JP5345982B2 - Wireless communication system, partially coordinated transmission method, and aggregation station - Google Patents

Description

  The present invention relates to a wireless communication system, a partially coordinated transmission method, and an aggregation station that transmit a signal to one or more wireless terminals by coordinating a plurality of wireless base stations.

  In a cellular mobile radio communication system, it is required to reduce the number of frequency repetitions as much as possible in order to improve the surface frequency utilization efficiency. For example, in the third-generation cellular system using a CDMA (Code Division Multiple Access) system, 1-cell frequency repetition (frequency repetition number = 1) using radio waves in the same frequency band in adjacent cells is realized.

  On the other hand, in the next generation cellular downlink, the OFDMA (Orthogonal Frequency Division Multiple Access) method is dominant. When the 1-cell frequency repetition is used in the cellular system using the OFDMA system, interference from adjacent cells and adjacent sectors is a major cause of characteristic deterioration. Specifically, SINR (Signal-to-Interference and Noise power Ratio) decreases as interference power from adjacent cells and adjacent sectors increases, and therefore, especially when performing MIMO (Multiple-Input Multiple-Output) transmission. It becomes difficult to exert the effect.

  Therefore, when 1-cell frequency repetition is used in a cellular system that performs MIMO transmission in the OFDMA system, it is necessary to avoid interference from adjacent cells and adjacent sectors in order to obtain a significant throughput increase effect by MIMO transmission.

  Thus, as an interference avoidance technique in the above-described case, attention has been focused on coordinated transmission in which a plurality of radio base stations are coordinated to simultaneously transmit signals to one or more radio terminals. According to this coordinated transmission, the space in the coordinated cluster formed by a set of cells or sectors of multiple coordinated radio base stations can be orthogonalized, so interference in the coordinated cluster (that is, between radio base stations performing coordinated transmission) (For example, Non-Patent Document 1 and Non-Patent Document 2).

  Specifically, in the coordinated transmission shown in Non-Patent Document 1, a plurality of radio base stations installed in a predetermined range are connected to the aggregation station, and the aggregation station coordinates the plurality of radio base stations. The cooperative cluster CL is formed by a set of cells C of a plurality of wireless base stations that cooperate. In the cooperative cluster CL, cooperative transmission by a plurality of radio base stations is performed by multi-user MIMO transmission. When this precoding method for multi-user MIMO transmission is used, the space in the cooperative cluster CL can be orthogonalized, so that interference in the cooperative cluster CL can be avoided and user throughput is improved.

  Further, in the coordinated transmission shown in Non-Patent Document 2, three adjacent radio base stations are connected to the aggregation station, and the aggregation station coordinates the three radio base stations 1. The cooperative cluster CL is formed by three adjacent sectors of three wireless base stations that cooperate. Further, the three adjacent sectors forming the cooperative cluster CL are configured such that the beams from the sector antennas of the respective radio base stations 1 face each other. In the cooperative cluster CL, cooperative transmission by three radio base stations is performed by multi-user MIMO transmission. When this precoding method for multi-user MIMO transmission is used, the space in the cooperative cluster CL can be orthogonalized, so that interference in the cooperative cluster CL can be removed, and user throughput and cell throughput are improved. .

A. Benjebbour, M. Shirakabe, Y. Ohwatari, J. Hagiwara, and T. Ohya, “Evaluation of user throughput for MU-MIMO coordinated wireless networks,” IEEE PIMRC 2008, pp.1-5, Sept. 2008. CMCC, “Downlink CoMP-MU-MIMO transmission schemes,” 3GPP RAN1 # 56, R1-090922, Feb. 2009.

  However, the above-described interference avoidance technique using coordinated transmission by a plurality of radio base stations can avoid interference within the coordinated cluster (that is, interference between radio base stations performing coordinated transmission), but interference from outside the coordinated cluster. There is a problem that (that is, interference from other than the radio base station performing coordinated transmission) cannot be avoided.

  In addition, inter-cluster interference avoidance directivity that avoids inter-cluster interference by assigning directivity patterns so that directional beams do not face each other in the same frequency region between adjacent radio base stations. It is possible to adopt a pattern. However, when the inter-cluster interference avoidance type directivity pattern is applied, there is no interference in the cluster, and there is a problem that the cooperation (interference superposition) effect in the cluster is low.

  The present invention has been made in view of the above points, and can improve the inter-cluster interference avoidance effect and partially increase the interference superposition effect in the cluster, a partially coordinated transmission method, An object is to provide an aggregation station and a radio base station.

  The radio communication system of the present invention is a radio communication system including a plurality of radio base stations each forming a cell composed of a plurality of sectors, and a cooperation target radio base station serving as a center of cooperation from the plurality of radio base stations and A radio base station determination unit that determines normal radio base stations around the target radio base station and an interference avoidance type directivity pattern in which a directional beam does not face between adjacent cells in the same frequency domain. Are assigned to each of the plurality of normal radio base stations for each frequency domain, and each interference avoidance type is assigned to the cooperation target radio base station. A directivity pattern determining unit that assigns an interference superimposition type directivity pattern in which a directional beam faces in the same frequency region. A station transmits a directional beam according to the interference avoidance directivity pattern, and directs according to the interference superimposition directivity pattern in the same time slot as the normal radio base station with which the cooperation target radio base station cooperates. Transmitting a sex beam.

  According to this configuration, the interference avoidance directivity pattern is assigned to the normal radio base station for each frequency domain, and the same for each interference avoidance directivity pattern for the cooperation target radio base station. In the frequency domain, an interference superposition type directivity pattern in which directional beams face each other is assigned. Therefore, in a communication area in which a plurality of clusters composed of cooperation target radio base stations and surrounding normal radio base station cells are arranged, inter-cluster interference The avoidance effect can be enhanced, and the interference superposition effect within the cluster can be partially enhanced, and the throughput of the entire system can be increased.

  In the wireless communication system according to the present invention, the wireless base station determination unit may dynamically determine the cooperation target wireless base station according to a change in request of the wireless base station, The base station may be fixed. By dynamically determining the cooperation target radio base station, it is possible to flexibly cope with a change in request of the radio base station, and if the cooperation target radio base station is fixed, the process up to determining the directivity pattern can be simplified.

  Further, the present invention is directed to the above-described radio communication system, wherein the cooperation target radio base station and the normal radio base station use directivity using multiuser MIMO transmission for precoding or coordinated beamforming for coordinating beamforming between cells. Form a beam.

  Further, the present invention is the above wireless communication system, wherein the plurality of frequency regions are a plurality of frequency blocks of an OFDMA scheme, and the cooperation target wireless base station and the normal wireless base station An interference avoidance directivity pattern and an interference superimposition directivity pattern are assigned.

  In the wireless communication system according to the present invention, the directivity pattern determination unit may correspond to each of the time domain and the interference avoidance directivity pattern and the interference superimposed directivity corresponding to each of the time domains. Assign sex patterns.

  According to the present invention, it is possible to achieve a high inter-cluster interference avoidance effect by the inter-cluster interference avoidance type directivity pattern, and to partially increase the interference superposition effect in the cluster.

1 is a schematic configuration diagram of a wireless communication system according to a first embodiment. It is a figure which shows the cooperation area formed with the radio | wireless communications system which concerns on this Embodiment 1. FIG. It is a figure which shows the directivity pattern which concerns on this Embodiment 1. FIG. It is a figure which shows the beam pattern which allocated only the interference directivity directivity pattern. It is a figure which shows the beam pattern which allocated the directivity pattern of interference avoidance, and the directivity pattern of interference superimposition. It is a figure which shows the cluster pattern which combined the directivity pattern of multiple frequencies. It is a figure which shows the example of a mapping of the beam pattern and frequency block of a normal radio base station. It is a figure which shows the example of mapping of the beam pattern of a cooperation object radio base station, and a frequency block. 2 is a functional block diagram of an aggregation station according to the first embodiment. FIG. 2 is a functional block diagram of a radio base station according to the first embodiment. FIG. 2 is a sequence diagram of the wireless communication system according to the first embodiment. FIG. It is a figure which shows the cluster arrangement | positioning which forms the cooperation area at the time of applying a dynamic switch. It is a figure which shows the cluster arrangement | positioning which forms the cooperation area at the time of applying a static switch. It is the figure which illustrated the switch unit (granularity) of the frequency. It is a figure which shows the example of a mapping of the beam pattern and frequency block of a normal radio base station. It is a figure which shows the example of mapping of the beam pattern of a cooperation object radio base station, and a frequency block. It is a schematic block diagram of the radio | wireless communications system which concerns on this Embodiment 2. FIG. FIG. 6 is a functional block diagram of a radio base station according to the second embodiment.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

<Overall Schematic Configuration of Radio Communication System According to this Embodiment>
FIG. 1 is a schematic configuration diagram of a wireless communication system according to the present embodiment. The radio communication system according to the present embodiment includes a plurality of radio base stations 10 (10-1 to 10-7,...), An aggregation station 30 connected to the plurality of radio base stations 10 through an optical fiber 20, and an aggregation station 30. And a network 40 connected to the network. A central cell C-1 formed by the wireless base station 10-1 disposed in the center and a plurality of other wireless base stations 10-2 to 10- disposed so as to surround the central wireless base station 10-1. A plurality of adjacent cell cells C-2 to C-7 formed adjacent to the periphery of the central cell C-1 form one cluster CL. As shown in FIGS. 11 and 12, a cluster CL, which is a set of a plurality of cells, is two-dimensionally arranged to form a wide communication area. The present embodiment is a wireless communication system that realizes interference suppression between clusters and realizes interference superposition capability within the cluster.

  FIG. 2A is a diagram showing a partial cooperation area formed in a cluster in the wireless communication system according to the present embodiment, and FIG. 2B is a diagram showing a sector configuration of one cell. . In this embodiment, one cell is composed of six sectors S1 to S6, but the sector configuration is not limited to six sectors.

  The radio base station 10-1 forming the central cell is a cooperation target base station, and the neighboring radio base stations 10-2 to 10-7 are normal radio base stations. Between the cooperation target base station 10-1 and the normal radio base station 10-2, a directional beam is transmitted in the same frequency region (for example, frequency f1) in a direction facing each other to form a cooperation area CL1 capable of interference superimposition. doing. Similarly, between the cooperation target base station 10-1 and the normal radio base station 10-4, directional beams of frequency f1 are transmitted in directions facing each other to form a cooperation area CL3, and the cooperation target base station 10- 1 and the normal radio base station 10-6 transmit the directional beams having the frequency f1 in the direction facing each other to form the cooperative area CL5. Moreover, between the cooperation object base station 10-1 and the normal radio base station 10-3, the directional beam of the frequency f2 different from the frequency f1 is transmitted in the direction which mutually faces, and the cooperation area CL2 is formed. Similarly, between the cooperation target base station 10-1 and the normal radio base station 10-5, the directional beams of the frequency f2 are transmitted in directions facing each other to form the cooperation area CL4, and the cooperation target base station 10- 1 and the normal radio base station 10-7 transmit the directional beams of the frequency f2 in the direction facing each other to form the cooperation area CL6.

  In the cooperative areas CL1 to CL6, the radio base stations 10-1 to 10-7 simultaneously transmit signals to the wireless terminals 50 located in the cooperative areas CL1 to CL6 by multiuser MIMO transmission. The BD-ZF method or the like can be used as a precoding method for this multiuser MIMO transmission. By multi-user MIMO precoding, the space of the cooperative areas CL1 to CL6 can be orthogonalized, so that interference between the radio base stations 10 performing cooperative transmission in the cooperative cluster CL1 can be avoided. Instead of multi-user MIMO transmission, Coordinated Beamforming that coordinates beamforming between cells may be used.

  In the radio communication system according to the present embodiment, a directivity pattern is assigned to the radio base station 10 corresponding to the interference avoidance capability or interference superposition capability required for each cluster from among a plurality of directivity patterns. FIG. 3 is a diagram showing a directivity pattern used in the wireless communication system of the present embodiment. The directivity patterns 1a and 1b (FIGS. 3 (1) and 4) are composed of three directional beams having peaks in directions of 30 degrees, 150 degrees, and 270 degrees clockwise with respect to the vertical direction. . The directivity patterns 2a and 2b (FIGS. 3 (2) and (3)) are obtained from three directional beams having peaks in directions of 30 degrees, 150 degrees, and 270 degrees counterclockwise with respect to the vertical direction. Composed.

  FIG. 4A shows a state in which the directivity pattern 1a is assigned to each of the radio base stations 10-1 to 10-7 constituting the cluster. When all the radio base stations 10-1 to 10-7 transmit, for example, a directional beam having the frequency f1 according to the directional pattern 1a, the directional beams do not face each other between adjacent cells in the same frequency region (f1). Become. Therefore, it is possible to avoid interference of directional beams transmitted simultaneously from a plurality of radio base stations 10 within a cluster (particularly near the cell edge) and between clusters.

  FIG. 4B shows a state in which the directivity pattern 2a is assigned to each of the radio base stations 10-1 to 10-7 constituting the cluster. When all the radio base stations 10-1 to 10-7 transmit, for example, a directional beam having the frequency f2 according to the directional pattern 2a, the directional beams do not face each other between adjacent cells in the same frequency region (f2). Become. Therefore, it is possible to avoid interference of directional beams transmitted simultaneously from a plurality of radio base stations 10 within a cluster (particularly near the cell edge) and between clusters.

  As described above, the directional patterns 1a and 2a are configured so that the directional beams do not face each other between adjacent cells, and the directional patterns 1a and the directional patterns 2a correspond to different frequency regions. Therefore, the directivity pattern 1a and the directivity pattern 2a are simultaneously assigned to all the radio base stations 10-1 to 10-7, and the directivity beams are simultaneously transmitted in the corresponding frequency domain according to the directivity pattern 1a and the directivity pattern 2a. Even if it is transmitted, a high interference avoidance capability within and between clusters can be realized. In FIG. 4, only the directivity pattern in one cluster is illustrated, but the adjacent cluster is assigned by assigning the directivity pattern 1a and the directivity pattern 2a to the other radio base stations 10 constituting the adjacent cluster. High inter-cluster interference avoidance capability can be realized even between. In this specification, the directivity pattern 1a and the directivity pattern 2a are referred to as interference avoidance directivity patterns.

  In the present invention, in order to compensate for the problem that the intra-cluster interference superimposition ability is reduced only by the interference avoidance directivity pattern, the intra-cluster interference superposition directivity pattern having a high interference superposition ability is partially (specifically, coordinated). Applies to target base station 10-1).

  In the inter-cluster interference avoidance type cell / sector configuration shown in FIG. 4A, the directivity pattern assigned to the cooperation target radio base station 10-1 forming the central cell C-1 is rotated by 60 degrees from the directivity pattern 1a. (Flipping). By flipping only the directivity pattern 1a assigned to the cooperation target wireless base station 10-1, as shown in FIG. 5A, the cooperation target wireless base station 10-1 and several wireless base stations around it ( Specifically, directional beams face each other in the same frequency region (frequency f1) with the normal radio base stations 10-3, 10-5, 10-7). That is, by flipping only the directivity pattern assigned to the cooperation target radio base station 10-1, it is possible to form a cooperation area (CL2, CL4, CL6 in FIG. 2) having a high interference superposition effect in a part of the cluster. it can. Similarly, in the inter-cluster interference avoidance type cell / sector configuration shown in FIG. 4 (b), only the directivity pattern 2a assigned to the cooperation target radio base station 10-1 is flipped, so as shown in FIG. 5 (b). As described above, the directional beams (frequency f2) face each other between the cooperation target radio base station 10-1 and some normal radio base stations 10-2, 10-4, and 10-6, and within the cluster also in the frequency domain f2. A cooperative area (CL1, CL3, CL5 in FIG. 2) having a high interference superimposing effect is formed in a part of. As described above, by flipping only the directivity pattern assigned to the cooperation target radio base station 10-1 for each frequency region, a cooperation area with a high interference superposition effect can be formed for each frequency region.

  In the inter-cluster interference avoidance type cell / sector configuration shown in FIG. 4A, the directivity pattern 2b shown in FIG. 3 (with the same frequency region f1 as the directivity pattern 1a) for the cooperation target radio base station 10-1. And the direction of the directional beam is rotated by 60 degrees), the same pattern as the directional pattern obtained by flipping only the directional pattern of the cooperation target radio base station 10-1 is obtained. Similarly, in the inter-cluster interference avoidance type cell / sector configuration shown in FIG. 4B, by assigning the directivity pattern 1b shown in FIG. This is the same as the directivity pattern obtained by flipping only the directivity pattern 2a of the station 10-1. In this specification, the directivity pattern 1b and the directivity pattern 2b are referred to as interference superimposed directivity patterns.

  As shown in FIG. 6, the interference avoidance directivity patterns 1a and 2a are assigned to the normal radio base stations 10-2 to 10-7 for each frequency domain, and the frequency is set to the cooperation target radio base station 10-1. Interference superimposed directivity patterns 1b and 2b are assigned to each region. As a result, a high interference avoidance effect can be realized between the clusters, and a high interference superposition capability can be realized in the cluster centered on the cooperation target radio base station 10-1.

  Next, mapping between the directivity patterns of the cooperation target radio base station 10-1 and the normal radio base stations 10-2 to 10-7 and a plurality of frequency regions will be described.

  FIG. 7 shows an example of mapping of directivity patterns and frequency blocks of normal radio base stations 10-2 to 10-7. As described above, the directivity pattern 1a or the directivity pattern 2a which is an interference avoidance directivity pattern is assigned to the normal radio base stations 10-2 to 10-7. The system band of the wireless communication system is divided into a plurality of frequency blocks, and directivity patterns 1a are determined corresponding to odd frequency blocks 2n + 1 (n = 0, 1, 2,...), And even frequency blocks 2n (n = 1, 2, ...), the directivity pattern 2a is determined. The directivity pattern is fixed in the time axis direction for each frequency domain. In the OFDMA scheme, the system band can be divided into a plurality of frequency blocks, and frequency resources can be handled in frequency block units. When the wireless communication system adopts the OFDMA scheme, the frequency blocks shown in FIGS. 7 and 8 may correspond to the frequency blocks of the OFDMA scheme.

  FIG. 8 shows an example of mapping between the directivity pattern and frequency block of the cooperation target radio base station 10-1. As described above, the directivity patterns 1b and 2b, which are interference superimposed directivity patterns, are assigned to the cooperation target radio base station 10-1. Directivity pattern 2b is determined corresponding to odd frequency block 2n + 1 (n = 0, 1, 2,...), And directivity corresponding to even frequency block 2n (n = 1, 2,...). Pattern 1b is defined. The directivity pattern 2b is assigned to the odd frequency block 2n + 1 with respect to the cooperation target radio base station 10-1. The directivity pattern 1a is assigned to the odd frequency block 2n + 1 with respect to the normal radio base stations 10-2 to 10-7. This is because the directivity pattern 2b can exhibit interference superposition ability in relation to the directivity pattern 1a. Similarly, the directivity pattern 1b is assigned to the even frequency block 2n with respect to the cooperation target radio base station 10-1. The directivity pattern 2a is assigned to the even frequency block 2n with respect to the normal radio base stations 10-2 to 10-7. (Directivity pattern 1b can exhibit interference superposition ability in relation to directivity pattern 2a). The directivity pattern is fixed in the time axis direction for each frequency domain.

  As described above, the interference avoidance directivity patterns 1a and 2a are alternately switched between adjacent frequency blocks, and the interference superimposed directivity patterns 2b and 1b are alternately switched, thereby preventing the intercluster interference shown in FIG. A cluster pattern that simultaneously realizes the capability and the intra-raster interference superposition capability can be configured.

<Functional Configuration of Radio Communication System According to this Embodiment>
Next, the functional configuration of the aggregation station 30 and each radio base station 10 configuring the radio communication system according to the present embodiment will be described. 9A and 9B are functional block diagrams of the aggregation station 30 and each radio base station 10. In the present embodiment, the number of radio base stations 10 is M, the number of antenna elements 11 of each radio base station 10 is Nt, and the number of radio terminals 50 is Nu.

  The radio base station determination unit 41 determines, for each radio terminal 50 that is a communication target, a radio base station 10 that transmits transmission data to the target radio terminal 50. When cooperative transmission is simultaneously performed from a plurality of radio base stations 10 to the target radio terminal 50, a plurality of radio base stations 10 are determined. The cooperation target radio base station 10-1 and the normal radio base stations 10-2 to 10-7 that are the center of the cooperation are determined from the plurality of radio base stations 10 that transmit simultaneously to the target radio terminal 50. A method for determining a cooperation target radio base station is not limited in the present invention. The cooperation target radio base station may be determined and fixed periodically at the system design stage or the operation stage, or may be determined dynamically based on the traffic volume, the base station request, or the terminal request. The radio base station 10-1 at the center of the cluster is selected as the cooperation target radio base station, and the radio base station 10 that is arranged around the cooperation target radio base station 10-1 and forms an adjacent cell is designated as the normal radio base station 10-2. Select from 10 to 7-7. The radio base station determination unit 41 may be arranged on the core network side or in the aggregation station 30.

  The aggregation station 30 assigns the interference superimposition type directivity pattern shown in FIG. 8 to the cooperation target radio base station 10-1 determined by the radio base station determination unit 41, and normal radio base stations 10-2 to 10-7. The interference avoidance type directivity pattern shown in FIG. The aggregation station 30 includes a directivity pattern selection unit 31, a signal distribution unit 32, a modulation unit 33 with Nu radio terminals that transmit at the same transmission timing, a precoding unit 34, and a transmission with M radio base stations. Part 35.

  The directivity pattern selection unit 31 selects and assigns the interference avoidance directivity pattern 1a or 2a for each frequency domain to the normal radio base stations 10-2 to 10-7, and assigns them to the cooperation target radio base station 10-1. On the other hand, in the relationship with the interference avoidance directivity pattern 1a or 2a for each frequency region, the interference superimposition directivity pattern 2b or 1b that exhibits the interference superposition capability is selected and assigned. The directivity pattern selector 31 implements interference avoidance directivity corresponding to each frequency region as shown in FIG. 7 in order to realize directivity pattern allocation corresponding to the normal radio base station and the cooperation target radio base station. Patterns 1a and 2a and interference superimposed directivity patterns 2b and 1b corresponding to each frequency region as shown in FIG. 8 are held in advance in a memory (not shown) as directivity pattern selection information. Directivity pattern selection information composed of interference avoidance directivity patterns 1a and 2a assigned to the normal radio base stations 10-2 to 10-7 for each frequency domain, and a frequency for the cooperation target radio base station 10-1. Directivity pattern selection information including the interference superimposition directivity patterns 2b and 1b assigned to each region is input to the precoding unit.

  The signal distribution unit 32 receives data signals for all the radio terminals 50-1 to 50 -Nu connected to all the radio base stations 10 under the aggregation station 30 from the network network 40, and the data signals received from the network network 40. Are distributed to the wireless terminals 50-1 to 50-Nu. The signal distribution unit 32 inputs the data signal distributed for each of Nu wireless terminals to the first modulation unit 33 to the Nu modulation unit 33, respectively.

  The modulation unit 33 includes an encoding unit 331, an interleaving unit 332, a serial-parallel conversion unit 333, and a signal modulation unit 334 for each subcarrier number L and transmission stream number Nr (ie, subcarrier number L × transmission stream number Nr). Signal modulators 334).

  The encoding unit 331 performs encoding on the data signal input from the signal distribution unit 32 using a predetermined encoding method. Here, as an encoding method, a turbo code may be used, a convolutional code may be used, or an LDPC code may be used, and the present invention can be implemented regardless of the encoding method. The encoding unit 331 inputs the encoded data signal to the interleaving unit 332.

  The interleaving unit 332 performs interleaving on the data signal input from the encoding unit 331. Here, any method may be used as the interleaving method, and the present invention can be implemented regardless of the interleaving method. The interleaving unit 332 inputs the interleaved data signal to the serial / parallel conversion unit 333.

  The serial / parallel conversion unit 333 converts the data signal sequence input from the interleaving unit 332 into data signals for the number of subcarriers L and the number of transmission streams Nr in parallel. The serial / parallel converter 333 inputs the data signal for each subcarrier number L and each transmission stream number Nr to the signal modulation unit 334 provided for each subcarrier number L and each transmission stream number Nr.

  Each signal modulation unit 334 performs multi-level modulation on the data signal input from the serial / parallel conversion unit 333. Here, the modulation multi-level number may be fixed or may be adaptively changed according to the channel condition. Each signal modulation unit 334 inputs a data signal subjected to multilevel modulation to the precoding unit 34.

  The precoding unit 34 performs precoding on the data signals input from the signal modulation units 334 of the modulation units 33 having the number of wireless terminals Nu. The precoding unit 34 is a cluster that can be coordinated according to the input directivity pattern selection information (sectors in which the beam of an adjacent cell and the beam face each other at the same frequency) multi-user MIMO (BD-ZF, ZF, etc.) In the sector where multiple cell simultaneous precoding by (CB) etc. is selected and interference can be avoided according to the directivity pattern selection information (sector where the beam of the adjacent cell sector does not face the same frequency) by single cell MIMO / Beamforming etc. Select single cell precoding. The precoding unit 34 multiplies the input data signal by the selected transmission weight for precoding, and the data signal for the total number of antenna elements Nt of the M radio base stations 10 under the aggregation station 30. (That is, the number of radio base stations M × data signals corresponding to the number of antenna elements Nt of each radio base station 10). The M × Nt data signals generated by the precoding unit 34 are respectively input to the first transmission unit 35 to the Mth transmission unit 35 provided for each of the M radio base stations 10.

  The transmission unit 35 includes an inverse Fourier transform unit 351, a parallel / serial conversion unit 352, a guard interval insertion unit 353, a carrier frequency modulation unit 354, and an electro-optical conversion for each antenna element number Nt of each radio base station 10. Part 355.

  The inverse Fourier transform unit 351 transforms the data signal input from the precoding unit 34 from the frequency domain to the time domain. The inverse Fourier transform unit 351 converts the data signal converted into the time domain into a parallel / serial conversion unit 352.

  The parallel-serial conversion unit 352 serially converts the data signal sequence for the subcarrier number L and the antenna elements input from the inverse Fourier transform unit 351 into a data signal sequence for the antenna element number Nt. The parallel-serial converter 352 inputs a data signal sequence for each antenna element number Nt to a guard interval insertion unit 353 provided for each antenna element number Nt.

  The guard interval insertion unit 353 inserts a guard interval into the data signal sequence input from the parallel / serial conversion unit 352, and inputs the data signal sequence into which the guard interval is inserted to the carrier frequency modulation unit 354.

  The carrier frequency modulation unit 354 modulates the data signal sequence input from the guard interval insertion unit 353 to the carrier frequency, and inputs the modulated data signal to the electro-optical conversion unit 355.

  The electro-optical conversion unit 355 modulates the data signal input from the carrier frequency modulation unit 354 from an electric signal to an optical signal, and inputs the modulated data signal to the radio base station 10 via the optical fiber 20.

<< Functional Configuration of Radio Base Station 10 According to the Present Embodiment >>
Each radio base station 10 is connected to the aggregation station 30 via the optical fiber 20. The radio base station 10 includes Nt antenna elements 11 and Nt optical-electrical converters 12 connected to the Nt antenna elements 11, respectively.

  The optical-electrical converter 12 demodulates the data signal input from the aggregation station 30 via the optical fiber 20 from an optical signal to an electrical signal, and inputs the demodulated data signal to the antenna element 11. The data signal input to the antenna element 11 is radiated into space.

  As described above, the aggregation station 30 generates data signals to be input to the individual antenna elements 11 of each radio base station 10, and the directivity transmitted from each radio base station 10 by precoding in the precoding unit 34. The direction of the sex beam is controlled. For example, when the first radio base station is a cooperation target radio base station, a directional beam emitted from the first radio base station by precoding transmission data supplied to each antenna element of the first radio base station. Are controlled so as to be interference superimposed directivity patterns 2b and 1b. When the second radio base station is a normal radio base station, the directional beam emitted from the second radio base station by precoding the transmission data supplied to each antenna element of the second radio base station, The interference avoidance directivity patterns 1a and 2a are controlled.

<Operation of Radio Communication System According to this Embodiment>
Next, a transmission method in the wireless communication system configured as described above will be described. FIG. 10 is a sequence diagram in the wireless communication system according to the present embodiment. Here, in this sequence diagram, it is assumed that the radio base stations 10-1 and 10-2 transmit signals to the radio terminals 50-1 and 50-2 located in the cluster.

  The aggregation station 30 transmits a reference signal for channel estimation to the radio base stations 10-1 and 10-2 (step S101). The radio base station 10-1 transmits a reference signal from the aggregation station 30 to the radio terminals 50-1 and 50-2 (that is, the radio terminals 50 located in the cooperation areas CL1 to CL6) connected to the radio base station 10-1. Transmit (step S102). Similarly, the radio base station 10-2 transmits a reference signal from the aggregation station 30 to the radio terminals 50-1 and 50-2 connected to the radio station 10-2 (steps S103 and S104).

  The radio terminals 50-1 and 50-2 perform channel estimation using the reference signals received from the radio base stations 10-1 and 10-2, and channel information that is a channel estimation result is transmitted to each radio base station 10-1. And 10-2 (step S105). Here, the radio terminals 50-1 and 50-2 may transmit the channel estimation result of the entire frequency domain as channel information, or the channel estimation result of a part of the frequency domain in order to prevent uplink congestion. May be sent.

  Each of the radio base stations 10-1 and 10-2 transmits the channel information received from the radio terminals 50-1 and 50-2 to the aggregation station 30 (step S106). The aggregation station 30 performs precoding for MIMO transmission processing based on the channel information received from each of the radio base stations 10-1 and 10-2, and the radio terminals 50-1 and 50-2 on which precoding has been performed. The addressed data signal is transmitted to the radio base stations 10-1 and 10-2 (step S107).

  Here, wireless terminals 50-1 and 50-2 are located in the cluster shown in FIG. 1, and a plurality of wireless base stations 10-1 and 10-2 are connected to the wireless terminals 50-1 and 50-2. The operation in the case of cooperative transmission is described. Coordinate transmission of transmission data from the plurality of radio base stations 10-1 to 10-2 to the radio terminals 50-1 and 50-2 in which the radio base station determination unit 41 or the host system is located in the cluster Is selected. The radio base station determination unit 41 selects the radio base station 10-1 at the center of the cell as the cooperation target radio base station that is the center of the cooperation in the cluster shown in FIG. Select station 10-2.

  The directivity pattern determination unit 31 assigns the interference avoidance directivity patterns 1a and 2a to the normal radio base station 10-2. The interference avoidance directivity pattern 1a is assigned to the odd frequency block, and the interference avoidance directivity pattern 2a is assigned to the even frequency block. Moreover, the interference superimposition type directivity patterns 1b and 2b are assigned to the cooperation target radio base station 10-1 (FIG. 7). The interference superimposed directivity pattern 2b is assigned to the odd frequency block, and the interference superimposed directivity pattern 1b is assigned to the even frequency block (FIG. 8).

If the wireless terminal 50-1 that exists in the cluster is in a cell edge cooperative target radio base station 10-1 and a normal radio base station 10-2, for example, the first transmission unit 35 ₁ in the central station 30 is coordinated target and transmitting process signals to each antenna element of the radio base station 10-1, the second transmission unit 35 ₂ transmits processed signals for each antenna element of the ordinary radio base station 10-2.

The precoding unit 34 applies the interference superimposed directivity patterns 1b and 2b for each frequency block to transmission data of the cooperation target radio base station 10-1 among transmission data to be transmitted to the radio terminal 50-1. Coding. Thus, the transmission data entered first to the transmission unit 35 ₁ corresponding to the respective antenna elements of the cooperative target radio base station 10-1, so that the directivity pattern shown in FIG. 5 (a) (b) This is a precoded signal. Further, the precoding unit 34 applies the interference avoidance directivity patterns 1a and 2a for each frequency block to the transmission data of the normal radio base station 10-2 among the transmission data to be transmitted to the radio terminal 50-1. Precode. Thus, typically the transmission data entered second to the transmission unit 35 ₂ corresponding to the respective antenna elements of the radio base station 10-2, the pre so that directivity pattern shown in FIG. 5 (a) (b) This is a coded signal.

First interference superposition type directional pattern 1b to each antenna element from the transmitting unit 35 ₁ cooperative target radio base station 10-1 of the central station 30, the pre-coded transmission data is given as a 2b, cooperative target radio The base station 10-1 transmits directional beams having interference directivity patterns 1b and 2b. At the same time, each antenna element to the interference avoidance type antenna pattern 1a ordinary radio base station 10-2 from the second transmitting portion 35 ₂ of the central station 30, the pre-coded transmission data is given such that 2a, Ordinary radio base station 10-2 transmits directional beams of interference avoidance directional patterns 1a and 2a. As a result, in the vicinity of the cell edge of the cooperation target radio base station 10-1 where the radio terminal 50-1 exists and the normal radio base station 10-2, as shown in FIGS. Facing each other, there is a high interference superposition effect. On the other hand, the directional beams directed from the normal radio base station 10-2 toward the adjacent cluster are the interference avoidance directional patterns 1a and 2a. If the interference avoidance directivity patterns 1a and 2a are applied to the radio base station in the adjacent cluster, a high intercluster interference avoidance effect can be expected.

  In the above radio communication system, the directivity pattern assigned to the cooperation target radio base station 10-1 of the central cell is switched to the interference superposition type directivity patterns 1b and 2b only in the cluster that requires the interference superimposition type effect (gain). (Hereinafter referred to as dynamic switch). In a cluster in which it is determined that the interference superimposing effect (gain) is not necessary, the directivity patterns assigned to all the radio base stations 10-1 to 10-7 in the cluster are the interference avoidance directivity patterns 1a and 2a. Before switching the directivity pattern of the central cell to the interference superposition type, the interference avoidance directivity patterns 1a and 2a shown in FIGS. 4A and 4B are applied to all the cells. Then, when a cluster requiring an interference superimposing effect (gain) is generated, the directivity pattern of the central cell of the cluster is switched to the interference superimposing type. Whether the switch is on or off is determined by the radio base station determination unit 41 upon receiving a request from the radio base station 10. For example, when a request to increase the throughput is received from the radio base station 10, the directivity pattern of the central cell of the cluster to which the request radio base station 10 belongs is switched to the interference superposition type.

  The switch trigger criteria for the dynamic switch may be other than a request for increasing throughput. For example, it may be a throughput improvement from a cell edge user or a request for an increase in average throughput due to an increase in traffic volume. Moreover, it is good also considering the generation | occurrence | production of the cell user who may increase the feedback information regarding the channel required in order to exhibit the effect of cooperative transmission as a trigger.

  FIG. 11 shows an example of a cell configuration in which the directivity pattern is switched only for the cells that need to improve the throughput based on the cell deployment by the interference avoidance type cell / sector configuration as a baseline (dynamic switch). A cluster is made up of cells that need to improve throughput and their surrounding cells. The directional beams are always adjusted between the clusters so as not to face each other in the frequency domain. Since a cooperative area is formed in the cluster, throughput can be improved.

  FIG. 12 shows an example of a cell configuration in which the normal radio base station and the cooperation target radio base station are fixed. For each cluster, a central radio base station is fixedly set as a cooperation target radio base station, and peripheral base stations in the cluster are fixedly set as normal radio base stations (static switch). In this manner, the allocation of directivity patterns may be fixed to the central cooperation target radio base station and the normal radio base station for each cluster.

  Although switching of a dynamic switch and a static switch is possible for each frequency block, in the above description, a frequency switch unit (granularity) is a frequency block. The unit of switching for each frequency can be set to an arbitrary size. For example, in LTE, a system band is expanded by combining a plurality of component carriers (maximum 20 MHz). As shown in FIG. 13A, the frequency switching unit may be a component carrier unit. Further, as shown in FIG. 13B, the component carrier is divided into a plurality of (for example, two) subbands to be used, but the unit of frequency switching may be a subband unit. In LTE, frequency resources are allocated in units of resource blocks. However, as shown in FIGS. 13C and 13D, frequency switching units may be set as resource block units. Note that two patterns may be alternately assigned to consecutive resource blocks as shown in FIG. 13 (c), and the same pattern may be assigned continuously to consecutive resource blocks as shown in FIG. 13 (d). Also good.

  The directivity pattern can also be determined for each frequency block (frequency domain) and for each time slot (time domain). FIG. 14 shows an example of mapping between directivity patterns and frequency blocks of a normal radio base station, and FIG. 15 shows an example of mapping between directivity patterns and frequency blocks of a cooperation target base station. For example, it is possible to improve the throughput in the radio communication system by defining different directivity patterns for each frequency domain and time domain based on the traffic volume in the cluster.

  In the wireless communication system of the above-described embodiment, the OFDMA method is used as the communication method, but a single carrier FDMA method or a CDMA method may be used as the communication method. When the single carrier FDMA method or the CDMA method is used as the communication method, the present invention can be applied by selecting the directivity pattern for each carrier frequency instead of selecting the directivity pattern for each frequency block.

  Further, in the coordinated transmission method of the above-described embodiment, in order to perform MU-MIMO precoding, BD-ZF method, Zero-Forcing method, non-linear precoding, minimum square error (MMSE), etc. Precoding may be performed using other methods.

  In the above description, the precoding unit in the aggregation station precodes for MIMO transmission processing and generates transmission data of the directivity pattern for each radio base station, but the aggregation station described in Embodiment 1 above The function may be installed in the radio base station.

  16 and 17 are diagrams showing a radio communication system according to Embodiment 2, FIG. 16 is a schematic configuration diagram of the radio communication system, and FIG. 17 shows functional blocks of each radio base station.

  In the radio communication system according to the second embodiment, each radio base station has a precoding function for MIMO transmission processing, instead of each radio base station receiving transmission data precoded for MIMO transmission processing from the aggregation station. . The radio communication system includes a plurality of radio base stations 10 (from the first radio base station to the Mth radio base station) having the same configuration.

  The radio base station 10 includes a modulation unit 33, a precoding unit 34, and a transmission unit 35. Each of these constituent elements has the same function as each corresponding functional element in the aggregation station 30 described above. The radio base station 10 normally uses interference avoidance directivity patterns 1a and 2a as directivity patterns. When the radio base station 10 becomes a cooperation target radio base station that is the center of cooperation, the interference avoidance directivity pattern 1a, 2a is switched to the interference superimposed directivity patterns 1b and 2b. When it is determined that cooperation is necessary, the directivity pattern switch unit 36 changes the directivity pattern from the interference avoidance directivity patterns 1a and 2a, which are normal directivity patterns, to the interference superimposed directivity patterns 1b and 2b. Switch to The fact that the directivity pattern is switched to the interference superposition type directivity patterns 1b and 2b via the directivity pattern switch information exchanging means 37 with respect to the adjacent radio base stations that form a cluster around the cooperation target radio base station. Notice. Further, the plurality of radio base stations 10-1 to 10-7 forming the cluster receive the sector information of the radio base station to be coordinated before data transmission, and each radio base station from the radio terminal 50 which is a connection terminal. The transmitted channel information and transmission data to the target wireless terminal 50 for cooperative transmission are shared via the transmission data / channel information exchanging means 38.

  The directivity pattern switch unit 36 determines the necessity of the directivity pattern switch from the request from the connected terminal, the sector information of the radio base station shared via the transmission data / channel information exchanging means 38, the channel information, and the like. be able to. Further, the directivity pattern switch unit 36 notifies the adjacent radio base station via the directivity pattern switch information exchanging means 37 that the adjacent radio base station has switched to the interference superimposed directivity patterns 1b and 2b. If it is received, the precoding unit 34 performs precoding for the MIMO transmission processing, and transmits transmission data that becomes an interference superimposition type directivity pattern with the cooperation target radio base station. Also, if neither the local station nor the adjacent station switches to the interference superimposition type directivity patterns 1b and 2b, the precoding unit 34 performs precoding for the MIMO transmission processing, and the interference avoidance type which is a normal directivity pattern. Transmission data based on the directivity patterns 1a and 2a is generated and transmitted.

  The directivity pattern switch information exchanging means 37 and the transmission data / channel information exchanging means 38 may be provided in all the radio base stations 10 or only in a specific radio base station 10 and other radio base stations. Necessary information may be notified to the station.

DESCRIPTION OF SYMBOLS 10 ... Wireless base station, 20 ... Optical fiber, 30 ... Aggregation station, 40 ... Network network, 50 ... Wireless terminal, 11 ... Antenna element, 12 ... Optical-electricity conversion part, 31 ... Directional pattern selection part, 32 ... Signal Distribution unit 33 ... Modulation unit 34 34 Precoding unit 35 Transmission unit 36 Directional pattern switch information unit 37 Directional pattern switch information exchange unit 38 Transmission data / channel information exchange unit 41 Wireless Base station determination unit, 331 ... encoding unit, 332 ... interleave unit, 333 ... serial-parallel conversion unit, 334 ... signal modulation unit, 351 ... inverse Fourier transform unit, 352 ... parallel-serial conversion unit, 353 ... guard interval insertion unit, 354... Carrier frequency modulation unit, 355... Electro-optical conversion unit, C, C1 to C7... Cell, CL, CL1 to CL6.

Claims (9)

A wireless communication system comprising a plurality of radio base stations each forming a cell composed of a plurality of sectors,
A radio base station determining unit that determines a cooperation target radio base station that is the center of cooperation from the plurality of radio base stations and a normal radio base station around the cooperation target radio base station;
Interference avoidance directivity patterns in which directional beams do not face each other between adjacent cells in the same frequency region are determined corresponding to each of the plurality of frequency regions. The interference avoidance type directivity pattern is assigned to each of the interference target directivity patterns, and the interference target directivity pattern in which the directivity beam faces in the same frequency region with respect to each interference avoidance type directivity pattern with respect to the cooperation target radio base station. A directivity pattern determination unit for assigning
Each normal radio base station forms a directional beam according to the interference avoidance type directivity pattern, and the interference superimposition type directivity in the same time slot as the normal radio base station with which the cooperation target radio base station cooperates A sector by multi-user MIMO transmission is formed between the directional beams formed between the normal radio base stations facing each other at the same frequency as the directional beam of the cooperation target radio base station. A wireless communication system characterized by coordinating data transmission between the two.   The radio communication system according to claim 1, wherein the radio base station determination unit dynamically determines the cooperation target radio base station according to a change in request of the radio base station.   The radio communication system according to claim 1, wherein the cooperation target radio base station is fixed.   Coordinate transmission of data using simultaneous transmission multi-user MIMO transmission or coordinated beamforming that coordinates beam forming between cells between the directional beams of the normal radio base stations facing the directional beams of the cooperation target radio base stations The wireless communication system according to claim 1.   The plurality of frequency regions are a plurality of frequency blocks of the OFDMA scheme, and the interference avoidance directivity pattern and the interference superposition type for each frequency block with respect to the cooperation target radio base station and the normal radio base station. 4. The radio communication system according to claim 1, wherein a directivity pattern is assigned.   2. The directivity pattern determination unit assigns the interference avoidance directivity pattern and the interference superimposition directivity pattern in accordance with each of time domains in addition to the frequency domain. The wireless communication system according to 1. A partially coordinated transmission method in a wireless communication system comprising a plurality of wireless base stations, each communication area comprising a plurality of sectors,
Determining a cooperation target radio base station that is the center of cooperation from the plurality of radio base stations and a normal radio base station around the cooperation target radio base station; and
Interference avoidance directivity patterns in which directional beams do not face each other between adjacent cells in the same frequency region are determined corresponding to each of the plurality of frequency regions, and for each of the plurality of normal radio base stations for each frequency region. The interference avoidance type directivity pattern is allocated, and the interference superposition type directivity pattern in which directivity beams face each other in the same frequency region is allocated to the cooperation target radio base station with respect to each interference avoidance type directivity pattern. A process comprising:
Each normal radio base station forms a directional beam according to the interference avoidance type directivity pattern, and the interference superimposition type directivity in the same time slot as the normal radio base station with which the cooperation target radio base station cooperates Forming a directional beam according to the sexual pattern;
Coordinating data transmission between sectors by multi-user MIMO transmission between the directional beams formed between the normal radio base stations facing at the same frequency as the directional beam of the cooperation target radio base station. And a partially coordinated transmission method. An aggregation station connected to each radio base station in a radio communication system comprising a plurality of radio base stations each forming a cell composed of a plurality of sectors,
A radio base station determining unit that determines a cooperation target radio base station that is the center of cooperation from the plurality of radio base stations and a normal radio base station around the cooperation target radio base station;
Interference avoidance directivity patterns in which directional beams do not face each other between adjacent cells in the same frequency region are determined corresponding to each of the plurality of frequency regions. The interference avoidance type directivity pattern is assigned to each of the interference target directivity patterns, and the interference target directivity pattern in which the directivity beam faces in the same frequency region with respect to each interference avoidance type directivity pattern with respect to the cooperation target radio base station. A directivity pattern determination unit for allocating the transmission data, and transmission data in which a directional beam formed by the cooperation target radio base station forms the interference superimposition type directivity pattern to the cooperation target radio base station. Transmission means for transmitting transmission data in which a directional beam formed by the normal radio base station forms the interference avoidance directional pattern with respect to the base station. Central station which is characterized. An interference avoidance type directivity pattern is used as a normal directivity pattern, and when the cooperation target radio base station becomes the center of cooperation, the interference avoidance type directivity pattern is switched to the interference superposition type directivity pattern. A directivity pattern switch to
When the directivity pattern switch unit switches the directivity pattern to the interference superimposition type directivity pattern, a notification means for notifying that the directional beam is switched to an adjacent radio base station;
A sharing means for sharing channel information and / or transmission data with a sector of a radio base station to be coordinated before data transmission;
When it becomes the cooperation target radio base station, an interference superimposed directivity pattern is formed between a directional beam transmitted by the cooperation target radio base station and a directional beam of an adjacent radio base station facing at the same frequency. Transmitting transmission data, and in the case of a normal radio base station, the directional beam transmitted by the normal radio base station and the directional beam of an adjacent radio base station that does not face each other at the same frequency A transmission means for transmitting transmission data serving as a directivity pattern;
A radio base station comprising:

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