WO2010073293A1

WO2010073293A1 - Radio communication system and radio communication method

Info

Publication number: WO2010073293A1
Application number: PCT/JP2008/003900
Authority: WO
Inventors: 下村剛史
Original assignee: 富士通株式会社
Priority date: 2008-12-22
Filing date: 2008-12-22
Publication date: 2010-07-01

Abstract

A radio communication system includes: a plurality of antenna devices distributed in respective cells for performing a radio communication with a mobile station; and a signal processing device connected to each of the antenna devices. Adjacent antenna devices positioned to sandwich a cell boundary and belonging to different cells have filters each having a transmission band set to transmit a downlink signal in the system band without suppressing the signal. The transmission bands of the respective filters of the adjacent antenna devices are set so that the bands are not overlapped. Accordingly, the bands of the downlink signals from the adjacent antenna devices to a mobile station are not overlapped. This reduces the inter-cell interference of the downstream link for the mobile station in the vicinity of the cell boundary.

Description

Wireless communication system and wireless communication method

In the present invention, each of a plurality of antenna devices arranged geographically dispersed in a cell performs radio communication with a mobile station, and is provided in each cell and connected to each antenna device through a predetermined transmission link. The present invention relates to a radio communication system and a radio communication method in which a signal processing device processes an uplink signal and a downlink signal.

Allocation of high frequency bands is assumed in next-generation wireless communication systems that require high-speed transmission at 100 M to 1 Gbit / sec. In general, it is known that a signal in a high frequency band is more straight ahead than a signal in a low frequency band, and many dead zones where radio waves do not reach occur. Therefore, when it is assumed that the transmission power of the base station is the same as that of a currently commercialized radio communication system, cell coverage (service area) is reduced due to allocation of a high frequency band. This is not preferable not only from the viewpoint of increasing the cost due to the increase in the number of base stations, but also from the point that frequent handover occurs.

In order to solve the above problem, for example, a distributed antenna system has been proposed (for example, Patent Document 1). A distributed antenna system includes a plurality of antenna devices (antenna units) that are geographically dispersed in a cell, and a signal processing device (central processing unit) that is connected to each antenna device via an optical fiber cable. It is done. In the distributed antenna system, each antenna device performs radio communication with a mobile station (user device), and a downlink signal from the signal processing device and an uplink signal from each antenna device are a predetermined transmission link (optical fiber cable). Etc.). In this distributed antenna system, the coverage of a cell is an aggregate of a relatively narrow range of coverage by each antenna device. Thereby, in the distributed antenna system, even when a high frequency band is assigned, not only does the cell coverage not decrease compared to the conventional system, but also the generation of dead zones is suppressed.

JP 2007-53768 A

The problem with conventional distributed antenna systems is that no measures are taken for inter-cell interference. Specifically, a mobile station located at a cell boundary transmits both a downlink signal (a signal from a nearby antenna device) in a cell to which the mobile station belongs and a signal from another antenna device in an adjacent cell. Since both signals can be received in a strong signal strength state, downlink inter-cell interference occurs. In addition, the antenna device located at the cell boundary transmits an uplink signal (a signal from a nearby mobile station) in a cell to which the own device belongs and a signal from a mobile station in another adjacent cell, both signals Since the signal can be received in a strong signal strength state, downlink inter-cell interference occurs.

In view of the above viewpoint, an object is to provide a radio including a plurality of antenna devices that are distributed in each cell and perform radio communication with a mobile station, and a signal processing device connected to each of the plurality of antenna devices. In a communication system, it is to reduce inter-cell interference.

A wireless communication system for achieving the above object is as follows:
A plurality of antenna devices that are distributed in each cell and perform wireless communication with a mobile station, and a signal processing device connected to each of the plurality of antenna devices,
Proximity antenna devices that are close to each other across cell boundaries and belong to different cells have a filter in which a transmission band that allows transmission without transmitting a downlink signal is set in the system band,
The transmission band of each filter of the proximity antenna device is set so as not to overlap.

According to this radio communication system, the band of the downlink signal from the proximity antenna device that is close to each other across the cell boundary and belongs to different cells does not overlap with the mobile station. Therefore, downlink inter-cell interference for mobile stations near the cell boundary is reduced. Inter-cell interference is similarly reduced in a wireless communication method having the same operation as this wireless communication system.

A wireless communication system for achieving the above object is as follows:
A plurality of antenna devices that are distributed in each cell and perform wireless communication with a mobile station, and a signal processing device connected to each of the plurality of antenna devices,
Proximity antenna devices that are close to each other across cell boundaries and belong to different cells have a filter in which a transmission band for transmitting uplink signals without being suppressed is set in the system band,
It is set so that the transmission band of each filter of the proximity antenna device does not overlap,
The signal processing device is a signal included in an uplink signal from a mobile station, and evaluates the signal quality of each band based on a reference signal for each of a plurality of bands dividing the system band, Allocation of uplink signal frequency resources to mobile stations is performed.

According to this wireless communication system, the uplink signal from the mobile station to the proximity antenna apparatus is transmitted to the signal processing apparatus connected to each antenna apparatus in a non-overlapping transmission band. In each signal processing device, the frequency resource of the uplink signal is assigned to the mobile station based on the signal quality of the reference signal included in the uplink signal. Therefore, the setting of the transmission band of each antenna apparatus is reflected in the allocation of uplink frequency resources to mobile stations that perform radio communication with each antenna apparatus. As a result, uplink inter-cell interference from mobile stations near the cell boundary is reduced. Inter-cell interference is similarly reduced in a wireless communication method having the same operation as this wireless communication system.

It is a figure for demonstrating the structure in the unit cell of the radio | wireless communications system of this embodiment. It is a block diagram which shows the principal part of the internal structure of a central processing unit (CU). It is a block diagram which shows the principal part of the internal structure of an antenna unit (RAU). It is a block diagram which shows the principal part of the internal structure of a mobile station (MS). It is a figure which illustrates the relationship of the frequency-power spectral density (PSD) as a filter characteristic. It is a figure which shows an example of the filter characteristic of each antenna unit in a multicell environment. It is a figure which shows an example of the filter characteristic of each antenna unit in a multicell environment. It is a figure which shows an example of the filter characteristic of each antenna unit in a multicell environment. It is a figure shown about communication with the antenna unit of the microcell adjacent between cells, and a mobile station.

Explanation of symbols

CU: Central processing unit 10, 11: Encoding modulation unit, 12: Signal multiplexing unit, 13 ... Subcarrier mapping unit, 14 ... IFFT unit, 15 ... CP adding unit, 16 ... Transmission radio unit, 17 ... Optical transmitter, DESCRIPTION OF SYMBOLS 18 ... Optical receiver, 19 ... Reception radio part, 20 ... OFDM demodulation part, 21 ... Pilot signal extraction part, 22 ... Reception quality measurement part, 23 ... Subcarrier allocation part, 24 ... MCS determination part, 25 ... Control information generation 26: CQI extraction unit RAU ... Antenna unit 30 ... Antenna, 31 ... Duplexer, 32 ... Optical receiver, 33, 35 ... Amplifier, 34, 36 ... Filter, 37 ... Optical transmitter MS ... Mobile station 50 ... Antenna, DESCRIPTION OF SYMBOLS 51 ... Duplexer, 52 ... Reception radio | wireless part, 53 ... OFDM demodulation part, 54 ... Control information extraction part, 55 ... Demodulation decoding part, 56 ... Subcarrier allocation information extraction part, 57 ... Pilot signal extraction unit, 58... MCS information extraction unit, 59... CQI measurement unit, 60... Encoding modulation unit, 61... Encoding modulation unit, 62. 65... CP adding section, 66... Transmitting radio section, 67.

1. First, the configuration of an embodiment (distributed antenna system) of a wireless communication system will be described with reference to FIG. FIG. 1 is a diagram for explaining a configuration in a unit cell of the wireless communication system of the present embodiment.

As shown in FIG. 1, this wireless communication system is abbreviated as a plurality of remote antenna units (hereinafter simply referred to as “antenna units” or RAUs (Remote Antenna Units), which are geographically distributed in a cell. RAUn (n = 0, 1, 2,...) And a central processing unit (hereinafter abbreviated as CU (Central processing unit)) as appropriate. The antenna unit is an embodiment of the antenna device, and the central processing unit is an embodiment of the signal processing device.

Each antenna unit RAU performs wireless communication with a mobile station (hereinafter abbreviated as MS (Mobile Station) as appropriate) within the signal reach of the unit. Here, the range in which each antenna unit RAU can communicate with the mobile station MS is referred to as a micro cell. In this wireless communication system, a single cell is formed by a plurality of microcells covered by each antenna unit RAU.

Each antenna unit RAU and the central processing unit CU are connected by an optical fiber cable. A downlink signal from the central processing unit CU to the mobile station MS is transmitted from the central processing unit CU to the antenna unit RAU via an optical fiber cable, and transmitted from the antenna unit RAU to the mobile station MS as a radio signal. . An uplink signal from the mobile station MS to the central processing unit CU is transmitted as a radio signal from the mobile station MS to the antenna unit RAU, and transmitted from the antenna unit RAU to the central processing unit CU via an optical fiber cable. . In this wireless communication system, the central processing unit CU has substantially the same function as a base station, except that it does not have an antenna.

The communication system of this radio communication system is preferably a multi-carrier transmission system that adaptively controls the downlink or uplink carrier frequency allocated to the mobile station within the system band (band allocated on the system). Typical examples of such multicarrier transmission systems include MC-CDMA (Multi-Carrier Code Division Multiple Access), OFDMA (Orthogonal).
Frequency Division Multiple Access) method. MC-CDMA system is 3GPP (Third Generation)
The Partnership Project has been studied. The OFDMA scheme is, for example, LTE (Long Term) which is being studied by 3GPP.
(Evolution) downlink transmission method.

Although any multicarrier transmission scheme can be applied to the wireless communication system of the present embodiment, a case will be described below as an example where the wireless communication system of the present embodiment adopts the OFDMA scheme.
In the OFDMA scheme, it is possible to adaptively allocate mobile stations MS (radio resource allocation) to a plurality of subcarriers in the system band. The OFDMA scheme is also a scheme with high frequency efficiency because the same system band (frequency) can be reused in a multi-cell environment.

2. Configuration of Each Part of Radio Communication System Hereinafter, the configuration of the central processing unit CU, the antenna unit RAU, and the mobile station MS in the radio communication system according to the present embodiment will be described with reference to FIGS. FIG. 2 is a block diagram showing a main part of the internal configuration of the central processing unit CU. FIG. 3 is a block diagram showing a main part of the internal configuration of the antenna unit RAU. FIG. 4 is a block diagram showing the main part of the internal configuration of the mobile station MS.

(2-1) Configuration of Central Processing Unit CU As shown in FIG. 2, the central processing unit CU includes coded

modulation units

10 and 11, a signal multiplexing unit 12, a subcarrier mapping unit 13, an IFFT unit 14, and a CP adding unit. 15, a transmission radio unit 16, an optical transmitter 17, an optical receiver 18, a reception radio unit 19, an OFDM demodulation unit 20, a pilot signal extraction unit 21, a reception quality measurement unit 22, a subcarrier allocation unit 23, an MCS determination unit 24, A control information generation unit 25 and a CQI extraction unit 26 are provided.

The encoding modulation unit 10 performs predetermined error correction encoding on the control information including the bit data sequence, and further uses a predetermined modulation multilevel modulation scheme (for example, BPSK modulation, QPSK modulation) to generate a symbol data sequence. Generate a signal. Here, as the coding rate and the modulation multi-level number when performing error correction coding, preset fixed values are used. In general, control information is transmitted using a low coding rate by BPSK modulation or QPSK modulation because high-quality transmission is required.

The encoding modulation unit 11 performs predetermined error correction encoding on user data composed of a bit data sequence, and further uses symbol data using a predetermined modulation multi-level modulation scheme (for example, QPSK, 16QAM, 64QAM modulation). A series signal is generated and output to the signal multiplexer 12. The signal multiplexing unit 12 multiplexes the inputs from the encoding modulation unit 10 and the encoding modulation unit 11 and outputs the multiplexed data as a frequency data block to the subcarrier mapping unit 13.

The subcarrier mapping unit 13 maps the frequency data block that is the output of the signal multiplexing unit 12 to a specific subcarrier (hereinafter referred to as subcarrier mapping), and outputs it to the IFFT unit 14. At this time, the subcarrier mapping unit 13 performs mapping using the subcarrier allocation information (number of subcarriers, subcarrier number, etc.) from the subcarrier allocation unit 23.

An IFFT (Inverse Fast Fourier Transform) unit 14 performs an inverse fast Fourier transform on the output of the subcarrier mapping unit 13 and outputs the result to the CP adding unit 15. The CP adding unit 15 adds CP (Cyclic) to the transmission data input from the IFFT unit 14.
A guard interval using Prefix) is inserted and output to the transmission radio unit 16.

The transmission radio unit 16 outputs the transmission data from the CP adding unit 65 to the optical transmitter 17 by up-converting the baseband frequency to the radio frequency. The optical transmitter 17 optically modulates the radio signal (downlink signal) from the transmission radio unit 16 to convert it into an optical signal, and transmits it to each antenna unit RAU0 to RAUn through the optical fiber cable OC1.

The optical receiver 18 receives an optical signal (a signal in which a radio signal is optical intensity modulated) transmitted from each of the antenna units RAU0 to RAUn through the optical fiber cable OC2, and uses the optical signal as an original radio signal (uplink signal). ). The reception radio unit 19 performs amplification processing, band limitation processing, and frequency conversion processing on the radio signal, and outputs the result as a complex baseband signal including an in-phase signal and a quadrature-phase signal.

The OFDM demodulator 20 performs OFDM demodulation on each input baseband signal. That is, after time and frequency synchronization processing, GI (Guard Interval) removal, FFT (Fast Fourier Transform) processing, and serial-parallel conversion processing are performed.

The pilot signal extraction unit 21 extracts the pilot signal transmitted from the mobile station from the reception signal input from the OFDM demodulation unit 20 and outputs the pilot signal to the reception quality measurement unit 22. The CQI extraction unit 26 extracts channel quality information (CQI: Channel Quality Information) transmitted from the mobile station from the received signal input from the OFDM demodulation unit 20 and outputs the channel quality information (CQI) to the subcarrier allocation unit 23.

The reception quality measurement unit 22 measures the reception quality for each subcarrier based on the output of the pilot signal extraction unit 21. Specifically, the reception quality measurement unit 22 measures the reception quality for each subcarrier using the pilot signal from the pilot signal extraction unit 21 and outputs it to the subcarrier allocation unit 23. As this reception quality, CIR (Carrier to Interferer Ratio) or SIR (Signal to Interferer Ratio), SNR (Signal
Use any measured value such as Noise Ratio).

The subcarrier allocation unit 23 allocates uplink subcarriers from each mobile station using the reception quality for each subcarrier measured by the reception quality measurement unit 22 (allocates frequency resources). Specifically, the subcarrier allocation unit 23 sets the number of subcarriers, the subcarrier number, and the like as the subcarrier allocation information. Here, subcarriers with high reception quality from each mobile station are assigned to each mobile station. Then, the subcarrier allocation unit 23 outputs uplink subcarrier allocation information from each mobile station to the subcarrier mapping unit 13 and the MCS determination unit 24.

Also, the subcarrier allocation unit 23 allocates downlink subcarriers to each mobile station (allocates frequency resources) using the CQI of each subcarrier extracted by the CQI extraction unit 26. Specifically, the subcarrier allocation unit 23 sets the number of subcarriers, the subcarrier number, and the like as the subcarrier allocation information. Here, subcarriers with good CQI (higher quality) from each mobile station are assigned to each mobile station. Then, the subcarrier allocation unit 23 outputs the subcarrier allocation information for the downlink to each mobile station to the subcarrier mapping unit 13 and the MCS determination unit 24.

Based on the subcarrier allocation information from the subcarrier allocation unit 23 and the information on the reception quality of each subcarrier, the MCS determination unit 24 performs modulation modulation for each subcarrier or for each subcarrier block in which a plurality of subcarriers are set. MCS (Modulation and Coding Schemes) information such as the number of values and code rate is adaptively selected and output to the control information generation unit 25. The control information generation unit 25 generates a control signal including MCS information and subcarrier allocation information, and outputs the control signal to the encoding modulation unit 10 as control information.

(2-2) Configuration of Antenna Unit RAU FIG. 3 shows only the internal configuration of antenna unit RAU0 among the plurality of antenna units RAU0 to RAUn, but other antenna units have the same configuration. . As shown in FIG. 3, the antenna unit RAU0 includes an antenna 30, a duplexer 31, an optical receiver 32, an amplifier 33 (for downlink signal), a filter 34 (for downlink signal), an amplifier 35 (for uplink signal), A filter 36 (for uplink signal) and an optical transmitter 37 are provided. The duplexer 31 (DPX) is provided to share the antenna 30 in the transmission / reception system.

The optical receiver 32 receives an optical signal transmitted from the central processing unit CU through the optical fiber cable OC1 (a signal obtained by modulating a radio intensity of the radio signal), and demodulates the optical signal into an original radio signal. The filter 34 is set so that a band through which the radio signal (downlink signal) amplified by the amplifier 33 is transmitted is a predetermined transmission band that is a part of the system band.

On the other hand, the radio signal received by the antenna 30 from the mobile station is amplified by the amplifier 35 and then input to the filter 36. The filter 36 is set so that the band that transmits the input radio signal (uplink signal) without being suppressed is a predetermined transmission band that is a part of the system band. The optical transmitter 37 converts the radio signal transmitted through the filter 36 into an optical signal by modulating the optical intensity, and outputs the optical signal to the central processing unit CU through the optical fiber cable OC2.

The

filters

34 and 36 are known BPFs (Band Pass Filters) and can be configured as digital filters or analog filters.

(2-3) Configuration of Mobile Station MS As shown in FIG. 4, the mobile station MS includes an antenna 50, a duplexer 51, a reception radio unit 52, an OFDM demodulation unit 53, a control information extraction unit 54, a demodulation / decoding unit 55, Carrier allocation information extraction unit 56, pilot signal extraction unit 57, MCS information extraction unit 58, CQI measurement unit 59, encoding modulation unit 60, encoding modulation unit 61, signal multiplexing unit 62, subcarrier mapping unit 63, IFFT unit 64 , A CP adding unit 65, a transmission radio unit 66, and a pilot signal generating unit 67. The duplexer 51 (DPX) is provided to share the antenna 50 in the transmission / reception system.

The encoding / modulation unit 60 performs predetermined error correction coding on user data consisting of a bit data sequence, and further uses a predetermined modulation multi-level modulation scheme (for example, QPSK, 16QAM, 64QAM modulation) to generate symbols. A data series signal is generated and output to the signal multiplexing unit 62. Here, the MCS information (Modulation and Coding Schemes) regarding the coding rate and the modulation multi-level number when performing error correction coding is an MCS information extraction unit that extracts MCS information from a control signal transmitted from the central processing unit CU. 58 based on the output of 58. This setting enables adaptive modulation according to the propagation path condition.

The encoding modulation unit 61 performs predetermined error correction encoding on the control information including the bit data sequence, and further uses a predetermined modulation multilevel modulation scheme (for example, BPSK modulation, QPSK modulation) to generate a symbol data sequence. Generate a signal. Here, the coding rate and the modulation multi-level number used for error correction coding are fixed in advance. Generally, since control information requires high-quality transmission, it is transmitted using a low coding rate by BPSK modulation or QPSK modulation.

The signal multiplexing unit 62 multiplexes the inputs from the

encoding modulation units

60 and 61 and outputs the multiplexed data as a frequency data block to the subcarrier mapping unit 63.

The subcarrier mapping unit 63 maps the frequency data block, which is the output of the signal multiplexing unit 62, to a specific subcarrier (hereinafter referred to as subcarrier mapping), and outputs it to the IFFT unit 64. At this time, the subcarrier mapping unit 63 performs mapping using the subcarrier allocation information (number of subcarriers, subcarrier number, etc.) extracted by the subcarrier allocation information extraction unit 56.

The IFFT unit 64 performs inverse fast Fourier transform on the output of the subcarrier mapping unit 63 and outputs the result to the CP adding unit 65. CP adding section 65 inserts a guard interval using CP (Cyclic Prefix) into the transmission data input from IFFT section 64 and outputs the result to transmission radio section 66. The transmission radio unit 66 radiates the transmission data from the CP adding unit 65 from the antenna 50 to the space by up-converting the baseband frequency to the radio frequency.

The reception radio unit 52 performs amplification processing, band limitation processing, and frequency conversion processing on the radio signal received by the antenna 50, and forms a complex baseband signal composed of an in-phase signal and a quadrature-phase signal. Output.

The OFDM demodulator 53 performs OFDM demodulation on each input baseband signal. That is, after time and frequency synchronization processing, GI (Guard Interval) removal, FFT (Fast Fourier Transform) processing, and serial-parallel conversion processing are performed.

The control information extraction unit 54 extracts control information from the central processing unit CU from the received signal input from the OFDM demodulation unit 53 and outputs the control information to the demodulation and decoding unit 55. This control signal includes subcarrier allocation information, pilot signals, and MCS information. The subcarrier allocation information extraction unit 56, pilot signal extraction unit 57, and MCS information extraction unit 58 are subcarrier allocation information, pilot signal, and MCS, respectively, from the control information demodulated and decoded by the demodulation and decoding unit 55. Extract information.

CQI measurement section 59 measures channel quality information (CQI) of each subcarrier based on the output of pilot signal extraction section 57. Specifically, CQI measurement unit 59 measures the CQI for each subcarrier using the pilot signal from pilot signal extraction unit 57 and outputs the CQI to signal multiplexing unit 62. CIR (Carrier based on pilot signal) as CQI
to Interferer Ratio), SIR (Signal to Interferer Ratio), SNR (Signal to Noise)
Any measured value such as Ratio) can be applied. The CQI of each subcarrier represents downlink signal quality for the mobile station. The CQI of each subcarrier is transmitted to the central processing unit CU, and is used for downlink subcarrier allocation to each mobile station.

The pilot signal generator 67 generates a pilot signal that is a signal sequence that is known in advance for the central processing unit CU, and outputs the pilot signal to the signal multiplexer 62. Here, the signal sequence used for the pilot signal is set based on the output of the pilot signal extraction unit 57.

3. Filter characteristics (3-1) Setting of filter characteristics (filter transmission band) In the wireless communication system of the embodiment, among the antenna units RAU0 to RAUn in the cell, the antenna of the micro cell near the cell boundary or close to the cell boundary. The characteristics of the unit filter 34 (for downlink signals) are such that the transmission band transmitted without suppressing the downlink signal is different from the transmission bands of other antenna units belonging to different cells that are close to each other across the cell boundary. It is set not to overlap. Similarly, the characteristics of the filter 36 (for uplink signal) of the antenna unit of the microcell in the vicinity of the cell boundary or in the vicinity of the cell boundary among the antenna units RAU0 to RAUn in the cell can suppress the uplink signal. The transmission band to be transmitted is set so as not to overlap with the transmission bands of other antenna units that are close to each other and belong to different cells across the cell boundary. That is, the filter characteristics of the proximity antenna units are set so as not to overlap.

The filter characteristics are set in order to reduce inter-cell interference between the antenna unit and the mobile station at the cell boundary. On the other hand, in the communication link in the same cell, interference is generally planned to be avoided by appropriate scheduling or the like. In this wireless communication system, setting of a filter for interference of the communication link in the same cell is planned. Is not considered. For example, there is no restriction on the filter characteristics of antenna units that are close together in the same cell.

As filter characteristics, a setting for suppressing (not completely blocking) a band other than the transmission band (hereinafter, filter setting FS1) and a setting for completely blocking a band other than the transmission band (hereinafter, filter setting FS2). You could think so. Either of these filter settings may be applied, but it is preferable to apply the filter setting FS2 to the uplink signal filter. This will be explained as follows when two mobile stations existing in close positions between adjacent cells are assumed.

That is, in the downlink, when the filter 34 (for downlink signal) is set to the filter setting FS2, the transmission power of a signal in a band other than the transmission band decreases in the antenna unit. The reach of is limited. That is, since radio waves do not reach the vicinity of the cell boundary, inter-cell interference (interference between downlink signals for each mobile station) is reduced unless the above-described transmission band overlap setting is made.

On the other hand, since no filter is set on the mobile station side in this wireless communication system, the transmission power itself of two mobile stations existing at positions close to each other in adjacent cells does not decrease in the uplink. Therefore, when the filter 36 (for the uplink signal) is set to the filter setting FS1 (a setting that does not completely cut off the band other than the transmission band), the distance between the two mobile stations is short. Interference can occur. From this viewpoint, it is preferable to apply the filter setting FS2 (setting for completely blocking bands other than the transmission band) to the uplink signal filter.

Note that the filter characteristics of the filter 34 (for downlink signal) and the filter 36 (for uplink signal) can be set separately according to the downlink band and the uplink band specified in the system, respectively. Further, a filter may be provided substantially only in either the downlink or the uplink (that is, either one is set to transmit all bands).

(3-2) Examples of filter characteristics in a multi-cell environment As described above, the filter characteristics of each antenna unit in a multi-cell environment are set in consideration of the following two requirements (requirement A and requirement B). It is determined.
(Requirement A) The filter characteristics (transmission bands that pass through without suppressing signals) of the proximity antenna units belonging to different cells do not overlap each other.
(Requirement B) There is no limitation on the filter characteristics of antenna units that are adjacent to each other in the same cell.

Hereinafter, setting examples of filter characteristics in a multi-cell environment will be described with reference to FIGS. FIG. 5 is a diagram illustrating the relationship between frequency and power spectral density (PSD) as a filter characteristic. FIG. 5A is a characteristic that transmits the entire system band (hereinafter referred to as a full band transmission characteristic), and FIG. Is a characteristic of transmitting only the band F1 without being suppressed in the system band (hereinafter referred to as F1 band transmission characteristic), and (c) is a characteristic of transmitting only the band F2 of the system band without being suppressed (hereinafter referred to as F2). (Band transmission characteristics) and (b) show characteristics (hereinafter referred to as F3 band transmission characteristics) that allow transmission without suppressing only the band F3 in the system band. 6 to 7 are diagrams showing the characteristics of the antenna unit RAU in three mutually adjacent cells C1 to C3. F0 to F3 described together with the antenna unit have filter characteristics of the antenna unit shown in FIG. a) to (d).

6 to 8, the cell C1 is provided with a central processing unit CU1 and a plurality of antenna units RAU10 to RAU16. The central processing unit CU1 and each antenna unit are connected by an optical fiber cable (not shown). Yes. The cell C2 is provided with a central processing unit CU2 and a plurality of antenna units RAU20 to RAU26, and the central processing unit CU2 and each antenna unit are connected by an optical fiber cable (not shown). The cell C3 is provided with a central processing unit CU3 and a plurality of antenna units RAU30 to RAU36, and the central processing unit CU3 and each antenna unit are connected by an optical fiber cable (not shown).

Here, in particular, attention is paid to the filter characteristics of the antenna units of the microcells adjacent to each other across the cell boundary, that is, the antenna units RAU12 to 14, the antenna units RAU24 to 26, and the antenna units RAU31 to 32,36.

First, FIG. 6 is an example in which the filter characteristics of each antenna unit are set such that the filter characteristics of the antenna units existing at the cell boundary of the same cell are the same and the filter characteristics are different between different cells. is there. For example, in FIG. 6, the antenna units RAU12 to 14 belonging to the cell C1 are all set to the F1 band transmission characteristics, and the antenna units RAU24 to 26 belonging to the cell C2 are all set to the F2 band transmission characteristics, and the antenna units RAU31 belonging to the cell C3. 32 to 36 are all set to F3 band transmission characteristics. Thereby, the transmission band of the proximity antenna unit of the adjacent micro cell across the cell boundary does not overlap (the above requirement A). The

antenna units RAU

10, 20, and 30 at the center of each cell do not need to consider inter-cell interference, so there is no limitation on the filter characteristics (requirement B above), and here the full-band transmission characteristics are used.

7 and 8 are examples in which the filter characteristics of each antenna unit are set when the filter characteristics of the antenna units existing at the cell boundary of the same cell can be different for each microcell.

In FIG. 7, the filter characteristic of the antenna unit RAU13 belonging to the cell C1 is the F1 band transmission characteristic, and the filter characteristic of the antenna unit RAU31 adjacent to the antenna unit RAU13 across the cell boundary is the F3 band transmission characteristic. Further, the filter characteristics of the antenna unit RAU13 belonging to the cell C1 and the antenna unit RAU25 of the other cell C2 adjacent to the antenna unit RAU31 belonging to the cell C3 across the cell boundary are F2 band transmission characteristics. Thereby, the transmission bands of the proximity antenna units RAU13, RAU31, and RAU25 between the three cells do not overlap (the above requirement A).

At this time, for example, the antenna unit RAU14 of the cell C1 has the F3 band transmission characteristic as a filter characteristic different from the antenna unit RAU36 (F2 band transmission characteristic) that is adjacent to each other across the cell boundary. As a result, the antenna unit RAU14 has a filter characteristic that is different from the antenna unit RAU13 (F1 band transmission characteristic) that is adjacent in the same cell.

Similarly, the filter characteristics of other antenna units are set. The

antenna units RAU

In FIG. 8, the filter characteristic of the antenna unit RAU13 belonging to the cell C1 is the F1 band transmission characteristic, and the filter characteristic of the antenna unit RAU31 adjacent to the antenna unit RAU13 across the cell boundary is the F2 band transmission characteristic. Further, the filter characteristics of the antenna unit RAU13 belonging to the cell C1 and the antenna unit RAU25 of another cell C2 adjacent to the antenna unit RAU31 belonging to the cell C3 across the cell boundary are F3 band transmission characteristics. Thereby, the transmission bands of the proximity antenna units RAU13, RAU31, and RAU25 between the three cells do not overlap (the above requirement A).

At this time, for example, the antenna unit RAU14 of the cell C1 has the F2 band transmission characteristic as a filter characteristic different from the antenna unit RAU36 (F3 band transmission characteristic) that is adjacent to each other across the cell boundary. As a result, the antenna unit RAU14 has a filter characteristic that is different from the antenna unit RAU13 (F1 band transmission characteristic) that is adjacent in the same cell.

Similarly, the filter characteristics of other antenna units are set. The

antenna units RAU

Note that the antenna unit filters (for downlink signals and uplink signals) do not need to be provided for all antenna units in the cell, and are located near the cell boundary where they are severely positioned against inter-cell interference. It is only necessary to provide the antenna unit. Further, even when the filter is provided for all antenna units in the cell, it can be set so that the transmission band becomes wider as the distance from the cell boundary increases. This is because an antenna unit closer to the center of the cell is more advantageous for inter-cell interference.

4). Operation Example of Radio Communication System Next, the operation of the radio communication system according to the present embodiment will be described with reference to FIG. FIG. 9 is a diagram illustrating communication between an antenna unit of a micro cell adjacent between cells and a mobile station.

In FIG. 9, RAU 13 and RAU 31 (see FIG. 6 or FIG. 7) as an example of antenna units of microcells adjacent between cells, and central processing units CU1 and CU3 connected to each antenna unit by an optical fiber cable, Mobile stations MS1 and MS3 that perform wireless communication with each antenna unit are shown. Further, as shown in the figure, the filter characteristics of the antenna units RAU13 and RAU31 are an F1 band transmission characteristic and an F3 band transmission characteristic, respectively. In the following description, it is assumed that the higher the CQI value as quality information, the better (higher quality).

(4-1) Downlink Operation In FIG. 9, the antenna unit RAU13 demodulates the optical signal transmitted from the central processing unit CU1 into an original radio signal, and performs filtering of F1 band transmission characteristics on the radio signal. Apply. When receiving a radio signal from the antenna unit RAU13, the mobile station MS1 extracts a pilot signal included in each subcarrier and measures the CQI of each subcarrier. Here, since the signal of the band other than the band F1 is attenuated in the radio signal from the antenna unit RAU13, in the measurement of CQI in the mobile station MS1, the CQI of the subcarrier corresponding to the band F1 becomes high, and the band F1 The CQI of the subcarriers in the bands other than is low.

The CQI of each subcarrier measured by the mobile station MS1 is mapped to the uplink signal together with the pilot signal of each subcarrier and fed back to the central processing unit CU1.

In the central processing unit CU1, the CQI of each subcarrier is extracted based on the uplink signal from the mobile station MS1, and this CQI is reflected in the assignment of the downlink subcarrier to the mobile station MS1 (frequency resource assignment). Is done. In the example shown in FIG. 9, the CQI of the subcarrier corresponding to the band F1 is high, and the CQI of the subcarrier in the band other than the band F1 is low. For this reason, the central processing unit CU1 allocates subcarriers corresponding to the band F1 to the downlink addressed to the mobile station MS1.

As a result of the same operation, in the central processing unit CU3, a subcarrier corresponding to the band F3 is assigned to the downlink addressed to the mobile station MS3. Accordingly, the subcarrier frequencies of the downlink signals for mobile stations MS1 and MS3 existing in different adjacent cells are separated from each other, and interference is avoided.

In the case of the downlink, inter-cell interference is suppressed even if frequency resources are not allocated on the central processing unit CU side. That is, in FIG. 9, the received signals of the mobile stations MS1 and MS3 are not related to the frequency resource allocation in the central processing unit CU because the bands other than the bands F1 and F3 are suppressed or blocked, respectively. , Downlink signal interference to the mobile stations MS1 and MS3 is suppressed. However, it is preferable to assign frequency resources by the central processing unit CU in order to reliably avoid interference because the subcarriers assigned to the mobile stations MS1 and MS3 are reliably distinguished.

(4-2) Uplink Operation As described above, the mobile station MS1 maps the pilot signal of each subcarrier together with the CQI of each subcarrier to the uplink signal. Based on this pilot signal, the central processing unit CU1 measures (evaluates) the reception quality of each subcarrier of the uplink signal from the mobile station MS1. That is, the central processing unit CU1 extracts the pilot signal of each subcarrier from the uplink signal from the mobile station MS1, and based on this pilot signal, the reception quality (for example, signal power to interference power ratio) of each subcarrier. SIR) is measured.

The measurement result of the reception quality of each subcarrier is reflected in the subcarrier allocation (frequency resource allocation) to the uplink from the mobile station MS1. In the example shown in FIG. 9, the reception quality of subcarriers corresponding to the band F1 is high, and the reception quality of subcarriers in bands other than the band F1 is low. For this reason, the central processing unit CU1 allocates subcarriers corresponding to the band F1 to the uplink from the mobile station MS1.

As a result of the same operation, the central processing unit CU3 allocates a subcarrier corresponding to the band F3 for the uplink from the mobile station MS3. Therefore, the subcarrier frequencies of the uplink signals from mobile stations MS1 and MS3 existing in different adjacent cells to each antenna unit are separated from each other, and interference is avoided.

In this case, the filter characteristics of the filters (for uplink signals) of the antenna units RAU13 and RAU31 are preferably FS2 characteristics (setting for completely blocking bands other than the transmission band) as described above. Thereby, the inter-cell interference in the uplink from the mobile stations MS1 and MS3 is further reduced.

Claims

A wireless communication system including a plurality of antenna devices distributed in each cell and performing wireless communication with a mobile station, and a signal processing device connected to each of the plurality of antenna devices,
Proximity antenna devices that are close to each other across cell boundaries and belong to different cells have a filter in which a transmission band that allows transmission without transmitting a downlink signal is set in the system band,
The transmission band of each filter of the proximity antenna device is set not to overlap,
Wireless communication system.
The signal processing device includes:
Allocation of downlink signal frequency resources to the mobile station based on quality information for each of a plurality of bands that divide the system band, which is information included in an uplink signal from the mobile station;
The wireless communication system according to claim 1.
The plurality of antenna devices have a filter in which a transmission band that allows transmission without suppressing a downlink signal is set in the system band,
The transmission band set for each filter of the plurality of antenna devices is set to become wider as the distance from the cell boundary increases.
The wireless communication system according to claim 1 or 2.
A wireless communication system including a plurality of antenna devices distributed in each cell and performing wireless communication with a mobile station, and a signal processing device connected to each of the plurality of antenna devices,
Proximity antenna devices that are close to each other across cell boundaries and belong to different cells have a filter in which a transmission band for transmitting uplink signals without being suppressed is set in the system band,
It is set so that the transmission band of each filter of the proximity antenna device does not overlap,
The signal processing device is a signal included in an uplink signal from a mobile station, and evaluates the signal quality of each band based on a reference signal for each of a plurality of bands dividing the system band, Assigns uplink signal frequency resources to mobile stations,
Wireless communication system.
The filter blocks bands other than the transmission band for uplink signals.
The wireless communication system according to claim 4.
A wireless communication method between a plurality of antenna devices distributed in each cell and performing wireless communication with a mobile station, and a signal processing device connected to each of the plurality of antenna devices in the cell,
Among the proximity antenna devices that are close to each other across the cell boundary and belong to different cells, the first antenna device limits the transmission band of the system band without suppressing the downlink signal to the first transmission band,
Among the adjacent antenna devices, the second antenna device restricts a band to be transmitted without suppressing a downlink signal to a second transmission band that does not overlap with the first transmission band,
The signal processing apparatus for each cell is a downlink signal for the mobile station based on information included in an uplink signal from the mobile station and quality information for each of a plurality of bands that divide the system band. Frequency resource allocation,
Wireless communication method.
A wireless communication method between a plurality of antenna devices distributed in each cell and performing wireless communication with a mobile station, and a signal processing device connected to each of the plurality of antenna devices in the cell,
Among the proximity antenna devices that are close to each other across the cell boundary and belong to different cells, the first antenna device limits the band to be transmitted without suppressing the uplink signal in the system band to the third transmission band,
Of the proximity antenna devices, the second antenna device restricts a band to be transmitted without suppressing an uplink signal to a fourth transmission band that does not overlap with the third transmission band,
The signal processing device for each cell evaluates the signal quality of each band based on a reference signal for each of a plurality of bands that are signals included in an uplink signal from a mobile station and divides the system band. Assign frequency resources of uplink signals to the mobile station,
Wireless communication method.
The first antenna device blocks a band other than the third transmission band for an uplink signal, and the second antenna device blocks a band other than the fourth transmission band for an uplink signal;
The wireless communication method according to claim 7.