KR20080087211A - Apparatus and method for downlink transmit beamforming considering neighbor cell interference in wireless communication system - Google Patents

Abstract

A downlink transmission beamforming method for considering neighboring cell interference in a wireless communication system and a device therefor are provided to enable each base station to generate transmission beamforming weight by considering interference on users of neighboring base stations and beamforming gains for self users, thereby improving reception performance of users at cell edges. Signals received from neighboring base stations are measured at certain intervals to measure average channel information from each base station(601-605). A candidate base station set including at least one base station which largely influences on an average signal to interference and noise power ratio among the neighboring base stations is determined by using the average channel information(607). The candidate base station set and the average channel information of the base stations included in the candidate base station set are transmitted to a self serving base station(609,611).

Description

Method and apparatus for downlink transmission beamforming considering neighboring cell interference in wireless communication system {APPARATUS AND METHOD FOR DOWNLINK TRANSMIT BEAMFORMING CONSIDERING NEIGHBOR CELL INTERFERENCE IN WIRELESS COMMUNICATION SYSTEM}

1 is a diagram illustrating a downlink transmission beam fobbing method considering interference of neighbor cells in a wireless communication system;

2 is a block diagram of a terminal in a wireless communication system according to the present invention;

3 is a block diagram of a base station in wireless communication according to the present invention;

4 is a diagram illustrating a procedure for determining a candidate base station in a terminal according to an embodiment of the present invention;

5 is a diagram illustrating a data reception procedure in a terminal according to an embodiment of the present invention;

6 is a diagram illustrating a procedure for determining transmission beamforming and performing scheduling at a base station according to an embodiment of the present invention;

7 is a diagram illustrating a performance graph according to the degree of antenna correlation in the prior art and the embodiment of the present invention;

8 is a view showing a performance graph according to the number of users in the prior art and the embodiment of the present invention, and

FIG. 9 is a diagram showing a graph for demonstrating validity of Equation 4 according to a distance for obtaining a candidate base station set of the present invention. FIG.

The present invention relates to a method and apparatus for downlink transmission beamforming in a wireless communication system, and more particularly, to a method and apparatus for downlink transmission beamforming considering an amount of interference and feedback information of neighboring base stations in a multi-input single output system.

Multiple input single output (MIS) systems can achieve higher signal-to-noise power ratios and diversity gains than single-input single output (SISO) systems by using transmit beamfobbing.

Conventionally provided transmission beamforming techniques include a coherent beamforming technique, an original beamforming technique, an opportunistic beamforming technique, and the like.

First, the matched beamforming technique can simultaneously obtain a signal-to-noise ratio gain and diversity gain, but has a problem in that the amount of feedback information at the receiver is large because instantaneous channel information is required at the transmitter. In contrast, the inherent beamforming technique is a technique for performing beamforming using only the antenna correlation information in an environment where antenna correlation is present, and although the performance is lower than that of the matched beamforming technique, feedback is not used because it does not use instantaneous channel information. With the advantage that the amount of information is small, the greater the antenna correlation, the closer the matching beamforming performance can be obtained. In addition, the opportunistic beamforming technique generates a random beam in a technique similar to that of the matched beamforming without using the instantaneous channel information, and then generates a signal-to-interference plus noise ratio for each user. By selecting and scheduling an optimal user with only power ratio (SINR) information, a multi-user diversity gain can be obtained.

However, the above-described techniques have a problem of insufficient consideration for a user located at the edge of a cell in a multi-cell environment. In the multi-cell environment, the user located at the edge of the cell is far from their serving base station, so the signal power is greatly reduced due to a large path-loss, and interference from base station signals of neighboring cells located at similar distances. Will receive. Accordingly, there is a need to provide a method for improving the reception performance of a user located at the edge of the cell.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a method and apparatus for downlink transmission beamforming in a multi-input single output system.

Another object of the present invention is to provide a method and apparatus for generating a downlink transmission beamforming weight in consideration of a beamforming gain for a user and interference in a neighbor base station user in a base station of a multi-input single output system.

Another object of the present invention is to provide a method and apparatus for generating a beamforming weight using only a small amount of feedback information in a base station of a multi-input single output system.

Another object of the present invention is to provide a method and apparatus for determining a neighbor base station that affects its reception performance in a terminal of a multi-input single output system and feeding back channel information thereof.

According to the first aspect of the present invention for achieving the above object, the method of operation of the terminal for generating the downlink transmission beamforming weight in a multi-input single output system, by measuring the signal received from the adjacent base stations at regular intervals Measuring average channel information from each base station, and using at least one base station having a significant influence on its average signal-to-interference and noise power ratio among the adjacent base stations by using the measured average channel information of each base station; Determining a candidate base station set, and transmitting average channel information of the candidate base station set and the base stations included in the candidate base station set to its serving base station.

According to a second aspect of the present invention for achieving the above object, the operation method of the base station for generating a downlink transmission beamforming weight in a multi-input single output system, determining the service order of the terminal receiving the service from itself A process of exchanging a set of candidate base stations and corresponding average channel information with neighboring base stations from the service sequence and the terminal at regular intervals, and identifying terminals of neighboring base stations that have determined themselves as candidate base stations from the exchanged information. And generating a beamforming weight using average channel information of the terminal receiving the service from the terminal and the identified neighboring base station terminals.

According to a third aspect of the present invention for achieving the above object, the apparatus of the terminal for generating a downlink transmission beamforming weight in a multi-input single output system, the average channel information of each base station in the signal received from the adjacent base stations A candidate base station set including a reception signal checking unit measuring at least one and at least one base station having a significant influence on its average signal-to-interference and noise power ratio among the neighboring base stations using the measured average channel information of each base station; And a transceiver for receiving a signal from the neighboring base stations and transmitting the determined candidate base station set and corresponding average channel information to its own serving base station.

According to a fourth aspect of the present invention for achieving the above objects, the base station apparatus for generating a downlink transmission beamforming weight in a multi-input single output system, the candidate base station set and the average channel information according to the signal received from the terminal A received signal confirming unit for confirming, a target order determining unit for determining a service order of a terminal receiving a service from the base station itself, and exchange information and the service order of the terminal identified in the received signal confirming unit with neighboring base stations. A base station information exchange unit and a terminal of a neighboring base station having determined itself as a candidate base station from the exchanged information, and using the average channel information of the terminal receiving the service from the base station and the neighboring base station terminal to obtain a beamforming weight; Characterized in that it comprises a beamforming weight generator for generating The.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

In the present invention, in order to improve the reception performance of the multi-Z user, each base station generates a transmission beamforming weight in consideration of the beamforming gain for the user and the interference of the neighbor base station users with only a small amount of feedback information And the apparatus will be described. Hereinafter, in the present invention, the channel covariance matrix, average signal power, and total noise power average value information, rather than instantaneous channel information, will be used for the small feedback information.

FIG. 1 illustrates a downlink transmission beam fobbing technique considering interference of adjacent cells in a wireless communication system.

As shown in FIG. 1, users A, B, and C located at the edge of each cell receive data from their serving base station, and each serving base station receives a service from itself. The beamforming weight is set to improve the reception performance of the user. In this case, each user is affected by neighboring base stations that are separated by a similar distance from their serving base station. Therefore, the beamforming weights set to improve reception performance for each user at the serving base station of each user may affect users of neighboring base stations. For example, the beamforming weights set by the base station of cell 1 (100) to maximize the reception performance of user A (102) are such that users B and C located at the edges of adjacent cells 2 and 3 are each serving base stations of their own. It determines the amount of interference to receive the signal from.

Accordingly, each serving base station should set beamforming weights that can reduce interference to users of neighboring base stations affected by the base station while improving reception performance for the user. That is, the base station of the cell i should be set such that the beamforming weights (W _{i , k} ) for the user k improves the reception performance of the user k while reducing the amount of interference to the user located in another cell.

In the present invention, at each data transmission time, the base station of each cell determines the beamforming weight for one of its users. In the present invention, the predetermined user is defined as a target user, and the set of beamforming weights according to time is defined as a beam pattern.

Here, the average average interference power felt by the target users who are served from the base station of the other cell at the same time by the beamforming weight W _{i , k} determined by the cell i for the user k is the average jamming power. When defined as J _{i , k} , the average jamming power may be expressed as Equation 1 below.

In Equation 1, E {x} represents an expected value of random variable x, h _{i, j} represents a channel value between a base station of cell i and a user j of another cell, and R _{i , j} is Represents the covariance matrix of the channel. And, P _{i , j} represents the power of the average signal transmitted from the base station of the cell i to the user j, the superscript * represents the Hermitian operator. Here, the user j of the other cell refers to a target user considered by the base station of the other cell at the same time that the cell i determines the beamforming weight for the user k.

As in Equation 1, although the beamforming weight W _{i , k} determined by cell i for user k affects users in other cells, users of other cells far from cell i of the average power of the received signal transmitted from the base station is relatively small or antenna correlation of the channel is substantially not is not significantly affected by the W _{i, k.} Accordingly, in the present invention, in order to reduce the complexity of the entire system, only the base stations having a large antenna correlation are determined as the candidate base stations while each user provides a large average power to each user, and each base station determines the candidate base station. Only the users will be considered to determine the beamforming weight. That is, each of the users determines the base stations whose beamforming weights among neighboring base stations greatly affect their average signal-to-interference and noise power ratios as candidate base stations.

Therefore, the average jamming power J _{i , k} shown in Equation 1 may be redefined as in Equation 2 below.

Here, Ψ _i is a jamming user set and means a user set including the base station of cell i as its candidate base station set.

Then, in the following, the user determines his candidate base station, and each base station has the average beamforming gain of the user provided with the service from him and the interference, that is, the average jamming power of the user of the other base station that determined itself as the candidate base station Considering this, a method of setting the beamforming weights will be described.

2 is a block diagram of a terminal in a wireless communication system according to the present invention. Here, the terminal includes a receiver 200, a received signal checking unit 202, a candidate base station set generator 204, and a transmitter 210, the candidate base station set generator 204 is a candidate base station set A component 206 and a channel capacity calculator 208 are included.

Referring to FIG. 2, first, the receiver 200 converts signals from neighboring base stations received through an antenna into baseband signals, and then demodulates and decodes the signals according to a predetermined modulation scheme and code rate. The signal is output to the received signal checking unit 202.

The received signal checking unit 202 classifies signals of each base station based on the information on the received signal input from the receiving unit 200, and uses a channel covariance matrix and the maximum and minimum corresponding to the signals of the separated base stations. After obtaining the eigenvalues, the average power of the signal and the average value of the total noise power, and output them to the candidate base station set generator 204 and the transmitter 210.

The candidate base station set generation unit 204 includes the candidate base station set configuration unit 206 and the channel capacity calculation unit 208, so that the signal is stored using the data input from the received signal confirmation unit 202. A candidate base station set is determined among the received base stations.

That is, the channel capacity calculating unit 208 calculates the maximum channel capacity that can be obtained when the specific base station among the base stations from which the signal is received is included in the candidate base station set using Equation 3 below, and the calculated The maximum channel capacity is output to the candidate base station aggregation configuration unit 206. Here, the channel capacity calculator 208 calculates the maximum channel capacity in order of the base stations having the largest average received power among the base stations from which the signal is received.

Equation 3 below shows an equation for calculating the maximum channel capacity of the candidate base station set.

Here, C _upper (Ω) represents the maximum channel capacity when the candidate base station set is Ω, and γ _{i, k} represents the instantaneous signal to interference and noise power ratio from the serving base station i of the user k, and the E {γ _{i, k} } is an expected value of γ _{i, k} and can be calculated using Equation 4 below.

Where N _Ω represents the number of base stations included in the candidate base station Ω, and λ _{i, k} ^max , λ _{i, and k} ^min are the maximum and minimum uniqueness of the channel covariance matrix between the base station of cell i and user k, respectively. And α and β represent cell indexes of base stations included in the candidate base station set in addition to the serving base station. In general, since there are one or two cells which have a large interference in the structure of the cellular system, the present invention will consider only the case where the candidate base station set consists of two or three cell base stations.

The candidate base station set configuration unit 206 calculates a performance gain when the base station is included in the candidate base station set based on the maximum channel capacity input from the channel capacity calculator 208. Here, the performance gain may be calculated using Equation 5 below.

Equation 5 below shows a performance gain when a specific base station is included in a candidate base station.

Here, C (Ω ') means channel capacity when the specific base station is included in the candidate base station set, and C (Ω) indicates channel capacity when the specific base station is not included in the candidate base station set. it means.

The candidate base station set configuration unit 206 compares the performance gain ζ calculated using Equation 5 with a predetermined reference value ζ ₀ and selects the specific base station when the calculated performance gain ζ is greater than the reference value ζ ₀ . Include in the candidate base station set, otherwise do not include the particular base station in the candidate base station. In this case, when the candidate base station set Ω that does not include the specific base station is empty, the value of C (Ω) becomes 0, so that the performance gain ζ becomes ∞. In this case, the specific base station is always included in the candidate base station, and the specific base station becomes the serving base station of the user. Here, the reference value ζ ₀ may be determined in consideration of the performance gain and complexity of the entire system when the specific base station is included in the candidate base station set.

The candidate base station set configuration unit 206 outputs information on the base stations included in the candidate base station set to the transmitter 210 when a candidate base station set for all base stations for which a signal is received is generated.

The transmitter 210 transmits instantaneous signal-to-interference and noise power ratio information input from the received signal checking unit 202 to a serving base station every data transmission period. Further, according to the present invention, the candidate base station set generation unit 206 receives information on the base station included in the candidate base station set, and the base station included in the candidate base station set among the data input from the received signal confirming unit 202. The multiplication factor of the channel covariance matrix and the average signal power and the average value of the total noise power are identified and transmitted to the serving base station at regular intervals.

3 is a block diagram of a base station in wireless communication according to the present invention. In this case, the base station includes a receiver 300, a received signal checking unit 302, a beam pattern determination unit 304, a scheduling unit 312, a transmitter 314, and the beam pattern determination unit 304. The target user order determination unit 306, the base station information exchange unit 308, and a beamforming weight generator 310.

Referring to FIG. 3, first, the receiver 300 converts a signal of a radio frequency band received through an antenna into a baseband signal, and then performs demodulation and decoding according to a predetermined modulation scheme and a code rate. The signal is output to the signal checking unit 302.

The received signal checking unit 302 classifies a signal input from the receiving unit 300 and outputs the signal to the beam pattern determination unit 304 and the scheduling unit 312. For example, a signal including instantaneous signal-to-interference and noise power ratio information received from a user terminal, a signal including candidate base station set information, a value obtained by multiplying a channel covariance matrix according to the candidate base station set and an average signal power and a total value. A signal containing average value information of noise power is distinguished.

The beam pattern determination unit 304 includes the target user order determination unit 306, the base station information exchange unit 308, and the beamforming weight vector generator 31 to transmit a user terminal for receiving a service from the same. Determine the beam pattern.

The target user order determiner 306 determines the service order of the user terminal receiving the service from the base station itself, that is, the order of the target users, and periodically repeats the order. The target user order determining unit 306 outputs the order of the target user and the information input from the received signal checking unit 302 to the base station information exchange unit 308.

The base station information exchanger 308 is a candidate base station set from the target user order inputted from the target user order determiner 306 and the information from the received signal checking unit 302, and a candidate channel covariance matrix and an average signal. The power multiplied value is transmitted to the neighbor base station, and the information necessary for generating the beamforming weight is received from the neighbor base station. Subsequently, the base station information exchanger 308 configures a user set that designates the base station itself as a candidate base station set, that is, a jamming user set, and a channel based on antenna correlation with the average signal power of the user included in the jamming user set. The beamforming weight generator 310 outputs a value obtained by multiplying the covariance matrix.

The beamforming weight generation unit 310 generates a beamforming weight based on the information input from the base station information exchange unit 308 and outputs the beamforming weight to the scheduling unit 312. The beamforming weight may be calculated using Equation 6 below.

Equation 6 below shows an optimal beamforming weight in consideration of the average beamforming gain and the average jamming power.

는 셀 i의 기지국에서 단말 k를 위해 생성하는 빔포밍 가중 치를 나타내고, 상기 R_{i ,j}는 상기 셀 i의 기지국과 단말 j사이 채널의 공분산 행렬을 나타낸다. 그리고, 여기서, N₀ ^k는 사용자 k의 후보 기지국 집합에 속하지 않는 기지국들로부터의 간섭 신호 및 총 잡음 전력의 평균값을 나타내며, I_M은 (M×M)단위행렬(Identity matrix)을 나타내고, ζ_max(X)는 S의 최대 고유값에 대응하는 고유벡터를 나타낸다. here,

Denotes a beamforming weight value generated for the terminal k by the base station of cell i, and R _{i , j} denotes the covariance matrix of the channel between the base station of cell i and terminal j. Here, N ₀ ^k represents the average value of the interference signal and the total noise power from the base stations that do not belong to the set of candidate base stations of the user k, I _M represents the (M × M) identity matrix, ζ _max (X) represents the eigenvector corresponding to the maximum eigenvalue of S.

The scheduling unit 312 receives the beamforming weights from the beamforming weight generation unit 310 of the beam pattern determination unit 304, and based on the channel state information input from the received signal checking unit 302. Scheduling is performed by selecting the best users according to the beamforming weights generated by each base station. Here, the channel state information input from the received signal checking unit 302 means an instantaneous signal-to-interference and noise power ratio received from a user every transmission data period.

The transmitter 314 transmits data of a user scheduled according to a scheduling result of the scheduling unit 312.

4 illustrates a procedure of determining a candidate base station in a terminal according to an embodiment of the present invention.

Referring to FIG. 4, first, when the UE reaches a preset period in step 401, the terminal proceeds to step 403 to initialize the candidate base station set Ω to the empty set and acquire signal synchronization of the base station existing in the neighboring cell.

Then, the terminal measures the average received power and channel covariance matrix and corresponding maximum and minimum eigenvalues of each base station using the signals received from the base stations that have acquired the signal synchronization in step 405. In step 407, the terminal selects the base station having the largest average reception power without being included in the candidate base station set from which the signal synchronization is obtained, and proceeds to step 409 to determine whether the candidate base station set is empty. Check.

If the candidate base station set is empty, the terminal proceeds to step 423 and determines the selected base station as its own serving base station, and then proceeds to step 419. In this case, the terminal includes the selected base station in the candidate base station set, and calculates and stores the maximum channel capacity of the candidate base station set including the selected base station using Equation (3).

On the other hand, if the candidate base station set is not empty, the terminal calculates the maximum channel capacity of the candidate base station set when the selected base station is included in the candidate base station set using Equation 3 in step 411. Thereafter, the terminal uses the maximum channel capacity when the candidate base station set includes the selected base station and the maximum channel capacity when the selected base station does not include the base station as shown in Equation 5 in step 413. The performance gain when the candidate base station set includes the selected base station set is measured.

In step 415, the terminal compares the measured performance gain with a preset reference value. If the measured performance gain is greater than the reference value, the terminal proceeds to step 417 to include the selected base station in the candidate base station set and the maximum channel capacity calculated in step 411 to the maximum channel of the current candidate base station set. After storing as a capacity, proceed to step 419 below. On the other hand, if the measured performance gain is less than or equal to the reference value, the terminal proceeds to step 425 and proceeds to step 419 without including the selected base station in the candidate base station set.

In step 419, if the base station determines whether or not the candidate base station set is included in all the base stations for which the signal synchronization has been determined, and if it is not determined whether the candidate base station set is included in all the base stations, the process returns to step 407. Rerun the step.

On the other hand, when it is determined whether the candidate base station set is included for all the base stations, the terminal proceeds to step 421 in which channel state information about the base station set and the base station included in the candidate base station set, that is, the channel covariance matrix and the like. After transmitting the average signal power multiplied by the average value of the total noise power to the serving base station, the algorithm according to the present invention is terminated.

5 is a flowchart illustrating a data reception procedure in a terminal according to an embodiment of the present invention.

Referring to FIG. 5, first, at step 501, the terminal checks the signal received from all base stations included in the preset candidate base station set at every instant to check the channel state and beamforming weights from the base stations. In step 503, the instantaneous signal-to-interference and noise power ratios from the base stations are calculated and transmitted to the serving base station.

In step 505, the terminal receives the control channel of the serving base station and checks whether its data is scheduled. In this case, the control channel means all kinds of base station signals informing the scheduling result of the base station.

When the own data is not scheduled, the terminal returns to step 501 to perform the following steps again, and when the own data is scheduled, the terminal proceeds to step 507 after receiving the scheduled data. The algorithm according to the present invention is terminated.

6 is a flowchart illustrating a procedure for determining transmission beamforming and performing scheduling in a base station according to an embodiment of the present invention.

Referring to FIG. 6, the base station first determines a service order, ie, a target user order, for users who receive a service from themselves in step 601. Here, the target user order is updated according to users who receive a service from the base station at regular intervals.

Thereafter, the base station exchanges information necessary for generating the beamforming weight with the neighboring base station in step 603. The information exchanged with the neighboring base station includes a product of a sequence of target users determined by the base station, a set of candidate base stations of each user, and a channel covariance matrix based on average signal power and antenna correlation.

 The base station exchanging information with the neighboring base station configures a jamming user set, which is a set of users including the base station itself in the candidate base station set using the exchanged information in step 605, and then based on Equation 6 in step 607. A beamforming weight is generated to determine the beam pattern.

In step 609, the base station performs scheduling of each user by using the channel state information received from the users. In step 611, the base station transmits the scheduled user data using the beamforming weights. Here, the instantaneous signal-to-interference and noise power ratios received from each user in every data transmission period may be used as the channel state information.

The base station then terminates the algorithm according to the invention.

7 shows a performance graph according to the degree of antenna correlation in the prior art and the embodiment of the present invention. In the following description, the horizontal axis represents the absolute value of the two antenna correlations, and the vertical axis represents the spectral efficiency. Here, the closer the absolute value of the two antenna correlations to 0, the smaller the correlation between the two antennas, and the closer to 1, the greater the correlation between the two antennas.

7 is a performance graph in the case of applying an opportunistic beamforming technique and a unique beamforming technique according to the related art, and in the case where two or three candidate base station sets are applied according to the present invention. The performance graph of the case is shown.

As shown in FIG. 7, the higher the antenna correlation, the more efficient the beamforming technique using the unique beamforming technique and the beamforming technique according to the present invention than the opportunistic beamforming technique using the random beam. It can be seen that it is higher. In addition, the greater the antenna correlation, the greater the interference mitigation effect in the adjacent cell. Thus, it can be seen that the beamforming technique according to the present invention has a higher frequency efficiency than the inherent beamforming technique.

8 shows a performance graph according to the number of users in the prior art and the embodiment of the present invention. In the following description, the horizontal axis represents two user numbers, and the vertical axis represents frequency efficiency.

8 is unique to the opportunistic beamforming technique according to the prior art in an environment in which there is little correlation between the two antennas (| ρ | = 0.01) and in an environment in which the correlation between the two antennas is large (| ρ | = 0.99). The performance graph when the beamforming technique is applied and the performance graph when the beamforming technique is applied when two or three candidate base station sets are used according to the present invention are shown.

As shown in FIG. 8, in the environment where there is little antenna correlation, both the conventional opportunistic beamforming technique, the unique beamforming technique, and the beamforming technique according to the present invention can obtain similar frequency efficiency according to the number of users. In the environment where the antenna correlation is large, it can be seen that the beamforming technique according to the present invention has higher frequency efficiency than the prior art even when the number of users is small.

9 shows a graph for demonstrating the validity of Equation 4 according to the distance for obtaining the candidate base station set of the present invention. In the following description, the horizontal axis represents the distance from the center of the cell to the user terminal, and the vertical axis represents the frequency efficiency.

FIG. 9 illustrates a case in which two or three base stations are included in a candidate base station set, and according to the antenna correlation degree, the terminal uses only specific channel information based on the result of the experiment and the actual maximum channel capacity according to the present invention. The comparison result of the maximum channel capacity that can be obtained is shown.

As shown in FIG. 9, it can be seen that the maximum channel capacity obtained based on Equation 4 is almost identical to the experimental result of the actual maximum channel capacity according to the present invention. Therefore, in the present invention, the candidate base station set may be determined using the channel capacity value obtained based on Equation 4.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, in the multi-input single-output system, the base station generates a transmission beamforming weight in consideration of the beamforming gain for the user and the interference of the neighbor base station user, thereby receiving the user located at the cell edge. Performance can be improved, and a large gain can be obtained as the antenna correlation is large or the number of base stations included in the candidate base station set increases. In addition, the beamforming weight may be generated by feeding back only a small amount of information related to the average value such as the channel covariance matrix, the average signal power, and the average noise power, without feedback of the instantaneous channel information.

Claims (21)

A method of operating a terminal for generating downlink transmission beamforming weights in a multi-input single output system, Measuring average channel information from each base station by measuring signals received from adjacent base stations at regular intervals; Determining a candidate base station set including at least one base station having a large influence on its average signal-to-interference and noise power ratio among the adjacent base stations using the measured average channel information of each base station; And transmitting average channel information of the candidate base station set and the base station included in the candidate base station set to its serving base station. The method of claim 1, Wherein said average channel information comprises at least one of an average signal power, a channel covariance matrix, and an average value of total noise power. The method of claim 1, The process of determining the candidate base station set, Selecting a specific base station among neighbor base stations not included in the candidate base station set; Calculating a channel capacity when the selected base station is included in a candidate base station set and measuring a performance gain; And determining whether to include the selected base station in the candidate base station set by comparing the measured performance gain with a predetermined reference value. The method of claim 3, wherein The process of determining the candidate base station set, And determining whether to include the base station in the candidate base station set by selecting the base station having the largest average reception power among the adjacent base stations. The method of claim 3, wherein Determining whether to include the selected base station in the candidate base station set, Determining that the selected base station is included in the candidate base station set when the measured performance gain is greater than a predetermined reference value. The method of claim 5, And determining that the selected base station is not included in the candidate base station when the measured performance gain is less than or equal to a preset reference value. The method of claim 3, wherein The channel capacity may be calculated using Equation 7 below.

Here, C _upper (Ω) represents the maximum channel capacity when the set of candidate base stations is Ω, and γ _{i, k} represents the instantaneous signal to interference and noise power ratio from the serving base station i of the user terminal k, and E {γ _{i, k} } represents an expected value of γ _{i, k} . The method of claim 3, wherein The performance gain can be measured using the following Equation (8).

Here, C (Ω ') means channel capacity when the specific base station is included in the candidate base station set, and C (Ω) indicates channel capacity when the specific base station is not included in the candidate base station set. Indicates. A method of operating a base station for generating downlink transmission beamforming weights in a multi-input single output system, Determining a service order of terminals receiving services from themselves; Exchanging a set of candidate base stations and corresponding average channel information received from the terminals at regular intervals from the terminals and neighboring base stations; Identifying terminals of neighboring base stations that have determined themselves as candidate base stations from the exchanged information; And generating a beamforming weight using average channel information of the terminal receiving the service from the terminal and the identified neighbor base station terminals. The method of claim 9, Wherein said average channel information comprises at least one of an average signal power, a channel covariance matrix, and an average value of total noise power. The method of claim 9, The beamforming weights are generated using Equation 9 below.

here,

Is a beamforming weight value generated by the base station of cell i for terminal k, R _{i , j} is a covariance matrix of the channel between the base station of cell i and terminal j, P _{i , j} is the base station of cell i The average signal power delivered to terminal j, N ₀ ^k is the average value of the interference signal and total noise power from the base stations that do not belong to the set of candidate base stations of the terminal k, the I _M (M × M) unit matrix ( Identity matrix), ζ _max (X) represents the eigenvector corresponding to the maximum eigenvalue of S. An apparatus of a terminal for generating a downlink transmission beamforming weight in a multi-input single output system, A received signal checking unit measuring average channel information of each base station from signals received from neighboring base stations; A candidate base station set generation unit for determining a candidate base station set including at least one base station having a large influence on its average signal-to-interference and noise power ratio among the adjacent base stations by using the measured average channel information of each base station; And a transmitter / receiver for receiving signals from the neighbor base stations and transmitting the determined candidate base station set and corresponding average channel information to its serving base station. The method of claim 12, Wherein said average channel information comprises at least one of an average signal power, a channel covariance matrix, and an average value of total noise power. The method of claim 12, The candidate base station set generation unit, A channel capacity calculating unit for calculating a channel capacity when a specific base station is included in the candidate base station set among adjacent base stations not included in the candidate base station set; And a candidate base station set configuration unit configured to calculate a performance gain using the calculated channel capacity, and determine whether to include the base station in the candidate base station set by comparing the calculated performance gain with a preset reference value. Device. The method of claim 14, The channel capacity calculator, And calculating the corresponding channel capacity by selecting the base stations having the highest average reception power among the adjacent base stations. The method of claim 14, The candidate base station set configuration unit, When the measured performance gain is greater than a preset reference value, the selected base station is included in the candidate base station set, and when the measured performance gain is less than or equal to a preset reference value, the selected base station is set to the candidate base station set. Device not included in the. The method of claim 14, The channel capacity may be calculated using Equation 10 below.

Here, C _upper (Ω) denotes a maximum channel capacity when the candidate base station set is Ω, and γ _{i, k} denotes an instantaneous signal to interference and noise power ratio from the serving base station i of the terminal k, and E { γ _{i, k} } represents the expected value of γ _{i, k} . The method of claim 14, The performance gain can be measured using Equation 11 below.

Here, C (Ω ') means channel capacity when the specific base station is included in the candidate base station set, and C (Ω) indicates channel capacity when the specific base station is not included in the candidate base station set. Indicates. A base station apparatus for generating downlink transmission beamforming weights in a multi-input single output system, A received signal checking unit for checking a candidate base station set and corresponding average channel information in a signal received from a terminal; A target order determination unit for determining a service order of a terminal receiving a service from the base station itself; A base station information exchange unit which exchanges the information confirmed by the received signal checking unit and the service order of the terminal with an adjacent base station; A beamforming weight generation unit for identifying a terminal of a neighboring base station that has determined itself as a candidate base station from the exchanged information, and generating a beamforming weight using average terminal information of the terminal receiving the service from the terminal and the neighboring base station terminal; Apparatus comprising a. The method of claim 19, Wherein said average channel information comprises at least one of an average signal power, a channel covariance matrix, and an average value of total noise power. The method of claim 19, The beamforming weights are generated using Equation 12 below.

here,

Is a beamforming weight value generated by the base station of cell i for terminal k, R _{i , j} is a covariance matrix of the channel between the base station of cell i and terminal j, P _{i , j} is the base station of cell i The average signal power delivered to terminal j, N ₀ ^k is the average value of the interference signal and total noise power from the base stations that do not belong to the set of candidate base stations of the terminal k, the I _M (M × M) unit matrix ( Identity matrix), ζ _max (X) represents the eigenvector corresponding to the maximum eigenvalue of S.

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