JP2009260851A - Base station and frame synchronization method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To promote effective utilization of a time slot and perform frame synchronization at an arbitrary time without impeding communication of a mobile station at another time slot by minimizing the time slot that receives a control signal to be synchronized. <P>SOLUTION: A base station 120 includes a control signal acquisition part 222 that acquires a control signal of a base station to be synchronized by performing open search when a frame synchronization processing request is issued, a frame synchronizing part 226 that synchronizes the frame timing of the base station in accordance with the timing at which the control signal is acquired, and a position storing part 224 that stores the frame position corresponding to the timing at which the control signal is acquired, and when the frame synchronization processing request is issued again, the control signal acquisition part does a setting to receive only a predetermined time slot at the frame position stored in the position storing part and acquires the control signal of a base station to be synchronized. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a base station and a frame synchronization method for performing frame synchronization between base stations.

  In a wireless communication system represented by PHS (Personal Handy phone System), in order to realize simultaneous bidirectional communication, a communication path is divided on a time axis, and transmission and reception are alternately performed on TDD (Time Division Duplex). TDMA (Time Division Multiple Access) in which the transmission / reception time (frame) is time-divided into a plurality of time slots is adopted (TDMA / TDD system). In one setting example of the wireless communication system, a frame timing at which transmission / reception can be performed comes every 5 msec, and each mobile station including a PHS terminal is assigned a 625 μsec channel obtained by time-dividing the transmission / reception time into eight time slots.

  Such a channel is allocated by the base station, and the mobile station establishes communication with the base station through the allocated channel. Therefore, the mobile station must synchronize with the transmission / reception timing (frame timing) of the TDMA / TDD system in the base station. For example, the base station broadcasts a control signal (control signal transfer channel (CCH)) once every 20 frame timings, that is, once every 100 msec, and the mobile station is synchronized with the control signal. Thus, preparation for wireless communication is performed.

  Further, not only between the mobile station and the base station but also the base stations must perform frame timing synchronization (frame synchronization). In the TDMA / TDD system, a plurality of base stations perform radio communication with a plurality of mobile stations using the same radio frequency band, so that each base station performs radio communication with the mobile station at independent frame timings. If it is established, a collision between signals exceeds the guard time for compensating for radio wave interference and fading.

  Further, even when a so-called handover is performed in which the mobile station connection base station is switched in accordance with a change in radio wave environment between the mobile station and the base station, the frame timing between the base stations is different, Wireless signals cannot be acquired effectively, and smooth handover is hindered. Therefore, before synchronization between the mobile station and the base station, first, it is necessary to perform frame synchronization between the base stations so that a plurality of base stations arranged have the same frame timing.

  Therefore, in a wireless communication system, a technique (for example, Patent Document 1) that uses a base station identification number to synchronize with the reception timing of a TDMA frame from the base station, or a plurality of antennas with respective directivity null points. Various methods such as a technique (for example, Patent Document 2) that performs an open search by arranging so as to supplement are proposed.

  In frame synchronization between base stations, an open search as shown in Patent Document 2 is usually executed. For example, in the open search whose processing procedure is shown in FIG. 7, first, the generation of a new call is limited for a predetermined period in order to secure time for detecting the control signal of the base station to be synchronized (S10). ). At this time, if there is another base station nearby, it is possible to forcibly perform handover. Meanwhile, other base stations can handle incoming and outgoing calls from mobile stations. When the time is secured, an open search is executed for 160 frames (800 msec), for example (S12). Here, control signals of a plurality of base stations other than the own station are detected. The base station ID (CSID) is used for the identification.

When the control signals of a plurality of base stations are detected, the control signal having the best radio wave condition is selected (S14), and the current frame timing and the frame timing of the selected control signal are selected based on the reference clock of the local station. (S16), and the current frame timing is shifted by the derived difference (S18). In this way, the frame timing of the own station can be synchronized with the frame timing of the target base station.
JP 7-46659 A JP 2005-348194 A

  A base station that has completed frame synchronization has at least the same transmission / reception timing with the synchronization destination base station. However, since the subsequent timing maintenance depends on the accuracy of the reference clock of each base station, it will eventually occur with the passage of time. Therefore, the frame synchronization with the open search described above is performed periodically, for example, once a day.

  In such an open search, the occurrence of a new call is limited and an attempt is made to secure a time for detecting a control signal, but the base station does not function effectively during this time. Conventionally, there was little traffic with mobile stations, and base stations were able to compensate each other. However, in recent years when traffic has increased, the occupation of resources based on each open search may hinder smooth wireless communication. .

  In view of such a problem, the present invention aims at effective use of time slots by minimizing the time slots for receiving control signals to be synchronized in frame synchronization that is repeatedly executed every predetermined time. It is an object of the present invention to provide a base station and a frame synchronization method capable of executing frame synchronization at an arbitrary time without interfering with communication of a mobile station in the time slot.

  In order to solve the above problems, a typical configuration of the present invention is a base station that performs radio communication with a mobile station and another base station, and a timer that generates a frame synchronization processing request every predetermined time; When a frame synchronization processing request occurs, a control signal acquisition unit that performs an open search and acquires a control signal of a base station to be synchronized, a frame synchronization unit that synchronizes the frame timing of the base station according to the timing of acquiring the control signal, A position storage unit that stores a frame position corresponding to the timing at which the control signal is acquired, and when the frame synchronization processing request is generated again, the control signal acquisition unit is configured to store the predetermined position at the frame position stored in the position storage unit. And receiving a control signal of a base station to be synchronized.

  Once the control signal acquisition unit acquires the control signal through the open search, the output timing of the control signal of the base station to be synchronized can be grasped, and the frame position is stored in the position storage unit for the next frame synchronization. . When frame synchronization processing is requested again, frame synchronization can be performed with reception settings for only a predetermined time slot at the stored frame position, so that the time slot for receiving the control signal to be synchronized is minimized. It is possible to effectively use the time slot while limiting to the limit, and to perform frame synchronization at an arbitrary time without interfering with the communication of the mobile station in other time slots.

  The control signal acquisition unit acquires the control signals of a plurality of base stations at the time of the first frame synchronization processing request, and the frame synchronization unit acquires the base signals according to the timing obtained by averaging the control signal acquisition timings from the plurality of base stations. The frame timing of the stations is synchronized, the position storage unit stores a plurality of frame positions corresponding to the timing at which the control signals of the plurality of base stations are acquired, and the control signal acquisition unit further performs the second and subsequent frame synchronization processes. At the time of the request, only a predetermined time slot at each of a plurality of frame positions stored in the position storage unit may be received and set.

  Conventionally, only one control signal having the best radio wave condition is subject to frame synchronization. In the present invention, by averaging the timings of a plurality of control signals from a plurality of base stations, the fluctuations of the control signals of the individual base stations are absorbed with high accuracy while achieving effective use of the time slots described above. Frame synchronization can be performed.

  The control signal acquisition unit acquires a plurality of base station control signals at the time of the initial frame synchronization processing request, and the position storage unit acquires a plurality of frame positions corresponding to the timing at which the plurality of base station control signals are acquired. The control signal acquisition unit further stores a predetermined time at each of the plurality of frame positions stored in the time slot not used in the base station and the position storage unit at the time of the second and subsequent frame synchronization processing requests. If any of the slots match, only the matching time slot may be set to receive.

  With such a configuration, it is possible to perform frame synchronization by effectively using unused time slots that are not being used, and frame synchronization can be completed in a short time without waiting for disconnection of time slots in which calls have already occurred. It becomes possible.

  Another typical configuration according to the present invention is a frame synchronization method in which a base station that performs radio communication with a mobile station synchronizes a frame with another base station, and generates a frame synchronization processing request every predetermined time. The timing at which the control signal is acquired by performing an open search in response to the first frame synchronization processing request, acquiring the control signal of the base station to be synchronized, synchronizing the frame timing of the base station according to the timing at which the control signal is acquired When a frame synchronization processing request occurs again, only the predetermined time slot at the stored frame position is received and set, and the control signal of the base station to be synchronized is acquired and controlled. The frame timing of the base station is synchronized according to the timing at which the signal is acquired.

  The above-described components based on the technical idea of the base station and the description thereof can be applied to the frame synchronization method.

  As described above, according to the base station of the present invention, in the frame synchronization that is repeatedly executed every predetermined time, the time slot that receives the control signal to be synchronized is minimized, thereby effectively utilizing the time slot. At the same time, it is possible to execute frame synchronization at an arbitrary time without interfering with mobile station communication in other time slots. Accordingly, the user capacity of the base station is increased, and the total throughput of the entire base station is improved.

  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.

  A base station that has completed frame synchronization has at least the same transmission / reception timing with the synchronization destination base station. However, since the subsequent timing maintenance depends on the accuracy of the reference clock of each base station, it will eventually occur with the passage of time. Therefore, in the wireless communication system, frame synchronization is periodically performed in order to calibrate the deviation of the reference clock that each base station has individually. In the assumed conventional frame synchronization, an open search is performed each time, and the time when the base station does not function effectively frequently occurs.

  The inventor of the present application pays attention to the fact that a frame shift slightly occurs between a plurality of base stations when a long time elapses after the completion of frame synchronization, but the shift is less than the width of the time slot. The structure that reflects this in the next frame synchronization was materialized, and the time slot was effectively used.

  In the embodiment shown below, although the open search is performed for the first time, the timing at which the control signal is output from the target base station in one open search is stored, and the control is limited to that timing from the next time. By receiving the signal, it becomes possible to execute frame synchronization at an arbitrary time without interfering with the communication of the mobile station in the time slot other than the stored timing. In order to facilitate understanding of the present embodiment, the normal operation of the entire radio communication system will be described first, and then the specific configuration of the base station will be described.

(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 a communication network 130 including mobile stations 110 (110A, 110B), base stations 120 (120A, 120B, 120C), an ISDN (Integrated Services Digital Network) line, the Internet, a dedicated line, and the like. And the relay server 140.

  In the wireless communication system 100, when a user connects a communication line from his / her mobile station 110A to another mobile station 110B, the mobile station 110A makes a wireless connection request to the base station 120A within the communicable range. . The base station 120A that has received the wireless connection request requests the relay server 140 to establish a communication connection with the communication partner via the communication network 130. The relay server 140 refers to the location registration information of the other mobile station 110B, and others. The base station 120B within the wireless communication range of the mobile station 110B is selected to secure a communication path between the base station 120A and the base station 120B, and communication between the mobile station 110A and the mobile station 110B is established.

  Here, when the mobile station 110B, which is the communication partner, moves, the distance between the mobile station 110B and the base station 120B increases, and finally, wireless communication with the base station 120B becomes difficult. The mobile station 110B predicts that wireless communication becomes difficult due to the attenuation of the electric field strength of the signal from the base station 120B, performs carrier sense again, and performs wireless communication with the base station 120C with high electric field strength. To request. When the base station 120B notifies the relay server 140 to that effect, the relay server 140 performs a handover from the base station 120B to the base station 120C.

  Thus, in order to establish radio communication with the mobile station 110 and to perform handover between the base stations 120, each base station 120 must first match the frame timing with other base stations. For example, when the base station 120B in FIG. 1 is a master base station, the base stations 120A and 120C around it receive the control signal indicated by the ripples in the figure from the base station 120B, Frame synchronization is performed in synchronization with the frame timing of the local station. A configuration in which the base station 120A and the base station 120C are in frame synchronization with the control signal of the base station 120B is shown below.

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

  The control unit 210 manages and controls the entire base station 120 by a semiconductor integrated circuit including a central processing unit (CPU). The control unit 210 also functions as a timer 220 that measures the required time interval of frame synchronization processing and a control signal acquisition unit 222 that acquires control signals from other base stations. Specific operations of the timer 220 and the control signal acquisition unit 222 will be described later. The 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 control unit 210. The memory 212 also functions as a position storage unit 224 that stores a frame position corresponding to the timing at which the control signal is acquired. Specific operation of the position storage unit 224 will be described later.

  The wireless communication unit 214 establishes wireless communication with the mobile station 110 by, for example, the TDMA / TDD method or the OFDMA (Orthogonal Frequency Division Multiplexing Access) method, and adapts the modulation method according to the communication state with the mobile station 110. (Adaptive modulation). The wireless communication unit 214 also functions as a frame synchronization unit 226 that synchronizes the frame timing of the base station according to the timing at which the control signal is acquired. The specific operation of the frame synchronization unit 226 will be described later. The wired communication unit 216 can be connected to various servers including the relay server 140 via the communication network 130.

  In the present embodiment, frame synchronization processing is performed mainly by the timer 220, the control signal acquisition unit 222, the position storage unit 224, and the frame synchronization unit 226 described above. Hereinafter, the operation of each component will be described through a plurality of variations based on differences in synchronization targets.

  FIG. 3 is an explanatory diagram for explaining a frame synchronization processing operation. Here, in addition to the base station 120 as its own station, the frame synchronization processing will be described with reference to other base stations 120D, 120E, and 120F that can be synchronized. First, a case where the frame synchronization target is a control signal of one base station 120 will be described. The timer 220 measures time based on the reference clock of its own station, and generates a frame synchronization processing request when a predetermined time has elapsed. For example, when the frame synchronization process is performed once a day at a predetermined time with a low communication frequency, the timer 220 measures one day.

  When a predetermined time is reached and a frame synchronization processing request is generated from the timer 220, it is determined whether or not the frame position is stored in the position storage unit 224, that is, whether or not the frame synchronization processing is the first time.

  If the frame synchronization processing is the first time or the first processing after the position storage unit 224 is reset for some reason, the control signal acquisition unit 222 may, for example, have 160 frames (800 msec) as shown in FIG. ) To obtain a control signal. The control signal of each base station 120 is controlled so as not to be superimposed, and is broadcast at least one frame apart. When the control signal acquisition unit 222 detects the control signals of the three base stations 120D, 120E, and 120F as shown in FIG. 3B, the radio wave state is the best from the plurality of control signals (the electric field strength is high or A control signal having good signal quality, for example, a control signal of the base station 120E is selected as a control signal to be synchronized. Here, each control signal is identified by a base station ID included in the control signal.

  The frame synchronization unit 226 receives the timing at which the control signal acquisition unit 222 acquires the selected control signal, here, the control signal of the base station 120E, and synchronizes the frame timing of the own station. Specifically, as shown in FIG. 3C, the current frame timing 250 based on the reference clock of the local station is compared with the frame timing 252 of the base station 120E based on the control signal, and the difference d is derived. As indicated by an arrow in FIG. 3C, frame synchronization is performed by shifting by the difference d from which the current frame timing 250 is derived. The actual transition of the difference d may be performed immediately after waiting for the transmission time slot in progress (no need to wait in the reception time slot), or at various arbitrary timings such as after the end of the frame in progress. Can be accomplished with Time slots are also synchronized by frame synchronization.

  At this time, the base station 120 also has a propagation delay due to the distance to the base station 120 to be synchronized. However, since the base station 120 is fixedly arranged, the propagation delay is estimated in advance from the distance between the base stations 120. In addition, absolute synchronization can be achieved by advancing the actual synchronization timing by that much. In addition, when the base stations 120 are arranged at a predetermined interval, for example, the synchronization timing can be accelerated by uniformly equaling a predetermined time such as 1 frame length × 0.5 symbols / 120 symbols = 2.6 μsec. Substantially accurate frame synchronization is possible.

  At this time, the position storage unit 224 stores a frame position 260 corresponding to the timing at which the control signal acquisition unit 222 acquires the control signal, as shown in FIG. The frame position 260 does not indicate a specific time point. For example, if the timing at which the control signal is broadcast is once every 20 frames, that is, once every 100 msec, as shown in FIG. Indicates the relative position of the periodic frame arriving at.

  When the timer 220 reaches the next predetermined time, a frame synchronization processing request is generated again. When it is determined that the frame synchronization processing is not the first time, the control signal acquisition unit 222 performs an open search this time. Rather, only the predetermined time slot 262 at the frame position 260 stored in the position storage unit 224, for example, the first time slot is set to be received, and the control signal of the base station 120E to be synchronized is acquired. Similarly to the first time, the frame synchronization unit 226 synchronizes the frame timing of the own station according to the timing of the acquired control signal.

  As described above, in the present embodiment, once the control signal acquisition unit 222 acquires the control signal through the open search, the output timing of the control signal of the base station 120 to be synchronized can be grasped, and the frame position 260 is set to the next time. Is stored in the position storage unit 224 for frame synchronization. When the frame synchronization process is requested again, the frame synchronization can be performed with the reception setting of only the predetermined time slot 262 at the stored frame position 260.

  Here, although open search is performed for the first time, frame synchronization limited to the timing is repeated after the second time. Therefore, the time slot that receives the control signal to be synchronized is minimized to effectively use the time slot, and the frame synchronization is executed at an arbitrary time without interfering with the communication of the mobile station 110 in another time slot. It becomes possible.

  FIG. 4 is an explanatory diagram for explaining another processing operation of frame synchronization. Here, a case where the frame synchronization target is a plurality of control signals in a plurality of base stations 120 will be described.

  First, as shown in FIG. 4A, the control signal acquisition unit 222 acquires a plurality of control signals from a plurality of base stations 120 when the first frame synchronization processing request is made, and the frame synchronization unit 226 As shown in FIG. 4B, the frame timing 250 of the base station 120 is synchronized according to the timing 270 obtained by averaging the acquisition timings of the control signals from the plurality of base stations 120.

  At this time, the position storage unit 224 stores all the plurality of frame positions corresponding to the timings of the acquired plurality of control signals. In this way, even in the second and subsequent frame synchronization processing requests, the control signal acquisition unit 222 performs the predetermined time at each of the plurality of frame positions stored in the position storage unit 224 as shown in FIG. Only the slot 272 is set to be received, and the control signals of the plurality of base stations 120 to be synchronized are acquired again. As in the first time, the frame synchronization unit 226 synchronizes the frame timing of the base station 120 according to the timing 270 obtained by averaging the acquisition timings of the plurality of control signals acquired in this way.

  Unlike the case where only one control signal with the best radio wave state is subjected to frame synchronization, here, the timings of the plurality of control signals from the plurality of base stations 120 are averaged to obtain the time slot described above. It is possible to perform high-accuracy frame synchronization by absorbing fluctuations in the control signals of the individual base stations 120, for example, delay due to jitter and fading.

  FIG. 5 is an explanatory diagram for explaining another processing operation of frame synchronization. Here, a case where a frame synchronization target is selected from a plurality of control signals in a plurality of base stations 120 each time will be described.

  First, as shown in FIG. 5A, the control signal acquisition unit 222 acquires a plurality of control signals from a plurality of base stations 120 at the time of the first frame synchronization processing request, and the frame synchronization unit 226 As shown in FIG. 5B, the control signal with the best radio wave state, here, the control signal of the base station 120E is selected as the control signal to be synchronized, and the frame timing 250 of the base station 120 is synchronized according to the acquired timing 252. Let

  At this time, the position storage unit 224 stores all the plurality of frame positions corresponding to the timing at which the control signals of the plurality of base stations 120 are acquired. Here, when the second or subsequent frame synchronization processing request arrives, the control signal acquisition unit 222 determines whether or not there is an empty time slot in the base station 120 where communication with the mobile station 110 is not performed. If there is an empty time slot 280 as shown in (c), the empty time slot 280 is compared with a predetermined time slot at each of the stored frame positions, and whether there is an identical time slot. Judge whether. If any time slot matches, only the predetermined time slot 280 at the matched frame position is received and set, the control signal of the base station 120 corresponding to this frame position is acquired again, and the frame synchronization unit 226 As in the first time, the frame timing of the base station 120 is synchronized according to the timing of the control signal acquired in this way.

  With such a configuration, it is possible to perform frame synchronization by effectively using unused time slots that are not being used, and frame synchronization can be completed in a short time without waiting for disconnection of time slots in which calls have already occurred. It becomes possible.

(Frame synchronization method)
Next, a frame synchronization method in which any of the plurality of base stations 120 that perform radio communication with the mobile station 110 synchronizes other base station frames will be described.

  FIG. 6 is a flowchart showing the overall flow of the frame synchronization method. When a frame synchronization processing request is generated based on the timer 220, the control signal acquisition unit 222 first determines whether or not a frame position is already stored in the position storage unit 224 (S300). If the frame position is not stored, In order to secure the time for detecting the control signal of the base station 120 to be synchronized, the generation of a new call is limited for a predetermined period (S302). When the time is secured, an open search is executed for 160 frames (800 msec), for example (S304). Here, control signals of a plurality of base stations 120 other than the own station are detected.

  When control signals of a plurality of base stations 120 are detected, the control signal having the best radio wave condition is selected (S306), and the current frame timing and the frame timing of the selected control signal based on the reference clock of the local station are selected. Is derived (S308), and the current frame timing is shifted by the derived difference (S310). In this way, the frame timing of the own station can be synchronized with the frame timing of the target base station 120. At this time, the position storage unit 224 stores a plurality of frame positions corresponding to the timing at which the control signal is acquired (S312). This eliminates the need for an open search in frame synchronization from the next time.

  When the frame synchronization processing request time comes again, the control signal acquisition unit 222 determines whether or not the frame position is already stored in the position storage unit 224 (S300), and refers to the frame position stored in the position storage unit 224. Next, a predetermined time slot at the frame position is received and set, and the difference between the current frame timing and the frame timing of the selected control signal is derived based on the reference clock of the local station (S314). The current frame timing is shifted by the difference (S316).

  Finally, it is confirmed whether or not the frame synchronization is successful (S318). If the frame synchronization is not successful, the next frame position candidate is extracted from the frame positions of the plurality of stored control signals (S320), and the frame synchronization is performed again. Try. Here, when the synchronization is not successful in all the frame position candidates, it is assumed that the frame position is not stored, and the open search is executed.

  Even in such a frame synchronization method, by minimizing the time slot that receives the control signal to be synchronized, the time slot is effectively used, and the communication of the mobile station in the other time slot is not hindered, that is, the call Thus, it is possible to execute frame synchronization at an arbitrary time without stopping the communication service. Therefore, the user capacity of the base station 120 is increased, and the total throughput of the entire base station is improved.

  Also, according to the present embodiment, since the time slot can be used effectively, the frequency of frame synchronization that has been once a day can be increased.

  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.

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

  The present invention can be used for a base station and a frame synchronization method for performing frame synchronization between base stations.

It is explanatory drawing which showed the rough connection relation of the radio | wireless communications system in this embodiment. It is the block diagram which showed the schematic structure of the base station. It is explanatory drawing for demonstrating the processing operation | movement of a frame synchronization. It is explanatory drawing for demonstrating other process operation | movement of a frame synchronization. It is explanatory drawing for demonstrating the other process operation | movement of a frame synchronization. It is the flowchart which showed the whole flow of the frame synchronization method. 5 is a flowchart showing an overall flow of a frame synchronization method in the prior art.

Explanation of symbols

110 ... Mobile station 120 ... Base station 220 ... Timer 222 ... Control signal acquisition unit 224 ... Position storage unit 260 ... Frame position

Claims (4)

A base station that performs radio communication with a mobile station and another base station,
A timer for generating a frame synchronization processing request every predetermined time;
A control signal acquisition unit that performs an open search and acquires a control signal of a base station to be synchronized when the frame synchronization processing request occurs;
A frame synchronization unit that synchronizes the frame timing of the base station according to the timing at which the control signal is acquired;
A position storage unit that stores a frame position corresponding to the timing at which the control signal is acquired;
With
When the frame synchronization processing request occurs again, the control signal acquisition unit receives and sets only a predetermined time slot at the frame position stored in the position storage unit, and transmits a control signal of the base station to be synchronized. A base station characterized by acquiring. The control signal acquisition unit acquires the control signals of a plurality of base stations at the time of the first frame synchronization processing request,
The frame synchronization unit synchronizes the frame timing of the base station according to the timing obtained by averaging the acquisition timing of the control signals from the plurality of base stations,
The position storage unit stores a plurality of frame positions corresponding to the timing at which the control signals of the plurality of base stations are acquired,
The control signal acquisition unit is further configured to receive and set only predetermined time slots at each of a plurality of frame positions stored in the position storage unit at the time of a second or subsequent frame synchronization processing request. Item 4. The base station according to Item 1. The control signal acquisition unit acquires the control signals of a plurality of base stations at the time of the first frame synchronization processing request,
The position storage unit stores a plurality of frame positions corresponding to the timing at which the control signals of the plurality of base stations are acquired,
The control signal acquisition unit further includes a time slot that is not used in the base station and a predetermined time slot at each of a plurality of frame positions stored in the position storage unit when a second frame synchronization request is made. 2. The base station according to claim 1, wherein when either of the two matches, reception setting is performed only for the matching time slot. A frame synchronization method in which a base station that performs radio communication with a mobile station synchronizes a frame with another base station,
Generate a frame synchronization processing request every predetermined time,
An open search is performed in response to the first frame synchronization processing request to obtain a control signal of a base station to be synchronized,
Synchronize the frame timing of the base station according to the timing of acquiring the control signal,
Storing a frame position corresponding to the timing at which the control signal is acquired;
When the frame synchronization processing request occurs again, only the predetermined time slot at the stored frame position is received and acquired, and the control signal of the base station to be synchronized is acquired, and according to the timing at which the control signal is acquired A frame synchronization method characterized by synchronizing frame timing of the base station.

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