KR102228883B1 - Apparatus and method for canceling inter cell interference in a multi cell system sharing information among base station through a backhaul - Google Patents

Abstract

In a multi-cell system including a plurality of base stations provided by the present invention and sharing information between base stations through a backhaul, the method of removing inter-cell interference includes SA (scale and angle) symbol information for a received signal of another base station. Receiving from a backhaul and removing inter-cell interference using the received SA symbol information from a received signal of a current base station, wherein the SA symbol information includes It is characterized by including a hard decision symbol value and a {magnitude, phase} value for changing the size and phase of the hard decision symbol.

Description

An apparatus and method for removing inter-cell interference in a multi-cell system that shares information between base stations through backhaul {APPARATUS AND METHOD FOR CANCELING INTER CELL INTERFERENCE IN A MULTI CELL SYSTEM SHARING INFORMATION AMONG BASE STATION THROUGH A BACKHAUL}

The present invention relates to a method and apparatus for canceling inter-cell interference in a multi-cell system in which information is shared between base stations through a backhaul.

In wireless communication standards such as IEEE 802.11n (WiFi), IEEE 802.16e (WiMAX), and 3GPP LTE-A, a multiple-input multiple-output (MIMO) antenna technique is used. In the MIMO scheme, by installing a plurality of antennas in the transceiver, it is possible to increase the channel capacity and reliability during signal transmission/reception without using additional frequency or time resources. For reference, the channel capacity and reliability are linearly proportional to the product of the number of the smaller of the number of transmitting and receiving antennas and the number of transmitting and receiving antennas, respectively.

On the other hand, in a multi-cell environment, it is inevitable to reuse resources between adjacent cells in order to meet the rapidly increasing communication demand under the limitation of communication resources. This causes inter-cell interference. For this reason, the actual gain value in the MIMO method does not reach the theoretical gain value.

For the above reasons, it is essential to use a technique for reducing inter-cell interference in a multi-cell environment. On the other hand, considering the current wireless communication system, it is difficult to reduce the inter-cell interference occurring in the uplink at the user terminal side. Therefore, in general, a technique for canceling inter-cell interference in the uplink must be performed in the base station.

In LTE-A, a recently commercialized wireless communication system, it is possible to reduce interference between cells in uplink by connecting base stations through a high-speed backhaul network to exchange necessary information between base stations. The information shared between the base stations at this time may be channel estimation information of the base station, a received signal of the base station, and the like. However, the data transmission/reception capacity of a backhaul network connecting base stations is limited to a certain range. Therefore, information shared between base stations should be selected in consideration of the capacity of the backhaul network and the efficiency of reducing inter-cell interference.

An embodiment of the present invention provides a method and apparatus for reducing inter-cell interference in uplink between base stations through a backhaul network in a multi-cell wireless communication system.

In addition, an embodiment of the present invention provides a method and apparatus for efficiently reducing uplink inter-cell interference in consideration of the data capacity of a backhaul room in a multi-cell wireless communication system.

A method of removing inter-cell interference in a multi-cell system including base stations provided by an embodiment of the present invention and sharing information between base stations through a backhaul, is an SA (scale and angle) symbol for a received signal of another base station. A process of receiving information from a backhaul, and a process of removing inter-cell interference using the received SA symbol information from a received signal of a current base station, wherein the SA symbol information is included in the signal received by the other base station. It includes a value of a hard-decision symbol and a value of {magnitude, phase} for changing the size and phase of the hard-decision symbol.

Here, the process of determining the final signal-to-interference ratio (SINR) of the current base station in consideration of the inter-cell interference cancellation capability of the other base station, and determining the code rate and modulation order (MCS) information based on the determined SINR. And transmitting the determined MCS information to the user terminal, and receiving uplink data transmitted according to the MCS information from the user terminal.

Meanwhile, the process of determining the signal-to-interference ratio of the local base station includes a process of receiving a reference signal from the user terminal, a process of determining a first SINR using the reference signal, and an ICT previously stored in the current base station. A process of determining a first ICT index corresponding to the determined first SINR value from the (interference cancellation table) table, and transmitting the determined first ICT index through the backhaul.

In addition, in consideration of the process of receiving the ICT index of the other base station from the backhaul and the first ICT index of the other base station, determining a second SINR, which is a signal-to-interference ratio after removing the interference by the other base station. Includes more processes.

Here, from the ICT table, a second ICT index is determined in consideration of the first SINR and the second SINR, the determined second ICT index is transmitted to the backhaul, and the second ICT index of the other base station is transmitted from the backhaul. It further includes a process of repeating the process of receiving the ICT index.

In addition, the repeating process may be terminated when a base station cooperation completion message is received from the backhaul or the second ICT index is received a predetermined number of times.

Meanwhile, the ICT table may include an SINR index before intercell interference cancellation, an SINR index after intercell interference cancellation, and an ICT index corresponding to the two SINR indices.

In addition, the ICT table may further include a predetermined number of {size, phase} sets for changing the size and phase of the hard decision symbol, and information indicating the interference cancellation capability of the corresponding base station.

In addition, the {magnitude, phase} value may be determined as a {magnitude, phase} value such that a difference between the soft decision symbol value of the received signal and the SA symbol value is minimized.

Meanwhile, in a multi-cell system that includes a plurality of base stations provided by an embodiment of the present invention and shares information between base stations through a backhaul, a base station for removing inter-cell interference includes a receiving unit and a control unit for controlling the receiving unit. Including, wherein the control unit receives SA (scale and angle) symbol information for a received signal of another base station from the backhaul, and removes inter-cell interference by using the received SA symbol information in the received signal of the current base station, , The SA symbol information includes a hard-decision symbol value for a signal received by the other base station, and a {magnitude, phase} value for changing the size and phase of the hard-decision symbol. Inter-cell interference can be eliminated in the system.

In a multi-cell system including a plurality of base stations provided by the present invention, a method of removing inter-cell interference in a backhaul for sharing information between the base stations is an ICT index (interference cancellation table) of each base station from the plurality of base stations. ), and transmitting ICT indexes of base stations other than any of the base stations to the random base station using the received ICT indexes, wherein the ICT index comprises: Can be used to re-determine their current ICT index.

Repeating the process of receiving the ICT index of each base station re-determined by reflecting the ICT index of the other base stations, and transmitting the ICT index of the other base stations to the random base station using the re-determined ICT index of each base station Include more.

Here, the repeating process may be terminated when values of ICT indexes of all base stations included in the multi-cell system are not changed.

In this case, when the values of the ICT indexes of all the base stations are not changed, a process of transmitting a message indicating that cooperative communication between base stations has been completed to the random base station is further included.

Meanwhile, the repeating process may be repeated within a predetermined number of times.

1 is a diagram illustrating a method of receiving an uplink signal in a base station to which an embodiment of the present invention is applied;
2 is a diagram illustrating a transmission chain of a user terminal 101 for uplink transmission according to an embodiment of the present invention;
3 is a diagram illustrating a reception chain of a base station 103 for uplink reception according to an embodiment of the present invention;
4 is a diagram illustrating a signal reception method of a base station using a conventional hard decision or soft decision method to reduce inter-cell interference;
5 is a diagram illustrating, for example, a constellation diagram according to 4-QAM (quadrature amplitude modulation) modulation that a hard decision symbol and a soft decision symbol are displayed on a constellation diagram;
6 is a diagram illustrating an SR interference cancellation scheme according to an embodiment of the present invention;
7 is a diagram illustrating a situation that affects mutual interference cancellation capability between base stations according to an embodiment of the present invention;
8 is a diagram illustrating a method of exchanging ICT indexes between base stations connected through a backhaul according to an embodiment of the present invention;
9 is a diagram illustrating a process of exchanging ICT and receiving uplink data according to an embodiment of the present invention;
10 is a diagram illustrating an operation of a base station determining an ICT index according to an embodiment of the present invention;
11 is a diagram illustrating a configuration of a base station apparatus according to an embodiment of the present invention for each functional block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The detailed description of the present invention described below refers to the accompanying drawings, which illustrate specific embodiments in which the present invention may be practiced. These embodiments are described in detail sufficient to enable a person skilled in the art to practice the present invention. It should be understood that the various embodiments of the present invention are different from each other, but need not be mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention in relation to one embodiment. Further, the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the present invention. Accordingly, the detailed description to be described below is not intended to be taken in a limiting sense, and the scope of the present invention is limited only by the appended claims, along with all scopes equivalent to those claimed by the claims, if appropriately described. Like reference numerals in the drawings refer to the same or similar functions over several aspects.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings in order to enable those of ordinary skill in the art to easily implement the present invention.

Since the embodiments of the present invention described below are for reducing inter-cell interference in a multi-cell environment, in the present specification, other interference factors such as intra-cell interference and inter-stream interference will not be considered in addition to inter-cell interference. First, signal transmission/reception between a base station and a user terminal to which an embodiment of the present invention is applied will be described.

First, signal transmission/reception between a base station and a user terminal to which an embodiment of the present invention is applied will be described.

1 is a diagram illustrating a method of receiving an uplink signal in a base station to which an embodiment of the present invention is applied.

The embodiment of the present invention is based on a multi-cell environment in which inter-cell interference may occur, and the base station 101 of FIG. 1 is assumed to be the k-th base station among any K cells that may cause inter-cell interference. . _{Accordingly, a signal x k} transmitted by the user terminal 101 to the base station 101 is indicated and a signal y _k received by the base station is indicated.

Referring to FIG. 1, first, in step 111, the user terminal 101 transmits an uplink reference signal to the base station 103. The base station 103 estimates an uplink channel using the received reference signal and determines a MIMO reception method. In addition, a code rate and modulation that calculates the signal to interference and noise ratio (SINR) and makes the uplink transmission less than the target error rate according to the calculated SINR. Determine the modulation order. In step 115, the base station transmits the determined code rate and modulation order to the user terminal. At this time, the code rate and modulation order are typically provided through an MCS index stored in an MCS table shared by the base station 103 and the user terminal 101. An example of the MCS table is shown in Table 1 below.

SINRk range MCS index Code rate Modulation order [2,4) 0 1/3 2 [4,6) One 1/2 2 [6,8) 2 1/3 4 (8,∞) 3 1/2 4

In step 117, the user terminal 101 performs channel coding, interleaving, symbol mapping, etc. on the uplink data bits using the received code rate and modulation order information, and transmits a _{signal (x k) in step 119.} . In step 121, the base station 103 receives a signal using the previously determined MIMO reception method (y _k ).

2 is a diagram illustrating a transmission chain of a user terminal 101 for uplink transmission according to an embodiment of the present invention.

First, data bits for uplink transmission are input to the channel encoder 201 to perform channel encoding. At this time, the code rate at the time of channel coding is determined according to the code rate information received from the base station as described in step 115 of FIG. 1. Channel-coded data bits are input to the interleaver 203 and interleaved. The interleaved data bits are input to the symbol mapping unit 205, mapped to an appropriate modulation symbol according to a modulation order, output (x _k ), and uplink transmitted through an antenna.

3 is a diagram illustrating a reception chain of the base station 103 for uplink reception according to an embodiment of the present invention.

The base station 103 receives and outputs the uplink signal using the MIMO receiver according to the MIMO reception method determined by receiving the uplink reference signal (y _k ), and then restores the signal through the reverse process of uplink transmission. . That is, the signal is restored using the symbol demapping unit 303, the deinterleaver 305, and the channel decoding unit 307 (309). At this time, the symbol demapping unit 303 and the channel decoding unit 307 perform symbol demapping and channel decoding using the code rate and modulation order determined in step 113 of FIG. 1.

Meanwhile, assuming that the number of base stations capable of inter-cell interference is K as previously assumed, the received signal y _k of the k-th base station is represented by the following <Equation 1>.

에 속하는 사용자 k의 심볼을 의미한다. 이때 사용자 단말k의 심볼의 전력 값은

가 된다.Here, x _k is a modulation scheme corresponding to the modulation order, for example, constellation of QPSK, 4-QAM, etc.

It means the symbol of user k belonging to. At this time, the power value of the symbol of user terminal k is

Becomes.

h _k,j is an actual channel between the user terminal j and the base station k and an effective channel that has passed through the MIMO receiver 301 of the base station k.

인 백색 가우시안(Gaussian) 잡음 신호를 의미한다. n _k has a mean of 0 and a variance of

It means a white Gaussian noise signal.

Meanwhile, the received signal-to-interference and noise ratio of Equation 1 is expressed by Equation 2 below.

Hereinafter, an existing method for reducing cell interference in a multi-cell environment will be briefly described.

The basic concept of the inter-cell interference scheme is that base stations within a certain range primarily estimate the received signal, share the estimated signal for each base station with each other through backhaul, and the base station backhaul from the previously estimated signal. It is to remove the signal component by other base stations shared through. Assuming a total of K base stations, the process of obtaining a signal with reduced interference from the k-th base station is mathematically expressed as <Equation 3>. A performance gain can be obtained by estimating a signal with reduced interference according to Equation 3 below.

는 기지국 k에서 간섭이 감소된 신호,

Is the signal with reduced interference at base station k

,y _k is the received signal of the base station k

, h _k,j denotes an actual channel between the user terminal j and the base station k and an effective channel passing through the MIMO receiving unit 301 of the base station k,

는 기지국k의 1차 추정 신호로서, 다른 기지국들과 공유되는 신호.

Is the primary estimation signal of base station k, and is a signal shared with other base stations.

)를 결정하는 방식에 따라 두 가지로 분류된다. 하나는 경판정(hard-decision) 방식이고, 다른 하나는 연판정(soft-decision) 방식이다.On the other hand, the first estimation signal of the base station k shared between the base stations (

) Is classified into two types according to the method of determining. One is a hard-decision method, and the other is a soft-decision method.

4 is a diagram illustrating a signal reception method of a base station using a conventional hard decision or soft decision method to reduce inter-cell interference.

Since the basic structure of FIG. 4 is similar to that of FIG. 3, differences from FIG. 3 will be described.

)를 생성한다. 이후, 기지국k의 1차 추정 신호(

)는 백홀(415)로 전달된다. 한편, 다른 기지국 j의 추정 신호(

)를 백홀(415)로부터 전달받아 곱셈기에 입력하여 유효 채널(

)에 곱한다. 이후에는 수신 신호(

)에서 다른 기지국 j의 추정 신호(

)와 유효 채널(

)을 곱한 값을 감산하여 간섭이 감소된 수신 신호(

)를 얻을 수 있다.In FIG. 4, interleaving is performed by transmitting the output of the channel decoding unit 307 to the interleaver 411, and symbol mapping is performed by the hard or soft decision symbol mapping unit 413 to perform a first-order estimation signal of the base station k (

). Thereafter, the first estimation signal of the base station k (

) Is transmitted to the backhaul 415. On the other hand, the estimated signal of the other base station j (

) Is transmitted from the backhaul 415 and inputted to the multiplier to provide an effective channel (

). After that, the received signal (

) From the other base station j's estimated signal (

) And the effective channel (

The received signal with reduced interference by subtracting the value multiplied by) (

) Can be obtained.

)를 결정하기 위하여 송신측에서 신호를 변조할 때 사용한 변조 방식에 따른 성좌와 동일한 성좌를 이용한다. 따라서 백홀 망을 이용한 데이터 사용량이 최소화되는 장점이 있다. 그러나 경판정 방식에 따라 추정된

가 송신측에서 실제로 송신한 신호와 다른 값이 될 경우, 수신측에서

를 이용하여 셀 간 간섭을 제거하게 되면, 간섭 제거 시에 에러가 더 커지는 에러 확산(error propagation) 현상이 발생할 수 있다. The hard decision method uses the estimated signal (

), the same constellation as the constellation according to the modulation method used when modulating the signal at the transmitting side is used. Therefore, there is an advantage of minimizing data usage using a backhaul network. However, according to the hard decision method,

If is different from the signal actually transmitted by the transmitting side, the receiving side

When inter-cell interference is removed by using, error propagation may occur in which an error becomes larger when the interference is removed.

)에 남아 있는 간섭의 양은 하기 <수학식 5>로 표현할 수 있다.For reference, the received signal with reduced interference in Equation 3 according to the error diffusion phenomenon (

The amount of interference remaining in) can be expressed by the following <Equation 5>.

)를 수학식으로 표현하면 하기 <수학식 6>이 된다.Meanwhile, the soft decision method uses a conditional expected value when determining an estimated signal in order to minimize the value of <Equation 5>, which is the amount of interference remaining in the interference cancellation method using the hard decision. Estimated signal determined according to the soft decision method (

) Is expressed by the following equation (Equation 6).

의 원소를 의미한다.Here, s _j,a is a set of modulation symbols on a constellation determined according to the modulation order

Means the element of.

)의 신뢰도를 고려하여 신뢰도의 크기에 따라 간섭의 양을 제거하는 방식이다. 따라서 경판정 방식을 이용한 간섭 제거 방식에서 발생하는 에러 확산을 최소화할 수 있다. The interference cancellation method using soft decision according to Equation 6 is an estimated signal (

It is a method of removing the amount of interference according to the magnitude of the reliability in consideration of the reliability of ). Therefore, it is possible to minimize the spread of errors occurring in the interference cancellation method using the hard decision method.

)로 칭할 수 있고, 연판정 방식에 따라 추정된 신호는 연판정 심볼(

)로 칭할 수 있다. Meanwhile, the symbol estimated according to the above-described hard decision method is a hard decision symbol (

), and the signal estimated according to the soft decision method is a soft decision symbol (

) Can be called.

FIG. 5 is a diagram illustrating, as an example, a constellation diagram according to 4-QAM (quadrature amplitude modulation) modulation that a hard decision symbol and a soft decision symbol are displayed on a constellation diagram.

)은 4개의 점(501)으로 표현되지만, 연판정 심볼(

)은 상기 4개의 점 내부의 사각형 영역(503)으로 표현된다. 상기 연판정 심볼(

)에 해당하는 영역(103)은 연속적이다. 따라서 기지국들 간에 연판정 심볼(

)을 백홀 망을 통하여 공유하기 위해서는 많은 양의 데이터 용량이 필요하다. 그러나 상술한 것처럼 백홀 망은 그 데이터 용량에 있어서 제한이 있다. 따라서 이하에서 설명하는 본 발명의 실시예에서는 에러 확산을 최소화하면서도 기지국들 간에 공유하는 신호(또는 심볼)의 데이터 양을 줄이기 위한 방식을 제안한다.In Fig. 5, the hard decision symbol (

) Is represented by four dots 501, but the soft decision symbol (

) Is represented by a rectangular area 503 inside the four points. The soft decision symbol (

The area 103 corresponding to) is continuous. Therefore, the soft decision symbol (

) To be shared through the backhaul network, a large amount of data capacity is required. However, as described above, the backhaul network has limitations in its data capacity. Accordingly, the embodiment of the present invention described below proposes a method for reducing the amount of data of a signal (or symbol) shared between base stations while minimizing error spread.

In the embodiments of the present invention described below, error diffusion may occur when inter-cell interference is removed by using a hard decision symbol, but error diffusion may be minimized when inter-cell interference is removed by using a soft decision symbol. It focuses on what can be done. In an embodiment of the present invention, the received signal (or symbol) is first estimated using the hard decision method, and the size and phase of the first estimated hard decision symbol are appropriately adjusted to obtain an interference cancellation performance similar to that of the soft decision symbol. To be there. The interference cancellation scheme proposed in the present invention will be referred to as "Scaled and Rotated (SR) interference cancellation" in the sense of adjusting the size and phase of the hard decision symbol.

Hereinafter, the configuration of the embodiment of the present invention will be described by dividing it into the following three processes.

First, the concept of a scaled and rotated (SR) interference cancellation scheme proposed in an embodiment of the present invention will be described.

Second, a criterion for selecting a size and a phase value of a hard decision symbol in an SR interference cancellation scheme and a criterion for determining an optimal SA (scale and angle) set will be described.

Third, a method of transmitting and receiving signals between a base station, a backhaul, and a user terminal by the SR interference cancellation method according to an embodiment of the present invention will be described.

1. Concept of SR(Scaled and rotated) interference cancellation method

는 하기 <수학식 7>로 표현된다.As described above, when interference between cells is removed by directly using the first-order hard decision symbol, an error spreading phenomenon may occur, but by changing the first-estimated hard decision symbol, the error spreading phenomenon can be minimized. In an embodiment of the present invention, after estimating a hard decision symbol, the size and phase are appropriately adjusted to obtain a performance close to the soft decision symbol. At this time, the estimated signal shared through the backhaul between base stations

Is represented by the following <Equation 7>.

,r _k is a size component for adjusting the size of the hard decision symbol and is a real value within [0,1],

θ _k is a phase component for adjusting the phase of the hard decision symbol and is a real value within [-π/4, π/4].

로 나타낼 수 있다. 참고로 {크기, 위상} 값들의 집합인 Uj에서 <수학식 7>에서 사용된 r, θ 대신에 γ, Φ를 사용한 이유는, 상기 <수학식 7>에서 r, θ는 변수인데 U_j에서는 변수인 r, θ 대신에 특정한 {크기, 위상} 값임을 나타내기 위하여 γ, Φ로 표기하였다.Meanwhile, the {magnitude, phase} value of Equation 7 is determined as a quantized value, and may be shared among base stations in the form of a set including at least one {magnitude, phase} value according to a predetermined criterion. . For example, a set of {magnitude, phase} values

It can be expressed as For reference, the reason why γ and Φ are used instead of r and θ used in <Equation 7> in Uj, which is a set of {magnitude, phase} values, is that r and θ in Equation 7 are variables, but in U _j Instead of the variables r and θ, γ and Φ were used to indicate specific values of {size, phase}.

For convenience of description, the set of {size, phase} values hereinafter may be abbreviated as “scale and angle (SA) set”. Meanwhile, when the base stations store the SA set, they may store the SA set in the form of an index corresponding to each set value.

When the interference cancellation is performed using the hard decision symbol according to the conventional method, the size of the data bit used to transmit and receive one hard decision symbol with the backhaul is log ₂ A _k . On the other hand, in the case of changing the size and phase of the hard decision symbol according to the embodiment of the present invention, the size of the data bit required to transmit and receive information on one SA symbol with the backhaul is greater by log ₂ B _{k than the hard decision symbol.} Big.

6 is a diagram illustrating an SR interference cancellation method according to an embodiment of the present invention.

FIG. 6 is mostly similar to the diagram of the interference cancellation method according to the hard decision or soft decision method described in FIG. 4, and thus only a portion different from that of FIG. 4 will be described.

)"을 생성한다. SA 심볼이 백홀(415)로 전달되고, 다른 기지국들의 SA 심볼을 백홀로(415)로부터 전달받아 간섭 제거에 사용함은 앞서 도 4에서 설명된 바와 같다.In FIG. 6, a multiplier 615 is added after the hard decision symbol mapping unit 613. The multiplier 615 multiplies the hard decision symbol output from the hard decision symbol mapping unit 613 by a magnitude (r _k ) and a phase (θ _k ) component selected from one of the SA sets to change the size and phase of the "SA symbol (

)". The SA symbol is transmitted to the backhaul 415, and SA symbols of other base stations are transmitted from the backhaul 415 and used for interference cancellation, as described in FIG. 4 above.

2. A criterion for selecting the size and phase value of the hard decision symbol in the SR interference cancellation method and a criterion for determining the optimal set of SA (scale and angle)

The {magnitude, phase} values of the individual SA elements constituting the SA set should be determined to minimize the error diffusion phenomenon occurring in the interference cancellation method using the hard decision symbol. Conditions for minimizing the error diffusion phenomenon can be expressed by the following <Equation 8>.

과의 본 발명의 실시예에 따른 SA 심볼(

)과의 차이값

의 크기가 최소화되도록 하는 조건이다. 본 발명의 실시예가 경판정 심볼의 크기와 위상을 변화시켜서 연판정 심볼에 가장 근접한 SA 심볼을 만드는 것이기 때문에 상술한 조건에 따라 연판정 심볼과 SA 심볼 간의 차이값이 최소가 되도록 하면, 기지국의 수신 신호에서도 연판정 심볼에 의한 간섭 제거 방식과 유사하게 간섭이 최소가 될 수 있다. 따라서 상기 <수학식 8>을 만족하는 크기와 위상을 갖도록 SA 심볼(

)의 크기와 위상을 결정하면 된다. The above <Equation 8> is a soft decision symbol

SA symbol according to an embodiment of the present invention of

) And the difference value

This is a condition that allows the size of the to be minimized. Since the embodiment of the present invention makes the SA symbol closest to the soft decision symbol by changing the size and phase of the hard decision symbol, if the difference between the soft decision symbol and the SA symbol is minimized according to the above-described conditions, the base station receives In the signal, interference can be minimized, similar to the interference cancellation method by the soft decision symbol. Therefore, the SA symbol (

You can determine the magnitude and phase of ).

를 대입한 뒤 평균을 취하면 하기 <수학식 9>로 표현할 수 있다. The SA set should be made in a direction that minimizes the average value of the remaining interference shown in Equation 5 above. To <Equation 5>

Substituting for and taking the average can be expressed by the following <Equation 9>.

는 전체 간섭의 양에서 크기 및 위상과는 무관한 성분이다. 따라서 전체 간섭의 양이 최소화되도록 하는 SA 집합은

의 값이 최소화하도록 하는 {위상, 크기} 값들로 구성될 수 있다. 한편, 상기

값은 1차원 상의 값으로 이 값이 최소화되도록 하는 SA 집합은 통상적으로 로이드 알고리즘(Lloyd’s algorithm)을 이용하면 구할 수 있다.
In the above <Equation 9>, Es means the power value of the symbol as described in <Equation 1>, E _s and

Is a component independent of magnitude and phase in the total amount of interference. Therefore, the SA set that minimizes the total amount of interference is

It can be composed of {phase, size} values that minimize the value of. Meanwhile, the above

The value is a one-dimensional value, and an SA set that minimizes this value can be obtained by using Lloyd's algorithm.

3. A method of transmitting and receiving signals between base stations, backhaul, and user terminals by SR interference cancellation method

As described above, the signal-to-interference ratio (SINR _SR,k ) of the received signal after SR interference cancellation can be calculated by the following <Equation 10> by using the above <Equation 2> and <Equation 9>.

로서, SR 간섭 제거 이후 감소된 간섭의 양을 의미한다. 즉, E_c,j는 기지국j가 본 발명의 실시예에 따라 간섭을 제거할 경우 기지국j의 간섭 제거 능력을 의미한다.Where E _c,j is

As is, it means the amount of interference reduced after SR interference cancellation. That is, E _c,j denotes the interference cancellation capability of the base station j when the base station j cancels the interference according to the embodiment of the present invention.

Meanwhile, in order for the base station k to obtain the maximum data rate, the signal-to-interference ratio (SINR _SR,k ) after the SR interference cancellation of the base station k must be estimated as accurately as possible. To this end, the value of the interference cancellation capability (Ec,j) of another base station, for example, base station j must be received. However, in the embodiment of the present invention, since the base stations share the SA symbol with each other, the interference cancellation capability of base station j (Ec,j) and the interference cancellation capability of base station k (Ec,k) affect each other.

7 is a diagram illustrating a situation that affects mutual interference cancellation capability between base stations according to an embodiment of the present invention.

In a multi-cell environment, there will be a number of base stations that cause inter-cell interference. But

7 is a diagram illustrating two base stations k (701) and base station j (703) assuming for convenience of description.

The signal-to-interference ratio (SINR _SR,k ) 705 after the interference cancellation of the base station k 701 affects the coding rate and modulation order of the base station k 701, that is, the _{determination of the MCS k} 707, and the MCS _k 707 affects the back base station k (701), their interference cancellation performance (Ec, k) (709) .

Meanwhile, in an embodiment of the present invention, an SA symbol is shared between base stations through a backhaul. Accordingly, the interference cancellation performance (Ec,k) 709 of the base station k701 _{affects the signal-to-interference ratio (SINR SR,j} ) 711 after the SR interference cancellation of the base station j 703. In addition, SINR _SR,j (711) again affects the interference cancellation capability (Ec,j) 713 of the base station j (703), and the interference cancellation capability Ec, j (715) of the base station j (703) is the base station k The signal-to-interference ratio (SINR _SR,k ) 705 after interference cancellation of 701 is affected.

After all, when using the SR interference cancellation method according to the embodiment of the present invention, the signal-to-interference ratio (SINR _SR,x ) after interference cancellation of each of the random base stations is a set of base stations configured by base stations causing inter-cell interference ("base station It can be referred to as "cluster".) They influence each other.

Therefore, in an embodiment of the present invention, in order to allow the base station to reflect the SINR of other base stations in order to accurately calculate the _{signal-to-interference ratio SINR SR} after interference by other base stations in the cluster is removed, an interference cancellation table (ICT: An interference cancellation table) index is introduced, and the ICT index is exchanged between each base station so that the SINR _SR in which the interference that may be generated by other base stations is removed as much as possible can be calculated.

<Table 2> shows an example of the ICT proposed in the embodiment of the present invention.

ICT index SINR _k index SINR _SR,k index SA set (log ₂ B _k = 1) E _c,k 0 0 0 {{1,0},{1,0}} One One 0 One {{0.9,0},{0.4,π/4}} 0.9 2 0 2 {{0.85,0},{0.5,π/4}} 0.85 3 0 3 {{0.8,0},{0.6,π/4}} 0.8 4 One One {{1,0},{1,0}} One 5 One 2 {{0.95,0},{0.5,π/4}} 0.91 6 One 3 {{0.9,0},{0.45, π/4}} 0.89 7 2 2 {{1,0},{1,0}} One 8 2 3 {{1,0},{0.6,0}} 0.93 9 3 3 {{1,0},{1,0}} One

The ICT of <Table 2> includes ICT index, SINR _k index, SINR _SR,k index, {magnitude, phase} set, and E _c,k items.

SINR _k denotes the SINR calculated before interference cancellation of the base station k, and the SINR _k index is an index corresponding to a section in which the _{calculated SINR k is quantized in a predetermined unit.} For example, SINR _k may be set up to 10db as SINR _k index 0, SINR _{k up} to 12db _{may be set as SINR k} index 1, or the like.

SINR _SR,k means the SINR calculated under the assumption that the base station k has performed SR interference cancellation, and the SINR _SR,k index is an index corresponding to the interval quantized by the _{calculated SINR SR,k in a predetermined unit.} .

As described above, the SA set is a set of {magnitude, phase} for changing the hard decision symbol into an SA symbol, and is predetermined by Lloyd's algorithm to minimize the above-described Equation 9 In the embodiment of the present invention, it is assumed that the SA set is composed of two {magnitude, phase} values per ICT index in order to represent the SA set by 1 bit. However, the bit order of the SA set may vary depending on the configuration. For example, when the SA set is expressed in 2 bits, the number of possible {magnitude, phase} values will be 4.

k)의 SINR_SR,j를 정확히 계산할 수 있게 해준다.E _c,k denotes the amount of interference reduced after SR interference cancellation according to an embodiment of the present invention. That is, E _c,k is the other base station j (j

It makes it possible to accurately calculate _{the SINR SR,j} of k).

The ICT index is _{an index value determined by the combination of SINR k} and SINR _SR,k , and is transmitted and received between the base station and the backhaul in the embodiment of the present invention to be SINR _k index, SINR _{SR, k} index, SA set, E _{c, k} You can announce the value.

For example, if the base station k transmits the ICT index "3" in the backhaul, it is _{the SINR value corresponding to the SINR k} index 0 before the inter-cell interference cancellation, and the SINR after the inter-cell interference cancellation is SINR _{SR ,k} is an SINR value corresponding to index 3, and indicates that the {magnitude, phase} value minimizing its own signal is one of {0.8, 0} or {0.6, π/4}.

Then, based on the above-described ICT table, the operation between the base station and the backhaul according to an embodiment of the present invention will be described.

For reference, in an embodiment of the present invention, "backhaul" may mean a network network itself for information exchange between base stations, or may be an entity that controls a network network for information exchange between base stations. In the former case, since the backhaul is a simple network, information exchange between base stations will actually be controlled within the base stations without the control of other functional blocks in the middle. On the other hand, in the latter case, the backhaul may have a function of controlling the transmission of information received from the base stations to different base stations.

Hereinafter, for convenience of description, backhaul will be used as the latter meaning. Therefore, it is assumed that information exchange between base stations can be controlled in the backhaul itself. However, this is only for convenience of description, and the backhaul is not limited to the latter form in the embodiment of the present invention.

8 is a diagram illustrating a method of exchanging ICT indexes between base stations connected through a backhaul according to an embodiment of the present invention.

For the same reason as in FIG. 7, FIG. 8 will be described under the assumption that only two base stations k 845 and j 850 are assumed.

In step 801, user terminal k 840 transmits an uplink reference signal to base station k 845, which is a base station of the cell in which it is located. In step 805, the base station k (845) calculates the signal-to-interference ratio (SINR _k ) before interference cancellation and the signal-to-interference ratio (SINR _SR,k ) after interference cancellation by using the uplink reference signal, and stores the table in advance. _{ICT indexes corresponding to SINR k} and SINR _SR,k calculated using the ICT table of 2> are determined, and the determined ICT index is transmitted to the backhaul 860. However, the base station k 845 has not yet acquired the ICT index of another base station. Therefore, the signal-to-interference ratio (SINR _SR,k ) after interference cancellation will be the same value as the signal-to-interference ratio (SINR _{k) before interference cancellation.} In step 805, it is assumed that the ICT index of the base station k 845 is "0".

For reference, when the base station calculates SINR using the uplink reference signal, the calculated value at that time becomes SINR _k , and for the above-described reason, the SINR _SR,k at that time becomes the same value as _{SINR k.} Therefore, the first ICT index value that the base station may have _{is possible only when the SINR k} index and the SINR _SR,k index have the same value. Referring to the example of <Table 2>, the base station is the ICT index "0", ICT index "4", ICT index "7", ICT index "9" according _{to the SINR k index value corresponding to the initially calculated SINR value.} Will be able to have.

The same operations as those in steps 801 and 805 are also performed in steps 803 and 807 at the base station j (850) side, and a description of the same operation will be omitted. However, in step 807, the ICT index value of the base station j (850) is assumed to be "4".

The backhaul 860 has ICT indexes for each base station received from base station k 845 and base station j 850. In steps 809 and 811, the backhaul 860 transfers the ICT index of another base station to the corresponding base station. That is, in step 809, the ICT index value (4) of the base station j (850) is transferred to the base station k (845), and in step 811, the ICT index value (0) of the base station k (845) is transferred to the base station j (850). do.

_{In step 813, the base station k (845) recalculates the SINR SR,k} using the ICT index (4) of the base station j (850), determines the corresponding ICT index using <Table 2>, and backhauls it again. Pass it to 860. _{The SINR SR,k} calculated in step 813 is calculated again under the assumption that the inter-cell interference corresponding to the ICT index value 4 of the base station j (850) has been removed. Here, it is assumed that the SINR _{SR,k index value corresponding to the recalculated SINR SR,k} value is "2". _{In step 813, the SINR and k} indices, which are the indexes of the SINR before interference, are the same as _{the SINR and k} indices based on the SINR value calculated in step 805. In the end step 813 SINR, _k the index is "0" and, SINR _{SR, k} indexes values in the case as described above is a re-calculated SINR _{SR, k} indexes a value reflecting the ICT index value of the base station j (850) "2 Since "is assumed, the SINR, _k index will be "0" and _{the ICT index value corresponding to the SINR SR,k} index value "2" will be "2" in <Table 2>.

In step 815, base station j (850) determines a new ICT index value by reflecting the ICT index value (0) of base station k (845) in the same manner as in step 813, and transmits it to the backhaul 860. Here, it is assumed that the determined ICT index value is "5".

In steps 817 and 819, the updated ICT index value for each base station is transmitted to the counterpart base station in the same manner as in steps 809 and 811.

Summarizing the process so far, each of the base stations determines its own ICT index value and transmits it to the backhaul 860, and the backhaul 860 transmits the ICT index values of other base stations to each of the corresponding base stations. The corresponding base station, which has received the ICT index values of the base stations, reflects this, determines the ICT index value again, and transmits the ICT index value back to the backhaul 860. In addition, in principle, this process is repeated until all base stations do not change the ICT index value. That the ICT index values of all the base stations are not changed means that the interference cancellation capability of each of the base stations affecting each other is reflected to the maximum between the base stations. Therefore, it is no longer necessary to exchange ICT index values between base stations.

This example is shown in steps 821 to 835 in FIG. 8. That is, in step 821, the ICT index value of the base station k 845 is "3", and the ICT index value of the base station j 850 is "6". However, the ICT index value determined next by the base station k 845 in step 829 is "3", which is the same as the previously determined ICT index value. In addition, the ICT index value determined next by the base station j (850) in step 831 is "6", which is the same as the previously determined ICT index value. Therefore, the ICT index values of all base stations are no longer changed. In this case, since it is no longer necessary to exchange ICT index values between base stations, the backhaul 860 in steps 833 and 835 sends a completion message (or OK message) to each base station indicating that cooperative communication between the base stations has been completed. Will be delivered.

However, if the number of processes for exchanging ICT index values between base stations described above is not limited, excessive resource waste will occur. Therefore, in order to prevent this, the number of exchanges of the ICT index value may be limited to a predetermined threshold value by system setting or by self setting of the backhaul. As an example, if the backhaul 860 has received the ICT index from each base station for N times and the ICT index is changed in any of the base stations, a further ICT index exchange procedure may be terminated.

Until now, the ICT exchange process between base stations has been described with reference to FIG. 8. Hereinafter, the entire process of receiving uplink data from a terminal after calculating an accurate SINR by ICT exchange will be described based on one base station.

9 is a diagram illustrating a process of exchanging ICT and receiving uplink data according to an embodiment of the present invention.

The user terminal 901 transmits the uplink reference signal to the base station k 903 in step 911. The base station k 903 calculates the SINR using the reference signal, determines the ICT index using the calculated SINR and the ICT table according to an embodiment of the present invention, and transmits it to the backhaul 913. In step 913, the ICT index k(0) was marked to indicate that the first determined ICT index. In step 915, ICT index values of other base stations are received from the backhaul. The number of other base stations may be at least one or more. In addition, in step 915, an ICT index (j)0 is indicated to indicate that it is the first determined ICT index of another base station.

Thereafter, the base station k (903) repeats the process of determining a new ICT index value by reflecting the ICT index values of other base stations, and transmitting it to the backhaul 905 again. If an N-th ICT index value of other base stations is received from the backhaul 905, or a completion message (or OK message) is received from the backhaul, the repetition of the ICT exchange process will be terminated. Steps 917 and 919 represent this process.

After the completion of the ICT exchange process, the base station k 903 finally calculates _{the SINR (that is, SINR SR,k) after interference cancellation at the time when the ICT index exchange procedure ends.} That is, if the ICT index of another base station is received for the Nth time, the final SINR _SR,k is calculated by reflecting the last received ICT index. Alternatively, upon receiving the end message (OK message) from the backhaul 905, the SINR _SR,k calculated immediately before will be determined as the final SINR _{SR,k. The final SINR SR,k} determined in this way will be a signal-to-interference ratio that can be obtained in a state where cell interference by other base stations is removed as much as possible at base station k 903. Accordingly, the base station k 903 determines a code rate and a modulation order (ie, MCS index) for signal transmission/reception with the user terminal 901 according to the SINR after the finally determined inter-cell interference cancellation. In step 921, the base station k (901) transmits the determined MCS information to the user terminal (901).

In step 923, the user terminal 901 performs channel coding, interleaving, and modulation symbol mapping according to the received MCS information, and transmits the uplink data symbol to the base station k 903 in step 923.

In step 925, the base station k 903 receives a data symbol using the previously determined MCS information. In this case, the base station k 903 generates the hard decision symbol and {magnitude, phase} information for the SA symbol to generate the SA symbol according to an embodiment of the present invention, and transmits it to the backhaul 905. The method of determining the {magnitude, phase} values for the SA symbol has been described above through <Equation 8>, and the description thereof will be omitted here.

In step 927, the backhaul 905 transfers the hard decision symbol and {magnitude, phase} value information received from another base station to the base station k 903. This is because the backhaul 905 has information on a hard decision symbol and {magnitude, phase} value for each received bit of each base station from other base stations in the same manner as the backhaul 905 received from the base station k 903 in step 925. For reference, in this case, the size of the data bit required to transmit and receive {size, phase} information was 1 bit in the example of <Table 2> above. However, the size of the data bit will vary depending on how many components constituting the SA set, which is a set of {size, phase} for changing the hard decision symbol into an SA symbol, is set. At this time, the {size, phase} value of the other base station can be found in the SA set corresponding to the final ICT index exchanged in steps 917 and 919.

In step 929, the base station k 903 finally determines the value of the received symbol using SR interference cancellation according to an embodiment of the present invention. That is, the base station k 903 is finally step 923 in a state in which interference by other base stations is removed using the SA symbol values of other base stations, that is, the hard decision symbol and {magnitude, phase} information acquired in step 927. The value of the uplink data symbol received at is determined.

10 is a diagram illustrating an operation of a base station determining an ICT index according to an embodiment of the present invention. This describes the contents described in FIG. 8 from the viewpoint of one base station.

In step 1001, the base station determines its own ICT index. If the base station receives the uplink reference signal from the user terminal, the ICT index is determined by using the uplink reference signal, and the determined value will be the initial value of the ICT index.

In step 1003, the base station transmits its ICT index determined in step 1001 through the backhaul.

In step 1005, the base station receives from the backhaul, and determines whether the received information is an OK message or an ICT index of another base station.

If the information received in step 1005 is an OK message, the process proceeds to step 1009 to determine the current ICT index as its final ICT index.

If the information received in step 1005 is an ICT index of another base station, the process proceeds to step 1007 and it is determined whether the number of times the index of the other base station is received is a predetermined threshold value N. If N times are received, the process proceeds to step 1009 and the current ICT index is determined as its final ICT index. If the number N is not received, it proceeds to step 1001 again. That is, it proceeds to step 1001 to determine its own ICT index again. At this time, when determining the ICT, the own ICT index will be determined again by reflecting the ICT index value of another base station received in step 1005. On the other hand, after the final ICT index is determined in step 1009, the MCS index is determined using the _{SINR (i.e., SINR SR,k} ) after inter-cell interference cancellation corresponding to the final ICT index as described in FIG. 9 above. , It will be delivered to the user terminal. Since subsequent operations have been described in FIG. 9, repeated descriptions are omitted here.

11 is a diagram illustrating a configuration of a base station apparatus according to an embodiment of the present invention for each functional block.

The base station apparatus 1100 transmits and receives a signal with a user terminal or a backhaul through the transmission/reception unit 1101. That is, the SA symbol (or information on the SA symbol) generated by the corresponding base station is transmitted through the backhaul, or the SA symbol (or information on the SA symbol) of the other base station is received.

The interference canceling unit 1103 generates a signal by removing inter-cell interference from the received signal received from the user terminal by using SA symbol information of another base station.

The control unit 1105 controls most operations according to an embodiment of the present invention.

Specifically, before receiving the SA symbol information, a final signal-to-interference ratio (SINR) of the current base station is determined in consideration of the inter-cell interference cancellation capability of another base station, and signal transmission/reception with a user terminal is based on the final SINR. The code rate and modulation order (MCS) information to be used is determined and transmitted to the user terminal through the transmission/reception unit 1101. In addition, uplink data transmitted according to the MCS information is received. In addition, a reference signal is received from the user terminal, a signal-to-interference ratio (SINR,k) before inter-cell interference cancellation is determined using the reference signal, and from an interference cancellation table (ICT) table previously stored in the storage unit 1107. The ICT index corresponding to the, SINR,k value is determined, and the determined ICT index is transmitted through the transmission/reception unit 1101 through the backhaul. In addition, the ICT index of the other base station is received from the backhaul, and the signal-to-interference ratio (SINR _SR,k ) after interference by the other base station is removed is determined in consideration of the ICT index of the other base station. In addition, the _{ICT index is determined again in consideration of SINR SR,k} , transmitted through the backhaul, and the process of receiving the updated ICT index of another base station from the backhaul is repeated. This repetition is the same as receiving the base station cooperation completion message from the backhaul, or receiving the second ICT index a predetermined number of times, or the ICT indexes of other base stations currently received are the same as the ICT indexes of other base stations previously received. If you do, it is finished.

Up to now, embodiments of the present invention have been described in detail.

According to an embodiment of the present invention, a quantized SA symbol close to the soft decision symbol is generated by appropriately changing the size and phase of the hard decision symbol, and interference is removed by sharing the generated SA symbol between base stations. In addition, prior to this, in order to accurately calculate SINR in a state in which inter-cell interference is removed from the base station, and to determine the code rate and modulation order to be used for signal transmission and reception with the user terminal, based on this, an ICT table including an ICT index is Suggested. Accordingly, the base stations may determine the ICT index based on the current SINR, share this between base stations, and determine the SINR under the assumption that inter-cell interference has been removed again based on the ICT index of other base stations. However, the process of exchanging ICT indexes between base stations continues until the ICT indexes are not changed in all base stations. However, in order to avoid repetition of the exchange procedure indefinitely, the exchange procedure of the ICT index may be limited to a predetermined number of times.

According to the above-described embodiment of the present invention, even in a limited backhaul environment, inter-cell interference cancellation performance close to a soft decision interference cancellation technique using infinite backhaul can be obtained. In addition, it is possible to more accurately measure the SINR of the base station in consideration of the situation in which inter-cell interference is removed as much as possible, thereby increasing the efficiency of MCS determination.

Claims (23)

In a method for a base station to cancel inter-cell interference in a multi-cell system including a plurality of base stations and sharing information between base stations through a backhaul,
Receiving a reference signal from a user terminal;
Determining a first signal-to-interference ratio (SINR) using the reference signal;
Determining a first ICT index of the base station corresponding to the determined first SINR value from an interference cancellation table (ICT) table previously stored in the base station;
Transmitting the first ICT index of the base station through the backhaul; And
Including the process of receiving a first ICT index of another base station from the backhaul,
The first ICT index of the other base station is used to re-determine the ICT index of the base station. The method of claim 1,
And determining a second SINR, which is a signal-to-interference ratio after removing the interference by the other base station, in consideration of the first ICT index of the other base station. The method of claim 2, wherein from the ICT table, a second ICT index of the base station is determined using the first SINR and the second SINR, and a second ICT index of the base station is transmitted through the backhaul, and the back The method further comprising the step of repeating the process of receiving the second ICT index of the other base station from the hole, the base station cancels the inter-cell interference. The method of claim 3, wherein the repeating process,
The method for removing inter-cell interference by the base station is terminated when a base station cooperation completion message is received from the backhaul or the second ICT index of the other base station is received a predetermined number of times. The method of claim 1,
Receiving, by the other base station, information on a scale and angle (SA) symbol for a signal received from the user terminal from a backhaul; And
The base station further comprises a process of removing inter-cell interference from the signal received from the user terminal by using the received SA symbol information,
The SA symbol information includes a hard-decision symbol value for a signal received from the user terminal by the other base station, and a {magnitude, phase} value for changing the size and phase of the hard-decision symbol. To, how the base station cancels the inter-cell interference. The method of claim 5,
Determining a final SINR of the base station in consideration of the inter-cell interference cancellation capability of the other base station;
Determining code rate and modulation order (MCS) information based on the determined final SINR; And
Transmitting the determined MCS information to the user terminal, and receiving the uplink data transmitted according to the MCS information from the user terminal, a method for the base station to cancel inter-cell interference. The method of claim 1, wherein the ICT table,
An SINR index before intercell interference cancellation, a SINR index after intercell interference cancellation, and an ICT index corresponding to the two SINR indices. The method of claim 7, wherein the ICT table,
A method for a base station to cancel inter-cell interference, further comprising a predetermined number of {magnitude, phase} sets for changing a size and a phase of a hard decision symbol, and information indicating an interference cancellation capability of a corresponding base station. The method of claim 5, wherein the {magnitude, phase} value is
The base station prevents inter-cell interference, which is determined as a {size, phase} value that minimizes the difference between the soft decision symbol value for the signal received from the user terminal and the SA symbol value determined based on the SA symbol information. How to get rid of it. In a base station for removing inter-cell interference in a multi-cell system including a plurality of base stations and sharing information between base stations through a backhaul,
A transmission/reception unit; And
It includes a control unit for controlling the transmission and reception unit,
The control unit:
A first SINR of the base station corresponding to the determined first SINR value is received from a reference signal received from a user terminal, a first SINR is determined using the reference signal, and from an interference cancellation table (ICT) table previously stored in the base station Determine an ICT index, transmit a first ICT index of the base station through the backhaul, receive a first ICT index of another base station from the backhaul,
The first ICT index of the other base station is a base station for removing inter-cell interference in a multi-cell system used to re-determine the ICT index of the base station. The method of claim 10, wherein the control unit,
A base station performing the method of claim 2. delete delete delete delete delete delete delete In a method for removing inter-cell interference in a backhaul for sharing information between the base stations in a multi-cell system including a plurality of base stations,
Receiving ICT indexes (interference cancellation tables) of each base station from the plurality of base stations; And
Using the received ICT indices, transmitting ICT indexes of other base stations other than a certain base station among the base stations to the random base station,
The ICT index is to be used to re-determine the current ICT index of each base station, a method for removing inter-cell interference in a backhaul. The method of claim 19,
Repeating the process of receiving the ICT index of each base station re-determined by reflecting the ICT index of the other base stations, and transmitting the ICT index of the other base stations to the random base station using the re-determined ICT index of each base station A method for removing inter-cell interference in a backhaul, further comprising. The method of claim 19, wherein the process of repeating the reception of the re-determined ICT index of each base station and the transmission of the ICT index of the other base stations,
A method of removing inter-cell interference in a backhaul, which is terminated when values of ICT indexes of all base stations included in the multi-cell system are not changed. The method of claim 20,
When the values of the ICT indexes of all base stations included in the multi-cell system are not changed, inter-cell interference in a backhaul further comprising a process of transmitting a message indicating that cooperative communication between base stations has been completed to the random base station How to get rid of it. The method of claim 19, wherein the process of repeating the reception of the re-determined ICT index of each base station and the transmission of the ICT index of the other base stations is repeated within a predetermined number of times.

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