JP5091020B2 - Wireless communication system, base station, management server, and wireless communication method - Google Patents

Description

  The present invention relates to a radio communication system, a base station, a management server, and a radio communication method capable of radio communication using the OFDMA scheme.

  In recent years, communication terminals represented by PHS (Personal Handy phone System) and mobile phones have become widespread, making it possible to make calls and obtain information regardless of location or time. Especially in recent years, the amount of available information has been increasing, and high-speed and high-quality wireless communication systems have been introduced to download large amounts of data.

  In such wireless communication, it is necessary to duplicate signals in order to transmit and receive. Typical duplexing methods include TDD (Time Division Duplex) that switches between transmission and reception by time division and FDD (Frequency Division Duplex) that duplexes transmission and reception by changing the frequency. In addition, as a method for multiple access to communicate with a plurality of communication terminals at the same time, TDMA (Time Division Multiple Access) for switching a plurality of communication terminals by time division, FDMA (Frequency) for dividing a frequency band Typical examples include Division Multiple Access (frequency division multiple access) and CDMA (Code Division Multiple Access) that multiplies a different code for each communication terminal.

  In such wireless communication, a channel (frequency channel) of a predetermined frequency band is assigned to each base station so as not to cause interference with neighboring base stations. Specifically, a predetermined frequency channel is assigned to the base station so that the same frequency band as that of the adjacent base station is not used. As a method for assigning frequency channels to base stations, dynamic frequency assignment (DCA: hereinafter referred to simply as DCA) is widely used.

  DCA is a technology that dynamically determines the frequency channel to be assigned to each base station according to the traffic of each base station. As long as the required communication quality is satisfied, all frequency channels used by the wireless communication system are , It becomes selectable in all base stations.

Moreover, various techniques have been proposed as techniques for assigning frequency channels to base stations more flexibly. For example, in Patent Document 1, the number of groups to which each base station belongs is determined based on interference between base stations, and the group to which each base station belongs is determined so that the shortest distance between base stations belonging to the same group is constant. Then, the frequency band allocated to the base stations belonging to the determined group is determined for each group, and a different frequency band is allocated for each group. Thereby, the flexibility of frequency channel allocation control for each base station can be improved.
JP 2005-27189 A

  By the way, there are ARIB (Association of Radio Industries and Businesses) STD T95 and PHS MoU (Memorandum of Understanding) as next-generation PHS communication standards enabling high-speed digital communication. In such communication standards, OFDMA / TDMA TDD Broadband The Wireless Access System (next generation PHS system) is being formulated.

  OFDMA (Orthogonal Frequency Division Multiple Access) performs multiple access in OFDM (Orthogonal Frequency Division Multiplexing). OFDM is a method developed from FDM (Frequency Division Multiple), which divides a carrier signal into a large number of subcarriers on the frequency axis and orthogonalizes the phase of a signal wave between adjacent subcarriers. This is a method of effectively using the frequency band by partially overlapping the subcarrier bands. In OFDM, all subcarriers are occupied by one communication terminal, but in OFDMA, several subcarriers (for example, 24) are grouped to form a subchannel, and a plurality of communication terminals share all subchannels. Multiple access. For example, the sub-channel divides the frequency band of 18 MHz into 20 pieces.

  Further, in the next generation PHS system, in addition to OFDMA, multiple access by TDMA is performed. TDMA is a system in which a frequency is divided into a plurality of time slots on a time axis and communication is performed with a plurality of opponents. At present, it is assumed that the uplink (Up Link: communication terminal to base station) and the downlink (Down Link: base station to communication terminal) are each divided into four. That is, in the next generation PHS system, communication blocks are subdivided on both the frequency axis and the time axis, and communication is efficiently performed by dynamically allocating communication blocks to a large number of communication terminals. A communication block determined by one time slot in one subchannel is referred to as PRU (Physical Resource Unit), and it is assumed that 36 to 40 PRUs are used per base station. .

  As described above, the base station can use 20 subchannels, one of which is used as a control channel (CCH), and the remaining subchannels are dynamically used for communication terminals using DCA. Assign to. An anchor channel or an extra channel is allocated to the PRU included in the subchannel used for communication. One anchor channel is assigned to each communication terminal, and includes a map of PRUs to which an extra channel for the communication terminal is assigned. An extra channel is a channel that actually contains data, and a plurality of extra channels are assigned to one communication terminal in accordance with the amount of data and communication status. The notification of the extra channel assignment by the map included in the anchor channel is referred to as FM-mode (Fast access channel based on Map-Mode).

  The anchor channel is assigned to the PRU having the best communication quality obtained by performing carrier sense on all PRUs. The extra channel is basically not subjected to carrier sense. However, when the base station newly uses a PRU that is not performing communication, the extra channel is assigned after performing carrier sense. Thus, since the base station can dynamically change the position and number of extra channels via the anchor channel, it is possible to transmit and receive a large amount of data at high speed.

  However, in the OFDMA / TDMA TDD system, the communication status and the distance from the base station are different for each communication terminal, and the modulation method, power, and delay amount may differ accordingly, so that interference occurs between adjacent PRUs. There is a case. As for the delay amount, interference can be effectively prevented by a guard band in TDMA. However, since the frequency bands of subcarriers are overlapped in OFDMA, if the modulation method or power is greatly different, it is affected by the radio waves of PRUs adjacent in the frequency direction.

  Further, unlike the conventional TDMA-TDD system, the OFDMA / TDMA TDD system has a limited number of subchannels, and as a result of carrier sensing, all PRUs may not be allocated.

  When the PRU allocation control is attempted using the technique of Patent Document 1 described above, there is a limit to the frequency band that can be used in the group, so even if there is a PRU in the vacant frequency band, it is vacant. If the frequency band is not assigned to the group to which the base station belongs, it cannot be used. Therefore, communication cannot be established if the PRU in the frequency band assigned to the group to which the base station belongs cannot be used due to interference from neighboring base stations.

  In view of such a problem, the present invention, when the base station performs carrier sense, as a result of not being able to allocate all the PRUs, by notifying the surrounding base stations to that effect, It is an object of the present invention to provide a radio communication system, a base station, a management server, and a radio communication method that can suppress interference and can reliably establish communication.

  In order to solve the above problems, a typical configuration of the present invention includes a first base station that performs radio communication with a communication terminal using the OFDMA scheme, one or more second base stations, and the first base station. And a management server for managing the second base station, wherein the first base station has a PRU that can be used by performing carrier sense in response to a communication establishment request from a communication terminal. A carrier sense determination unit that determines whether or not the carrier sense determination unit determines that there is no PRU that can be used, and an NG notification unit that notifies the management server of carrier sense failure information including information on a predetermined PRU that is not available When the release PRU information including the information of the PRU released by the second base station or the power reduced is notified from the management server, the PRU indicated by the released PRU information is communicated. The management server includes information indicating that the second base station is requested to release a predetermined PRU when the carrier sense failure information is notified from the first base station. A release request notification unit that notifies a channel release request, and a server notification unit that notifies the first base station of the release PRU information when the release PRU information is notified from the second base station; When the channel release request is notified from the management server, the base station in the base station can determine whether or not the predetermined PRU included in the channel release request can be released, and the predetermined PRU can be released. In some cases, the predetermined PRU is released, and when the predetermined PRU is not releasable, the PRU release unit that lowers the power of the predetermined PRU, and the PRU released by the PRU release unit or reduced in power And PRU notifying unit for notifying the release PRU information including information to the management server, characterized in that it comprises a.

  With this configuration, when the base station (first base station) cannot allocate a PRU to a communication terminal due to interference from a neighboring base station (second base station), the management server uses it for the second base station. A request to release the PRU in the middle is made. Furthermore, since the second base station notified of the release request releases the PRU or lowers the power of the PRU, the interference from the second base station to the PRU of the first base station can be reduced. .

  Therefore, even if all the PRUs cannot be allocated due to interference from a neighboring base station (second base station), it is possible to reliably establish communication without performing handover to another base station. It becomes.

  The management server of the wireless communication system further includes a map indicating the position of the PRU used by the first and second base stations managed by the management server, and the release request notification unit of the management server is connected via the map. Then, the channel release request may be notified using the base station using the predetermined PRU included in the carrier sense failure information from the first base station as the second base station.

  With the configuration in which the management server includes the map, the release request notification unit of the management server notifies the channel release request only to the base station using the predetermined PRU included in the carrier sense failure information from the first base station. It will be. Therefore, the channel release request is not unnecessarily transmitted to the base station that does not use the PRU included in the channel release request.

  The release request notification unit of the management server of the wireless communication system may notify a channel release request with a base station within a predetermined range from the first base station as a second base station.

  With this configuration, a channel release request can be notified only to a base station that is within a predetermined range that is estimated to be causing interference to the first base station.

  Here, “within a predetermined range” means that a communication quality value or the like is measured in advance between base stations, even if the communication terminal is a predetermined location registration area that is uniquely determined when a location registration is performed, It may be within a certain range.

  The PRU determination unit of the second base station determines that the predetermined PRU included in the channel release request is releasable when an extra channel is assigned, and is not releasable when an anchor channel is assigned. May be determined.

  Since only one anchor channel is allocated to each communication terminal and includes information (map) on the number and position of extra channels, communication itself is impossible if the anchor channel cannot be used. Therefore, the PRU determination unit determines that it cannot be released when an anchor channel is assigned to a predetermined PRU.

  On the other hand, an extra channel is a channel that actually includes data, and a plurality of extra channels are assigned to one communication terminal according to the amount of data and communication status. Therefore, even if the extra channel assigned to one PRU is released, the data communication speed is slightly reduced. Therefore, the PRU determination unit determines that the predetermined PRU can be released when an extra channel is allocated.

  The PRU release unit of the second base station may reduce the power of the PRU that cannot be released to a minimum value. Thereby, interference with the first base station can be suppressed to the maximum.

  In order to solve the above problems, another typical configuration of the present invention is a base station that performs radio communication with a communication terminal using the OFDMA scheme, and performs carrier sense in response to a communication establishment request from the communication terminal. Carrier sense determination unit that determines whether there is an available PRU, and carrier sense failure information including information on a predetermined PRU that is not available when the carrier sense determination unit determines that there is no PRU available. When the NG notification unit that notifies the management server that manages the base station and the release PRU information that includes information on the PRU that has been released at another base station or has been powered down from the management server, A channel allocation unit that allocates a PRU indicated by the released PRU information to a communication terminal.

  In order to solve the above-described problem, another typical configuration of the present invention is a base station that performs radio communication with a communication terminal using the OFDMA scheme, and from a management server that manages the base station to another base station A PRU determination unit that determines whether or not a predetermined PRU included in the channel release request is releasable when a channel release request including information to request the release of the predetermined PRU is notified from A PRU that releases the predetermined PRU when the PRU is releasable, and a PRU release unit that lowers the power of the predetermined PRU when the predetermined PRU is not releasable, and a PRU that the PRU release unit releases or reduces the power And a PRU notification unit for notifying the management server of released PRU information including the above information.

  In order to solve the above problems, another exemplary configuration of the present invention is a management server that manages a first base station and a second base station that perform radio communication with a communication terminal using an OFDMA scheme. When a carrier sense failure information including information on a predetermined PRU that cannot be used is notified from the first base station, a channel release request including information requesting the second base station to release the predetermined PRU A release request notification unit that notifies the release PRU information, and a server notification unit that notifies the first base station of the release PRU information when the release PRU information is notified from the second base station.

  In order to solve the above-described problem, another exemplary configuration of the present invention includes a first base station that performs radio communication with a communication terminal using an OFDMA scheme, a second base station, and the first and first base stations. Whether or not there is a PRU that can be used by performing carrier sense in response to a communication establishment request from a communication terminal, using a wireless communication method using a management server that manages two base stations If the management server determines that there is no PRU that can be used, the management server notifies the management server of carrier sense failure information including information on a predetermined PRU that cannot be used, and the management server notifies the carrier sense failure information from the first base station. Is notified, the second base station is notified of a channel release request including information indicating that the predetermined PRU is requested to be released, and the second base station is notified of the channel release request from the management server. , The channel It is determined whether or not the predetermined PRU included in the release request is releasable. If the predetermined PRU is releasable, the predetermined PRU is released. If the predetermined PRU is not releasable, the predetermined PRU When the release PRU information including the information of the PRU with the power reduced and released or with the power reduced is notified to the management server, and the release PRU information is notified from the second base station, the management server The released PRU information is notified to the station, and the first base station is notified of the released PRU information including information on the PRU released by the second base station or the power reduced from the management server. In this case, the PRU indicated by the released PRU information is allocated to the communication terminal.

  The component corresponding to the technical idea in the radio | wireless communications system mentioned above and its description are applicable also to the said base station, a management server, and a radio | wireless communication method.

  As described above, in the wireless communication system of the present invention, even if all the PRUs cannot be allocated as a result of the carrier sense performed by the base station (first base station), the fact that the neighboring base stations (the first base station) 2 base station), interference from neighboring base stations can be suppressed, and communication can be reliably established.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  Communication terminals such as PHS terminals and mobile phones construct a wireless communication system that performs wireless communication with base stations that are fixedly arranged at predetermined intervals. Here, the entire wireless communication system will be described first, and then specific configurations of the base station and the management server will be described. In the present embodiment, a PHS terminal is cited as a communication terminal. However, the present invention is not limited to such a case. Various electronic devices capable of wireless communication such as game devices, DVD players, and remote controllers can also be used as communication terminals.

(Wireless communication system 100)
FIG. 1 is an explanatory diagram showing a schematic connection relationship of the wireless communication system 100. The wireless communication system 100 includes PHS terminals 110A and 110B having a common configuration, first base stations 120A and 120B having a similar configuration, second base stations 130A and 130B having a similar configuration, ISDN ( (Integrated Services Digital Network) including a communication network 140 constituted by a line, the Internet, a dedicated line, etc., a relay server 150, and a management server 160.

  In the wireless communication system 100, when a user connects a communication line from his / her PHS terminal 110A to another PHS terminal 110B, the PHS terminal 110A establishes communication with the first base station 120A within the communicable range. Make a request (wireless connection request). The first base station 120A that has received the communication establishment request requests the relay server 150 to establish a communication connection with the communication partner via the communication network 140, and the relay server 150 refers to the location registration information of the PHS terminal 110B and refers to the PHS terminal 110B. For example, the first base station 120B within the wireless communication range of the terminal 110B is selected to secure a communication path between the first base station 120A and the first base station 120B, and the communication between the PHS terminal 110A and the PHS terminal 110B. Establish.

  In such a wireless communication system 100, various techniques are employed to improve the communication speed and communication quality between the PHS terminal 110A and the first base station 120A or the PHS terminal 110B and the first base station 120B. . In the present embodiment, for example, next-generation PHS communication technologies such as ARIB STD T95 and PHS MoU are adopted, and wireless communication based on the OFDMA / TDMA-TDD scheme is executed between the PHS terminal and the base station.

  In the present embodiment, the first base station 120A that has received the communication establishment request from the PHS terminal 110A performs carrier sense and determines whether there is an assignable PRU. At this time, if the first base station 120A that establishes communication with the PHS terminal 110A receives interference from the second base stations 130A and 130B, it is determined that all PRUs cannot be allocated as a result of performing carrier sense. There is a case. Therefore, the first base station 120A notifies the second base stations 130A and 130B through the management server 160 that all PRUs cannot be allocated due to interference, and the second base stations 130A and 130B. By performing a predetermined operation, it becomes possible to suppress interference from the second base stations 130A and 130B, and to establish communication reliably.

  Hereinafter, the management server 160 that manages the first base stations 120A and 120B, the second base stations 130A and 130B, and the first base stations 120A and 120B and the second base stations 130A and 130B in the wireless communication system 100. The specific configuration and operation of will be described. In the following description, the PHS terminal 110A and the PHS terminal 110B have the same configuration, and therefore will be described using the PHS terminal 110A as a representative.

  In the following embodiments, since the first base stations 120A and 120B have the same configuration, the configuration of the first base station 120A will be described as a representative, and the second base stations 130A and 130B have the same configuration. Therefore, the configuration of the second base station 130A will be described as a representative.

  Further, in the present embodiment, the first base station 130A and the second base station 130A will be described as separate bodies, but both may have both functions and configurations.

(First base station 120A)
FIG. 2 is a block diagram showing a schematic configuration of the first base station 120A. The first base station 120A includes a first base station control unit 210, a base station memory 212, a base station wireless communication unit 214, and a base station wired communication unit 216.

  The first base station control unit 210 manages and controls the entire first base station 120A by a semiconductor integrated circuit including a central processing unit (CPU). Further, the first base station control unit 210 controls communication connection of the PHS terminal 110A to the communication network 140 and other PHS terminals using a program in the base station memory 212. The base station memory 212 includes a ROM, a RAM, an EEPROM, a nonvolatile RAM, a flash memory, an HDD, and the like, and stores a program processed by the first base station control unit 210, time information, and the like.

  The base station wireless communication unit 214 establishes communication with the PHS terminal 110A and transmits / receives data. The base station wired communication unit 216 can be connected to various servers including the relay server 150 and the management server 160 via the communication network 140.

  In the present embodiment, the first base station control unit 210 also functions as a carrier sense determination unit 220, an NG notification unit 222, and a channel allocation unit 224.

  The carrier sense determination unit 220 performs carrier sense in response to a communication establishment request from the PHS terminal 110A and determines whether there is an available PRU.

  FIG. 3 is an explanatory diagram for explaining a frame configuration according to the present embodiment. OFDMA / TDMA has a two-dimensional map in the time axis direction and the frequency direction. A plurality of subchannels are arranged with a uniform baseband distance in the frequency axis direction, and a PRU is arranged for each time slot (TDMA slot) in each subchannel.

  When there is a communication establishment request from the PHS terminal 110A that has not yet performed communication, the carrier sense determination unit 220 performs carrier sense for PRUs that are not currently in use among all PRUs.

  When the carrier sense determination unit 220 determines that there is no usable PRU as a result of the carrier sense determination unit 220 performing carrier sense, the NG notification unit 222 indicates the carrier sense failure information including that fact and information on a predetermined PRU that is not available. The management server 160 is notified via the station wired communication unit 216.

  The predetermined PRU that cannot be used in the present embodiment is a PRU that is closest to the threshold (has the smallest interference) as a result of carrier sense performed by the carrier sense determination unit 220, but is not limited thereto, and is not limited to this. A plurality of PRUs may be used.

  The channel allocation unit 224 receives the released PRU information including information on the PRU released by the second base station 130A or 130B giving interference, or the power of which has been reduced, notified from the management server 160. When received via the station wired communication unit 216, the PRU indicated by the released PRU information is allocated to the PHS terminal 110A.

(Second base station 130A)
FIG. 4 is a block diagram showing a schematic configuration of the second base station 130A. Note that components having substantially the same functions as those of the first base station 120A described above are denoted by the same reference numerals and description thereof is omitted. The second base station 130A includes a second base station control unit 310, a base station memory 212, a base station wireless communication unit 214, and a base station wired communication unit 216.

  The second base station control unit 310 manages and controls the entire base station 120 using a semiconductor integrated circuit including a central processing unit (CPU). In addition, the second base station control unit 310 controls communication connection of the PHS terminal 110A to the communication network 140 and other PHS terminals using a program in the base station memory 212.

  In the present embodiment, the second base station control unit 310 also functions as a PRU determination unit 320, a PRU release unit 322, and a PRU notification unit 324.

  The PRU determination unit 320 is included in the channel release request when the second base station 130A, which is its own station, interferes with the PRU of the first base station 120A and the channel release request is notified from the management server 160. It is determined whether or not the PRU included in the predetermined PRU used by the second base station 130 </ b> A that is its own station can be released.

  In the present embodiment, the PRU determination unit 320 determines that the predetermined PRU included in the channel release request is not releasable when an anchor channel is allocated, and determines that it is releasable when an extra channel is allocated. To do.

  FIG. 5 is an explanatory diagram for explaining a channel configuration according to the present embodiment. A control channel (CCH) 350 is assigned to a predetermined subchannel of the PRU, and an anchor channel (ANCHor CHannel, hereinafter referred to as ANCH) 352 relating to a control signal for each PHS terminal already communicating with the second base station 130A. In addition, an extra channel (hereinafter referred to as EXCH) 354 for storing data is allocated. For example, in FIG. 3, one ANCH 352 and seven EXCHs 354 (354a to 354g) are allocated to the PHS terminal 110A.

  The ANCH 352 is an FM-Mode control signal. For example, a map indicating the allocation information of the EXCH 354, a timing control bit, a transmission output control bit, and HARQ (Hybrid Automatic Repeat reQuest) data arrival which is one of automatic retransmission requests It includes an ACK bit for notifying whether or not it is possible. Since only one ANCH 352 is assigned to each PHS terminal, if the ANCH 352 is released, communication with the PHS terminal 110A itself becomes impossible. Therefore, the PRU determination unit 320 determines that the release is not possible when the ANCH 352 is assigned to the predetermined PRU included in the channel release request.

  On the other hand, the EXCH 354 is a channel that actually includes data, and a plurality of EXCHs 354 (354a to 354g in the present embodiment) are assigned to one PHS terminal 110A according to the data amount and communication status. Therefore, even if the PRU (for example, EXCH 354e) included in the channel release request is released, the data communication speed is slightly reduced. Therefore, the PRU determination unit 320 determines that the release is possible when the EXCH 354 is assigned to the predetermined PRU included in the channel release request.

  In the present embodiment, the PRU determination unit 320 further determines whether there is an EXCH 354 assigned to the PHS terminal 110A other than the predetermined PRU included in the channel release request. In FIG. 5, there are seven EXCHs 354 assigned to the PHS terminal 110A, EXCHs 354a to 354g. However, if the EXCH 354 is assigned only to a predetermined PRU included in the channel release request, the PRU determination unit 320 can be released. It can also be determined that it is not.

  In the present embodiment, the PRU determination unit 320, when the EXCH 354 is assigned to a predetermined PRU included in the channel release request and the EXCH 354 used by the PHS terminal 110A is also assigned to other PRUs, Although it is determined that it can be released, the present invention is not limited to this, and even if a plurality of EXCHs 354 are assigned to the PHS terminal 110A, it may be determined that the release is not possible.

  The PRU release unit 322 releases the predetermined PRU when the predetermined PRU can be released, and reduces the power of the predetermined PRU to an allowable minimum value when the predetermined PRU cannot be released. Thereby, the interference to the first base station 120A to which interference is given can be minimized.

  In the present embodiment, the PRU release unit 322 reduces the power of the PRU that has been determined not to be released by the PRU determination unit 320 to the allowable minimum value, but is not limited to this, and the interference to the first base station 120A The power may be reduced to such an extent that interference does not become a problem for communication in the first base station 120A, that is, can be assigned when carrier sensing is performed.

  The PRU notification unit 324 notifies the management server 160 of the released PRU information including information on the PRU released by the PRU release unit 322 or reduced in power via the base station wired communication unit 216.

(Management server 160)
FIG. 6 is a block diagram illustrating a schematic configuration of the management server 160. The management server 160 includes a server control unit 410, a server memory 412, and a server communication unit 414.

  The server control unit 410 manages and controls the entire management server 160 by a semiconductor integrated circuit including a central processing unit (CPU). In addition, the server control unit 410 manages the first base station 120A and the second base station 130A via the communication network 140 using the program in the server memory 412 and establishes communication connection with the relay server 150. Or control.

  The server memory 412 includes a ROM, a RAM, an EEPROM, a nonvolatile RAM, a flash memory, an HDD, and the like, and stores a program processed by the server control unit 410, time information, and the like. In the present embodiment, the server memory 412 also stores a map 416 indicating the positions of PRUs used by the first base station 120A and the second base station 130A managed by the management server 160.

  The server communication unit 414 can be connected to various servers including the first base station 120A and the second base station 130A, the relay server 150, and the like via the communication network 140.

  In this embodiment, the server control unit 410 also functions as a release request notification unit 420 and a server notification unit 422.

  When the carrier sense failure information is notified from the first base station 120A that has received interference from the second base station 130A and cannot establish communication with the PHS terminal 110A, the release request notification unit 420 receives the interference via the map 416. A channel release request is notified to the second base stations 130A and 130B using the predetermined PRU included in the carrier sense failure information from the first base station 120A.

  Thereby, the release request notifying unit 420 notifies the channel release request only to the second base stations 130A and 130B using the predetermined PRU included in the carrier sense failure information from the first base station 120A. It becomes. Therefore, the channel release request is not unnecessarily transmitted to the second base station that does not use the PRU included in the channel release request.

  In the present embodiment, the release request notification unit 420 notifies the channel release request only to the second base stations 130A and 130B using the predetermined PRU included in the carrier sense failure information via the map 416. However, the present invention is not limited to this, and the channel release request may be notified from the first base station 120A to the second base station within a predetermined range.

  Thereby, it is possible to notify the channel release request only to the second base station within a predetermined range that is estimated to be causing interference to the first base station 120A. Here, “within a predetermined range” means that a communication quality value or the like is measured in advance between base stations, even if a predetermined position registration area uniquely determined when the PHS terminal 110A performs position registration, May be within a certain range.

  The server notifying unit 422 receives the released PRU information including the information of the PRU released from the second base stations 130A and 130B or reduced in power, via the server notifying unit 422, the first base station 120A is notified of the released PRU information.

  In the wireless communication system 100 described above, when the first base station 120A cannot allocate a PRU to the PHS terminal 110A due to interference from the predetermined second base stations 130A and 130B in the vicinity, the management server 160 The base station 130A, 130B will be requested to release the PRU in use. Further, since the second base stations 130A and 130B notified of the release request release the PRU or lower the power of the PRU, the second base stations 130A and 130B with respect to the PRU of the first base station 120A Interference can be reduced. Next, a wireless communication method for performing wireless communication using the first base station 120A, the second base stations 130A and 130B, and the management server 160 described above will be described.

(Wireless communication method)
FIG. 7 is a sequence diagram showing a processing flow of the wireless communication method according to the present embodiment.

  First, when the first base station 120A receives a communication establishment request transmitted from the PHS terminal 110A (establishment request step: S500), all the carrier sense determination units 220 of the first base station 120A are not currently using it. The carrier sense is performed on the PRU of the current and it is determined whether there is an available PRU (carrier sense determination step: S502).

  If it is determined in carrier sense determination step S502 that there is no usable PRU, the NG notification unit 222 of the first base station 120A includes information indicating that there is no usable PRU and information on a predetermined PRU that is not usable. The carrier sense failure information is notified to the management server 160 (NG notification step: S504). Further, the first base station 120A transmits a communication establishment standby request to the PHS terminal 110A (standby request step: S506), and the PHS terminal 110A that has received the communication establishment standby request starts a timer and enters a standby state (establishment). Standby step: S508).

  The management server 160 notified of the carrier sense failure information from the first base station 120A sends each of the second base stations 130A and 130B using the predetermined PRU included in the carrier sense failure information via the map 416. A channel release request is notified (release request notification step: S510).

  The PRU determination unit 320 of the second base station 130A or 130B notified of the channel release request from the management server 160 can release the PRU used by the own station among the predetermined PRUs included in the channel release request. If the release is possible, the PRU is released. If the release is not possible, the power of the predetermined PRU is reduced (PRU release step: S512).

  In the PRU release step S512, the second base stations 130A and 130B notify the management server 160 of released PRU information including information on the released or reduced power PRU (release notification step: S514).

  The management server 160 notified of the released PRU information from the second base stations 130A and 130B notifies the released PRU information to the first base station 120A (PRU notification step: S516).

  When the timer of the PHS terminal 110A that has been in the standby state in the establishment standby step S508 times out (timeout step: S518), the PHS terminal 110A again transmits a communication establishment request to the first base station 120A (establishment rerequest step: S520).

  Then, the first base station 120A performs carrier sense again, and if it is equal to or greater than the threshold, assigns a predetermined PRU to the PHS terminal 110A (PRU assignment step: S522) and starts communication (communication start step: S524). .

  As described above, in the wireless communication method according to the present embodiment, the first base station 120A receives interference from the second base stations 130A and 130B and cannot newly assign a PRU to the PHS terminal 110A. Even if there is, the PRU of the second base stations 130A and 130B giving interference can be released by notifying the management server 160 to that effect, so that the first base station 120A can be used. Therefore, it is possible to reliably establish communication with the PHS terminal 110A without performing handover and communicating with other base stations.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the embodiment described above, the first base station 120A and the second base station 130A transmit / receive carrier sense failure information, channel release request, and release PRU information via the management server 160. However, the present invention is not limited to this, and the first base station 120A and the second base station 130A can directly transmit / receive the carrier sense failure information, the channel release request, and the release PRU information.

  Note that each step in the wireless communication method of the present specification does not necessarily have to be processed in time series in the order described as a sequence diagram, and may include processing in parallel or by a subroutine.

  The present invention can be used for a radio communication system, a base station, a management server, and a radio communication method capable of radio communication using the OFDMA scheme.

It is explanatory drawing which showed the rough connection relation of the radio | wireless communications system. It is the block diagram which showed the schematic structure of the 1st base station. It is explanatory drawing for demonstrating the flame | frame structure concerning this embodiment. It is the block diagram which showed the schematic structure of the 2nd base station. It is explanatory drawing for demonstrating the channel structure concerning this embodiment. It is the block diagram which showed the schematic structure of the management server. It is the sequence diagram which showed the flow of the process of the radio | wireless communication method concerning this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Wireless communication system 110A, 110B ... PHS terminal 120A, 120B ... 1st base station 130A, 130B ... 2nd base station 140 ... Communication network 150 ... Relay server 160 ... Management server 210 ... 1st base station control part 212 ... base station memory 214 ... base station wireless communication unit 216 ... base station wired communication unit 220 ... carrier sense determination unit 222 ... NG notification unit 224 ... channel allocation unit 310 ... second base station control unit 320 ... PRU determination unit 322 ... PRU Release unit 324 PRU notification unit 350 Control channel (CCH)
352 ... Anchor channel (ANCH)
354 ... Extra channel (EXCH)
410 ... server control unit 412 ... server memory 414 ... server communication unit 416 ... map 420 ... release request notification unit 422 ... server notification unit

Claims (9)

Wireless communication comprising a first base station that performs wireless communication with a communication terminal using the OFDMA method, one or a plurality of second base stations, and a management server that manages the first and second base stations A system,
The first base station is
A carrier sense determination unit that determines whether there is an available PRU by performing carrier sense in response to a communication establishment request from the communication terminal;
When the carrier sense determination unit determines that there is no usable PRU, an NG notification unit that notifies the management server of carrier sense failure information including information on a predetermined PRU that is not available;
A channel for allocating the PRU indicated by the released PRU information to the communication terminal when the management server notifies the released PRU information including the information of the PRU released by the second base station or whose power is reduced An allocator;
With
The management server
When the carrier sense failure information is notified from the first base station, a release request notifying unit that notifies the second base station of a channel release request that includes information requesting release of the predetermined PRU;
When the released PRU information is notified from the second base station, a server notification unit that notifies the released PRU information to the first base station;
With
The second base station is
A PRU determination unit that determines whether or not a predetermined PRU included in the channel release request can be released when the management server is notified of the channel release request;
A PRU release unit that releases the predetermined PRU when the predetermined PRU is releasable, and reduces the power of the predetermined PRU when the predetermined PRU is not releasable;
A PRU notifying unit for notifying the management server of released PRU information including information on a PRU released by the PRU releasing unit or having reduced power;
A wireless communication system comprising: The management server
A map showing the location of the PRU used by the first and second base stations managed by the management server;
The release request notifying unit of the management server uses the base station using a predetermined PRU included in the carrier sense failure information from the first base station via the map as the second base station to release the channel. The wireless communication system according to claim 1, wherein the request is notified.   2. The radio according to claim 1, wherein the release request notifying unit of the management server notifies the channel release request with a base station within a predetermined range from the first base station as a second base station. Communications system.   The PRU determining unit determines that the predetermined PRU included in the channel release request is releasable when an extra channel is allocated, and determines that it is not releasable when an anchor channel is allocated. The wireless communication system according to any one of claims 1 to 3, wherein the wireless communication system is characterized in that:   5. The wireless communication system according to claim 1, wherein the PRU release unit reduces the power of the PRU that is not releasable to a minimum value. 6. A base station that performs radio communication with a communication terminal using an OFDMA scheme,
A carrier sense determination unit that determines whether there is an available PRU by performing carrier sense in response to a communication establishment request from the communication terminal;
When the carrier sense determination unit determines that there is no usable PRU, an NG notification unit that notifies carrier management failure information including information on a predetermined PRU that cannot be used to a management server that manages the base station;
Channel allocation for allocating the PRU indicated by the released PRU information to the communication terminal when the management server is notified of released PRU information including information on the PRU released by another base station or whose power is reduced And
A base station comprising: A base station that performs radio communication with a communication terminal using an OFDMA scheme,
When a channel release request including information requesting release of a predetermined PRU is notified from another base station from the management server that manages the base station, the predetermined PRU included in the channel release request can be released. A PRU determination unit for determining whether or not there is,
A PRU release unit that releases the predetermined PRU when the predetermined PRU is releasable, and reduces the power of the predetermined PRU when the predetermined PRU is not releasable;
A PRU notifying unit for notifying the management server of released PRU information including information on a PRU released by the PRU releasing unit or having reduced power;
A base station comprising: A management server that manages a first base station and a second base station that perform radio communication with a communication terminal using an OFDMA scheme,
When carrier sense failure information including information on a predetermined PRU that cannot be used is notified from the first base station, a channel release including information requesting the second base station to release the predetermined PRU A release request notification unit for notifying the request;
When the released PRU information is notified from the second base station, a server notification unit that notifies the released PRU information to the first base station;
A management server comprising: A wireless communication method using a first base station that performs wireless communication with a communication terminal using an OFDMA scheme, a second base station, and a management server that manages the first and second base stations. ,
The first base station is
In response to a communication establishment request from the communication terminal, carrier sense is performed to determine whether there is an available PRU,
When it is determined that there is no usable PRU, the management server is notified of carrier sense failure information including information on a predetermined PRU that is not usable,
The management server
When carrier sense failure information is notified from the first base station, a channel release request including information requesting release of the predetermined PRU is notified to the second base station,
The second base station is
When the channel release request is notified from the management server, it is determined whether or not a predetermined PRU included in the channel release request can be released;
If the predetermined PRU is releasable, release the predetermined PRU; if the predetermined PRU is not releasable, reduce the power of the predetermined PRU;
Notifying the management server of released PRU information including information on the released or reduced PRU,
The management server
When the released PRU information is notified from the second base station, the released PRU information is notified to the first base station;
The first base station is
When release PRU information including information on a PRU released at the second base station or whose power is reduced is notified from the management server, the PRU indicated by the released PRU information is allocated to the communication terminal. A wireless communication method characterized by the above.

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