KR20100060958A - A method for alternate transmission relaying with interference cancellation in a wireless communication network and a system thereof - Google Patents

Abstract

PURPOSE: A system for alternate transmission method interference removal based using relay in wireless communication system and a system therefor are provided to transmit a received signal from a source node in a plurality of relay nodes thereby reducing data transmission time. CONSTITUTION: A source node(100) transmits a signal. The first relay node(210) is located in the one-hop distance from the source node. The first relay node receives the signal from the source node in the first transfer time. The first relay node relays the signal to a target node(300) in the second transfer time. The second relay node(220) receives the signal from the source node in the second transfer time. The second relay node relays the signal to the destination node in the first transfer time.

Description

A method for alternating transmission relaying with interference cancellation in a wireless communication network and a system

The present invention relates to a transmission scheme using a repeater and a system for the same in a wireless communication network, and more particularly, a repeater capable of improving the capacity of the system through alternating transmission in the transmission scheme using the repeater and eliminating interference in the relay period. The present invention relates to an interference cancellation based alternate transmission scheme in a wireless communication system and a system therefor.

In recent wireless communication networks, especially cellular communication, the use of repeaters (or relay nodes) has been considered to expand the cell area and improve the data rate. The system considering the repeater is largely composed of a source node, a relay node, and a destination node.

In such a wireless communication network, assuming that the distance between the source node and the target node is far enough to communicate directly with each other, it is possible to communicate between the source and the target node by utilizing a relay node located between the source and the target node.

In general, when the data is sent from the source node to the destination node in the system as described above, a method of transmitting using two time resources using a repeater is used.

That is, in the first time resource, the signal is transmitted from the source node to the relay node, and in the second time resource, the relay node transmits the signal to the destination node. Meanwhile, a plurality of relay nodes may be used in such a general wireless communication network.

1 is a diagram for describing a transmission scheme in a wireless communication network using a plurality of such general relay nodes.

Referring to FIG. 1, the source node 1 transmits data to the relay nodes 2 in a first time slot, and the relay nodes 2 transmit a second time slot. Sends data to the destination node (3). As such, the relay nodes 2 simultaneously receive signals from the source node 1 and simultaneously transmit signals to the destination node 3, which has two problems. First, the system capacity is lost due to the use of two time resources. Second, in order to benefit from using multiple relay nodes, cooperation between relay nodes (eg, sharing of the received signals with each other and pre-processor application) is required. However, in a general wireless communication environment, relay nodes are separated from each other and have a structure in which practical cooperation is difficult. In such a prior art, it is difficult to obtain a performance improvement of a system without cooperation between relay nodes.

Accordingly, an object of the present invention in view of the above-described conventional problems is an interference cancellation based alternate transmission scheme using a repeater in a wireless communication network that can effectively improve the performance of a system without requiring cooperation between relay nodes. To provide a system.

A system for interference cancellation based shift transmission using a relay node in a wireless communication network according to a preferred embodiment of the present invention for achieving the above object includes a source node for transmitting a signal; A first relay node positioned one hop from the source node and receiving a signal from a source node at a first transmission time and relaying a signal to a destination node at a second transmission time; A second relay node positioned one hop from the source node and receiving a signal from a source node at a second transmission time and relaying a signal to a destination node at a first transmission time; And the destination node for receiving signals from the first and second relay nodes.

When one of the first and second relay nodes receives an interference signal from another node, the relay node estimates an effective channel in which a null space between the first and second relay nodes exists, and the interference signal. Is removed using the interference cancellation matrix calculated from the effective channel.

Any one of the first and second relay nodes estimates an effective channel in which null space exists between the first and second relay nodes, and uses the interference cancellation matrix calculated from the effective channel to transfer to another node. The interference signal is characterized in that the transmission.

The first and second relay nodes transmit a signal obtained by multiplying a power distribution matrix calculated by calculating a power distribution matrix to the target node.

When the destination node receives a signal from one of the first and second relay nodes, the destination node estimates an interference signal using a signal received before the received signal, and removes the interference using the estimated signal. It is characterized by.

In order to achieve the above object, the interference cancellation based alternate transmission method using a relay node in a wireless communication network according to an embodiment of the present invention,

In a first transmission time, the first relay node receives a signal from the source node, the second relay node transmits a signal previously received from the source node to the destination node, and at the second transmission time, And a second process, wherein the second relay node receives a signal from the source node, and the first relay node transmits the signal received from the source node to the destination node.

In the first and second processes, when one of the first and second relay nodes receives an interference signal from another node, a null space between the first and second relay nodes exists. The channel is estimated, and the interference signal is removed using the interference cancellation matrix calculated from the effective channel.

In the first and second processes, any one of the first and second relay nodes may estimate an effective channel having a null space between the first and second relay nodes, and remove the interference calculated from the effective channel. It is characterized in that the interference signal is removed using a matrix and transmitted to another relay node.

In the first and second processes, the first and second relay nodes transmit a signal obtained by multiplying the power distribution matrix calculated by calculating a power distribution matrix to the target node.

When the target node receives a signal from one of the first and second relay nodes, estimating an interference signal using a signal previously received from the received signal and removing the interference using the estimated signal It characterized in that it further comprises.

According to the present invention, a plurality of relay nodes alternately transmit a signal received from a source node, thereby reducing data transmission time without requiring cooperation between relay nodes, and improving system performance.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, only parts necessary for understanding the operation according to the embodiment of the present invention will be described, and the description of other parts will be omitted so as not to disturb the gist of the present invention.

The terms or words used in the specification and claims described below should not be construed as being limited to the ordinary or dictionary meanings, and the inventors are appropriate to the concept of terms in order to explain their invention in the best way. It should be interpreted as meanings and concepts in accordance with the technical spirit of the present invention based on the principle that it can be defined. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only one of the most preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

First, a structure of a wireless communication network according to an embodiment of the present invention will be described. 2 is a view for explaining the structure of a wireless communication network according to an embodiment of the present invention.

2, a wireless communication network according to an exemplary embodiment of the present invention includes a source node 100, a relay node 200, and a destination node 300. Hereinafter, a generic reference numeral 200 is used to refer to a relay node, and the relay node includes first and second relay nodes 210 and 220.

Here, when the wireless communication network is a cellular-based mobile communication system, the source node may be a base station, each of the relay nodes 210 and 203 may be a repeater, and the destination node 300 may be a terminal.

, 중계기 2에서는

)의 안테나를 갖고 있다고 가정한다. It is assumed that the source node 100 and the destination node 300 each have M transmit / receive antennas, and each repeater has N (relay 1).

, In repeater 2

Assume that you have an antenna of).

,

), 중계 노드(210, 220)에서 목적 노드(300)간의 채널은 포워드(forward) 채널(

,

)로 구분한다. 또한, 중계 노드는 2개로 가정하며, 중계 노드간(210, 220)의 채널은

,

이다. For convenience of description, the channel between the relay nodes 210 and 220 in the source node 100 is a backward channel (

,

), The channel between the destination node 300 in the relay node (210, 220) is a forward channel (

,

). In addition, it is assumed that two relay nodes, and channels between the relay nodes 210 and 220

,

to be.

As described above, a transmission scheme using two general time resources is in the capacity reduction of the system. Therefore, according to an embodiment of the present invention, a technique of transmitting as follows is used to solve this problem.

First, the source node 100, each relay node 210 and 220, each relay node 210 and 220 and the destination node 300 are each located one hop away. At this time, the source node 100 and the second relay node 220 transmit at odd-numbered transmission time slots, and the source node 100 and first relay node at even-numbered transmission time slots. 210 transmits. At this time, the source node 100 transmits in consideration of the channel with each relay node (210, 220). That is, in the odd numbered transmission time, only the channel for the first relay node 210 is considered and the channel for the second relay node 220 is not considered. In addition, at the even transmission time, the source node 100 considers only the channel for the second relay node 220 and communicates without considering the channel for the first relay node 210.

Each relay node 210 or 220 transmits a signal in consideration of a channel with the destination node 300.

As such, when the source node 100 and the relay nodes 210 and 220 alternately transmit signals, time resources required for transmitting data from the source node 100 to the target node can be cut in half.

Assuming that the signal transmission time between each node 100 and 200, 200 and 300 is T, the prior art has an average transmission time of 2T from the source node to the destination node. In contrast, the proposed transmission scheme requires a time resource of T.

개의 심벌 벡터를 전송한다고 가정할 때, 필요한 총 시간 자원은 (2

+ 1)T가 되고 소스 노드(100)에서 목적 노드(300)까지의 평균 전송 시간은 다음의 <수학식 1>과 같이 구할 수 있다.According to an embodiment of the present invention, since different data may be sent through the first and second relay nodes 210 and 220, a total of 2

Suppose we send t symbol vectors, then the total time resources needed are (2

+ 1) T and the average transmission time from the source node 100 to the destination node 300 can be obtained as shown in Equation 1 below.

가 커질수록, 즉 여러 번의 전송을 계속 했을 경우 평균 전송 시간이 종래 기술에 비해 절반으로 줄어드는 효과를 얻을 수 있게 된다. 따라서 중계 노드간(210, 220)의 교대 전송을 통하여 시간 자원의 손실을 막을 수 있고 이를 통해 시스템의 용량 개선을 얻을 수 있다. 또한 제1 중계 노드와 제2 중계 노드(210, 220)가 서로 다른 시간 자원을 통해 송신을 하므로 중계 노드(210, 220)간의 협력 없이도 송신이 가능하게 된다. Referring to <Equation 1>,

As is increased, that is, when several transmissions are continued, the average transmission time can be reduced by half compared to the prior art. Therefore, loss of time resources can be prevented through alternating transmission between relay nodes 210 and 220, thereby improving system capacity. In addition, since the first relay node and the second relay nodes 210 and 220 transmit through different time resources, transmission is possible without cooperation between the relay nodes 210 and 220.

On the other hand, the transmission technique through the alternate transmission can prevent the loss of time resources, but the signal transmitted from one relay node to the target node acts as an interference signal to the other relay node. That is, when the first relay node 210 transmits to the destination node 300, since the second relay node 220 receives the signal from the source node 100, the signal transmitted from the first relay node 210 is transmitted. The second relay node 220 acts as an interference signal. Therefore, in the embodiment of the present invention, interference cancellation between relay nodes is performed in order to maximize performance improvement due to alternating transmission.

The interference cancellation method between relay nodes according to an embodiment of the present invention may be two types. First, there is a method of removing interference at the destination node and second, a method of removing interference at the relay node. For this interference cancellation, it is assumed that all nodes transmitting data know the channel information. That is, it is assumed that the source node has channel information with the relay node, and the relay node knows channel information from the source node and channel information to the destination node.

In an embodiment of the present invention, it is assumed that linear processing based on singular value decomposition (SVD) is performed between nodes. In addition, it is assumed that the relay node according to an embodiment of the present invention operates in an amplify-and-forward (AF) mode. This method according to an embodiment of the present invention is applicable to the repeater in the decode-and-forward (DF) mode in the same manner.

에 대하여 다음의 <수학식 2>를 사용한다. Arbitrary matrix

Use Equation 2 below.

를 곱한다. 이러한 과정을 선처리 과정이라 한다. 또한, 후처리기는 특정 신호에

의 허미션(Hermitian), 즉,

을 곱한다. 이러한 과정을 후처리 과정이라 한다. Referring to Equation 2, in an embodiment of the present invention, the preprocessor of each node (particularly a relay node) may be applied to a specific signal.

Multiply by This process is called a pretreatment process. The postprocessor can also

Hermitian, that is,

Multiply by This process is called post-processing.

First, the interference cancellation method in the destination node 300 according to an embodiment of the present invention will be described. 3 is a diagram for describing a method for canceling interference at a target node according to an exemplary embodiment of the present invention.

Here, the relay node 200 only plays a role of relaying a signal without removing interference. Accordingly, the first or second relay nodes 210 and 220 in FIG. 3 perform the same operation.

Referring to FIG. 3, the source node 100 transmits a signal to the relay node 200. Then, the relay node 200 receives a signal in step S301. The signal received by the relay node 200 is expressed by Equation 3 below.

는 소스 노드(100)와 중계 노드(k) 사이의 채널이고,

는 소스 노드(100)에서 선처리기가 적용된 송신 신호이다.

는 중계기

로부터 중계노드

로의 채널이고 (

),

는 중계 노드

에서의 송신 신호이다. At this time,

Is a channel between the source node 100 and the relay node k,

Is a transmission signal to which the preprocessor is applied at the source node 100.

Repeater

Relay node from

Is a channel to (

),

Is a relay node

Is the transmission signal from.

)을 곱한다. 앞서 설명한 바와 같이, 중계 노드(200)는 소스 노드(100)와 중계 노드간의 채널인 백워드(backward) 채널을 알고 있다고 가정한다. 수신 신호인 <수학식 3>에 대하여 후처리기를 적용하여 다음과 같은 <수학식 4>를 얻을 수 있다. Then, the relay node 200 is a post-processor matrix of the backward channel to the signal received in step S303 (

Multiply by As described above, it is assumed that the relay node 200 knows a backward channel, which is a channel between the source node 100 and the relay node. The following Equation 4 can be obtained by applying a post-processor to the received signal <Equation 3>.

)과, 송신 전력 상수를 곱한다. 그러면, 중계 노드

에서의 전송 신호는 다음의 <수학식 5>과 같이 표현된다.Then, the relay node 200 in step S305 the preprocessor matrix of the forward channel (

) Is multiplied by the transmit power constant. The relay node

The transmission signal in is expressed as Equation 5 below.

는 중계 노드에서 송신 전력을 만족시키기 위한 상수이 다. In Equation 5,

Is a constant for satisfying the transmit power at the relay node.

As such, the interference cancellation scheme in the destination node 300 transmits a signal including the interference signal to the destination node 300 without performing interference cancellation at each relay node.

As described above, when the relay node 200 transmits a signal as shown in Equation 5, the destination node 300 receives the signal and applies the post processor. As such, the signal obtained by applying the post-processor to the signal received from the target node 300 may be represented by Equation 6 below.

Since the signal received from the destination node 300 includes the interference signal component, the interference signal component should be estimated and removed.

Therefore, the target node 300 estimates and removes the interference signal in step S307. Since the interference component of the signal received at the destination node 300 becomes a signal previously received at the destination node 300, the interference signal may be estimated using the interference component. The received signal is expressed as Equation 7 below.

The interference signal component can be estimated from Equation 7 as shown in Equation 8 below.

는

의 슈도-인버스(pseudo-inverse)를 나타낸다. 이와 같이, 추정된 간섭 신호 성분을 받은 신호에서 빼주면 다음의 <수학식 9>와 같은 간섭 제거가 이루어진 신호를 얻을 수 있다. Where,

Is

Pseudo-inverse of the (pseudo-inverse). In this way, if the estimated interference signal component is subtracted from the received signal, an interference canceled signal as shown in Equation 9 may be obtained.

Up to now, the method for canceling interference at the destination node 300 has been described. Next, the interference cancellation method in the relay node will be described.

In the relay node, interference cancellation can be divided into two types. First, there is a technique of applying a preprocessor so that a transmission signal from a repeater does not affect other repeaters, and there is a technique of applying and removing a postprocessor to an interference signal received from another repeater.

The former will be referred to as a transmit nulling technique and the latter as a receive nulling technique. Basically, the repeater aims to eliminate the interference signal rather than to reduce it completely.

First, a transmission nulling technique according to an embodiment of the present invention will be described. 4 is a diagram illustrating an interference cancellation method using a transmission nulling technique in a relay node according to an embodiment of the present invention.

Referring to Fig. 4, in order to prevent the transmission signal at the relay node from being affected by other relay nodes (to cause the interference signal to be "0"), the transmission signal is projected to the null space of the channel matrix between the relay nodes. (projection) However, when each relay node uses the same number of antennas, the null matrix does not exist because the channel matrix between the relay nodes becomes a square matrix.

Therefore, in the embodiment of the present invention, it should be modified so that a null space of a channel in the relay period exists.

)을 추정할 수 있다. Accordingly, when the relay node receives a signal from the source node 100 in step S401, the relay node estimates an effective channel in step S403. As described in Equation 4, each relay node applies a post-processor to a received signal, and according to Equation 10 below, an effective channel between relay nodes in which null space exists is present.

) Can be estimated.

Therefore, if the transmission signal of each repeater is multiplied by the following interference cancellation matrix, the signal is projected to the null space of the effective channel of the repeater period, so that no other interference signal is received by the other repeater.

Accordingly, the relay node calculates the interference cancellation matrix through Equation 11 below in step S405.

Subsequently, the relay node multiplies the postprocessor matrix of the backward channel in step S407, and multiplies the interference cancellation matrix calculated in step S409. Subsequently, the relay node multiplies the preprocessor matrix of the effective channel in step S411, and sequentially multiplies the transmission power constants in step S413 to transmit to the destination node 300. The transmission signal at this relay node is expressed by Equation 12 below.

로 변형되므로 원래 주어진 포워드 채널의 이득보다 적은 채널 이득을 얻게 된다. At this time, the channel between the destination node 300 in the relay node

Since it is transformed into, the channel gain is less than the gain of the originally given forward channel.

Following the transmission nulling technique, a reception nulling technique according to an embodiment of the present invention will be described. 5 is a diagram illustrating an interference cancellation method using a reception nulling technique in a relay node according to an embodiment of the present invention.

The reception nulling technique performs interference cancellation on the same principle as the transmission nulling technique. That is, the relay node removes interference by multiplying the interference cancellation matrix by the received signal from the source node 100. In this case, the interference cancellation matrix may be obtained according to Equation 13 below.

In addition, an effective channel between relay nodes is obtained according to Equation 14 below.

Referring to FIG. 4, the relay node estimates an effective channel of the relay period according to Equation 11 or Equation 14 in operation S501 and calculates an interference cancellation matrix according to Equation 13 in operation S503. .

Subsequently, the relay node multiplies the interference cancellation matrix calculated in step S505, multiplies the postprocessor matrix of the effective backward channel in step S507, multiplies the preprocessor matrix of the forward channel in step S509, and multiplies the transmit power constant in step S511. Multiply sequentially to transmit to the destination node (300).

로 변형되므로 백워드 채널에서 손실이 발생할 수 있다. When the receive nulling technique is used, the channel between the relay nodes at the source node 100 is reversed as opposed to the transmit nulling technique.

The loss may occur in the backward channel because

As described above, by applying the proposed SVD-based signal processing technique, an effective channel can be obtained in a diagonal matrix form at each relay node. As such, when the effective channel is diagonalized, several data may be separated by layers, thereby facilitating distribution of transmission power for each layer. In this case, the transmission power distribution matrix may also be obtained in the form of a diagonal matrix. Next, the transmission power distribution scheme according to the embodiment of the present invention will be described.

In the case of the transmission nulling technique, signal processing at each relay node can be obtained in a matrix form as shown in Equation 15 below.

In addition, the signal received by the destination node 300 can be obtained as shown in Equation 16 below.

At this time, the capacity formula that can be transmitted through the repeater k is shown in Equation 17 below.

Looking at Equation 17, since all matrices are made of diagonal matrices, they can be converted into the following Equation 18.

In addition, a method of finding a transmission power distribution matrix capable of maximizing the capacity of each relay node may be represented by an optimization problem as shown in Equation 19 below.

Equation 19 is a convex optimization problem, and an optimal solution can be easily obtained through simple derivatives. The solution to the above problem is obtained as shown in Equation 20 below.

를 찾아야 한다. 이러한 라그랑지 계수를 찾기 위하여 다음의 <수학식 20a>와 같은 함수를 이용한다. Lagrange multiplier to obtain the solution of Equation 20

You must find In order to find the Lagrangian coefficient, a function as shown in Equation 20a is used.

로 치환하고, <수학식 20a>과 같은 함수(

)를 중계 노드에서 각 데이터 계층별 송신 전력의 합으로 나타내면, 함수(

)는

값에 따라서 변화하게 되고, 이 값이 중계 노드에서의 송신 전력(

)과 같아지는 라그랑지 계수(

)를 찾으면, <수학식 20>에서 주어진 해를 얻을 수 있게 된다. 중계 노드에서의 송신 전력(

)을 만족하는 라그랑지 계수를 찾기 위하여 황금 분할 검색(golden section search) 방법을 사용한다. 이 때 목적 함수와

값의 범위는 다음의 <수학식 21>과 같이 나타낼 수 있다. To find the Lagrangian coefficients,

And replace it with a function such as <Equation 20a>

) Is expressed as the sum of the transmit powers of each data layer at the relay node.

)

Depending on the value, and this value is the transmit power at the

Lagrange modulus equal to

), The solution given by Equation 20 can be obtained. Transmit power at the relay node (

We use the golden section search method to find the Lagrangian coefficient that satisfies In this case, the objective function

The range of values can be expressed as Equation 21 below.

--------- (식 1)

--------- (Equation 1)

----------------------- (식 2)

----------------------- (Equation 2)

은

번째 계층의 송신 전력이

일 때의 라그랑지 계수의 값이다(식 2). 최적의 라그랑지 계수의 값은 항상 <수학식 21>의 최소값과 최대값 사이에 존재하므로, 제안된 방법을 사용하면 몇 번의 반복 과정을 통해 최적의 값을 얻을 수 있다. Looking at Equation 21,

silver

The transmit power of the first layer

It is the value of the Lagrangian coefficient when (Equation 2). Since the optimal Lagrangian coefficient always exists between the minimum and maximum values of Equation 21, the proposed method can obtain the optimal value through several iterations.

Using the method as described above, the transmission power distribution matrix can be calculated. Next, the signal transmission method of the relay node applying the transmission power distribution scheme will be described. 6 is a diagram illustrating a transmission power distribution scheme of a relay node according to an embodiment of the present invention.

)를 산출한다. 즉, <수학식 21>에 따라 라그랑지 계수(

)를 산출한다. Referring to FIG. 6, the relay node uses an optimal Lagrangian coefficient through a golden section search method in step S601.

) Is calculated. That is, the Lagrangian coefficient (

) Is calculated.

)를 이용하여, <수학식 19> 또는 <수학식 20>의 해를 구하는 것이다. The relay node then calculates a transmit power distribution matrix in step S603. At this time, the transmission power distribution matrix is calculated Lagrangian coefficient (

) To solve Equation 19 or Equation 20.

Then, the relay node multiplies the transmission power distribution matrix by the signal received from the source node 100 in step S605 and transmits to the destination node 300.

In the above, the interference cancellation scheme and the transmission power distribution scheme have been described.

In the above-described embodiment, the case in which all relay nodes are located at one hop distance of the destination node 300 has been described. Next, a wireless communication network using relay nodes in multi-hop will be described.

7 is a view for explaining the structure of a wireless communication network according to another embodiment of the present invention.

Referring to FIG. 7, a topology of a wireless communication network according to another exemplary embodiment of the present invention may sequentially include a source node 100, a first relay node 210, a second relay node 220, and a destination node 300. It is made, including. Each node is in one hop transmission range. That is, unlike the previous embodiment, the first relay node 210 transmits a signal to the destination node 300 through the second relay node 220. Here, as in the foregoing embodiment, the source node 100 may be a base station, each relay node may be a repeater, and the destination node 300 may be a terminal. In addition, although two relay nodes are assumed here and described, a plurality of relay nodes may be provided.

In such a system, relay nodes divide transmission time into odd- and even-hops according to their positions, and then alternately transmit groups by odd and even-hops (even-hops). do.

When odd-hop relay nodes, such as the first relay node 210, transmit, even-hop relay nodes, such as the second relay node 220, receive and even-hop. hop When relay nodes transmit, odd-hop relay nodes receive. In such a transmission scheme, an interference problem may occur in the relay period.

The destination node 300 receives data from the source node 100 through the first and second relay nodes 210 and 220.

In the time domain transmitted by the even hops, the source node 100 and the second relay node 220 transmit simultaneously, and the first relay node 210 receives a signal from the source node 100 and at the same time the second relay node. Receive an interference signal from 220. On the other hand, in the time domain transmitted by the odd hop, the first relay node 210 transmits a signal to the second relay node 220.

In the even hop transmission time domain, since the first relay node 210 receives the interference signal from the second relay node 220, the second relay node 220 applies the reception nulling technique to remove the interference, or The 1 relay node 210 may remove the interference by applying a transmission nulling technique.

The transmit nulling technique is to multiply the signal transmitted from the second relay node 220 to the destination node 300 by the interference cancellation matrix so that the interference signal does not affect the first relay node 210. The first relay node 210 removes the interference signal component included in the received signal by multiplying the interference cancellation matrix by the interference signal received from the second relay node 220. The method of canceling the interference signal using orthogonal projection has a disadvantage in that the number of antennas is additionally required, but the operation of the system can be simplified by completely removing the interference signal.

Next, an interference cancellation method using the transmission nulling technique in the second relay node 220 will be described. 8 illustrates an interference cancellation method using a transmission nulling technique according to an embodiment of the present invention.

Referring to FIG. 8, the second relay node 220 estimates a channel between the first and second relay nodes 210 and 220 in step S801.

Next, the second relay node 220 calculates an interference cancellation matrix based on the estimated channel between the first and second relay nodes 210 and 220 in step S803. That is, as described above, the transmission signal from the relay node may be projected to the null space of the channel matrix between the first and second relay nodes 210 and 220 so as not to be affected by other relay nodes. Produces a matrix

Then, the second relay node 220 transmits a signal to the destination node 300 by multiplying the interference cancellation matrix calculated in step S805. In this case, the signal transmitted to the destination node 300 is also transmitted to the first relay node 210. At this time, the signal transmitted by multiplying the interference cancellation matrix is projected to a null space, and thus does not act as interference to the first relay node 210.

Then, the interference cancellation method using the reception nulling technique in the first relay node 210 will be described. 9 is a diagram illustrating an interference cancellation method using a transmission nulling technique according to an embodiment of the present invention.

Referring to FIG. 9, the first relay node 210 estimates a channel between the first and second relay nodes 210 and 220 in step S901.

Then, the first relay node 210 calculates an interference cancellation matrix based on the estimated channel between the first and second relay nodes 210 and 220 in step S903. That is, as described above, the transmission signal from the relay node may be projected to the null space of the channel matrix between the first and second relay nodes 210 and 220 so as not to be affected by other relay nodes. Produces a matrix

Then, the first relay node 210 removes the interference by multiplying the interference cancellation matrix calculated by the interference signal received from the second relay node 220 in step S905. That is, in contrast to the interference cancellation described above with reference to FIG. 8, even if the second relay node 220 transmits a signal that does not remove interference to the first relay node 210, the first relay node 210 generates an interference cancellation matrix. In the case of multiplication, the received signal is projected to a null space and thus does not interfere with the first relay node 210.

Meanwhile, in the above-described wireless communication network as shown in FIG. 7, the target node 300 (terminal) needs three time resources to receive a signal from the source node 100 (base station). It can be obtained as shown in Equation 22.

은 소스 노드(100)와 제1 중계 노드(210)간의 용량,

는 제1 중계 노드(210)와 제2 중계 노드(220)간의 용량, 및

는 제2 중계 노드(220)와 목적 노드(300)간의 용량을 나타낸다. <수학식 22>에서 보여진 바와 같이, 시스템의 이론적인 최대 용량(upper bound)은 소스 노드(100)와 제1 중계 노드(210) 사이의 용량(

)에 의해서 결정됨을 알 수 있다. In Equation 22,

Is the capacity between the source node 100 and the first relay node 210,

Is the capacity between the first relay node 210 and the second relay node 220, and

Denotes the capacity between the second relay node 220 and the destination node 300. As shown in Equation 22, the theoretical maximum capacity of the system is the capacity between the source node 100 and the first relay node 210.

It can be seen that it is determined by).

,

,

의 최소값으로 결정되므로

값의 손실을 막는 것도 중요하지만,

,

값을

과 비슷하거나 크게 유지해주어야 시스템의 최대 용량값에 가까운 결과를 얻을 수 있다. That is, it can be seen that communication between the source node 100 and the first relay node 210 is the most important, and that there is a loss of data between the two nodes 100 and 210, which may lead to deterioration of the performance of the entire system. . Therefore, if the interference signal from the second relay node 220 is not properly processed, performance degradation will be caused. The capacity of the entire system is three

,

,

Is determined by the minimum of

It is also important to prevent the loss of value,

,

Value

It should be kept close to or larger than, so that the result is close to the maximum capacity of the system.

값을 그대로 유지할 수 있다. 또한, 제2 중계 노드(220)가 다른 노드보다 많은 안테나를 가지고 있으므로, 제1 및 제2 중계 노드(210, 220)간, 제2 중계 노드(220)와 소스 노드(300)간의 채널 이득이 소스 노드(100)와 제1 중계 노 드(210)간의 채널에 비하여 클 것을 예상할 수 있다. 따라서 제2 중계 노드(220)와 목적 노드(300)간의 채널 이득이 간섭 제거 행렬에 의한 효과 때문에 줄어들더라도,

값이

의 값과 유사하게 유지될 것을 예상할 수 있다. 수신 널링 기법을 사용하는 경우에도, 제1 중계 노드(210)에 더 많은 안테나를 설치함으로써, 동일한 효과를 기대할 수 있다. 따라서 이와 같은 다중 안테나를 사용한 간섭 제거 기법을 통하여 중계 노드에서의 간섭 제거 및 시스템의 성능 향상을 얻을 수 있다. For example, in the case of a transmission nulling scheme, the source node 100, the first relay node 210, and the destination node 300 have the same number of antennas, and the second relay node 220 may include the source node 100, It is assumed that the first relay node 210 has the antenna twice as large as that of the destination node 300. Then, the first relay node 210 does not receive the interference signal through the interference cancellation technique.

You can keep the value. In addition, since the second relay node 220 has more antennas than other nodes, the channel gain between the first and second relay nodes 210 and 220 and between the second relay node 220 and the source node 300 is increased. It can be expected to be larger than the channel between the source node 100 and the first relay node 210. Therefore, even if the channel gain between the second relay node 220 and the destination node 300 is reduced due to the effect of the interference cancellation matrix,

Value is

It can be expected to remain similar to the value of. Even when the reception nulling technique is used, the same effect can be expected by installing more antennas in the first relay node 210. Therefore, the interference cancellation and the performance improvement of the system can be obtained through the interference cancellation using the multiple antennas.

In the above, embodiments of the present invention have been described with respect to alternate transmission and interference cancellation techniques. Next, the effects of the alternate transmission and interference cancellation scheme according to the embodiment of the present invention will be described. 10A to 10K are diagrams for explaining the effects of alternate transmission and interference cancellation schemes according to an embodiment of the present invention.

Here, it is assumed that a channel between each node assumes "Rayleigh fading" and that each component of the channel matrix has a "complex Gaussian" distribution having an average of zero.

When performing interference cancellation using multiple antennas, when the source node 100, the relay nodes, and the destination node 300 each communicate in the range of 1 hop, the number of antennas of the relay node is increased. The number of antennas of the source node 100 and the destination node 300 is set to be twice. Here, M represents the number of antennas at the source node 100 and the destination node 300, and N represents the number of antennas at each relay node. In addition, when communicating using multi-hop, it is assumed that the number of antennas of the first relay node 210 or the second relay node 220 is twice the number of antennas of other nodes.

Alternate transmission schemes are divided into two schemes in FIGS. 10A to 10K. In the case of transmitting a total of 2M symbols, a technique of transmitting different M symbols through each relay node (AT-indep), and when transmitting a total of 2M symbols, M / 2 symbols are divided in half and M / 2 symbols are divided. It includes the technique of transmitting through each repeater (AT-split). In addition, transmitting as shown in FIG. 1 is indicated as "one-way".

10A to 10F show the performance when the relay node operates in amplify-and-forward (AF) mode, and the transmit power at each relay node is equal to 2 of the transmit power at the source node 100. It was set to double (Pr = 2Ps).

The graphs shown in FIGS. 10H and 10I assume a case where the transmission power of the source node 100, the first relay node 210, and the second relay node 220 are the same. The graph illustrated in FIG. 10J assumes that transmission powers of the first relay node 210 and the second relay node 220 are 10 dB lower than the transmission power of the source node 100. In addition, the graphs shown in FIGS. 10H to 10J assume that the relay node operates in a decode-and-forward (DF) mode.

10A shows performance when it is assumed that there is no interference between relay nodes. In FIG. 10A, it is assumed that the number of antennas of the source and destination nodes 300 is four, and each relay node has four antennas. It can be confirmed that the maximum capacity value of the system increases through the alternate transmission scheme compared to the prior art. In particular, when AT-indep is applied, it can be confirmed that a double multiplexing gain is obtained in a high SNR region. At this time, the AT-indep and AT-split schemes show the performance when each repeater operates in an amplify-and-forward (AF) mode.

FIG. 10B shows that additional gain is obtained when each relay node performs transmission power distribution in the environment as shown in FIG. 10A.

10c illustrates the performance of the interference cancellation scheme for the AT-indep scheme when M = 4 and N = 8. The black solid line indicates the performance when no interference cancellation is performed, and as the SNR increases, the performance converges to a low value, and thus no multiplexing gain can be obtained. The proposed interference cancellation schemes show similar performances and additional gains when the transmit power distribution is performed.

10D shows the performance of the interference cancellation scheme for the AT-split scheme when M = 4 and N = 4. As shown in Figure 10, the proposed interference cancellation schemes show similar performances and additional gains when the transmit power distribution is performed. In this case, the solid pink line indicates the performance when the interference node is removed from the target node 300. Since the channel matrix size becomes the square matrix (M = 4, N = 4), the interference estimation error is large. Performance degradation occurs. This can be improved by applying the antenna selection technique as indicated by the dotted black line.

FIG. 10E shows the performance of the interference cancellation scheme according to the increase in the number of antennas of the repeater for AT-indep when M = 4. As the number of antennas in the repeater increases, the performance of the proposed interference cancellation scheme converges when there is no interference in the relay period indicated by the solid blue line. This is because the loss of channel gain due to orthogonal projection is gradually reduced. When the number of antennas of the repeater becomes larger than the number of antennas at the source node 100, the loss of the forward channel gain is reduced in the case of the transmit nulling technique, and the backward in the case of the receive nulling technique (Rx-nulling). This is because the loss of (backward) channel gain is reduced to approximate the case where there is no interference in the relay period.

Figure 10f shows the performance of the interference cancellation scheme according to increasing the number of antennas of the repeater for the AT-split when M = 4. It can be seen that the trend is similar to the result of FIG. 10E.

10G and 10H show the performance of the interference cancellation scheme according to increasing the transmission power of the relay node when the SNRs from the source node 100 to the relay node are 0 dB and 30 dB, respectively. Performance was compared in decode-and-forward (DF) mode and amplify-and-forward (AF) mode. When the relay node is operated in DF mode, the performance is superior to that of AF mode. If the transmit power of the relay node is greater than the transmit power of the source node 100, the maximum capacity of the system is determined by the backward channel. The transmit nulling technique maintains the forward channel while maintaining the gain of the backward channel. forward) Since the gain of the channel is lost and the reception nulling technique is the opposite method, the performance of the transmission nulling technique is better. The transmission nulling technique shows that the maximum capacity value of the system converges easily when operating in the DF mode, and converges to the maximum capacity value when the transmit power of the repeater becomes large enough when operating in AF.

Therefore, in the embodiment of the present invention, when the transmission power of the relay node is larger than the transmission power of the source node 100, the relay node may be operated in the AF mode, but the result may be close to the maximum performance of the system. For example, when two terminals having low transmission power communicate through a repeater, it may be assumed that the source node 100 and the destination node 300 play a role of the terminal.

FIG. 10I is assuming multi-hop, and in particular, assumes a 3-hop system as described above. FIG. 10I also shows the performance when interference cancellation is performed in such a three hop system. The second relay node 220 removes the interference to the first relay node 210 by using a transmission nulling technique, and the source node 100, the first relay node 210, and the source node 300 have one single node. An antenna is assumed and it is assumed that the second relay node 220 has two antennas. It can be seen that the performance of the system is shown to be close to the maximum value by installing an antenna in addition to the second relay node 220 and using a simple transmit nulling technique.

FIG. 10J assumes an environment as shown in FIG. 10I, and shows performance when interference cancellation is performed by applying a reception nulling technique in the first relay node 210. Here, it is assumed that the first relay node 210 has two antennas and the remaining nodes have one antenna. It can be seen that the same result as in FIG. 10I is obtained due to the structural symmetry.

FIG. 10K has the same antenna configuration as that of FIG. 10J, and shows interference cancellation performance using the reception nulling technique when the transmission power of the first and second relay nodes 210 and 220 is 10 dB lower than that of the source node 100. It can be seen that the reduction of the transmit power of the relay node reduces the maximum capacity value of the system and the interference cancellation using the receive nulling technique approaches the maximum value.

While the present invention has been described with reference to several preferred embodiments, these embodiments are illustrative and not restrictive. As such, those of ordinary skill in the art will appreciate that various changes and modifications can be made according to equivalents without departing from the spirit of the present invention and the scope of rights set forth in the appended claims.

1 is a diagram illustrating a transmission scheme in a wireless communication network using a plurality of such general relay nodes.

2 is a view for explaining the structure of a wireless communication network according to an embodiment of the present invention.

3 is a view for explaining a method for canceling interference in a target node according to an embodiment of the present invention.

4 is a diagram illustrating an interference cancellation method using a transmission nulling technique in a relay node according to an embodiment of the present invention.

5 is a diagram illustrating an interference cancellation method using a reception nulling technique in a relay node according to an embodiment of the present invention.

6 is a diagram illustrating a transmission power distribution scheme of a relay node according to an embodiment of the present invention.

7 is a view for explaining the structure of a wireless communication network according to another embodiment of the present invention.

8 illustrates an interference cancellation method using a transmission nulling technique according to an embodiment of the present invention.

9 illustrates an interference cancellation method using a transmission nulling technique according to an embodiment of the present invention.

10A to 10K are diagrams for explaining the effects of alternating transmission and interference cancellation techniques in accordance with an embodiment of the present invention.

Claims (10)

A system for interference cancellation based shift transmission using a relay node in a wireless communication network, A source node for transmitting a signal; A first relay node positioned one hop from the source node and receiving a signal from a source node at a first transmission time and relaying a signal to a destination node at a second transmission time; A second relay node positioned one hop from the source node and receiving a signal from a source node at a second transmission time and relaying a signal to a destination node at a first transmission time; And And the destination node for receiving signals from the first and second relay nodes. 10. The system of claim 1, wherein the target node receives signals from the first and second relay nodes. The method of claim 1, When one of the first and second relay nodes receives an interference signal from another node, the relay node estimates an effective channel in which a null space between the first and second relay nodes exists, and the interference signal. And cancel using the interference cancellation matrix calculated from the effective channel. The method of claim 1, Any one of the first and second relay nodes Estimating an effective channel having a null space between the first and second relay nodes, and removing and transmitting an interference signal to another node using an interference cancellation matrix calculated from the effective channel. Interference Cancellation Based Shift Transmission Using Relay Nodes The method of claim 1, The first and second relay nodes transmit a signal obtained by multiplying the power distribution matrix calculated by calculating a power distribution matrix to the destination node for the interference cancellation-based shift transmission using the relay node in the wireless communication network. system. The method of claim 1, The destination node is When a signal is received from any one of the first and second relay nodes, an interference signal is estimated using a signal received before the received signal, and the interference is removed using the estimated signal. A system for interference cancellation based shift transmission using relay nodes in a wireless communication network. In the interference cancellation based alternate transmission method using a relay node in a wireless communication network, At a first transmission time, a first process of receiving a signal from a source node by a first relay node and transmitting a signal previously received from the source node to a destination node by a second relay node; And a second process, at a second transmission time, a second relay node receives a signal from a source node and the first relay node transmits a signal received from the source node to a destination node. Interference Cancellation Based Shift Transmission Method Using Relay Nodes in. The method of claim 6, The first and second process When any one of the first and second relay nodes receives an interference signal from another node, estimates an effective channel in which a null space between the first and second relay nodes exists, and the interference signal Removing interference using the interference cancellation matrix calculated from the effective channel. The method of claim 6, The first and second process Any one of the first and second relay nodes estimates an effective channel having a null space between the first and second relay nodes and removes an interference signal by using an interference cancellation matrix calculated from the effective channel. Interference cancellation based alternate transmission method using a relay node in a wireless communication network, characterized in that the transmission to another relay node. The method of claim 6, The first and second process And the first and second relay nodes transmit a signal obtained by multiplying a power distribution matrix calculated by the first and second relay nodes to the target node, and using the relay node in the wireless communication network. The method of claim 6, When the target node receives a signal from one of the first and second relay nodes, estimating an interference signal using a signal previously received from the received signal and removing the interference using the estimated signal The interference cancellation based alternate transmission method using a relay node in a wireless communication network, further comprising a.

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