JP2010062813A - Wireless synchronization method, wireless communication system, and wireless base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless synchronization method and a wireless communication system not lowering a channel use efficiency of a wireless communication of a time-sharing communication method, and to provide a wireless base station constituting the wireless communication system. <P>SOLUTION: The wireless synchronization method of the wireless communication system for conducting the wireless communications by the time-sharing communication method includes: a step of synchronizing each of a plurality of base stations 1_1, ..., 1_n with either a plurality of public network base stations 2_1, ..., 2_m; a step of comparing the number of first base stations expressing the number of base stations transmitting the annunciation signal that can be received in the complete form with the number of second base stations expressing the number of base stations transmitting the annunciation signal that cannot be received in the complete form; and a step of stopping the synchronization with the public network base station synchronized at the time of determination conducted by the base station that determines the number of second base stations larger than the number of first base stations, synchronizing with the other public network base station, and continuing the synchronization with the public network base station synchronized at the time of determination conducted by the base station that determines the number of second base stations not more than the number of first base stations. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radio communication system including a plurality of radio base stations that perform radio communication in a time division communication system, a radio synchronization method executed in the radio communication system, and a radio base station constituting the radio communication system, in particular. The present invention relates to a technique for establishing synchronization among a plurality of radio base stations (also simply referred to as “base stations”) constituting a radio communication system.

  In a radio communication system using a time division multiple access / time division duplex (TDMA / TDD) system (for example, a mobile phone system, a cordless phone system, etc.) Need to synchronize. As a synchronization method, there is a method in which each base station receives a notification signal transmitted from a reference base station serving as a reference for synchronization, and adjusts the phase based on the received notification signal so as not to interfere with the reference base station. (For example, refer to Patent Document 1). The reference base station is, for example, a GPS or a public network base station (also referred to as a “public network base station”).

JP-A-5-110498

  Although there are a plurality of public network base stations, since they are synchronized as a whole, they are suitable as reference base stations. However, the base station constituting the wireless communication system may be synchronized with the public network base station located beyond the synchronization limit distance depending on the external environment. In this case, interference will occur with a reference base station synchronized with GPS and a base station synchronized with a public network base station within the synchronization limit distance, and the frequency (channel) where the interference has occurred cannot be used. The problem arises that the available bandwidth decreases, that is, the channel utilization efficiency decreases.

  Therefore, the present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a wireless synchronization method, a wireless communication system, and a wireless communication method that do not reduce channel use efficiency in time division communication wireless communication. The object is to provide a radio base station constituting a radio communication system.

  A radio synchronization method according to the present invention is a radio synchronization method in a radio communication system including a plurality of base stations that perform radio communication in a time division communication method, wherein each of the plurality of base stations is connected to the plurality of base stations. A step of synchronizing with any one of a plurality of public network base stations capable of wireless communication; and each of the plurality of base stations synchronized with any of the plurality of public network base stations. The notification signal received by the base station other than the station and received in the complete form and the first base station number indicating the number of base stations that have transmitted the broadcast signal in the complete form and not received in the complete form Comparing the second base station number indicating the number of base stations that have transmitted signals, and the second base station number of the plurality of base stations being greater than the first base station number. The determined base station and the public network base station synchronized at the time of the determination The synchronization is stopped, the synchronization is performed with a public network base station other than the public network base station that has stopped the synchronization, and the second base station number among the plurality of base stations is the first base station number. The determined base station as described below has a step of continuing synchronization with the public network base station synchronized at the time of the determination.

  The radio communication system according to the present invention is a radio communication system including a plurality of base stations that perform radio communication in a time division communication system, wherein each of the plurality of base stations communicates with the plurality of base stations. Synchronizing means that synchronizes with any one of the plurality of public network base stations, and each of the plurality of base stations that synchronizes with any of the plurality of public network base stations is a local station of the plurality of base stations. The broadcast signal that was received in a complete form with the first base station number indicating the number of base stations that received the broadcast signal that was received in a complete form and received a broadcast signal transmitted from a base station other than Comparing means for comparing a second base station number indicating the number of base stations that have transmitted, and when the second base station number of the plurality of base stations is greater than the first base station number The determined base station is in sync with the public network base station that was synchronized at the time of the determination. The synchronization is synchronized with a public network base station other than the public network base station that has stopped the synchronization, and the second base station number of the plurality of base stations is equal to or less than the first base station number. The determined base station has control means for controlling so as to continue the synchronization with the public network base station synchronized at the time of the determination.

  Further, a radio base station according to the present invention is a radio base station that is one of the plurality of base stations in a radio communication system including a plurality of base stations that perform radio communication in a time division communication system, Synchronizing means that synchronizes with any one of a plurality of public network base stations, a notification signal transmitted from a base station other than the own station among the plurality of base stations, and the notification signal that has been received in a complete form Comparing means for comparing a first base station number indicating the number of base stations that have transmitted and a second base station number indicating the number of base stations that transmitted the broadcast signal that could not be received in a complete form; When it is determined that the number of second base stations is greater than the number of first base stations, the synchronization with the public network base station that was synchronized at the time of the determination is stopped, and other than the public network base station that stopped the synchronization And the second base station number is the same as the first base station number. When it is determined is below, is characterized by a control means for controlling to continue the synchronization between the PSTN base station which has been synchronized to the 該判 scheduled.

  According to the present invention, it is possible to reduce the occurrence of interference between base stations in radio communication using a time division communication method, and thus there is an effect that the channel utilization efficiency can be improved.

First Embodiment FIG. 1 shows a radio communication system 100 according to a first embodiment of the present invention (that is, a system that can implement the radio synchronization method according to the first embodiment) and a plurality of public network bases. FIG. 2 is a diagram illustrating stations 2_1,..., 2_m (m is a positive integer of 2 or more). As shown in FIG. 1, a radio communication system 100 includes a plurality of base stations 1_1,..., 1_n (n is a positive integer of 2 or more) that performs radio communication using a time division communication method such as TDM or TDD. For example, an indoor wireless communication system.

  Each of the plurality of base stations 1_1, ..., 1_n is synchronized with one of the plurality of public network base stations 2_1, ..., 2_m capable of wireless communication with the plurality of base stations 1_1, ..., 1_n. Each base station and public radio base station have, for example, 001,. For example, each of the plurality of base stations 1_1,..., 1_n directly receives notification signals (also referred to as “public network notification signals”) transmitted by the plurality of public network base stations 2_1,. , Receiving a broadcast signal transmitted by a base station other than the own base station among the plurality of base stations 1_1,..., 1_n and synchronized with one of the plurality of public network base stations 2_1,. To synchronize with one of the plurality of public network base stations 2_1,..., 2_m.

  In the wireless communication system 100 according to the first embodiment, each of the plurality of base stations 1_1,..., 1_n may be synchronized with the public network base station located at a position exceeding the synchronization limit distance. In this case, a base station (any one of 1_1,..., 1_n) synchronized with the public network base station at a position beyond the synchronization limit distance is within the public network base station within the synchronization limit distance or within the synchronization limit distance. It will cause interference with a base station synchronized with a certain public network base station. In order to reduce the occurrence of such interference, in the wireless communication system 100 according to the first embodiment, each of the plurality of base stations 1_1,..., 1_n synchronized with any of the plurality of public network base stations The following synchronous control is executed.

  First, each of the plurality of base stations 1_1,..., 1_n synchronized with any of the plurality of public network base stations is notified by a base station other than the own station among the plurality of base stations 1_1,. The first base station number indicating the number of base stations that have transmitted the broadcast signal that has been received in a complete form, and the first number indicating the number of base stations that have transmitted a broadcast signal that has not been received in a complete form 2 base station numbers are detected, and the first base station number and the second base station number are compared.

  Next, of the plurality of base stations 1_1,..., 1_n, the base station that has determined that the second base station number is greater than the first base station number is the public network base station that was synchronized at the time of the determination. Synchronization is stopped, and synchronization is performed with a public network base station other than the public network base station that has stopped the synchronization. In addition, the determined base station of the plurality of base stations 1_1,..., 1_n having the second base station number equal to or less than the first base station number is the same as the public network base station synchronized at the time of the determination. Continue synchronization.

  Of the plurality of base stations 1_1,..., 1_n, the base station that has determined that the second base station number is greater than the first base station number is a public network that cannot synchronize the public network base station that has stopped synchronization. It is desirable to record the data in the database means as a base station so that no public network base station that cannot be synchronized thereafter will be used.

  FIG. 2 is a block diagram schematically showing an internal configuration of the base station 1 (any one of the base stations 1_1,..., 1_n) constituting the wireless communication system 100 according to the first embodiment. As shown in FIG. 2, the base station 1 is a wireless receiver 11 that receives a radio signal, a broadcast information detector 12 that acquires broadcast information from a broadcast signal included in the received radio signal, and a synchronization destination. A phase adjustment unit 13 that synchronizes with a synchronization destination by correcting a phase difference of a signal with a reference base station (for example, a public network base station or a base station synchronized with the public network base station), and dependent synchronization that determines a synchronization destination And a determination unit 14. Further, the base station 1 detects whether the base station information and the broadcast information are damaged from the broadcast information, and determines whether or not the detectable base station is synchronized, and a base that cannot be connected It has a connectability database (DB) 16 for registering stations in a list, a radio control unit 17 that controls radio communication, and a radio transmission unit 18 that transmits radio signals.

  The dependent synchronization determination unit 14 determines a base station with which the base station of the local station is synchronized by a known method, for example, the technique described in Patent Document 1. The phase adjustment unit 13 and the dependent synchronization determination unit 14 operate as a synchronization unit 20 that determines a synchronization destination of the base station 1 and synchronizes the base station 1 to the synchronization destination.

  In addition, the synchronization availability determination unit 15 transmits the first base station number indicating the number of base stations that have transmitted the broadcast signal that has been received in a complete form and the broadcast signal that has not been received in a complete form. The second base station number indicating the number of base stations that have been detected is detected, and a function as comparison means for comparing the first base station number with the second base station number is provided. Further, when it is determined that the second base station number is larger than the first base station number, the synchronization availability determination unit 15 causes the synchronization unit 20 to synchronize with the public network base station synchronized at the time of the determination. Canceling, synchronizing to a public network base station other than the public network base station that stopped the synchronization, and when determining that the second base station number is less than or equal to the first base station number, It has a function as a control means for continuing the synchronization with the public network base station synchronized at the time of the determination.

  FIG. 3 is a block diagram schematically showing an internal configuration of the public network base station 2 (any one of the public network base stations 2_1,..., 2_m) shown in FIG. As shown in FIG. 3, the public network base station 2 includes a broadcast information transmitting unit 21 that transmits broadcast information (public network broadcast signal), a broadcast information receiving unit 22 that receives broadcast signals, and a synchronization clock for the entire system. A synchronous clock receiving unit 23 that receives a signal, a phase adjusting unit 24 that adjusts the phase of a wireless signal in accordance with the synchronous clock signal, a receiving unit 25 that receives a wireless signal, and a transmitting unit 26 that transmits a wireless signal. Have.

  FIG. 4 is a diagram illustrating an example of a table used for determining whether synchronization is possible in the synchronization availability determination unit 15 of the base station 1 illustrated in FIG. As shown in FIG. 4, in the radio signal of each receivable base station, the synchronization availability determination unit 15 synchronizes the base station that has transmitted the broadcast signal that has been received in a complete form with the base station. (Indicated by “◯” in FIG. 4), it is determined that the base station that transmitted the notification signal that could not be received in a complete form is a base station that is not synchronized with the own station (FIG. 4). (Indicated by “x” in FIG. 4). FIG. 4 shows an example of such a determination result as a table. Note that the specific example of the base station ID in FIG. 4 does not correspond to the specific example of the base station ID shown in FIG.

  FIG. 5 is an explanatory diagram illustrating an operation of the wireless communication system 100 according to the first embodiment. For example, the base stations 1_1,..., 1_n installed in the indoor system environment detect and synchronize with the radio signal of the reference base station. As the reference base station, for example, a base station mounted with a clock supply system such as GPS or a public network base station can be used. At the time of synchronization, synchronization is performed by determining the synchronization destination of the local station based on the notification signal transmitted intermittently from each base station and adjusting the phase of the transmission signal of the local station. The method of synchronizing based on the notification signal is a known technique and is described in, for example, Patent Document 1 described above.

  As shown in FIG. 5, base stations 1_1,..., 1_n installed in an indoor system environment preferentially select public network base stations 2_1,. , S2, S3, S5). For a base station (for example, base station 1_3) that has insufficient radio field intensity from the public network base station and cannot be synchronized, it operates to synchronize with a base station (for example, base station 1_4) synchronized with the public network base station (step 1). S4). Here, when the base station 1_1 detects the public network base station 2_1 located beyond the synchronizable distance, the base station 1_1 operates to synchronize with the public network base station 2-11 (step S5). A first base station number that indicates the number of base stations that have transmitted a broadcast signal that has received a broadcast signal in a complete form by measuring a synchronization situation with a base station (for example, base station 1_2, ..., 1_n); A second base station number indicating the number of base stations that have transmitted a broadcast signal that could not be received in a complete form is detected, and the first base station number and the second base station number are compared. When the base station 1_1 determines that the number of second base stations is greater than the number of first base stations, the base station 1_1 stops (disconnects) synchronization with the public network base station synchronized with the determination, and It is synchronized with a public network base station other than the public network base station that has been canceled, and the public network base station to which synchronization has been applied is registered to prohibit connection to the connectability DB 16 and operates to connect to another base station ( Step S6). Further, when the base station 1_1 determines that the second base station number is equal to or less than the first base station number, the base station 1_1 continues to synchronize with the public network base station synchronized at the time of the determination.

FIG. 6 is a flowchart illustrating a sequence (that is, a wireless synchronization method according to the first embodiment) in which the base stations configuring the wireless communication system 100 according to the first embodiment determine whether synchronization is possible. As shown in FIG. 6, when a trigger for changing the synchronization destination occurs in the base station 1 (step S11), the base station 1 receives a broadcast signal in each reception slot (step S12). The base station 1 determines a synchronization destination based on the received notification signal, and synchronizes with the synchronization destination (step S13). After successful synchronization, the base station 1 receives a broadcast signal in each reception slot,
1st base which shows the number of base stations which measured the synchronous condition with the surrounding base stations (for example, base station 1_2, ..., 1_n) after synchronization, and transmitted the alerting signal which has received the alerting signal in a complete form Detect the number of stations and the number of second base stations indicating the number of base stations that have transmitted broadcast signals that could not be received in a complete form, and compare the number of first base stations with the number of second base stations (Step S14). When the base station 1 determines that the number of second base stations is greater than the number of first base stations, the base station 1 determines that the own station has caused a synchronization shift, and the public that has been synchronized at the time of the determination. Registers that the synchronization with the network base station is canceled (disconnected), synchronized with a public network base station other than the public network base station that has stopped the synchronization, and the public network base station that has stopped the synchronization is prohibited from being connected to the connectability DB 16 (Step S15), the operation of searching for the synchronization destination again is performed. Further, when the base station 1 determines that the number of second base stations is equal to or less than the number of first base stations, the base station 1 determines that the own station has not caused a synchronization shift, and has synchronized with the public at the time of the determination. The synchronization with the network base station is continued and the normal operation is performed (step S16).

  As described above, according to the wireless synchronization method, the wireless communication system 100, and the wireless base station (base station 1) according to the first embodiment, a broadcast signal is detected and surrounding base stations are detected from the broadcast signal information. Is synchronized with its own station, and based on this determination result (comparison result between the number of first base stations and the number of second base stations), whether the synchronization destination of the own station has caused a synchronization shift , Change the synchronization destination, and record in the connectability DB so that connection of inappropriate base stations can be prohibited. For this reason, it is possible to prevent synchronization with an inappropriate base station that causes synchronization shift. As a result, the occurrence of interference between base stations in time division communication wireless communication can be reduced, and channel utilization efficiency in the wireless communication system 100 can be improved.

Second Embodiment FIG. 7 is a block diagram schematically showing an internal configuration of a base station 1a constituting a radio communication system according to a second embodiment of the present invention. In FIG. 7, the same or corresponding elements as those shown in FIG. As shown in FIG. 7, the base station 1a is a synchronization destination, a wireless reception unit 11 that receives a wireless signal, a notification information detection unit 12 that acquires notification information from a notification signal included in the received wireless signal, and A phase adjustment unit 13 that synchronizes with a synchronization destination by correcting a phase difference of a signal with a reference base station (for example, a public network base station or a base station synchronized with the public network base station), and dependent synchronization that determines a synchronization destination And a determination unit 14. Further, the base station 1 detects whether the base station information and the broadcast information are damaged from the broadcast information, and determines whether or not the detectable base station is synchronized, and a base that cannot be connected A connection availability database (DB) 16 for registering stations in a list, a radio control unit 17 for controlling radio communication, a radio transmission unit 18 for transmitting radio signals, and a subordinate synchronization destination recording unit for recording subordinate synchronization destinations 19. The phase adjustment unit 13, the dependent synchronization determination unit 14, and the dependent synchronization destination recording unit 19 operate as synchronization means 20a that determines the synchronization destination of the base station 1a and synchronizes the base station 1a with the synchronization destination.

  The radio base station 1a configuring the radio communication system according to the second embodiment determines that the number of second base stations is equal to or less than the number of first base stations, and uses a public network base station that has continued synchronization as a source. Is recorded in the dependent synchronization destination recording unit 19 as the second database means. Thereafter, the radio base station 1a determines that the number of second base stations is greater than the number of first base stations, stops synchronization with the public network base station synchronized at the time of determination, and cancels the synchronization. When synchronizing with a public network base station other than the public network base station, it synchronizes with the original synchronization destination public network base station recorded in the subordinate synchronization destination recording unit 19.

  FIG. 8 is a flowchart illustrating a sequence (that is, a radio synchronization method according to the second embodiment) in which the base stations configuring the radio communication system according to the second embodiment determine whether synchronization is possible. As shown in FIG. 8, when a trigger for changing the synchronization destination occurs in the base station 1a (step S21), the base station 1a records the ID of the base station that is currently dependently synchronized in the dependent synchronization destination recording unit 19. (Step S22). The base station 1a receives the broadcast signal in each reception slot (step S23). The base station 1a determines a synchronization destination based on the received notification signal, and performs synchronization processing (step S24). After the synchronization is successful, the base station 1a receives the broadcast signal in each reception slot and verifies whether the base stations are synchronized. The base station 1a receives the broadcast signal in each reception slot, measures the synchronization status with the surrounding base stations after synchronization, and indicates the number of base stations that have transmitted the broadcast signal that has been received in a complete form. The number of first base stations and the number of second base stations indicating the number of base stations that have transmitted broadcast signals that could not be received in a complete form are detected, and the number of first base stations and the second base station are detected. The number is compared (step S25). When the base station 1a determines that the number of second base stations is greater than the number of first base stations, the base station 1a determines that the own station has caused a synchronization shift, and has synchronized with the public at the time of the determination. Cancels (disconnects) the synchronization with the network base station, synchronizes with the public network base station other than the public network base station that canceled the synchronization, and registers that the public network base station whose synchronization has been stopped is prohibited from being connected to the connectability DB 16 Then (step S26), the operation is performed so as to synchronize with the base station that was previously dependently synchronized (step S27). Further, when the base station 1a determines that the number of second base stations is equal to or less than the number of first base stations, the base station 1a determines that the own station has not caused a synchronization shift, and has synchronized with the public at the time of the determination. The synchronization with the network base station is continued and the normal operation is performed (step S28).

  As described above, according to the wireless synchronization method, the wireless communication system 100, and the wireless base station (base station 1a) according to the second embodiment, in addition to the effects of the first embodiment, the synchronization destination is By recording the base station that was previously dependently synchronized when the change was made, it is possible to quickly restore the dependent synchronization when a synchronization shift is detected.

  In the second embodiment, points other than those described above are the same as in the case of the first embodiment.

1 is a diagram illustrating a wireless communication system and a plurality of public network base stations according to a first embodiment of the present invention. It is a block diagram which shows roughly the internal structure of the base station which comprises the radio | wireless communications system which concerns on 1st Embodiment. It is a block diagram which shows roughly the internal structure of the public network base station shown by FIG. FIG. 3 is a diagram illustrating an example of a table used for determining whether synchronization is possible in the synchronization availability determination unit of the base station illustrated in FIG. 2. It is explanatory drawing which shows operation | movement of the radio | wireless communications system which concerns on 1st Embodiment. 5 is a flowchart illustrating a sequence (that is, a wireless synchronization method according to the first embodiment) in which a base station configuring the wireless communication system according to the first embodiment determines whether synchronization is possible. It is a block diagram which shows roughly the internal structure of the base station which comprises the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the sequence in which the base station which comprises the radio | wireless communications system which concerns on 2nd Embodiment (namely, radio | wireless synchronization method which concerns on 2nd Embodiment) determines the propriety of a synchronization.

Explanation of symbols

1, 1a, 1_1, ..., 1_n base station (radio base station),
2, 2_1, ..., 2_m public network base station,
11 wireless receiver,
12 Notification information detection unit,
13 Phase adjustment unit,
14 Dependent synchronization determination unit,
15 Synchronism determination unit (comparison means, control means)
16 Connection availability DB (first database means),
17 wireless control unit,
18 wireless transmitter,
19 Subordinate synchronization destination recording unit (second database means)
20, 20a Synchronization means.

Claims (15)

A wireless synchronization method in a wireless communication system including a plurality of base stations performing wireless communication in a time division communication method,
Each of the plurality of base stations is synchronized with any of a plurality of public network base stations capable of wireless communication with the plurality of base stations;
Each of the plurality of base stations synchronized with one of the plurality of public network base stations receives a broadcast signal transmitted by a base station other than the base station of the plurality of base stations and receives it in a complete form. The first base station number indicating the number of base stations that transmitted the broadcast signal is compared with the second base station number indicating the number of base stations that transmitted the broadcast signal that could not be received in a complete form. And steps to
Of the plurality of base stations, the base station that has determined that the second base station number is greater than the first base station number stops synchronization with the public network base station that was synchronized at the time of the determination. , Synchronization with a public network base station other than the public network base station that stopped the synchronization, and determination that the second base station number of the plurality of base stations is less than or equal to the first base station number And a step of continuing synchronization with the public network base station synchronized at the time of the determination.   The base station that has determined that the number of the second base stations is greater than the number of the first base stations, sets the public network base station that has stopped the synchronization as a non-synchronizable public network base station to the first database means. The wireless synchronization method according to claim 1, further comprising a step of recording.   In the step of synchronizing with any of the plurality of public network base stations, each of the plurality of base stations receives a public network notification signal transmitted from the plurality of public network base stations, or Any of the plurality of public network base stations by receiving a broadcast signal transmitted by a base station other than the base station of the base station and synchronized with any of the plurality of public network base stations. The wireless synchronization method according to claim 1 or 2, wherein the synchronization is performed.   The base station that has determined that the number of the second base stations is equal to or less than the number of the first base stations records, in the second database means, the public network base station that has continued the synchronization as the original synchronization destination. The wireless synchronization method according to claim 1, further comprising:   5. The public network base station other than the public network base station that has stopped the synchronization is the original synchronization destination public network base station recorded in the second database means. Wireless synchronization method. A wireless communication system including a plurality of base stations performing wireless communication in a time division communication system,
Each of the plurality of base stations is
Synchronization means for synchronizing with any of a plurality of public network base stations capable of wireless communication with the plurality of base stations;
Each of the plurality of base stations synchronized with one of the plurality of public network base stations receives a broadcast signal transmitted by a base station other than the base station of the plurality of base stations and receives it in a complete form. The first base station number indicating the number of base stations that have transmitted the broadcast signal is compared with the second base station number indicating the number of base stations that have transmitted the broadcast signal that could not be received in a complete form. Comparing means to
Of the plurality of base stations, the base station that has determined that the second base station number is greater than the first base station number stops synchronization with the public network base station that was synchronized at the time of the determination. , Synchronization with a public network base station other than the public network base station that stopped the synchronization, and determination that the second base station number of the plurality of base stations is less than or equal to the first base station number And a control means for controlling the base station to continue synchronization with the public network base station synchronized at the time of the determination. Each of the plurality of base stations further comprises first database means;
When it is determined that the number of the second base stations is greater than the number of the first base stations, the control means sets the public network base station that has stopped the synchronization as a non-synchronizable public network base station. The wireless communication system according to claim 6, wherein the wireless communication system is recorded in the database means.   The synchronization by the synchronization means is performed by receiving a public network notification signal transmitted from the plurality of public network base stations, or a base station other than the own station among the plurality of base stations, 8. The wireless communication system according to claim 6, wherein the wireless communication system is executed by receiving a broadcast signal transmitted from a base station synchronized with any one of public network base stations. Each of the plurality of base stations further comprises second database means;
When the control means determines that the second base station number is less than or equal to the first base station number, the second database means uses the public network base station that has continued synchronization as the original synchronization destination. The wireless communication system according to claim 6, wherein the wireless communication system is recorded on the wireless communication system.   10. The public network base station other than the public network base station that has stopped the synchronization is the original synchronization destination public network base station recorded in the second database means. Wireless communication system. In a radio communication system including a plurality of base stations that perform radio communication in a time division communication system, a radio base station that is one of the plurality of base stations,
Synchronization means for synchronizing with any of a plurality of public network base stations;
1st base station number which shows the number of the base stations which received the alerting signal which base stations other than the self-station among the plurality of base stations originated, and which received the alerting signal which was able to be received completely A comparison means for comparing the second base station number indicating the number of base stations that have transmitted the broadcast signal that could not be received in any form;
When it is determined that the number of the second base stations is larger than the number of the first base stations, the synchronization with the public network base station synchronized at the time of the determination is stopped, and the synchronization is stopped. And when it is determined that the number of the second base stations is equal to or less than the number of the first base stations, synchronization with the public network base stations synchronized at the time of the determination is performed. And a control means for controlling to continue the radio base station. A first database means;
When it is determined that the number of the second base stations is greater than the number of the first base stations, the control means sets the public network base station that has stopped synchronization as the public network base station that cannot be synchronized. The radio base station according to claim 11, wherein the radio base station is recorded in the database means.   The synchronization by the synchronization means is performed by receiving a public network notification signal transmitted from the plurality of public network base stations, or a base station other than the own station among the plurality of base stations, The radio base station according to claim 11 or 12, wherein the radio base station is executed by receiving a notification signal transmitted from a base station synchronized with any one of the public network base stations. A second database means;
When the control means determines that the second base station number is less than or equal to the first base station number, the second database means uses the public network base station that has continued synchronization as the original synchronization destination. The radio base station according to claim 11, wherein the radio base station is recorded. 15. The public network base station other than the public network base station that has stopped the synchronization is the original synchronization destination public network base station recorded in the second database means. Wireless base station.

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