KR101181780B1 - Method For Allocating Communication Resource Reducing Inter-Cell Interference - Google Patents

Abstract

The present invention relates to a communication resource allocation method for reducing inter-cell interference. According to the present invention, a plurality of base stations commonly divides all frequency bands into area units including a specific number of unit frequency bands, and allocates resources therethrough, thereby reducing interference of pilot signals between adjacent cells.

Communication resource allocation, pilot signal

Description

Method for Allocating Communication Resource Reducing Inter-Cell Interference

1 is a diagram illustrating a structure of a transmitting end of a DFT-S-OFDM scheme.

2 illustrates a multi-base station multi-user communication environment.

3 illustrates an uplink subframe structure.

4 is a diagram illustrating a frequency domain scheduling method using an FDM method in uplink.

5A and 5B are diagrams for explaining a phenomenon that occurs when the pilot transmission bandwidth and the transmission band position between adjacent cells do not match, respectively.

6 is a diagram illustrating a method of performing frequency domain scheduling in uplink according to an embodiment of the present invention.

7 is a view for explaining an example of sequence allocation capable of minimizing interference between each other in a communication resource allocation method according to an embodiment of the present invention.

8 is a diagram for explaining a range to which a communication resource allocation method according to an embodiment of the present invention is applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication technology, and more particularly to a method for allocating communication resources to reduce intercell interference.

The present invention may be used in an OFDM, DFT-S-OFDM, or OFDMA communication scheme, or may be used in a communication scheme in which data is transmitted by a plurality of subcarriers while maintaining orthogonality between the plurality of subcarriers. Hereinafter, as an example of a communication method of the multi-carrier system, an OFDM scheme, a DFT-S-OFDM (DFT Spreading OFDM) scheme, and an OFDMA scheme will be described.

First, orthogonal frequency division multiplexing (OFDM) according to the prior art will be described. The basic principle of OFDM is to divide a high-rate data stream into a large number of low-rate data streams and transmit them simultaneously using multiple carriers. Each of the plurality of carriers is called a subcarrier. Since orthogonality exists between the multiple carriers of the OFDM, the frequency components of the carriers can be detected at the receiving end even if they overlap each other. The high data rate data stream is converted into a plurality of low data rate data streams through a serial to parallel converter, and each subcarrier is included in the parallel data streams. After multiplying, the respective data strings are summed and sent to the receiving end.

Multiple parallel data streams generated by the serial / parallel transform unit may be transmitted to a plurality of subcarriers by an inverse discrete fourier transform (IDFT), and the IDFT is an inverse fast fourier transform (IFFT). Can be implemented efficiently.

Since the symbol duration of the low carrier subcarrier is increased, relative signal dispersion in time caused by multipath delay spread is reduced. Inter-symbol interference can be reduced by inserting a guard interval longer than the delay spread of the channel between OFDM symbols. If a part of the OFDM signal is copied and arranged in such a guard period, the OFDM symbol may be cyclically extended to protect the symbol.

Hereinafter, orthogonal frequency division multiple access (OFDMA) according to the prior art will be described. OFDMA refers to a multiple access method for realizing multiple access by providing each user with a part of subcarriers available in a system using OFDM as a modulation method. OFDMA provides each user with a frequency resource called a subcarrier, and each frequency resource is provided to a plurality of users independently of each other so that they do not overlap each other. After all, frequency resources are allocated mutually exclusive.

Hereinafter, the conventional DFT-S-OFDM scheme will be described. The DFT-S-OFDM scheme is also called Single Carrier-FDMA (SC-FDMA). Conventional SC-FDMA technique is a technique that is mainly applied to uplink. Before generating an OFDM signal, spreading is first applied to a DFT matrix in a frequency domain, and then the result is modulated by a conventional OFDM scheme and transmitted. .

1 is a diagram illustrating a structure of a transmitting end of a DFT-S-OFDM scheme.

Several variables are defined to describe the operation of the conventional device. N denotes the number of subcarriers transmitting the OFDM signal, Nb denotes the number of subcarriers for any user, F denotes a discrete Fourier transform matrix, or DFT matrix, s denotes a data symbol vector, x Denotes a vector in which data is distributed in the frequency domain, and y denotes an OFDM symbol vector transmitted in the time domain.

In SC-FDMA, the data symbol s is converted into a parallel signal by the serial / parallel conversion unit 110 and distributed using a DFT matrix before the data symbol s is transmitted by the DFT spreading module 120. . This is expressed by the following formula.

는, 데이터 심볼(s)을 분산시키기 위해서 사용된 Nb 크기의 DFT 행렬이다. 이렇게 분산된 벡터(x)에 대하여 부반송파 매핑부(130)에서 일정한 부 반송파 할당 기법에 의해 부 반송파 매핑(subcarrier mapping)이 수행되고, IDFT 모듈(140)에 의해 시간영역으로 변환되어 병/직렬 변환부(150)를 거쳐 수신 측으로 전송하고자 하는 신호가 얻어진다. 상기 수신 측으로 전송되는 전송신호는 아래 식과 같다. In Equation (1)

Is an Nb-sized DFT matrix used to disperse the data symbols s. Subcarrier mapping is performed in the subcarrier mapping unit 130 using a predetermined subcarrier allocation scheme for the distributed vector x, and the IDFT module 140 converts the subcarrier into a time domain to perform parallel / serial conversion. The signal to be transmitted to the receiving side is obtained through the unit 150. The transmission signal transmitted to the receiving side is as follows.

는 주파수 영역의 신호를 시간 영역의 신호로 변환하기 위해 사용되는 크기 N의 IDFT 행렬이다. 상술한 방법에 의해 생성된 신호 y는, 순환 전치 삽입부(160)에 의해 순환 전치(cyclic prefix)가 삽입되어 전송된다. 상술한 방법에 의해 전송 신호를 생성하여 수신 측으로 전송하는 방법을 SC-FDMA 방법이라 한다. DFT 행렬의 크기는 특정한 목적을 위해 다양하게 제어될 수 있다.In Equation 2

Is an IDFT matrix of size N that is used to convert a signal in the frequency domain to a signal in the time domain. The signal y generated by the above-described method is transmitted by inserting a cyclic prefix by the cyclic prefix inserting unit 160. The method of generating a transmission signal and transmitting it to the receiving side by the above-described method is called an SC-FDMA method. The size of the DFT matrix can be variously controlled for a specific purpose.

Hereinafter, orthogonal frequency division multiple access (OFDMA) according to the prior art will be described. OFDMA refers to a multiple access method that realizes multiple accesses by providing each user with a part of subcarriers available in a modulation system using a plurality of orthogonal subcarriers. OFDMA provides each user with a frequency resource called a subcarrier, and each frequency resource is provided to a plurality of users independently of each other so that they do not overlap each other.

In the aforementioned SC-FDMA or OFDMA system, data of a UE may be transmitted in the following two ways.

1. Localized allocation: A method of transmitting UE data using a resource composed of several adjacent subcarriers.

2. Distributed allocation: A method of transmitting UE data using resources consisting of subcarriers separated at regular intervals.

Meanwhile, data, pilot, and control information are transmitted on the uplink. The data transmitted on the uplink is user data, and a band allocation or a transport format may be determined by the downlink control signal.

In addition, the pilot signal can be largely divided into the following two types depending on the application. CQ pilot for measuring channel quality (CQ) for user scheduling and adaptive modulation and coding (AMC), and DM (demodulation) pilot for channel estimation and data demodulation during data transmission. A pilot for channel estimation and demodulation during data transmission is a pilot transmitted in a specific time and frequency domain when the user is scheduled and transmits data.

In addition, the control information can be divided into two types. Data-associated control information is control information necessary for recovery of data transmitted by the UE. For example, information related to a transport format or HARQ related information may belong to this. The amount of such data-related control information may be adjusted according to the scheduling scheme of the uplink data. Meanwhile, non-data-associated control information is control information required for downlink transmission. For example, ACK / NACK for HARQ operation and channel quality indicator (CQI) for link adaptation of downlink may belong to this.

Meanwhile, a communication system including a plurality of base stations and a plurality of users serviced by each of them will be described below based on the above description.

2 is a diagram illustrating a multi-base station multi-user communication environment.

As shown in FIG. 2, a plurality of base stations (eg, base station A and base station B) serve UEs in each cell, and a cell serviced by each base station is divided into several sectors. The base station can operate each sector.

In addition, the base station allocates resources available to each UE to UEs in the cell through downlink communication, and the UE transmits signals through frequency resources allocated by the base station. The UE signal uplink transmitted through the allocated frequency resource has the following format.

3 illustrates an uplink subframe structure.

In the sub-frame structure shown in FIG. 3, LBs (long blocks; LB # 1 to LB # 6 in FIG. 3) are used for data and control information transmission, and SBs (short blocks; SB # 1 and SB # in FIG. 2) may be used for pilot and data transmission. On the other hand, CP indicates an area where the cyclic prefix is inserted.

4 is a diagram for describing a frequency domain scheduling method using an FDM method in uplink.

Frequency division multiplexing (hereinafter, referred to as "FDM") of FIG. 4 is a method of allowing UEs to be distinguished from each other by disposing UE signals in different frequency bands so as not to overlap each other. For example, FIG. 4 illustrates a method of dividing and allocating the data of the UE1 to the UE4 and the DM pilot transmission bands so that they do not overlap each other, wherein data of each UE is transmitted through the LB, and reference such as a pilot through the SB. The signal is transmitted.

Since the information on the location of each UE signal is known to the base station, it is possible to distinguish the signal received at the base station according to the UE.

However, in the conventional FDM as shown in FIG. 4, the position and size of the frequency band scheduled for the pilot signal of each user are not constant. That is, the base station allocates frequency bands having different sizes and locations to users according to the communication environment of each user. In the case of applying such a scheduling method, if the frequency band overlaps with another user of an adjacent base station in uplink communication in an environment in which multiple base stations exist as shown in FIG. 2, reception performance is deteriorated due to interference between pilot signals of each user. A problem occurs.

Therefore, a technique for solving the interference problem of pilot signals between adjacent cells in such FDM is required.

An object of the present invention for solving the above problems is to provide a method for allocating communication resources to a plurality of UEs of each base station in a plurality of base stations to reduce interference of pilot signals between adjacent cells.

Also, by applying a method of allocating similar communication resources to UEs in a plurality of sectors included in one base station, it is easy to reduce interference between UE pilot signals in adjacent sectors.

In a method in which a plurality of base stations according to an embodiment of the present invention for achieving the above object, the communication resource is allocated to the user equipment in the cell serviced by each of the plurality of base stations, the plurality of base stations in common Dividing the entire frequency band into an area unit including a specific number of unit frequency bands; And allocating, by the plurality of base stations, resources for pilot transmission to user equipment in the cell on a per-area basis.

In this case, when the plurality of base stations commonly divide the entire frequency band into the area units, the divided area units may each have the same frequency band location in the plurality of base stations. In the resource allocation step, When the area unit is allocated for data transmission of a plurality of user devices in the cell, the pilots of the user devices in the plurality of cells may be allocated in the area unit by applying code division multiplexing (CDM).

The plurality of base stations may be neighboring base stations, and an orthogonal code or a small cross-correlation code may be allocated to each of the plurality of base stations. Specifically, the orthogonal code is a CAZAC code to which different cyclic shifts are applied. The small cross-correlated code may be a CAZAC code having different indices.

In addition, the plurality of base stations may be base stations within an area serviced by one higher layer controller that adjusts resource allocation of the base station.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. For example, the following describes mainly the CAZAC sequence as a code sequence used as a pilot signal. For example, the code sequence used as a pilot signal is not limited thereto, as long as it includes the features of the present invention.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form, centering on the core functions of each structure and device, in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

The present invention proposes a method for allocating and scheduling communication resources in a frequency domain with pilot signals in an environment in which multiple base stations and multiple users exist on the uplink.

In general, "scheduling" means allocating communication resources to each user in consideration of channel conditions over time. Therefore, the communication resource allocation method according to the present invention can be used as a scheduling method.

In addition, although the pilot signal and the CQ pilot signal exist as described above, the pilot signal focuses on the DM pilot signal as an object to be scheduled in association with the data transmission band allocation of each user. Accordingly, it is assumed that the pilot signal refers to the DM pilot signal unless otherwise specified in the following description.

In addition, generally, terms such as “base station” and “cell” may be defined differently according to the characteristics of the system and the user environment, and may be variously called in the selection of the term. For example, the current 3GPP LTE refers to the base station and the spatial concept served by the base station as "node B", which node B includes a plurality of "cells" (ie, sectors in the foregoing description). do.

However, in the following description, for the sake of clarity, the spatial area in which one base station (or Node B) provides a communication service is referred to as a "cell", and the entity providing the communication service to the cell is referred to as a "base station" or " Assume that it is referred to as node B ". However, in the application of the present invention described below, the concept of "neighbor cell" may mean a cell serviced by one base station and a cell serviced by another base station, and within a region serviced by one base station. It may also refer to a plurality of cells included (ie, a conventional sector).

On the other hand, the pilot signal of each user in a single base station in the uplink can be distinguished between users through the FDM method as described above. However, in a multi-base station environment, since the frequency bands and positions of scheduled frequency bands of users in each base station are different, interference between users when the pilot signals allocated for each user of neighboring cells overlap in a specific frequency region Phenomenon occurs.

In addition, even when a code having a small cross-correlation value is used for each cell in order to reduce interference with other user signals of neighboring cells as described above, the lengths and positions of codes used are different. In this case, the interference between the codes is maintained to a considerable degree.

5A and 5B are diagrams for describing a phenomenon that occurs when pilot transmission bandwidths and transmission band positions between adjacent cells do not match, respectively.

In general, a code sequence used as a pilot signal has a constant size, a code sequence that can be easily distinguished from each other is used, and a CAZAC sequence is mainly used in 3GPP LTE. Such a sequence has a very small cross-correlation value between sequences having different sequence indices, and also has an orthogonal characteristic when different circular shifts of a predetermined length or more are applied. However, when the sequence lengths are different from each other or the positions of the sequences are different from each other, these characteristics are not maintained.

First, FIG. 5A illustrates a case where a bandwidth allocated to each user in neighboring cells A and B is different.

As such, the length of the code used by the UE1 and the UE2 of the cell A as the pilot signal (for example, CAZAC 1 and CAZAC 2) and the code used by the UE 3 of the cell B as the pilot signal (for example, CAZAC 3). CAZAC 3 is simultaneously affected by CAZAC 1 and CAZAC 2, because the lengths of the two are different from each other. Therefore, as CAZAC 3 has a large correlation with CAZAC 1 + CAZAC 2 located in the corresponding band, pilot signal interference between cell A and cell B occurs.

5B shows a case where the widths of the bands allocated to the users in neighboring cells A and B are the same, but the positions of the bands are different.

As such, the code used by the UE1 of the cell A as a pilot signal (for example, CAZAC 1) is a code used by the UE2 and UE3 of the cell B as the pilot signal (for example, CAZAC 2 and CAZAC 3). Can be affected at the same time, CAZAC 1 and CAZAC 2 + CAZAC 3 in the portion corresponding to the length of the CAZAC 1 has a large correlation value, this interference can not be ignored.

Therefore, in one embodiment of the present invention, the frequency band in which users can transmit pilots in each base station is set in an area unit including a predetermined unit frequency band (Resource block), and the size and frequency / time position of the area unit are set. Matching of adjacent base stations proposes a method. In this case, the actual pilot transmission band of the user may be a band corresponding to an integer multiple of the area unit, and in this case, a code having an area unit length may be transmitted in the entire transmission band.

6 is a diagram illustrating a method of performing frequency domain scheduling in uplink according to an embodiment of the present invention.

In general, as described above, each user's pilot signal is transmitted with the same bandwidth in the same frequency band as that user's data signal. Accordingly, when a plurality of users are differently allocated frequency bands according to respective data transmission amounts, pilots are also transmitted with different bandwidths.

However, according to an embodiment of the present invention as shown in FIG. 6, a plurality of base stations (for example, base station A, base station B,...) Are communication resources to UEs in a cell serviced by each base station. In the case of allocating a plurality of base stations, a plurality of base stations commonly divide a _total frequency band BW _total into an area unit (“Region” in FIG. 6) that includes a specific number of unit frequency bands. We propose a method of allocating resources for pilot transmission to UEs in a cell. 6 illustrates an example in which four resource blocks are set to a size of an area unit that is set in common, but the size of an area unit does not need to be limited to a specific size as long as they are commonly set in a plurality of base stations.

In this case, the common division of all frequency bands in a plurality of base stations means not only the size of each region unit but also the position in the frequency region of each region unit.

That is, when several users belonging to a cell serviced by each of the base stations A and B are divided and used in one frequency domain unit "Region 1" in FIG. 6, the pilot signal of each user is within "Region 1". Regardless of the bandwidth allocated for data transmission, the frequency band corresponding to the entire "Region 1" is allocated equally.

Therefore, while the conventional pilot signal was transmitted over the same bandwidth as the data transmission band, in one embodiment of the present invention, the data signal of each UE may not be equal to the size of the region to which the pilot signal is allocated. For example, in FIG. 6, even when the data signal requires a band smaller than the frequency band to which the pilot signal is allocated, such as "Region 1" of the base station A, "Region 1", and "Region 2" of the base station B, the pilot signal. As is proposed in one embodiment of the present invention is allocated to one area unit, the data signal can be transmitted by receiving only the required frequency resources.

Accordingly, when one region unit is allocated for data transmission of user equipment in a plurality of cells, as shown in "Region 1" of base station A, "Region 1" and "Region 2" of base station B of FIG. Since the pilot signal must be transmitted throughout the area unit, the same area unit must be shared and used for pilot transmission of a plurality of users. Accordingly, in such a case, according to an embodiment of the present invention, pilots of UEs in a plurality of cells may be allocated by area by applying code division multiplexing (CDM).

On the other hand, as shown in the base station A "Region 2" of FIG. 6, a UE can transmit data by allocating one frequency domain unit, and in addition, one UE can transmit a signal by being assigned an integer multiple of the area unit. .

That is, independent of the amount of data signals transmitted by the UE, the pilot signals are scheduled in frequency domain units as proposed in one embodiment of the present invention.

In this way, when the pilot signal is scheduled in the frequency domain, the code lengths used for the user classification can be equally applied, so that users can be distinguished by applying code division multiplexing to the pilot signal. . That is, pilot signals transmitted by the same frequency band and time by different users in the same base station or different users in adjacent base stations for the pilot signals of each user are transmitted through an orthogonal code sequence or a code sequence having low cross correlation. Transmission to reduce interference.

As an example of such a code sequence, a shift version or a CAZAC sequence having different indices may be used.

7 is a diagram for explaining an example of sequence allocation capable of minimizing interference between each other in the communication resource allocation method according to an embodiment of the present invention.

In an embodiment of the present invention, when an orthogonal code or a small cross-correlation code is allocated to a plurality of neighboring base stations, the following CAZAC sequence may be used as an example.

The CAZAC sequence has a small cross-correlation between sequences having different indices, and is orthogonal to each other between shift versions having different cyclic shifts over a constant ZCZ (Zero-Correlation-Zone) size to a single CAZAC sequence having the same index. Has the property to

Here, the ZCZ length is set in advance as a length necessary for distinguishing between CAZAC sequences to which different cyclic shifts are applied due to a delay in a transmission channel of a CAZAC sequence, and thus the number of cyclic shifts applicable to one CAZAC sequence. Is limited. Therefore, it is often difficult to set pilot division of UEs in all cells serviced by a plurality of base stations to use orthogonal CAZAC sequences to which different cyclic shifts are applied.

Accordingly, in one embodiment of the present invention, as an example of allocating a sequence to be transmitted as a pilot signal of a UE, different cyclic shifts are applied to a plurality of user equipments in a cell serviced by one base station, thereby generating a CAZAC sequence orthogonal to each other. And a method of minimizing mutual interference by allocating a CAZAC sequence having a small index to each other by having a different index to each of a plurality of base stations. This is because the signal of a plurality of user equipments in a cell serviced by one base station should be easier to distinguish than the interference between signals of other user equipments in a neighboring cell.

However, the sequence allocation method as described above may be allocated differently according to the number of shift versions that can be allocated and the length of the sequence to be used. For example, if the length of the CAZAC sequence used is long enough and the number of users transmitting pilots is small, orthogonal CAZAC sequences with different cyclic shifts may be allocated to all of them.

As described above, by allocating communication resources and allocating sequences to be used, reception performance degradation caused by interference by users existing in adjacent cells can be improved.

Meanwhile, in the above description of the present invention, the term 'neighbor' in terms of 'neighbor base station' or 'neighbor cell' may physically affect the target base station or cell. Geographically adjacent base station or cell. Accordingly, a plurality of base stations or cells served by the base station to which the above-described communication resource allocation scheme of the present invention is applied may be set to a plurality of base stations or cells within a predetermined range that may affect each other, and the specific range thereof is necessary. It can be set according to the specification and need not be limited to any particular range.

In addition to the physical point of view as described above, the base station in the area serviced by any upper layer controller that controls the communication resource allocation of the base station can be set as such a neighboring base station from a control point of view. In general, since a plurality of physically adjacent base stations are controlled by one higher layer means, both concepts may be substantially the same.

8 is a diagram for explaining a range to which a communication resource allocation method according to an embodiment of the present invention is applicable.

As illustrated in FIG. 8, a plurality of base stations including base station A and base station B may adjust resource allocation by one upper layer controller (hereinafter, referred to as a 'control unit'). Therefore, when a plurality of base stations for allocating resources according to the communication resource allocation method according to the embodiment of the present invention as described above are set in a range in which resource allocation is controlled by one or a predetermined number of control units, a range within the corresponding range is set. By the setting of the control unit, it is possible to easily control by unifying and setting the frequency bands allocated to the UEs by the unit of the area unit.

In addition, it is apparent to those skilled in the art that the upper layer control means for adjusting the resource allocation of the plurality of base stations need not be limited to any particular layer of the medium, and the present invention can be applied within a range where the setting can be easily changed.

On the other hand, even if the communication resource allocation method according to an embodiment of the present invention does not change the setting of the upper layer managing the plurality of base stations, for a plurality of sectors (or "cells" in 3GPP LTE) within one base station. By uniformly allocating the frequency in a common area unit, it is possible to mitigate pilot signal interference between users in a plurality of sectors served by the base station. For example, when the frequency allocation in each sector is assigned to the base station A of FIG. 8 to be allocated in units of areas having a predetermined bandwidth in common, a plurality of sectors serviced by the base station A (for example, sector A and sectors). The interference between the pilot signals of the users in B, sector C) can be reduced.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

According to the communication resource allocation method according to an embodiment of the present invention as described above, by unifying the bandwidth and the position of the area unit for allocating frequency resources to a plurality of UEs of each base station in a plurality of base stations, The interference can be reduced.

In addition, the above-described method of allocating communication resources may be applied to a wide range of base stations, and may also be applied to reducing interference between pilot signals between UEs in a plurality of sectors serviced by one base station. have.

Claims (6)

A method of allocating a communication resource to a user device in a cell serviced by each of the plurality of base stations, the plurality of base stations, Dividing all the frequency bands into area units including a specific number of unit frequency bands in common by the plurality of base stations; And And allocating, by the plurality of base stations, resources for pilot transmission to user equipment in the cell on a unit-by-region basis. The method of claim 1, And when the plurality of base stations commonly divide the entire frequency band into the area units, the divided area units each have the same frequency band location in the plurality of base stations. 3. The method according to claim 1 or 2, In the resource allocation step, When the area unit is allocated for data transmission of a plurality of user devices in the cell, the pilot of the user devices in the plurality of cells is allocated to the area unit by applying code division multiplexing (CDM). Way. 3. The method according to claim 1 or 2, The plurality of base stations are neighboring base stations, An orthogonal code or a small cross-correlation code is allocated to each of the plurality of base stations. The method of claim 4, wherein The orthogonal code is a CAZAC code to which different cyclic shifts are applied. The small cross-correlation code is a CAZAC code having different indices. 3. The method according to claim 1 or 2, And the plurality of base stations are base stations in an area serviced by one higher layer control unit for adjusting resource allocation of the base station.

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