding scheme (PNC). The transmitter 130 simultaneously broadcasts the signals encoded by the coding unit 120 to the plurality of user terminals through the antennas 10 and 20 using multi-frequency subcarriers. By transmitting the PNC-coded signals as described above, the corresponding transmission target signal can be exchanged between the plurality of user terminals.

The system 100 of the present invention performs signal exchange between two user terminals (U _A , U _B ) according to a multiple access (MA) process and a broadcast (BC, broadcast) process, as shown in FIG. 2 . As a bidirectional relay station system capable of relaying, the user terminals (U _A , U _B ) simultaneously transmit multi-frequency subcarrier signals to which space frequency block coding (SFBC) is applied, and receive them in the bidirectional relay station system 100 to receive the physical network By applying coding (PNC) to simultaneously transmit multi-frequency subcarrier signals to the user terminals (U _A , U _B ), the diversity gain of the space frequency block coding (SFBC) method and the counterpart in the physical network coding (PNC) method In order to obtain all the time efficiency that is unnecessary for the terminal to acquire channel information.

)를 두 개의 주파수 부반송파를 이용하여 중계국(R)로 동시에 전송하고, 양방향 중계국 시스템(100)의 수신부(110)는 안테나(10, 20)를 통하여 사용자 단말들(U_A, U_B)가 송신하는 신호를 수신한다(도 4의 S110 참조). 즉, 사용자 단말(U_A)은 두 개의 주파수에서 직교하는 전송 대상 신호들

을 전송하고, 사용자 단말(U_B)은 두 개의 주파수에서 직교하는 전송 대상 신호들

을 전송한다. 여기서 f∈{1,2}이다. In detail, first, in the multiple access (MA) process, the user terminals (U _A , U _B ) each receive two signals (

) is simultaneously transmitted to the relay station R using two frequency subcarriers, and the receiving unit 110 of the bidirectional relay station system 100 transmits the user terminals U _A and U _B through the antennas 10 and 20. to receive a signal (refer to S110 of FIG. 4). That is, the user terminal (U _A ) transmits orthogonal transmission target signals at two frequencies.

transmits, and the user terminal (U _B ) transmits orthogonal transmission target signals at two frequencies

to send where f∈{1,2}.

At this time, the signal (y ¹ ) of the first frequency band received by the receiver 110 from the user terminals (U _A , U _B ) may be expressed as a vector as in [Equation 1], and the user terminals (U _A , The signal (y ² ) of the second frequency band received by the receiver 110 from U _B ) may be expressed as a vector as in [Equation 2]. Here, n ¹ and n ² are noise in each frequency band, and h _A and h _B are channel coefficients indicating channel characteristics between each of the user terminals U _A and U _B and the relay station system 100 . .

[Equation 1]

[Equation 2]

In such a multi-frequency subcarrier transmission scheme such as OFDM, orthogonality is established between subcarriers, so the coding unit 120 of the bidirectional relay station system 100 uses this to decode the received signals y ¹ , y ² ). Thus, the original transmission target signals transmitted by the user terminals can be separated and extracted (refer to S120 of FIG. 4 ).

,

)에 대하여 브로드캐스트(BC) 과정에서 사용자 단말들(U_A, U_B)로 전송할 물리적 네트워크 코딩(PNC) 방식으로 코드화한 신호들

(

과

)을 생성한다(도 4의 S130 참조).The coding unit 120 decodes the extracted received signals (y ¹ , y ² ), and decodes the decoded signals (eg,

,

), signals coded in the physical network coding (PNC) method to be transmitted to the user terminals (U _A , U _B ) in the broadcast (BC) process

(

class

) is generated (refer to S130 of FIG. 4).

As a method of decoding the signals (y ¹ , y ² ) received in each frequency band, a non-linear method including a Maximum-Likelihood (ML) detector method, Zero-Forcing (ZF), MMSE ( A linear method including a Minimum Mean Square Error) filter method and the like may be used.

(

과

)을 추출하여, 이로부터 자신이 송신한 신호를 제거해 상대방이 송신한 신호를 획득할 수 있도록 디코딩된 신호들을 코드화한다. 예를 들어, U_A가

에서 자신이 송신한 신호(

)를 제거하여(자기간섭 제거) 상대방이 송신한 신호(

)를 얻을 수 있으며, 이와 동시에 U_B 역시

에서

를 제거하여

을 얻을 수 있는 방식으로 설계된 모든 네트워크 코딩 방식이, 물리적 네트워크 코딩(PNC) 방식으로 사용될 수 있다. 예를 들어, 전송 대상 신호 Q에 대하여 소정의 XOR 처리 신호 P에 의한 (Q XOR P)를 전송하고 수신측에서 (Q XOR P)에 다시 P를 이용해 한번더 XOR를 수행하여 본래의 신호 Q를 추출할 수 있다. In addition, as the physical network coding (PNC) method, an XOR method, a Modulo method, etc. are used, and signals coded from signals transmitted by the user terminals (U _A , U _B ), respectively.

(

class

) and code the decoded signals so that the signal transmitted by the other party can be obtained by removing the signal transmitted by the other party. For example, if U _A is

A signal sent by itself from

) by removing (removing self-interference) the signal (

) can be obtained, and at the same time U _B is also

at

by removing

Any network coding scheme designed in a way that can obtain For example, (Q XOR P) by a predetermined XOR processing signal P is transmitted with respect to the transmission target signal Q, and the original signal Q is obtained by performing XOR once again using P at the receiving side (Q XOR P). can be extracted.

을 생성하면, 브로드캐스트(BC) 과정에서 송신부(130)는 서로 다른 각각의 주파수 대역 부반송파를 이용하여

등 관련 신호들을 두 개의 안테나(10, 20)를 통해 사용자 단말들(U_A, U_B)로 동시에 브로드캐스트 전송한다(도 4의 S140 참조). 즉, 두 개의 안테나(10, 20)를 통해 제3주파수 대역의 부반송파를 이용해

과

을 전송하고, 동시에 두 개의 안테나(10, 20)를 통해 제4주파수 대역의 부반송파를 이용해

를 전송한다. *는 공액 복소수(complex conjugate)이다.Signals coded by the coding unit 120 using a physical network coding (PNC) method as described above

, the transmitter 130 uses subcarriers of different frequency bands in the broadcast (BC) process.

The related signals are simultaneously broadcast and transmitted to the user terminals U _A and U _B through the two antennas 10 and 20 (see S140 of FIG. 4 ). That is, using the subcarrier of the third frequency band through the two antennas 10 and 20

class

and simultaneously using the subcarrier of the 4th frequency band through the two antennas 10 and 20

to send * is a complex conjugate.

When the broadcast process is performed in this way, the signal (y _k ¹ ) received by the user terminals U _k (k∈{A, B}) in the third frequency band can be expressed as in [Equation 3], A signal (y _k ^2' ) received by the user terminals U _k (k∈{A, B}) in the 4th frequency band may be expressed as [Equation 4]. Here, n _k ¹ , n _k ² are Additive White Gaussian Noise (AWGN) noise in each frequency band for the user terminals U _A and U _B , and h _(k,1) , h _(k,2) is a channel coefficient indicating channel characteristics between the user terminals U _A and U _B and the first antenna 10 and the second antenna 20 .

[Equation 3]

[Equation 4]

At this time, [Equation 3] (y _k ¹ ) and [Equation 4] take the conjugated complex number (y _k ² ), and when expressed in matrix form, it is the same as [Equation 5] below, and expressed in the form of a vector: It is the same as [Equation 6] of

[Equation 5]

[Equation 6]

과

를 획득하기 위하여, [수학식6]의 신호 벡터(y_k)에

를 곱하는 매치트 필터링(matched-filtering)을 수행한다. 그 결과는 하기의 [수학식 7]과 같다.Accordingly, the user terminals (U _k ) in the received signal vector (y _k ) as in [Equation 6]

class

In order to obtain , in the signal vector (y _k ) of [Equation 6]

Matched filtering is performed by multiplying by . The result is as follows [Equation 7].

[Equation 7]

는 단일(unitary) 행렬이므로, 잡음 벡터의 성질을 변화시키지 않고 수신 신호의 신호 대 잡음비가 유지된다. [수학식7]에서 볼 수 있듯이, 신호의 채널이 사라지고 간단한 형태의 AWGN(Additive White Gaussian Noise) 채널의 형태가 되었고, 서로 다른 주파수의 신호를 간섭 없이 분리할 수 있으므로, U_k는 각 주파수 대역에서

과

을 간단하게 획득할 수 있게 된다. 이렇게 획득된

과

에서 자기 간섭인

과

를 네트워크 코딩의 성질을 이용하여 제거하면 상대방으로부터 온 정보(상대방이 전송한 전송 대상 신호)를 획득할 수 있다. 이에 따라 U_k 간에 해당 전송 대상 신호의 교환이 이루어질 수 있다. here,

Since is a unitary matrix, the signal-to-noise ratio of the received signal is maintained without changing the nature of the noise vector. As can be seen in [Equation 7], the signal channel disappears and becomes a simple AWGN (Additive White Gaussian Noise) channel, and since signals of different frequencies can be separated without interference, U _k is each frequency band at

class

can be obtained easily. obtained in this way

class

self-interfering in

class

is removed using the properties of network coding to obtain information from the other party (transmission target signal transmitted by the other party). Accordingly, U _k A corresponding transmission target signal may be exchanged between each other.

5 is a diagram for explaining an example of an implementation method of the bidirectional relay station system 100 according to an embodiment of the present invention. The bidirectional relay station system 100 according to an embodiment of the present invention may be formed of hardware, software, or a combination thereof. For example, it may be implemented as the computing system 1000 as shown in FIG. 5 .

The computing system 1000 includes at least one processor 1100 , a memory 1300 , a user interface input device 1400 , a user interface output device 1500 , a storage 1600 connected through a bus 1200 , and a network An interface 1700 may be included. The processor 1100 may be a central processing unit (CPU) or a semiconductor device that processes instructions stored in the memory 1300 and/or the storage 1600 . The memory 1300 and the storage 1600 may include various types of volatile or nonvolatile storage media. For example, the memory 1300 may include read only memory (ROM) and random access memory (RAM).

Accordingly, the steps of a method or algorithm described in connection with the embodiments disclosed herein may be directly implemented in hardware, a software module executed by the processor 1100 , or a combination of the two. A software module resides in a storage medium (ie, memory 1300 and/or storage 1600 ) such as RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM. You may. An exemplary storage medium is coupled to the processor 1100 , the processor 1100 capable of reading information from, and writing information to, the storage medium. Alternatively, the storage medium may be integrated with the processor 1100 . The processor and storage medium may reside within an application specific integrated circuit (ASIC). The ASIC may reside within the user terminal. Alternatively, the processor and storage medium may reside as separate components within the user terminal.

As described above, only unidirectional is considered in the relay station system to which the existing spatial frequency block coding (SFBC) technology is applied, but in the bidirectional relay station system 100 according to an embodiment of the present invention, physical network coding (PNC) is also applied. At the same time, by applying the SFBC technology to complete information exchange between each other in a two-step bidirectional transmission method in which two user terminals transmit and receive simultaneously, it is difficult to obtain a feedback path or the channel reversibility is established at a reliable level. Even in a situation in which it is difficult to obtain channel information due to the inability to obtain channel information, the temporal efficiency of PNC and diversity gain of SFBC can be obtained.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains.

Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Antenna (10, 20)
Receiver 110
coding unit 120
Transmitter 130

Claims (10)

A method for relaying signals in a bidirectional relay station device, the method comprising:
Receiving signals transmitted by a plurality of user terminals using multi-frequency subcarriers;
extracting the transmission target signals transmitted by the plurality of user terminals from the received signals, and encoding the transmission target signals according to a physical network coding scheme; and
transmitting coded signals to the plurality of user terminals using the multi-frequency subcarrier;
Transmitting using the multi-frequency subcarrier comprises:
A signal coded using a subcarrier of the third frequency band

class

and at the same time using the subcarrier of the 4th frequency band

to send,
The terminal receiving the transmission signal performs matched-filtering on the received signal vector, and acquires information of the counterpart by using the self-interference signal, Signal relay method. The method according to claim 1,
The signal relay method, characterized in that simultaneously receiving the transmission target signals from the plurality of user terminals and simultaneously transmitting the coded signals to the plurality of user terminals. The method according to claim 1,
Receiving the signals transmitted by the plurality of user terminals comprises:
The signal relay method, characterized in that the transmission target signals to which spatial frequency block coding is applied are received through a subcarrier of a first frequency band and a subcarrier of a second frequency band. The method according to claim 1,
The coding step is
decoding the received signals to obtain the transmission target signals; and
and generating the coded signals by coding the transmission target signals according to a physical network coding scheme. 5. The method of claim 4,
The step of obtaining the transmission target signals includes:
A signal relay method, characterized in that the received signals are acquired using a non-linear method or a linear method to obtain the transmission target signals. 5. The method of claim 4,
The physical network coding method is a coding method based on an XOR operation or a coding method based on a modular operation, a signal relay method. delete A communication device comprising:
processor;
a memory in electronic communication with the processor; And
including instructions stored in the memory;
When the instructions are executed by the processor, the instructions cause the communication device to:
receive signals transmitted by a plurality of user terminals using multi-frequency subcarriers;
extracting the transmission target signals transmitted by the plurality of user terminals from the received signals, and encoding the transmission target signals according to a physical network coding scheme; And
operative to cause transmission of coded signals to the plurality of user terminals using the multi-frequency subcarrier;
When transmitting using the multi-frequency subcarrier, the commands are signals coded using a subcarrier of a third frequency band.

class

and at the same time using the subcarrier of the 4th frequency band

to send,
The terminal receiving the transmission signal performs matched-filtering on the received signal vector, and obtains information of the counterpart by using the self-interference signal. 9. The method of claim 8,
When receiving signals transmitted by the plurality of user terminals, the instructions include:
and causing the to-be-transmitted signals to which spatial frequency block coding has been applied to be received through a subcarrier of a first frequency band and a subcarrier of a second frequency band.

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