KR101531172B1 - Efficient Shared Relay Beamforming Method for Multi-Cell Multi-User LTE-A Cooperative Networks and Communication System using the same - Google Patents

Abstract

The recent increase in interest in small cells is mainly driven by market demand for high network capacity. Cell coverage is problematic due to limited indoor propagation at high transmission frequencies. In this case, small cells can play an important role in providing indoor coverage and capacity. In an embodiment of the present invention, a multi-user multi-cell (MCMU) cooperative network shared relay beamforming method is proposed. Here, multi-cells share relay cells for cooperation. This increases the average throughput.

Description

[0001] The present invention relates to an efficient shared relay beamforming method in a multi-cell multi-user LTE-A cooperative network and a communication system employing the same.

The present invention relates to a beamforming method, and more particularly, to an efficient beamforming method in a multi-cell multi-user network and a communication system using the same.

Over the last decade, the tremendous growth of wireless communications has resulted in increased demand for new resources. Because multi-antenna communication systems can significantly increase the capacity of the wireless link, they have generated a great deal of interest. Recently, collaborative multipoint has been evaluated as an efficient technique for eliminating inter-cell interference. The core of multi - cell cooperative transmission is cooperative cell clustering and multi - cell beamforming design.

However, Long Term Evolution (LTE) and Mobile WiMAX have achieved improved spectral performance within a single cell using multiple-input multiple-output (MIMO) -orthogonal frequency-division multiplexing (OFDM). It has been theoretically proven that the uplink (UL) COMP may have a significant increase in throughput especially at the cell edge.

The base stations cooperate with each other and design their transmission beamformer in a coordinated manner. There have been many attempts to apply MCMUs to heterogeneous networks. 1) Inter-cell interference (ICI): This type of interference occurs between cells in a heterogeneous network (HetNet). 2) Inter-User Interference (IUI) and 3) Inter-Stream Interference (ISI): Joint Transmission (JT) is one of the CoMP transmission technologies that allows base stations in a cluster to simultaneously transmit the same signal, Let resources translate the ICI into the desired signals. If there are multiple service user terminals, an IUI will occur.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an efficient shared relay beamforming method in a multi-cell multi-user LTE-A collaborative network and beamforming Relay. ≪ / RTI >

According to an aspect of the present invention, there is provided a shared relay beamforming method including: receiving a signal from a base station by a relay station; The relay station performing beamforming on a signal received in the receiving step; And the relay station broadcasting the beamformed signal in the beam forming step, wherein the relay station is shared by a plurality of base stations.

The plurality of base stations may have a plurality of antennas, and the relay station may have one antenna.

Further, the signal received in the new step may be expressed as follows.

이며,

는 i 번째 베이스 스테이션에서 송신 신호이고,

와

는 각각 i 번째 베이스 스테이션에서 i 번째 모바일 스테이션의 채널 계수와 j 번째 베이스 스테이션에서 i 번째 모바일 스테이션의 채널 계수이며,

는 i 번째 베이스 스테이션에서 송신 파워를 나타내고,

는 i 번째 모바일 스테이션에 부가되는 평균이 제로이고 분산이 N₀, 즉,

인 백색 가우시안 잡음이다.here,

Lt;

Is the transmit signal at the i < th > base station,

Wow

Is the channel coefficient of the i-th mobile station in the i-th base station and the channel coefficient of the i-th mobile station in the j-th base station,

Represents the transmit power at the i < th > base station,

Lt; RTI ID = _0.0 > N0, < / RTI >

Is white Gaussian noise.

The beamformed signal in the beamforming step may be expressed as follows.

는 빔포밍 행렬이고,

이다.here,

Is a beamforming matrix,

to be.

Also, the signal broadcasted at the broadcasting step and received at the i < th > mobile station may be expressed as follows.

는 상기 릴레이 스테이션에서 i 번째 모바일 스테이션까지의 채널 계수이다.here,

Is the channel coefficient from the relay station to the i < th > mobile station.

The received SINR at the i < th > mobile station may be expressed as follows.

In addition, the beam forming step may optimize the reception performance by adjusting the beamforming matrix.

According to another aspect of the present invention, a mobile communication system includes: a plurality of base stations for transmitting signals; And a relay station for beamforming and broadcasting a signal received from the plurality of base stations, wherein the relay station is shared by the plurality of base stations.

The plurality of base stations have a plurality of antennas, and the relay station has one antenna

Also, the relay station may optimize reception performance by adjusting the beamforming matrix

As described above, according to embodiments of the present invention, efficient shared relay beamforming in a multi-cell multi-user LTE-A cooperative network is enabled. Thereby, the throughput can be increased directly over the throughput of the link, and the maximum-minimum SINR problem can be solved with less power.

Figure 1 illustrates a cooperative multi-cell relay beamforming system model (for a single user)
2 is a diagram illustrating a cooperative multi-cell relay beamforming system model (for a multi-user case)
FIG. 3 is a schematic diagram of an area to be achieved in the case of a 2-user,
FIG. 4 is a schematic diagram of an area to be achieved in case of a 3-
5 is a view showing a result of a Monte Carlo simulation,
6 is a diagram illustrating the effect of intra-cell-user channel correlation for a shared cell relay beamforming method.

Hereinafter, the present invention will be described in detail with reference to the drawings.

In the embodiment of the present invention, a shared relay cooperative network system is presented. And a cooperative multi-cell downlink system is assumed with a plurality of base stations (eNBs). The base stations share the same relay station (eRS). Further, as shown in FIG. 2, a multi-cell network including N cells and K mobile users (MS) is assumed. A single-user system is shown in FIG. 1, and a 3-user multi-cell system is illustrated in FIG. In the figure, a solid line represents a desired signal and a dotted line represents an interference signal. In addition, the channels are assumed to be frequency flat fading channels. eNB is equipped with N _t transmit antennas, and all eRS MS has a single antenna. There are two steps in a system according to an embodiment of the present invention: (1) Multiple Access (MAC) step and (2) Broadcast (BC) step. In the MAC step, both the MS and the eRS receive a signal from the i-th eNB. Therefore, the signal received at user i (i.e., the i < th > MS) is as follows.

는 단계 1(즉, MAC 단계)에서 i 번째 MS에 수신된 신호이고,

이며,

는 i 번째 eNB에서 송신 신호이고,

와

는 각각 i 번째 eNB에서 i 번째 사용자의 채널 계수와 j 번째 eNB에서 i 번째 사용자의 채널 계수이며,

는 i 번째 eNB에서 송신 파워를 나타내고,

는 i 번째 사용자에 부가되는 평균이 제로이고 분산이 N₀, 즉,

인 백색 가우시안 잡음이다. 목적지에서 수신 SINR(signal-to-interference-noise ratio)은 다음과 같이 주어진다.here,

Is the signal received at the i < th > MS in step 1 (i.e., the MAC step)

Lt;

Is the transmission signal in the i < th > eNB,

Wow

Is the channel coefficient of the i-th user in the i-th eNB and the channel coefficient of the i-th user in the j-th eNB,

Represents the transmission power in the i < th > eNB,

The average added to the i-th user is zero and the variance is N ₀ ,

Is white Gaussian noise. The received signal-to-interference-noise ratio (SINR) at the destination is given by

In a similar way, the signal received at the RS is:

는 수신 신호 RS이고,

는 i 번째 eNB에서 송신 파워를 나타낸다. 따라서, RS는 RS에 수신된 신호에 선형 빔포밍 기법을 사용한다. 빔포밍된 신호는 다음과 같이 쓸 수 있다.here,

Is the received signal RS,

Represents the transmission power in the i-th eNB. Thus, the RS uses a linear beamforming scheme for the signal received at the RS. The beamformed signal can be written as

는 빔포밍 행렬이고,

이다. 단계 2에서, RS는 MS에 빔포밍된 신호를 브로드캐스트한다. 수신기인 K 번째 MS에 수신된 신호는 다음과 같다.here,

Is a beamforming matrix,

to be. In step 2, the RS broadcasts the beamformed signal to the MS. The signal received at the Kth MS, which is the receiver, is as follows.

는 RS에서 i 번째 MS까지의 채널 계수이다. 따라서, i 번째 MS에서 수신 SINR은 다음과 같다.here,

Is the channel coefficient from RS to the ith MS. Therefore, the reception SINR at the i-th MS is as follows.

을 가지고 있다고 가정한다. (1)에서 최대 수신 SNR은 빔포밍 행렬 W를 최적화하여 이룰 수 있다. 이 문제는 다음과 같은 최적화에 의해 공식화 될 수 있다. (3)과 (4)에 기반하여, 최대-최소의 최적화에 기반한 최악-케이스는 다음과 같이 공식화될 수 있다.The design goal of the beamformer is to maximize the SINR of the minimum worst case of both destinations to ensure user fairness. In a relay, each antenna has a separate power constraint

. (1), the maximum received SNR can be obtained by optimizing the beamforming matrix W. [ This problem can be formulated by the following optimization. Based on (3) and (4), the worst-case based on maximum-minimum optimization can be formulated as

는

의 공객 전치(conjugate transpose)로 정의한다.
here,

The

Is defined as a conjugate transpose.

1) Achieved area analysis of the proposed method

Random beamforming assigns each beam to a user capable of achieving the highest SINR. Achieved throughput can be formulated as:

The sum of these can be written as

는 공분산 행렬이고:

(P는 총 전력)이다.here,

Is a covariance matrix:

(P is the total power).

FIG. 3 schematically shows the attainment region for the 2-user, and FIG. 4 illustrates the attainment region for the 3-user.

2) Failure probability analysis: However, remarkably, information theory guarantees the existence of a channel-state independent coding scheme which achieves stable communication if the condition is satisfied. When a MIMO channel does not satisfy the condition, we call it a fault. You can choose a transmission strategy (parameterized by covariance) to minimize the probability of failure:

Hereinafter, a monte carlo simulation result for confirming the performance of the method proposed by the embodiment of the present invention is presented.

As shown in FIG. 5, the shared relay beamforming method according to the embodiment of the present invention shows superior performance over the conventional method. Also, it can be seen that the total throughput of the shared relay beamforming method is higher than the total throughput of the direct link.

은 0.0, 0.5, 0.7 및 0.9로 설정된다. 이 결과에서, 인트라-사용자 채널들이 상관적일 때, 시스템에 도움이 된다는 것을 알 수 있다. 더 구체적으로, 전력이 적게 된다.
6 shows the effect of intra-cell-user channel correlation for a shared cell relay beamforming method. Correlation ratio

0.0 > 0.5, < / RTI > 0.7 and 0.9. From this result, it can be seen that the system is helpful when the intra-user channels are correlated. More specifically, the power is reduced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention.

NB: Base Station
RS: Relay station
MS: Mobile station

Claims (10)

The relay station receiving a signal from the base station;
The relay station performing beamforming on a signal received in the receiving step; And
Wherein the relay station broadcasts a beamformed signal in the beamforming step,
The relay station is shared by a plurality of base stations,
The beam forming step includes:
The reception performance is optimized by adjusting the beamforming matrix used for beamforming so that the maximum reception SINR is maximized under the power constraint,
The following formula maximizes the minimum SINR at the mobile station,

Where h _{i, i} and h _{i, j} are the channel coefficients of the i th mobile station in the i th base station and the channel coefficients of the i th mobile station in the j th base station, respectively, Where p _i and p _j are the transmit power at the i-th base station and the j-th base station, N ₀ is the noise, w is the beamforming matrix, P _R is the power constraint at the relay,

The

Wherein the shared relay beamforming is a conjugate transpose of the shared relay beamforming.
The method according to claim 1,
The plurality of base stations having a plurality of antennas,
Wherein the relay station has one antenna. ≪ Desc / Clms Page number 20 >
delete delete delete delete delete A plurality of base stations for transmitting signals; And
And a relay station for beamforming and broadcasting signals received from the plurality of base stations,
The relay station is shared by the plurality of base stations,
The relay station includes:
The reception performance is optimized by adjusting the beamforming matrix used for beamforming so that the maximum reception SINR is maximized under the power constraint,
The following formula maximizes the minimum SINR at the mobile station,

Where h _{i, i} and h _{i, j} are the channel coefficients of the i th mobile station in the i th base station and the channel coefficients of the i th mobile station in the j th base station, respectively, Where p _i and p _j are the transmit power at the i-th base station and the j-th base station, N ₀ is the noise, w is the beamforming matrix, P _R is the power constraint at the relay,

The

Wherein the mobile station is a conjugate transpose of the mobile station.
9. The method of claim 8,
The plurality of base stations having a plurality of antennas,
And the relay station has one antenna.
delete

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