KR101737834B1 - Method and apparatus of transmitting multiple data streams in mimo relay communication system - Google Patents

Abstract

The present invention relates to a method and apparatus for transmitting and receiving a multi data stream in a multi-antenna relay system, and in a multi-antenna relay communication system, a method for transmitting and receiving a multiple data stream including a first data and a second data, Receiving channel information between a source node and a relay node from a source node or a relay node; Acquiring channel information of a source node and a destination node and channel information of a relay node and a destination node through channel estimation; Calculating an optimal precoding matrix by calculating a data rate of the first data and a second data based on the obtained channel information; And feeding back the determined optimal precoding matrix component to the source node.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a multi-data relay system, and more particularly,

The present invention relates to data transmission and reception in a relay system, and more particularly, to a precoding technique for maximizing a data rate in a multi-antenna (MIMO) relay system and a method and apparatus for transmitting and receiving a multi-data stream using the precoding technique.

In recent years, wireless communication systems have been increasing in service frequency band and gradually decreasing cell radius in order to support high-speed data communication and to accommodate more calls, and there is a problem in operating the existing centralized cellular wireless network system in the future exist. That is, in the conventional method in which the position of the base station is fixed, the flexibility of the wireless link configuration is poor, and it is difficult to provide an efficient communication service in a wireless environment where the traffic distribution or the call request amount is greatly changed.

A next generation wireless communication system called LTE-Advanced (Long Term Evolution Advanced) system or E-UTRA (Evolved Universal Terrestrial Radio Access) system is a relay, more specifically a multi-hop relay multi-hop relay. The relay system can expand the cell service area by covering the partial shaded area existing in the cell area and not only can increase the system capacity but also reduce the burden on the installation cost in the initial introduction step in which the service requirement is relatively small There is an advantage that it can be.

In a relay system, a source node may transmit a plurality of data streams to a relay node and a destination node using superposition coding. The relay node receiving the multiple data streams from the source node can decode and re-encode it and perform cooperative data transmission to the destination node. This collaborative communication method improves the efficiency of data transmission and can improve the throughput of the whole network as well as the resource consumption of each node.

However, depending on the channel environment, mutual interference may occur between a plurality of data streams transmitted from the source node and the relay node. In this case, a problem arises that a plurality of data streams can not be normally decoded at the destination node.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and it is an object of the present invention to provide a data transmission and reception method and apparatus for relieving interference between multi data streams by relaying only partial information of multiple data streams received from a source node in cooperative data transmission using a relay node to provide.

Also, a precoding technique for maximizing a data rate in a multi-antenna (MIMO) relay system, and a method and apparatus for transmitting and receiving a multi-data stream using the precoding technique are provided.

According to an aspect of the present invention, there is provided a method of transmitting and receiving a multi data stream in a multi-antenna relay system, the multi data stream transmitting method comprising: receiving a multi data stream including a first data and a second data in a multi- A method for transmitting / receiving a stream, the method comprising: receiving channel information between a source node and a relay node from a source node or a relay node; Acquiring channel information between a source node and a destination node and channel information between a relay node and a destination node through channel estimation; Calculating an optimal precoding matrix by calculating a data rate of the first data and a second data based on the obtained channel information; And feeding back the determined optimal precoding matrix component to the source node.

Preferably, the second data is a part of data received from a relay node among the multi data streams, and the first data is data other than the second data among the multi data streams.

Preferably, the optimal precoding matrix determination step determines the precoding matrix so that a data rate having a minimum of a data rate of the first data and a data rate of the second data is maximized.

Advantageously, the method further comprises: receiving a multi-data stream from the source node; Receiving a partial data stream including the second data from the relay node; And performing a decoding on the first data through SIC (Successive Interference Cancellation) using the decoded second data, after performing a decoding on some data streams received from the relay node .

Preferably, the first data and the second data are subjected to Per Antenna Superposition Coding for each transmit antenna and are transmitted.

Preferably, the first data and the second data are separated and encoded according to transmission antennas (Multi-Layer Superposition Coding), and are transmitted.

According to an aspect of the present invention, there is provided an apparatus for transmitting and receiving a multi-data stream in a multi-antenna relay system, comprising: a multi-data relay apparatus for transmitting multiple data streams including first data and second data, stream receiving means for receiving channel information between a source node and a relay node from a source node or a relay node; A channel estimator for estimating channel information between a source node and a destination node and a channel state between a relay node and a destination node; A controller for calculating an optimal precoding matrix by calculating a data rate of the first data and a second data based on channel information obtained through the channel estimator; And a transmitter for feeding back the determined optimal precoding matrix component to the source node.

Preferably, the second data is a part of data received from a relay node among the multi data streams, and the first data is data other than the second data among the multi data streams.

Preferably, the controller is configured to determine the precoding matrix so that a data rate having a minimum of a data rate of the first data and a data rate of the second data is maximized.

Preferably, the receiver receives a multi-data stream from the source node during a first transmission interval and receives a data stream including the second data from the relay node during a second transmission interval, And performs decoding on some of the data streams received from the relay node, and then decodes the first data through SIC (Successive Interference Cancellation) using a part of the decoded data streams.

Preferably, the first data and the second data are subjected to Per Antenna Superposition Coding for each transmit antenna and are transmitted.

Preferably, the first data and the second data are separated and encoded according to transmission antennas (Multi-Layer Superposition Coding), and are transmitted.

According to the present invention, interference between multi-data streams is solved by relaying only partial information of multiple data streams received from a source node in cooperative data transmission using a relay node.

In addition, since the multi-data stream is transmitted / received through precoding considering both channel conditions of the source node, the relay node, the relay node, the destination node, and the source node and the destination node, the data transmission rate is maximized.

1 is a view schematically showing a configuration of a relay system.
2 is a diagram illustrating a process of transmitting a data stream through variable rate superposition coding in a relay system according to an embodiment of the present invention.
3 is a diagram schematically illustrating a partial information relay process through the PASC technique.
4 is a diagram schematically illustrating a partial information relay process through the MLSC scheme.
5 is a block diagram schematically illustrating a configuration of a destination node according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like or similar elements throughout the several views, and redundant description thereof will be omitted. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the purpose of facilitating understanding of the present invention, and should not be construed as limiting the scope of the present invention with reference to the accompanying drawings.

The communication system of the present invention includes a base station and a terminal as a system for providing various communication services such as voice and packet data, and a LTE (Long Term Evolution) system or an LTE-Advanced system will be described as a representative example.

The source node of the present invention may be a base station in case of downlink data transmission and may be a terminal in case of uplink data transmission. In addition, the destination node may be a terminal in case of downlink data transmission, and may be a base station in case of uplink data transmission. The relay node may also be a relay station that receives data from the source node and forwards the received data to the destination node.

The terminal of the present invention may be called a subscriber station (SS), a user equipment (UE), a mobile equipment (ME), a mobile station Such as a portable device or a PC, or a vehicle-mounted device.

The base station of the present invention is a fixed point communicating with a terminal and can be used as an evolved NodeB (eNB), a base station (BS), a base transceiver system (BTS), and an access point. One or more cells may exist in one base station and an interface for transmitting user traffic or control traffic may be used between the base stations. Also, a downlink means a communication channel from a base station to a terminal, and an uplink means a communication channel from a terminal to a base station.

A relay node (RN) of the present invention can be referred to as a relay, a relay station, a relay station (RS), or the like, and is installed between a base station and a terminal to relay a transmission / reception signal, Covers the shaded area, broadens the cell service area, and increases the system capacity. The relay node may be composed of multiple hops to efficiently relay data traffic generated between the base station and the terminals, or may be fixed or operated in one location or may have mobility.

The multiple access scheme applied to the wireless communication system of the present invention can be applied to various wireless communication systems such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Single Carrier- Frequency Division Multiple Access) or other modulation techniques known in the art.

In addition, the multiple access scheme for downlink and uplink transmission may be different from each other. For example, an OFDMA scheme may be used for the downlink and an SC-FDMA scheme may be used for the uplink.

Cooperative communication using a relay node can improve the stability of the information transmission when the source-to-destination link (SD link) state is not sufficient and the coverage of the cell with low cost and low power . The relay node amplifies or restores the information received from the source node and transmits it to the destination node. At this time, a multiple-input multiple-output (MIMO) antenna is used to increase the amount of information transmitted from the relay node. When information is transmitted using multiple antennas, a plurality of data streams can be transmitted at one time to increase the transmission capacity or service a plurality of users at once. If the state of the relay-to-destination link (RD link) is not sufficiently good or the receiving node's receiving capability is not sufficient in transmitting a plurality of data streams, all the data streams are transmitted from the relay node The data transmission efficiency is lowered. Also, in order to increase the transmission efficiency in the multi-antenna environment, separate signal processing must be performed at the source node and the relay node.

1 is a view schematically showing a configuration of a relay system.

Basic relay communication environment, communication over the MIMO channel from the source node (S), relay nodes (R) and the destination node (D) are _{SR link (H SR), SD} link (H SD), RD link (H RD) respectively, . As shown, the channel matrix values indicating the channel states of the respective links can be expressed as H _SR , H _SD , and H _RD , respectively.

During the first transmission time, the source node S transmits information composed of a plurality of multi-data streams to the relay node R and the destination node D. Then, during the second transmission time, the relay node R transmits the information received from the source node S to the destination node D, and finally the information received during the first and second transmission times at the destination node D And decodes the data in combination.

At this time, the relay node R is divided into the following two types according to the method of transmitting the information received from the source node S to the destination node D as follows.

(1) An amplify-and-forward (AF) method in which a signal received from a source node S is directly amplified without being decoded and transmitted to a destination node R

(2) a decode-and-forward (DF) scheme in which a signal received from a source node S is decoded and then re-encoded for signal transmission to a destination node

The AF and DF relay techniques have advantages and disadvantages, and the AF technique has advantages of simple implementation and less delay, while the noise components received by the relay node R are also amplified There are disadvantages. On the other hand, in the case of the DF scheme, since the relay node R must undergo a separate decoding procedure, the implementation complexity increases and the relay delay is relatively large.

In a relay system, when a plurality of information streams are transmitted using multiple antennas, the amount of information that can be obtained increases. However, when one of the SR link and the RD link is bad, the amount of information that can be transmitted It is limited. Therefore, it is preferable to variably adjust the second transmission time in order to alleviate the restriction of the amount of information when either one of the links is bad. That is, if the R-D link is good, the second transmission time is short, and if the R-D link is bad, the second transmission time may be long to reduce the information amount limitation. However, since a plurality of information streams are transmitted during the first time, if the R-D link is bad, the second transmission time becomes long and the information transmission amount per hour may be worse. In addition, since precoding in the existing relay communication environment is designed only for the SR link and the RD link in the source and the relay without considering the influence of the direct link (SD link) between the source and the destination, The information received through the SD link during the second time period can not be utilized effectively.

Therefore, in order for the destination node (D) to better utilize the information received over the S-D link during the first time, a precoding scheme considering the S-D link should be considered.

In the present invention, in order to improve the performance in the case where the relay node R retransmits all the data streams received from the source node S in the conventional DF scheme in the case where the information transmission amount of the system decreases, We propose a variable transmission time technique that can determine the second transmission time variably. At this time, both the relay node R and the destination node D propose a method of transmitting only the partial information in the relay node in consideration of the environment in which the successive interference cancellation (SIC) technique can be used.

The source node S encodes the information to be transmitted to the relay node R by information to be transmitted to the destination node D and information to be not transmitted by the relay node R. [ At this time, the source node S encodes the two pieces of information through superposition coding for each transmission antenna, or encodes the stream to be transmitted and the stream to be transmitted from the relay node R, separately. The relay node R and the destination node D decode one information with interference when receiving two pieces of information and remove the decoded information through the SIC from the existing signal to receive another information without interference .

2 is a diagram illustrating a process of transmitting a data stream through variable rate superposition coding in a relay system according to an embodiment of the present invention.

The source node 10 allocates M data streams with a specific data rate r and a power p, respectively, and performs superposition coding, and then transmits the data streams to the relay node 20 and the destination node 30.

The relay node 20 receives and decodes the M data streams transmitted from the source node 10 and assigns the L data streams among the M data streams to a specific data rate r _i and power p _i , 30).

The destination node 30 first decodes the L data streams transmitted from the relay node 20 and then decodes the M data streams transmitted from the source node 10 using the SIC based on the L data streams that have been successfully decoded And decodes the remaining data stream to complete decoding of the entire data stream.

That is, the source node 10 and the relay node 20 respectively transmit M data streams and L data streams to the destination node 30 by variable rate superposition coding (VRSC) , The destination node 30 firstly decodes the L data streams transmitted from the relay node 20 to complete the decoding of the remaining data streams. In this manner, the relay node 20 transmits only the entire data stream transmitted from the source node 10 to the destination node 30 without transmitting all the data streams to the destination node 30, And the destination node 30 can efficiently decode the M data streams using the SIC.

Advantageously, the VRSC coding scheme can be applied to data stream transmission through multiple transmit antennas by classifying the entire transmit antenna n _s into several subgroups n _si . For example, if it is assumed that the average channel gain information can be used, optimal transmission rate and power allocation for VRSC are performed first for each antenna group, and then VRSC coding is performed to transmit the multi data stream.

The relay node 20 receiving the multiplexed data stream encoded and transmitted from the source node 10 through the VRSC transmits the data stream to the destination node 30 through a Successive Decode and Forward And delivers the data stream. The SuDF means decomposing a parallel parallel data stream into a plurality of sub-parallel data streams through successive decoding, super-coding, and transmitting the data.

The relay node 20 arranges the decrypted data streams in descending order of data rate, and preferably forms a part of the data streams from the highest transmission rate to the destination node 30. Data streams with relatively low data rates may also perform data retransmission, such as H-ARQ, from the relay node 20 to the destination node 30 when a data transmission error occurs between the source node 10 and the destination node 30 Therefore, it can be stored in the buffer of the relay node 20 and utilized for data retransmission later.

Cooperative data streams transmitted from the relay node 20 to the destination node 30 through this method can be more successfully decoded at the destination node 30 because interference between data streams is reduced.

The partial information transmission relay scheme using the precoding scheme proposed in the present invention can be divided into a Per Antenna Superposition Coding (PASC) scheme and a Multi-Layer Superposition Coding (MLSC) scheme according to a method of dividing partial information to be transmitted in a relay node .

3 is a diagram schematically illustrating a partial information relay process through the PASC technique.

The PASC technique encodes Basic data and superposition data (hereinafter referred to as "SC data ") for each transmission antenna through superposition coding. The encoded information is multiplied by the precoding matrix Fs and transmitted to the relay node 20 and the destination node 30. [

The relay node 20 decodes the basic data and decodes the SC data by removing the basic data from the entire received signal using the SIC.

Thereafter, the relay station multiplies the decoded SC data by the relay precoding matrix F _R and transfers the result to the destination node 30. At this time, the relay precoding matrix F _R is designed as a precoding matrix for maximizing the information transmission amount of the RD link.

The destination node 30 removes the SC data received at the second transmission time from the signal received at the first transmission time through the SIC to restore the basic data.

For example, when the source node 10 super-codes and transmits Basic data and SC data, the power allocated to each data and the direction of the precoding matrix should be determined, and the sum of the power allocation and the precoding matrix Lt; / RTI > becomes an effective precoding matrix. In particular, in the case of data transmission through the PASC, the power allocation between the basic data and the SC data can be designed differently, and the precoding matrix can be determined so that the precoding directions of the basic data and the SC data are the same.

Hereinafter, the precoding matrix design technique will be described in detail.

The purpose of precoding is to maximize the amount of information transmitted by the system. Assuming that the source precoding matrix is F _S and A _b and A _s are matrices representing the power allocation ratios between the basic data and the SC data, respectively, the effective precoding matrixes for the basic data and the SC data are Q _b = F _S A _b , Q _s = F _S A _s , and letting R b and RS be the information transmission amounts of the basic data and the SC data, the amount of information received at the destination node will be expressed as shown in the following Equation 1 .

R ₁ and R ₂ in Equation (1) can be defined as Equation (2) below.

는 두 번째 전송시간 동안 R-D 링크를 통해 얻을 수 있는 SC 데이터의 정보량을 의미한다.In Equation (2), N _o denotes a power spectral density of a noise added to a relay node and a destination node, I denotes an identity matrix,

Means the amount of information of the SC data that can be obtained through the RD link during the second transmission time.

In order to maximize the information transmission amount in Equation (1), R ₁ and R ₂ The smallest value should be maximized. The precoding scheme proposed in the present invention selects a precoding matrix maximizing R ₁ and R ₂ , respectively, and finds an optimal precoding scheme through linear combination of selected matrices.

In Equation (2), R ₁ is an increasing function for Q _b and conversely is a form of decreasing function for Q _S. Therefore, the precoding matrices Q _{b , 1} and Q _{S , 1} that maximize R ₁ can be obtained by Equation (3).

의 전력제한조건(Power Constraint)을 가지고 워터필링 솔류션(Waterfilling solution)을 통해 얻어진 전력할당행렬이고, Ω_{S, 1}는

의 전력제한조건(Power Constraint)을 가지고 모든 전력을 가장 작은 singular vector에 할당하는 전력할당행렬이다. 즉, 프리코딩 행렬 Ω_b,1에서는 basic 데이터를 S-R 링크에서 전송률이 최대가 되도록 빔 방향과 전력을 할당해주는 반면, Ω_S,1에서는 SC 데이터를 S-R 링크에 전송률이 최소가 되도록 하여 릴레이 노드에서 얻을 수 있는 basic 데이터의 정보량을 최대로 얻도록 설계된다.And V _SR is the channel H _SR right singular matrix in equation 3, P _S is referred to as the transmit power of the source node and, Tr (x) is to as trace operation to obtain the sum of the diagonal elements of the matrix x, Ω _b is

Ω _{S, 1} is a power allocation matrix obtained through a waterfilling solution with a power constraint of

Is a power allocation matrix that assigns all power to the smallest singular vector with a power constraint of the power constraint. That is, in the precoding matrix Ω _{b, 1} , the beam direction and power are allocated so that the basic data is maximized in the SR link, while in the Ω _{S, 1} , the SC data is minimized in the SR link, It is designed to maximize the amount of basic data that can be obtained.

On the other hand, in Equation (2), R ₂ is an optimal precoding matrix depending on the sign of the molecule. However, in a typical relay environment, a molecule always has a negative component because the state of the RD link is better than that of the SD link. In this case R ₂ is in the form of an increasing function for Q _b and Q _s . Also, since there is a limitation that the beam directions of Q _b and Q _s must be the same as described above, the optimal precoding matrices Q _{b , 2} and Q _{s , 2} can be obtained as shown in Equation (4).

의 전력제한조건(Power Constraint)을 가지고 워터필링 솔류션(Waterfilling solution)을 통해 얻어진 전력할당행렬이다. 상기 프리코딩 행렬에서 Ω_b,2는 프리코딩 행렬의 방향의 제한에 의해 S-R 링크에 맞춰지게 되고, Q_{S ,2}는 S-R 링크 방향으로 설정해주어 릴레이 노드에서 얻을 수 있는 Basic 데이터의 정보량을 최대로 얻도록 한다.In Equation (4),? _{S, 2} is

Is a power allocation matrix obtained through a waterfilling solution with a power constraint of the power constraint. In the precoding matrix, Ω _{b, 2} is set to the SR link by limiting the direction of the precoding matrix, and Q _{S , 2} is set in the SR link direction to maximize the amount of basic data that can be obtained from the relay node .

From the above results, the precoding matrix for Basic data can be determined as Equation (5) because R ₁ and R ₂ are the same.

On the other hand, in the case of the precoding matrix Q _s for SC data, R ₁ and R ₂ have two different cases of power allocation. In the first case, the precoding matrix is designed to be minimized to the SR link to maximize the amount of basic data that can be obtained from the relay. In the second case, the precoding matrix is designed to be optimized for the SR link, The amount of information of the data is maximized. Thus, optimal power allocation can be found through a linear combination of the two cases. To find the optimal combination, Q _s can first be expressed as a linear combination as shown in Equation 6 below

If the value of? Is increased in the precoding matrix Q _S for Basic data represented by Equation (6), the information amount of R ₁ becomes large and the information amount of R ₂ becomes small. Conversely, if the value of? Is reduced, the information amount of R ₁ becomes smaller and the information amount of R ₂ becomes larger. With this principle, it is possible to maximize min {R ₁ , R ₂ } by changing the value of α from 0 to 1, increasing the smaller value of R ₁ and R ₂ while decreasing the larger value. It is also possible to determine the optimal power to be allocated to basic data and SC data while changing the value of β from 0 to 1. That is, in the precoding matrix determined in the form of a linear combination, α * and β *, which determine the optimal precoding matrix satisfying the following conditions while changing the values of α and β from 0 to 1, I can do it.

4 is a diagram schematically illustrating a partial information relay process through the MLSC scheme.

As shown in FIG. 4, the multi-layer superposition coding (MLSC) scheme is a technique for transmitting partial information by controlling the number of information streams transmitted by the relay node 20. First, the source node 10 divides the MJ non-forwarding streams x ₁ , which are not transmitted through the relay node 20, and the J forwarding streams x ₂ , which are transmitted through the relay node 20, into precoding matrices Q ₁ and Q ₂ to transmit. The non-forwarding stream x ₁ thus transmitted is decoded at the relay node 20 with the forwarding stream x ₂ interfering. Thereafter, the forwarding stream x ₂ is decoded through the SIC with the decoded non-forwarding stream x ₁ . Of the decoded data streams, the relay node 20 multiplies only the J forwarding streams x ₂ by the relay precoding matrix F _R , and transmits the result to the destination node 30. At this time, the relay precoding matrix F _R is designed as a matrix maximizing the information transmission amount of the RD link. Finally, the destination node 30 removes the J forwarding streams x ₂ received from the relay node 20 during the second transmission time in the signal received from the source node 10 during the first transmission time through the SIC, decodes the non-forwarding stream x ₁ .

In this MLSC scheme, the source precoding matrices Q ₁ and Q ₂ should be designed to maximize the information transmission capacity of the system. In the MLSC scheme, unlike the PASC described with reference to FIG. 3, the precoding matrices Q ₁ and Q ₂ have directional degrees of freedom.

The maximum amount of information that can be obtained when the MLSC technique is used is shown in Equation (8).

In Equation (8), R _A and R _B are respectively expressed by the following Equation (9).

는 두 번째 전송시간 동안 R-D 링크를 통해 얻을 수 있는 x₂의 정보량을 의미한다.In Equation (9)

Means the amount of information of x ₂ that can be obtained through the RD link during the second transmission time.

Likewise, to maximize the amount of information, the smaller of R _A and R _B must be maximized. In this way, a precoding matrix maximizing R _A and R _B is obtained, and a precoding matrix for maximizing a smaller one of the two values is obtained through the linear combination.

Referring to Equation (9), it can be seen that R _A is an increasing function for Q ₁ and conversely a decreasing function for Q ₂ . Therefore, the precoding matrices Q _{1 , A} and Q _{2 , A} that maximize R _A can be obtained as shown in Equation (10).

와

의 전력제한조건(Power constraint)를 가지고 워터필링(waterfilling)을 통해서 얻어질 수 있다. 이 과정에서 Q_{1 ,A}와 Q_{2 ,A}에 대한 전력 할당은 단순화를 위해 전송하는 스트림의 개수에 비례하여 할당한다. 즉 Q_{1 ,A}는 M-J개의 non-forwarding 스트림을 S-R 링크의 가장 큰 M-J 개의 eigenvector 방향으로 보냄으로써 릴레이에서 수신하는 non-forwarding 스트림의 정보량을 최대화하도록 설계되고, Q_{2 ,A}는 J개의 forwarding 스트림을 S-R 링크의 가장 작은 J 개의 eigenvector 방향에 맞추어 보내서 릴레이에서 디코딩하는 non-forwarding 스트림의 정보량을 최대화하게 된다. In equation (10), V _SR (1: MJ) denotes the largest MJ singular vector of the channel H _SR , and V _SR (M-J + 1: M) denotes the smallest J singular vector of the channel H _SR . do. Also, Ω _{1, A} and Ω _{2, and A} are

Wow

And can be obtained through waterfilling with a power constraint of the power constraint. In this process, the power allocation for Q _{1 , A} and Q _{2 , A} is allocated proportionally to the number of streams to be transmitted for simplification. That is, Q _{1 , A} is designed to maximize the amount of information of the non-forwarding streams received at the relay by sending MJ non-forwarding streams toward the largest MJ eigenvectors of the SR link, Q _{2 ,} To the J eigenvector direction of the SR link to maximize the amount of information in the non-forwarding stream that is decoded at the relay.

On the other hand, referring to Equation (9), R _B has an optimal precoding matrix depending on the sign of the molecule. However, in a typical relay environment, the sign of a molecule can be regarded as a negative number because the information transfer amount of the SD link is smaller than the information transfer amount of the RD link. In this case R _B is an increasing function for Q ₁ and also for Q ₂ in the form of an increasing function. Thus, the precoding matrices Q _{1 , B} and Q _{2 , B} that maximize R _B are obtained as: < EMI ID = 11.0 >

와

의 전력제한조건(Power constraint)를 가지고 워터필링(waterfilling)을 통해서 얻어질 수 있다. 상기 프리코딩 행렬에서 Q_{1 ,B}는 M-J개의 non-forwarding 데이터 스트림을 S-D 링크의 가장 큰 M-J 개의 eigenvector 방향으로 보냄으로써 목적지 노드(30)에서 수신하는 non-forwarding 데이터 스트림의 정보량을 최대화하도록 설계되고, Q_{2 ,B}는 J개의 forwarding 데이터 스트림을 S-R 링크의 가장 큰 J 개의 eigenvector 방향에 맞추어 보내서 릴레이 노드(20)에서 수신하는 forwarding 데이터 스트림의 정보량을 최대화하도록 설계된다.In Equation (11), V _SD (1: MJ) means the largest MJ singular vector of the channel H _SD , and V _SR (1: J) means the largest J singular vector of the channel H _SR . Also, Ω _{1, B} and Ω _{2, and B} are

Wow

And can be obtained through waterfilling with a power constraint of the power constraint. In the precoding matrix, Q _{1 and B} are designed to maximize the amount of information of the non-forwarding data stream received at the destination node 30 by sending MJ non-forwarding data streams toward the largest MJ eigenvectors of the SD link , Q _{2 , and B} are designed to maximize the amount of information of the forwarding data stream received at the relay node 20 by sending J forwarding data streams to the J eigenvector directions of the largest SR links.

Thus, to a precoding matrix Q ₂ for the precoding matrix Q ₁ and forwarding the data stream to the optimum non-forwarding the data stream to the linear combination of the obtained R _A and a precoding matrix optimized for R _B Equation (12) and Mathematical Can be expressed as Equation 13.

In the above equations (12) and (13), if the value of? Is increased, the information amount of R _A becomes larger and the information amount of R _B becomes smaller. On the contrary, if the value of? Is reduced, the information amount of R _A becomes smaller and the information amount of R _B becomes larger. With this principle, by changing the value of α from 0 to ₁ , it is possible to maximize the min {R ₁ , R ₂ } by decreasing the larger value of R ₁ and R ₂ while increasing the smaller value. Therefore, while changing the value of alpha from 0 to 1, it is possible to determine alpha * which determines an optimal precoding matrix satisfying the following expression (14).

In order to design the precoding matrix of the two schemes of PASC and MLSC proposed in the present invention, all channel information of the S-R link, the S-D link and the R-D link is required. According to an embodiment of the present invention, consideration is given to designing a precoding matrix at a destination node 30 in which channel information collection is easy.

Assuming that a fixed relay node is used in downlink data transmission / reception, a channel S-R link between a source node and a relay node is maintained at a constant value without being largely changed regardless of the mobility or scheduling of a user terminal as a destination node. The source node periodically broadcasts the channel value of the S-R link to the UEs through the downlink channel. However, according to another embodiment of the present invention, it is also possible to inform the UEs of the channel value of the S-R link at the relay node.

In this way, the users always have the channel information of the SR link, and the user scheduled at that time acquires the channel information of the SD link and the RD link through the downlink channel estimation. The user who has collected the SR, SD, and RD channel information as described above transmits R ₁ and R ₂ (R _A and R _B ), and determines optimal precoding matrices based on the calculated values. In this process, the precoding matrix has a component of a precoding matrix for a certain SR link (only the SR link component in case of PASC). Therefore, codeword can be found within a certain region of the codeword for the SR link without searching through the entire codebook. The codeword index thus determined is sent to the source node via the feedback link.

5 is a block diagram schematically illustrating a configuration of a destination node according to an embodiment of the present invention.

The destination node includes a receiving unit 201 for receiving channel information between the source node and the relay node from the source node, a decoding unit 203, channel information between the source node and the destination node, and channel information for estimating the channel state between the relay node and the destination node. A precoder 207 for calculating an optimal precoding matrix by calculating a transmission rate of the first data and a second data based on channel information obtained through the channel estimation unit 205 and the channel estimation unit 205, An encoding unit 209, and a transmitter 211 for feeding back the determined optimal precoding matrix component to the source node.

In the destination node, the channel information of the SR link, the SD link, and the RD link is received from the source node or the relay node, or acquired through channel estimation, and an optimal precoding matrix that can be transmitted through the PASC or MLSC technique described above is designed . Then, the designed precoding matrix component is fed back to the source node to form an optimal beam pattern at the source node to transmit the signal. The concrete precoding matrix design method has been described in detail above, and a detailed description thereof will be omitted.

In addition, the destination node may be a terminal in the case of downlink data transmission / reception, and may be a base station in case of uplink data transmission / reception.

The method according to the present invention described so far can be implemented in software, hardware, or a combination thereof. For example, the method according to the present invention may be stored in a storage medium (e.g., terminal internal memory, flash memory, hard disk, etc.) and executed by a processor Lt; RTI ID = 0.0 > and / or < / RTI >

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, May be modified, modified, or improved.

Claims (12)

A method for a destination node to receive a multiple data stream including a first data and a second data in a multi-antenna relay communication system,
Receiving channel information between a source node and a relay node;
Acquiring channel information between a source node and a destination node and channel information between a relay node and a destination node through channel estimation based on the channel information;
Calculating an optimal precoding matrix by calculating a data rate of the first data and a second data based on the obtained channel information; And
And feeding back the determined optimal precoding matrix component to the source node,
The second data is a part of data received from the relay node among the multi data streams and the first data is data other than the second data among the multi data streams, Determining the precoding matrix so that a data rate having a minimum value among data rates is maximized,
Wherein the first data and the second data are subjected to Per Antenna Superposition Coding for each transmission antenna and are transmitted, and when the first data is a data stream including the second data from the relay node, Performs decoding on the first data through Successive Interference Cancellation (SIC) using the decoded second data,
Wherein when the first data and the second data are superposition-encoded for each transmission antenna, the power allocation of the first data and the second data is set to be different from each other, and the precoding direction of the first data and the second data Are set to be the same. delete delete delete delete delete An apparatus for receiving a multiple data stream comprising first data and second data in a multi-antenna relay communication system,
A receiver for receiving channel information between a source node and a relay node;
A channel estimator for estimating channel information between a source node and a destination node based on the channel information and a channel state between a relay node and a destination node;
A controller for calculating an optimal precoding matrix by calculating a data rate of the first data and a second data based on channel information obtained through the channel estimator; And
And a transmitter for feeding back the determined optimum precoding matrix component to the source node,
The second data is a part of data received from the relay node among the multi data streams and the first data is data other than the second data among the multi data streams, Determining the precoding matrix so that a data rate having a minimum value among data rates is maximized,
Wherein the first data and the second data are subjected to Per Antenna Superposition Coding for each transmission antenna and are transmitted, and when the first data is a data stream including the second data from the relay node, Performs decoding on the first data through Successive Interference Cancellation (SIC) using the decoded second data,
Wherein when the first data and the second data are superposition-encoded for each transmission antenna, the power allocation of the first data and the second data is set to be different from each other, and the precoding direction of the first data and the second data Are set to be the same,
A multi-data stream receiving apparatus in a multi-antenna relay system. delete delete delete delete delete

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