KR20100027945A - Method and apparatus of data transmission based on multi-cell cooperation - Google Patents

Abstract

PURPOSE: A method and an apparatus of transmitting data based on multi cell cooperation are provided to realize MU-MIMO(Multi-User Multiple-Input Multiple-Output) while reducing interference between terminals. CONSTITUTION: Information about adjacent cells participating in cooperative transmission is transmitted to a terminal(S410). Feedback information for selecting a beam forming mode for multi cell cooperation is received from a terminal(S420). The feedback information includes statistical information of exterior interference due to the adjacent cells. The beam forming mode about the terminal is selected based on the feedback information(S430). A base station informs the selected beam forming mode to the terminal(S440). Data to which a beam forming vector is applied is transmitted to the terminal(S450).

Description

METHOD AND APPARATUS OF DATA TRANSMISSION BASED ON MULTI-CELL COOPERATION}

TECHNICAL FIELD The present invention relates to wireless communication, and in particular, to multi-cell cooperation in a wireless communication system.

Multiple-Input and Multiple-Output (MIMO) systems use transmission techniques to obtain spatial multiplexing and diversity gains, increasing transmission efficiency and improving communication signal quality. The general MIMO system is based on point-to-point communication and increases the diversity gain by considering the link between one base station having multiple antennas and one terminal having multiple antennas. Performance by increasing the rate of spatial multiplexing. As a method for maximizing diversity gain, a maximum singular vector obtained through singular value decomposition of a channel matrix between a base station and a terminal is used as a transmission beamforming vector.

Recently, a point-to-multipoint communication method that simultaneously transmits signals of multiple users has attracted attention. This is a method of considering a link between a base station having a plurality of antennas and a plurality of terminals having at least one antenna. Point-to-point based MIMO is called SU-MIMO (single user MIMO), whereas point-to-multipoint MIMO is called MU-MIMO (multi-user MIMO).

Recently, research on a multi-cell cooperative system capable of obtaining diversity gain using cooperative communication of a plurality of base stations has been actively conducted. Multi-cell coordination systems are being introduced to provide cell coverage extension, throughput enhancement, and performance enhancement at cell boundary regions.

In a multi-cell cooperative system, inter-user interference control is required to implement MU-MIMO. General MU-MIMO involves interference control between users, but does not consider interference from neighboring base stations due to multi-cell cooperation. In addition, if only the interference cancellation between users is considered, the user's signal quality may be lowered.

In a multi-cell cooperative system, a technique for improving signal quality and reducing interference between users is required.

The present invention has been made in an effort to provide a data transmission method and apparatus for alleviating user interference in a multi-cell cooperative system.

In one aspect, a data transmission method based on multi-cell cooperation is provided. The method includes transmitting information about neighbor cells participating in cooperative transmission to a terminal, and receiving feedback information for selecting a beamforming scheme for multi-cell cooperation from the terminal, wherein the feedback information is caused by the neighbor cells. Including statistical information of external interference, selecting a beamforming scheme for the terminal based on the feedback information, generating a beamforming vector corresponding to the selected beamforming scheme, and the beamforming vector And transmitting the applied data to the terminal.

The beamforming method may be selected based on the accuracy of the statistical information of the external interference. The selected beamforming scheme may be one of a scheme that considers interference mitigation between users, a scheme that considers interference mitigation and SINR maximization between users, and a scheme of maximizing the sum of transmission rates of multiple users.

In a multi-cell cooperative system, interference between terminals may be reduced. MU-MIMO can be implemented in a multi-cell cooperative system.

The following methods, apparatus, and techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), and single carrier frequency division multiple (SC-FDMA). It can be applied to various radio access technologies such as access). The radio access technology may be implemented in various wireless communication standard systems. Wideband CDMA (WCDMA) may be implemented with a radio technology such as Universal Terrestrial Radio Access Network (UTRAN) by the 3rd Generation Partnership Project (3GPP) standardization organization. CDMA2000 is a wireless technology based on CDMA. High Rate Packet Data (HRPD) by the 3rd Generation Partnership Project 2 (3GPP2) standardization organization provides high packet data services in a CDMA2000-based system. evolved HRPD (eHRPD) is the evolution of HRPD. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved-UTRAN (E-UTRAN), and the like. Long term evolution (LTE) is part of Evolved-UMTS (E-UMTS) using E-UTRAN, and employs OFDMA in downlink and single carrier frequency division multiple access (SC-FDMA) in uplink. LTE-A (Advanced) is the evolution of LTE.

A multiple antenna system or a multiple-input multiple-output (MIMO) system to which the following technology is applied is a system using a multiple transmit antenna and at least one receive antenna. The following techniques can be applied to various multiple input multiple output (MIMO) schemes. MIMO schemes include spatial diversity for transmitting the same stream to multiple layers and spatial multiplexing for transmitting multiple streams to multiple layers. In spatial multiplexing, when multiple streams are transmitted to one user, they are referred to as single user-MIMO (SU-MIMO) or spatial division multiple access (SDMA). In multiplexing, when multiple streams are transmitted to multiple users, it is called MU-MIMO (Multi User-MIMO). In addition, spatial diversity and spatial multiplexing may be divided into an open-loop and a closed-loop scheme according to whether feedback information reported from a user is used.

A base station (BS) 11 provides communication services for a particular geographic area (generally called a cell). The cell can in turn be divided into a number of regions (called sectors). The user equipment (UE) may be fixed or mobile, and may include a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), and a wireless modem. It may be called other terms such as a wireless modem and a handheld device. A base station generally refers to a fixed station communicating with a terminal, and may be referred to as other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), and an access point.

1 is an exemplary diagram illustrating a wireless communication system in a multi-cell environment. Base station A 20-A provides a communication service to terminal A 10-A, and base station B 20-B provides a communication service to terminal B 10-B. For terminal A 10-A, base station A 20-A is a serving base station and base station B 20-B is an adjacent base station. For the terminal B 10-B, the base station B 20-B is a serving base station and the base station A 20-A is an adjacent base station. A base station providing a communication service to a terminal is called a serving base station, and a base station adjacent to the serving base station is called a neighbor base station. A cell of a serving base station is called a serving cell, and a cell of an adjacent base station is called a neighbor cell.

The base station B 20 -B allocates radio resources to the terminal B 10 -B through scheduling and transmits downlink data. The downlink data transmitted by the base station B 20 -B may be received by the terminal A 10 -A as well as the terminal B 10 -B. Accordingly, the downlink data of the base station B 20 -B may act as interference with the terminal A 10 -A.

First consider a single user MIMO (SU-MIMO).

A Nr × 1 received signal vector received from a base station having Nt antennas by a terminal having Nr antennas is expressed as follows.

Here, H denotes a channel matrix of Nr × Nt, x denotes a transmission signal vector of Nt × 1, and r denotes additive white Gaussian noise (AWGN) of Nr × 1. The channel matrix is decomposed by single value decomposition (SVD) as follows.

Here, Σ = dig {σ ₁ , σ ₂ , ..., σ _{rank {H}} } is a diagonal matrix of singular values of the channel matrix H , U = [u ₁ , u ₂ ,. .., u _{rank {H}} ] and V = [v ₁ , v ₂ , ..., v _{rank {H}} ] are matrices of singular vectors corresponding to singular values.

이라 정의하고, 송신 및 수신 빔포밍 벡터로 v _m 및 u _m ^H 를 사용한다. 전송 데이터 심볼을 d라 하고 송신 신호 벡터 x=v _md 와 같이 생성하여, 선택된 수신 빔포밍 벡터를 사용하여 신호처리를 수행하면 다음 식과 같다.The singular value index with the maximum value m =

As it defined, and uses the u and v _{m m} ^H in the transmit and receive beamforming vector. If a transmission data symbol is called d and a transmission signal vector x = v _m d is generated and signal processing is performed using the selected reception beamforming vector, the following equation is obtained.

When the power of the AWGN component is σ ₁ ² , the signal-to-noise ratio (SNR) is as follows.

Now consider MU-MIMO. In the case of simultaneously transmitting signals for K terminals by using beamforming to remove interference between users, a transmission signal vector for a k-th UE UE _k is defined as follows.

및 d_k는 UE_k를 위해 사용된 전송 전력 및 전송된 데이터 심볼이다. Where M _{MU , k} is a multi-user precoding matrix, v _{SU , k} is a transmission beamforming vector in a single-user MIMO channel from which user-to-user interference is removed,

And d _k is the transmit power and transmitted data symbols used for UE _k .

When the channel matrix between UEk and the base station is H _i , the concatenated channel matrix is defined as follows.

SVD is performed on the concatenated channel matrix as follows.

Generate a multi-user precoding matrix M _{MU , k} = V _k ⁽⁰⁾ . Since it satisfies H _i M _{MU , j} = 0 for the case of i ≠ j, it performs the function of a signal processing matrix that completely eliminates interference between multiple users. In the case of using the interference cancellation signal processing matrix between users, K received signal vectors may be represented as a block diagonal channel without interference between users as shown in the following equation.

를 대상으로 maximum eigen-mode 단일 사용자 전송 방식을 사용하는 것이 가능하다. As a method for configuring a transmission beamforming vector for each user, an effective channel of UEk

It is possible to use the maximum eigen-mode single-user transmission scheme.

In a wireless communication system, interference from adjacent cells using the same frequency or time resource exists, which serves as one of the main causes of deterioration of the performance of the MIMO transmission scheme in a noisy environment. In particular, a terminal located in a cell boundary region may have a low signal-to-interference and noise ratio (SINR) and a lower transmission rate. In the case of using the transmission signal vector generated as shown in Equation 5, rather than increasing the SINR that directly affects the signal quality of each user, only interference between users may be eliminated, thereby ensuring a quality of service (QoS). .

Now, a case of collaborative transmission to a plurality of users through mutual cooperation between a plurality of base stations in a multi-cell environment is considered.

If the index set of the base station participating in the cooperative transmission for the K terminals in the cluster consisting of the base station participating in the cooperative signal transmission is named C, the signal received through the multiple antennas of the UEk is as follows.

을 정의하고, 각 기지국에서 UE_k를 위해 전송될 전송신호 벡터를 연접하여

을 정의한다. Where H _{k , b} is an Nr × Nt channel matrix between the Nt transmit antennas of the _b -th base station BS _b and the Nr receive antennas of the UE _k , and x _{k , b} is a transmission signal vector from BS _b to UE _k . X _b means a sum of transmission signal vectors transmitted from BS _b . When defining the number of elements in the C set as | C |, the channel matrix of each terminal is concatenated.

And concatenate the transmission signal vectors to be transmitted for UE _k in each base station.

Define.

으로 정의하면, 상기 수학식 9는 다음과 같이 표현될 수 있다.In addition, external interference and noise signal components caused by adjacent cells

Equation 9 may be expressed as follows.

는 협력적 신호 전송에 참여하는 기지국으로 이루어진 클러스터 내 다중 사용자 간 간섭에 해당하는 신호 성분이다. 수신 신호 r _k에 임의의 수신 빔포밍 벡터 u _k를 적용하면 다음 식과 같다.here,

Is a signal component corresponding to interference between multiple users in a cluster composed of base stations participating in cooperative signal transmission. If an arbitrary reception beamforming vector u _k is applied to the reception signal r _k , the following equation is obtained.

The covariance matrix of the cluster external interference and noise signals is defined as follows.

This may be referred to as statistical information of external interference due to neighboring cells, and accurately estimating this statistical information affects the performance of the beamforming method described later.

The SINR of the received signal to which the received beamforming is applied is as follows.

The minimum SINR to guarantee the specified rate can be set to QoS.

We now describe beamforming techniques for MU-MIMO in a multi-cell cooperative system. The base station may use three beamforming schemes. The base station may determine a beamforming method based on feedback information received from each terminal. The first scheme is an interference mitigation scheme considering interference mitigation between users and the interference mitigation between base stations, the second scheme is an SINR maximization scheme considering interference mitigation and SINR maximization between users, and the third scheme is a sum of transmission rates of multiple users. It is a method of maximizing bit rate for maximization.

(1) First method: interference mitigation method

In order to eliminate the interference between users, a transmission signal based on Equation 5 is used. Receive beamforming for inter-cluster interference mitigation may use OC (Optimal combining) or MMSE-ISD (Minimum Mean-Squared-Error based Intercell Spatial Demultiplexing). OC and MMSE-ISD can be used adaptively according to the method of obtaining statistical information of external interference.

First, for reception beamforming based on OC, a symbol index n is added to a reception signal r _k of UE _k on which block diagonalization is performed, as shown in Equation 8, to be represented as follows.

By correlating the received signals r _k [n] by N _corr lengths, the effective channel components are removed, and then the covariance matrix of the out-of-cluster interference and noise components is obtained based on OC as follows.

When the reception beamforming vector u _k is applied to the reception signal r _k of the UE _k on which the block diagonalization is performed, it is as follows.

The optimal combined received signal processing beamforming vector for maximizing the SINR of the received signal having interference is as follows.

Optimal performance can be obtained when R _{OC , k} (N _corr ) generated from Equation 15 accurately estimates the covariance matrix R _k of the cluster external interference and noise component of Equation 12, that is, statistical information of external interference.

Next, we propose receive beamforming based on MMSE-ISD. In order to detect the received signal, a covariance matrix is obtained by additionally using channel information of an interference signal transmitted from an adjacent base station not participating in the cooperative transmission as well as channel information between the base station and the terminal participating in the cooperative transmission.

Where v _b is a beamforming vector used by the _b -th base station, H _{k , b} v _b is an effective channel between the _b -th base station and the UE _k , and D is a base station outside the cluster that does not participate in cooperative transmission. Means a base station index set capable of valid channel estimation in the terminal.

The sum of channel powers from base stations for which channel estimation is not possible in the system is defined as follows.

Unlike the OC technique of estimating the covariance matrix of Equation 12, the MMSE-ISD uses the sum of estimable channel information and the power of the non-estimated channel to covariate the external cluster and interference signal components as shown in Equation 18. Construct a matrix approximately.

The received signal processing beamforming vector based on the MMSE-ISD is as follows.

Optimum performance can be obtained when R _{ISD , k} (D) generated from Equation 18 accurately estimates the covariance matrix R _k of the external interference and noise components of Equation 12.

(2) Method 2: SINR Maximization Method

The SINR in the case where the reception beamforming vector u _k is applied to the reception signal obtained from Equation 8 is as follows.

The optimal receive beamforming vector for maximizing SINR is given by the following equation.

The optimal receive beamforming vector can be obtained through the OC method of Equation 15 or the MMSE-ISD method of Equation 18. When the beamforming vector of Equation 22 is applied, the SINR of the received signal is as follows.

를 정의하고, 고유치 분해(eigenvalue decomposition)를 수행하면 다음 식과 같다.Hermitian procession

If we define and perform eigenvalue decomposition, we get

이라 정의하면, SINR을 최대화 하는 송신 신호 벡터는 다음 식과 같다.Eigenvalue index with maximum value m =

In this case, the transmission signal vector maximizing the SINR is as follows.

(3) Third Method: Rate Sum Maximization Method

It uses MMSE based beamforming vector. It satisfies the per-antenna power constraint (PAPC), which limits the average transmit power per antenna to be suitable in distributed antenna environments.

The following signal processing is performed on the received signal of Equation 10 to whiten the external cluster interference component.

을 사용한다. 표기의 편의를 위하여

및

로 정의하면 SINR을 최대화 하는 수신 빔포밍 벡터는 다음 식과 같다.Here, the transmission signal vector for UE _k

Use For convenience of notation

And

If it is defined as, the reception beamforming vector maximizing SINR is as follows.

A transmission beamforming vector for maximizing SINR in an uplink channel is generated as follows.

Here, q _k is a transmit power value allocated to UEk in the uplink channel.

In addition, power control that maximizes the average multi-user data rate per antenna can be performed by solving the optimization problem as

A matrix such as Equations 30 and 31 is defined.

으로 갖는 K×K 행렬을 A로, (i,j) 번째 원소값을

으로 갖는 K×K 행렬을 B로 정의한다.Also, the (i, j) th element value

The K × K matrix with A and the (i, j) th element

A K × K matrix having N is defined as B.

In considering the optimization problem, the γ _k and γ _k, the value of _ul uses the following formula values:

here,

Is defined.

Also, in order to express the PAPC constraint, | C | Nt × K matrix V is defined as follows.

The proposed power control vector update is as follows.

Here, α _{k∈ {1, ..., K}} and β _{k∈ {1, ..., K}} are as follows.

The μ and λ used are obtained through the same iterative update as follows.

Here, δ _n is a step size according to the number of repetitions.

및 전력 제어 벡터

가 지정되어 있어야 한다. 상향링크 채널에서 SINR을 최대화하는 송신 빔포밍 벡터 의 생성을 위해서 하향링크 채널의 수신 빔포밍 벡터 u _i 및 전력 제어 벡터

가 지정되어 있어야 한다. In order to generate a reception beamforming vector maximizing SINR in a downlink channel, a transmission beamforming vector of an uplink channel

And power control vector

Must be specified. Receive beamforming vector u _i and power control vector of downlink channel for generation of transmit beamforming vector maximizing SINR in uplink channel

Must be specified.

, 반복 횟수 i를 초기화한다(S210). 수학식 27을 이용하여 수신 빔포밍 벡터 u _{MMSE , k} 를 획득한다(S220). 수학식 35를 이용하여 상향링크 채널의 전력제어 벡터 q ⁽ⁱ⁾ 를 업데이트한다(S230). 수학식 28을 이용하여 송신 빔포밍 벡터

를 획득한다(S240). 수학식 35를 이용하여 하향링크 채널의 전력제어 벡터 p ⁽ⁱ⁾를 업데이트한다(S250). 원하는 QoS를 만족하는지 여부를 확인한다(S260). QoS의 만족 여부는 원하는 최소 SINR을 만족하는지 여부를 통해 확인할 수 있다. QoS가 만족하거나 반복 횟수 i가 최대 반복 횟수 i_max에 도달할 때까지 반복한다(S270, S280).2 is a flow chart illustrating beamforming vector and power control vector update. First, the transmit beamforming vector p ⁽⁰⁾ and the power control vector

In step S210, the repetition number i is initialized. The reception beamforming vector u _{MMSE , k} is obtained using Equation 27 (S220). The power control vector q ⁽ⁱ⁾ of the uplink channel is updated using Equation 35 (S230). Transmit Beamforming Vector Using Equation 28

It is obtained (S240). The power control vector p ⁽ⁱ⁾ of the downlink channel is updated using Equation 35 (S250). It is checked whether the desired QoS is satisfied (S260). Satisfaction of the QoS can be determined by satisfying the desired minimum SINR. Iterates until the QoS is satisfied or the number of iterations i reaches the maximum number of iterations i _max (S270, S280).

3 is a flowchart illustrating a multi-cell cooperation method according to an embodiment of the present invention. First, a cluster is configured for a base station participating in cooperative transmission and transferred to a terminal in the cluster (S310). A base station index set C is generated in a cluster by configuring a cluster by selecting base stations participating in the cooperative transmission. The base station index set C is delivered to the terminals in the cluster. The configuration of the cluster may be performed by a specific base station, or may be performed through a base station controller for managing a plurality of base stations.

The terminals in the cluster report feedback information (S320). UEs in the cluster may report feedback information to the serving base station. The feedback information may include channel state information, statistical information of external cluster interference, and / or QoS information of the terminal. The terminal may select one of the three beamforming schemes described above and include the selected beamforming scheme in the feedback information. Information included in the feedback information may vary according to the beamforming method.

Statistical information of the out-of-cluster interference is information about the covariance matrix R _k of the out-of-cluster interference and noise signals of Equation 12. When the first scheme is selected, the OC based and / or MMSE-ISD based covariance matrix R _k may be feedback. When using the equation (15) in the OC-based statistical information of the cluster external interference R _k = R _{OC, k} is a (N _corr), when using the method of the MMSE-ISD based on equation (18) of the statistical information in the cluster, external interference R _k = R _{ISD , k} (D) The reliability of R _{ISD , k} (D) is determined according to the size of the base station index set D not participating in the cooperative transmission and the accuracy of the channel estimation of the base station in the D set _, thereby determining whether to use the MMSE-ISD. The UE obtains the SINR of Equation 13 and selects OC or MMSE-ISD.

UEs in the cluster estimate channel state information between the transmit antenna of the base station and the receive antenna of the terminal participating in the cooperative transmission. In addition, the terminals in the cluster may set the minimum received SINR for guaranteeing a designated transmission rate according to the type of service and the amount of data transmitted.

Based on the feedback information, terminals for transmitting data are selected through multi-cell cooperation (S330).

A beamforming method is selected for each of the selected terminals (S340). One of the aforementioned first, second and third methods may be selected as a beamforming method. The first scheme is an interference mitigation scheme considering interference mitigation between users and the interference between base stations, the second scheme is an SINR maximization scheme considering interference mitigation and SINR maximization between users, and the third scheme is a transmission rate for maximizing the sum of transmission rates of multiple users. It is the sum maximization method. The first and second schemes may have a difference in performance depending on the accuracy of statistical information of external cluster interference. When more accurate statistical information is used, the second scheme exhibits higher interference mitigation performance than the first scheme. However, when the accuracy of the statistical information falls, the performance of the second scheme may be degraded rather than the first scheme. According to the accuracy of the statistical information can be adaptively taken between the first scheme and the second scheme. The third scheme can guarantee QoS than the first and second schemes in an iterative manner, but there is a burden on complexity and calculation amount. Accordingly, if the QoS required by the user is not satisfied through the first and second schemes, the third scheme may be taken.

The base station may select one of the first method and the second method if the statistical information is used, and select the third method if the statistical information is not used.

As the beamforming method, a beamforming method selected by the terminal in the feedback information may be selected. This may reduce signaling overhead by notifying the terminal of the beamforming scheme selected by the base station separately, or by notifying the terminal of whether the beamforming scheme selected by the terminal is applied.

The base station may select a beamforming method based on a priority among the first to third methods. For example, it is first checked whether the first scheme is applied, and if the desired QoS is not guaranteed through the first scheme, whether the second scheme is applied. If the desired QoS is not guaranteed through the second scheme, it is checked whether the third scheme is applied.

The base station generates a beamforming vector according to the selected beamforming scheme, and if necessary, performs power control for each antenna (S350). The base station transmits data to which the beamforming vector and power control are applied (S360).

By cooperative transmission between base stations constituting the cluster, inter-cell interference can be reduced and signal quality can be improved. In addition, by simultaneously transmitting signals for multiple users, high performance can be expected in terms of sum of data rates. In order to control user-to-user interference and external cluster interference, the beamforming scheme may be adaptively selected in consideration of the accuracy of variables affecting the performance of the signal processing scheme and the QoS required by the terminal.

4 is a signal flow diagram of multi-cell cooperation according to an embodiment of the present invention. The cluster is configured by selecting the base stations participating in the cooperative transmission, and the base station index set C in the cluster is transmitted to the terminal (S410).

The terminal reports the feedback information (S420). The feedback information may include channel state information, statistical information of external cluster interference, and / or QoS information of the terminal.

The base station selects a beamforming method based on the feedback information (S430). The base station informs the terminal of the selected beamforming scheme (S440). The base station transmits downlink data to which the beamforming vector and power control are applied (S450).

The simulations performed now are described. The number of cells in the system L = 19, the base station index set C = {1, 2, 3} participating in the cooperative transmission, and the number of terminals in the cluster K = 3. There is one terminal in the coverage of each base station, and the terminals are randomly distributed on concentric circles of the same distance from the base station. Nt = 6 and Nr = 2 are used as the number of transmit antennas of each base station and the number of receive antennas of the terminal.

5 is a graph showing a change in the average SINR according to the position of the terminal. d represents the normalization distance, which is a ratio of the distance between cell boundaries from the cell center. The smaller the normalization distance, the more it is located at the cell center and the normalization distance is 1 when it is at the cell boundary. Compared to the prior art, the first and second schemes exhibit higher SINRs. In addition, as the terminal is located closer to the normalization distance 1 where the influence of external interference is relatively increased, the width of the performance gain is increased.

이라 할 때, 궤환 정보의 정확도를 나타내기 위한 파라미터로 ρ를 사용한다. ρ=1 일수록 실제 단말에서 추정한 정보와 궤환 정보 간의 오차가 없는 것을 의미한다. 실험 결과를 통해 예상한 바와 같이 궤환 정보의 정확도가 줄어들수록 추가적으로 궤환 정보를 활용하는 제2 방식의 성능이 열화 되는 것을 확인할 수 있다. 따라서 궤환 정보의 정확도에 따라 제1 방식 또는 제2 방식을 적응적으로 선택할 필요가 있음을 보여준다.6 is a graph illustrating a performance comparison according to the accuracy of statistical information of external cluster interference. Statistical information R _k estimated by the terminal and the statistical information fed back to the base station

In this case, ρ is used as a parameter for indicating the accuracy of feedback information. ρ = 1 means that there is no error between the information estimated by the actual terminal and the feedback information. As expected from the experimental results, it can be seen that as the accuracy of the feedback information decreases, the performance of the second method that additionally uses the feedback information deteriorates. Therefore, it is shown that it is necessary to adaptively select the first method or the second method according to the accuracy of the feedback information.

7 is a graph comparing the performance of the second and third schemes. Experimental results show that the third scheme exhibits more bandwidth efficiency than the second scheme. In particular, the closer the terminal is to the normalization distance 1 where the influence of interference is greater, the greater the performance gain. Therefore, in case of a terminal that does not satisfy the required QoS through the first or second scheme-based beamforming scheme, it may be efficient to use a third scheme having high bandwidth efficiency.

8 is a block diagram of a base station and a terminal for implementing an embodiment of the present invention. The base station 1100 includes a processor 1110 and a transceiver 1120. The transceiver 1120 transmits and / or receives a wireless signal. The processor 1110 is connected to the transceiver 1120 to implement the aforementioned multi-cell cooperative technique.

The terminal 1200 includes a processor 1210, a transceiver 1220, and a user interface 1230. The transceiver 1220 transmits and / or receives a wireless signal. The processor 1210 is connected to the transceiver 1220 and receives data according to the aforementioned reporting of the feedback information and the beamforming scheme. The user interface 1230 is connected to the processor 1210 to provide an interface with a user. The user interface 1230 may include a display device providing a user environment and / or an input tool such as a well known keypad.

The invention can be implemented in hardware, software or a combination thereof. In hardware implementation, an application specific integrated circuit (ASIC), a digital signal processing (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, and a microprocessor are designed to perform the above functions. , Other electronic units, or a combination thereof. In the software implementation, the module may be implemented as a module that performs the above-described function. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

1 is an exemplary diagram illustrating a wireless communication system in a multi-cell environment.

2 is a flow chart illustrating beamforming vector and power control vector update.

3 is a flowchart illustrating a multi-cell cooperation method according to an embodiment of the present invention.

4 is a signal flow diagram of multi-cell cooperation according to an embodiment of the present invention.

5 is a graph showing a change in the average SINR according to the position of the terminal.

6 is a graph illustrating a performance comparison according to the accuracy of statistical information of external cluster interference.

7 is a graph comparing the performance of the second and third schemes.

8 is a block diagram of a base station and a terminal for implementing an embodiment of the present invention.

Claims (6)

In the data transmission method based on multi-cell cooperation, Transmitting information about neighbor cells participating in cooperative transmission to a terminal; Receiving feedback information for selecting a beamforming scheme for multi-cell cooperation from the terminal, wherein the feedback information includes statistical information of external interference due to the adjacent cells; Selecting a beamforming scheme for the terminal based on the feedback information; Generating a beamforming vector corresponding to the selected beamforming scheme; And And transmitting data to which the beamforming vector is applied to the terminal. The method of claim 1, The feedback information may further include information regarding a quality of service (QoS) desired by the terminal. The method of claim 1, The information on the QoS is characterized in that the minimum signal-to-interference noise ratio (SINR) to ensure a specific transmission rate. The method of claim 1, The beamforming method is selected based on the accuracy of the statistical information of the external interference. The method of claim 1, And informing the terminal of the selected beamforming scheme. The method of claim 1, The selected beamforming scheme is one of a scheme for mitigating interference between users, a scheme for maximizing SINR and inter-user interference, and a scheme for maximizing a sum of transmission rates of multiple users.

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