JP2007006196A - Synchronizing system between base stations, base station, and its method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a deviation at a timing correction time small by using one slot for synchronization, and performing timing correction for each frame. <P>SOLUTION: A PHS base station 10, a PHS base station 20, and a PHS base station 30 are connected to an Ethernet (R) LAN 40, and performs synchronous communication using synchronous information through the Ethernet (R) LAN 40. A PHS slave unit 11 performs communication with the PHS base station 10. A PHS slave unit 21 performs communication with the PHS base station 20. A PHS slave unit 31 performs communication with the PHS base station 30. A PBX 50 connects with the Ethernet (R) LAN 40, and performs circuit switching with a public digital communication network (not shown). Since the PHS base station 20 receives control channel information of the PHS base station 10, it takes synchronization with the PHS base station 10 for TDMA frame timing of the own station. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inter-base station synchronization system, a base station, and a method thereof, and more particularly to an inter-base station synchronization system, a base station, and a method thereof that perform inter-base station synchronization by transmitting and receiving synchronization information.

  In general, in a mobile communication system such as a PHS (Personal Handyphone System) in which a plurality of base stations are provided and each base station transmits / receives to / from a mobile station using a Time Division Multiple Access (TDMA) method, If the frame synchronization of the transmission / reception signal of the base station is not taken, a plurality of continuous time slots in the frame will be interfered with each other.

  Further, in an Ethernet (registered trademark) LAN connection type PHS base station, since Ethernet (registered trademark) is an asynchronous line, it is necessary to synchronize TDMA frames between the base stations. A conventional Ethernet (registered trademark) LAN connection type PHS base station corrects the TDMA frame timing by receiving a control channel transmitted by another PHS base station (see, for example, Patent Document 1). .)

  However, in Patent Document 1, the control channel of the PHS base station is not continuously transmitted, but is intermittently transmitted. Therefore, the following problems occur.

  In other words, when the local station corrects the TDMA frame timing for the synchronization destination PHS base station, the transmission timing of the local station also slightly shifts at that moment. The longer the timing correction period is, the larger this deviation is. The PHS slave connected to the PHS base station that performed the timing correction and the PHS base station that performs the timing correction based on the PHS base station On the other hand, it causes a reception error. The reception error causes noise, handover, and call disconnection for the PHS slave unit. In addition, the PHS base station may be out of synchronization.

  Furthermore, when the reception quality of the synchronization destination PHS base station is not good, there may be a case where timing correction cannot be performed due to a reception error. When the period for performing the timing correction is long, the influence of one reception error becomes large. For example, when the timing correction period is 150 ms, if a reception error occurs once, the timing correction is performed for the next 150 ms, so that it takes 300 ms for the timing correction.

  In addition, when selecting a synchronization destination PHS base station, if a PHS base station that is synchronized with the local station is selected, synchronization is not stable. Therefore, it is necessary to select a PHS base station that is not synchronized with the local station. There is. However, in the method using the control channel, the amount of information that can be notified to other PHS base stations over the radio is small. For this reason, in order to make a reliable selection, it is necessary to exchange control information individually on the LAN in parallel. For example, it is necessary to construct a mechanism for managing the association between a CSID (Cell Station Identifier) and an IP (Internet Protocol) address.

JP 2003-319451 A (pages 5-6 and 9-13)

  In the conventional inter-base station synchronization system and method described above, since the control channel is intermittently transmitted in a frame, the timing correction is large, and in an environment where the reception quality is not good, the PHS slave device in communication is remarkably used. It has the disadvantage of being easily adversely affected.

  In addition, since the amount of synchronization information that can be transmitted through the control channel is limited, there is a drawback that there is no guarantee that proper synchronization can be ensured.

  An object of the present invention is to provide an inter-base station synchronization system, a base station, and a method thereof that reduce a shift during timing correction.

The inter-base station synchronization system of the present invention,
Synchronizing means for transmitting and receiving synchronization information between base stations for each frame using at least one slot in one frame and performing synchronization between base stations in a synchronization system between base stations using a frame signal by time division multiplexing It is characterized by having prepared.

The inter-base station synchronization system of the present invention,
In a synchronization system between base stations using a frame signal by time division multiplexing, a first base station that transmits synchronization information using at least one slot in one frame, and a first base station that receives the synchronization information from the slot 2, and the second base station performs a timing correction for correcting the frame timing of the local station after determining that the first base station is appropriate as a synchronization destination from the received synchronization information. It is characterized by including a means.

  The first and second base stations are characterized in that the synchronization information is acquired and the frame timing is corrected for each frame.

  In addition, the second base station receives the synchronization information transmitted by the first base station, and confirms that there is no identification number of the own station in the synchronization information, and then the first base station The frame timing correction is performed with reference to the above, and the synchronization information is transmitted to another base station.

  Further, the timing correction means corrects using a timer held by the first base station when there is a deviation from the timing of the second base station.

  Furthermore, the base station is a PHS (Personal Handyphone System) base station.

The base station of the present invention
In a base station that performs inter-base station synchronization using a frame signal by time division multiplexing,
A transmission unit and a reception unit that transmit and receive synchronization information;
The presence / absence of the identification number of the local station is determined in the synchronization information received from the counterpart station, the identification number of the counterpart station is deleted when the identification number of the local station is present, and the identification number of the local station is absent. A base station manager that determines the other station as the synchronization destination;
A synchronization determination timing correction unit for comparing the reception timing from the partner station with the timing of the timer of the own station and performing synchronization determination and timing correction after determining the partner station as a synchronization destination;
It is characterized by having.

  Further, the base station management unit creates a list of the identification numbers and reception levels of neighboring base stations.

  Furthermore, the base station is a PHS (Personal Handyphone System) base station.

The synchronization method between base stations of the present invention,
In the inter-base station synchronization method using the frame signal by the time division multiplexing method, the synchronization information is transmitted / received between the base stations using at least one slot in one frame, and the inter-base station synchronization is performed.

The synchronization method between base stations of the present invention,
In the synchronization method between base stations using frame signals by time division multiplexing,
The first base station transmits synchronization information using at least one slot in one frame, the second base station receives the synchronization information from the slot, and receives the synchronization information from the received synchronization information. It is characterized in that the frame timing of the local station is corrected after the station determines that it is appropriate as a synchronization destination.

  Further, the first and second base stations are characterized in that the synchronization information is acquired and the frame timing is corrected for each frame.

  In addition, the second base station receives the synchronization information transmitted by the first base station, and confirms that there is no identification number of the own station in the synchronization information, and then the first base station The frame timing correction is performed with reference to the above, and the synchronization information is transmitted to another base station.

  Further, the frame timing correction is corrected by using a timer held by the first base station when there is a deviation from the timing of the second base station.

The synchronization method between base stations of the present invention,
In the synchronization method between base stations using frame signals by time division multiplexing,
Searching for a control channel when the base station is activated, and creating a list of unique identification numbers of neighboring base stations and their reception levels;
Transmitting a request for synchronization slot information to the base station having the highest reception level in the list, and receiving the synchronization information of the target base station from the response;
Determining whether or not there is a response to the synchronization slot information, and deleting the identification number of the target base station from the list if there is no response to the synchronization slot information;
If there is a response to the synchronization slot information, receiving synchronization information from the synchronization slot and determining whether the synchronization information includes an identification number of the own station;
Deleting the identification number of the target base station from the list when the synchronization information includes an identification number of the own station;
When the synchronization information does not include the identification number of the local station, performing timing correction for each frame and starting control channel transmission;
It is characterized by having.

  Further, the base station is a base station synchronization method using a PHS (Personal Handyphone System) base station.

  The synchronization system between base stations, the base station and the method of the present invention use one slot in one frame for synchronization, and perform timing correction for each frame using this synchronization slot. Reduce the deviation.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of an inter-base station synchronization system and method according to the present invention.

  The present embodiment shown in FIG. 1 includes PHS base stations 10, 20, 30, PHS slave units 11, 21, 31, Ethernet (registered trademark) LAN 40, and PBX 50.

The PHS base station 10, the PHS base station 20, and the PHS base station 30 connect to the Ethernet (registered trademark) LAN 40, and perform synchronous communication using the synchronization information via the Ethernet (registered trademark) LAN 40. The PHS slave unit 11 communicates with the PHS base station 10. The PHS slave device 21 communicates with the PHS base station 20.
The PHS slave unit 31 communicates with the PHS base station 30. The PBX 50 is connected to the Ethernet (registered trademark) LAN 40 and performs circuit switching with a public digital communication network (not shown).

  FIG. 2 is a detailed block diagram of the PHS base station of FIG.

  Referring to FIG. 2, each of the PHS base stations 10, 20, and 30 includes a LAN interface unit 101, a slave unit interface unit 102, a transmission unit 103, a reception unit 104, a base station management unit 105, and a synchronization determination. A timing correction unit 106 and a timer 107 are provided.

  The LAN interface unit 101 performs a transmission / reception interface with the Ethernet (registered trademark) LAN 40. The subunit | mobile_unit interface part 102 performs the transmission / reception interface with the PHS subunit | mobile_unit 11,21,31. Transmitter 103 transmits data to the PHS base station and the PHS slave unit. The receiving unit 104 receives data from other PHS base stations and PHS slave units. The base station management unit 105 performs management control of the entire PHS base station, and the like, creating a list of CSIDs (Cell Station Identifiers) of CSs that are neighboring PHS base stations and their reception levels. The synchronization determination timing correction unit 106 performs synchronization determination and timing correction processing. The timer 107 generates a timing signal for timing correction.

  In FIG. 1, the PHS base station 10 uses one of the slots in one frame and transmits its own synchronization information. The PHS base station 20 receives the synchronization information transmitted from the PHS base station 10, and determines whether the partner PHS base station 10 is appropriate as a synchronization destination, and then corrects the timing of the TDMA frame of the local station. .

  Next, an operation for performing timing correction will be described.

  The timing from the timer 107 in FIG. 2 held by the own station and the timing at which the slot of the synchronization destination PHS base station is received are compared by the synchronization determination timing correction unit 106, and if there is a deviation, the timer 107 of the own station is corrected. .

  For example, when receiving the synchronization destination slot at timing t1 at timing t2, the timer 107 of the own station is reset from t2 to t1. That is, the operation is performed so that the moment when the synchronization destination slot is received becomes t1.

  In this way, since the PHS base station can acquire synchronization information and correct TDMA frame timing for each frame, the reference timing due to unsuitable synchronization destination selection or temporary reception quality degradation. Loss (out of sync) can be prevented. Therefore, in a system in which PHS base stations are connected via an Ethernet (registered trademark) LAN, a stable synchronized state can be maintained independently only by the PHS base stations.

  Next, the operation of the present embodiment will be described in more detail with reference to FIG.

  The PHS base station 10 transmits synchronization information to other PHS base stations. The PHS base station 20 receives the synchronization information transmitted from the PHS base station 10 and confirms that the CSID (Cell Station Identifier) of the local station (PHS base station 20) is not included in the synchronization information. After confirming the absence, the PHS base station 20 corrects the timing of the TDMA frame with the PHS base station 10 as a reference, and transmits synchronization information to the other PHS base stations. The CSID is an identification number that each PHS base station has uniquely.

  FIG. 3 is a diagram of a frame format showing reception and transmission of synchronization information.

  In PHS, one frame (5 ms) is composed of eight slots (0 to 7), and one slot has a time width of 625 μs. Slots 0 to 3 are used for uplink (slave unit → base station), and slots 4 to 7 are used for downlink (base station → slave unit) communication. One PHS base station uses four slots and simultaneously holds lines for four calls. Since one slot is used exclusively for control information, three lines are used by using three slots for calls. .

In the present invention, one slot is further used from the call slot, and one line (one channel) is used for synchronization between base stations. Therefore, the call slot has two lines.
One of the call slots is used as a synchronization slot, but the name of this call slot is not always used exclusively for a call, and is also used for data other than a call. Since PHS is targeted here, it is called a call slot as call voice data.

  FIG. 4 is a diagram showing a slot configuration in the frame format of FIG.

  As shown in FIG. 4, one slot has a time width of 625 μs, and is composed of 240-bit data. As a slot for synchronization, synchronization information is stored in 180 bits in the I frame. R, SS, PR, UW, CRC, G, CI, and SA shown in FIG. 4 are defined in RCR STD-28, which is a PHS standard. The number of each block in FIG. 4 represents the number of bits.

  “R” of each symbol is a ramp time for transient response, “SS” is a start symbol, “PR” is a preamble, “UW” is a synchronization word, “CRC” is a cyclic redundancy code for error detection, and “G” is Indicates a guard bit. “CI” constituting the “I” frame means a channel type, and “SA” means a low-speed associated control channel (SACCH).

  The synchronization information consists of two pieces of synchronization slot information and synchronization destination CSID information. The synchronization slot can take a multi-frame configuration, and frame number information for that purpose is stored as synchronization slot information. The synchronization destination CSID information section stores the CSID of the synchronization destination PHS base station.

  For example, when storing a 42-bit CSID, it is possible to store three CSIDs in one frame. Since 144 bits are reserved for synchronization destination CSID information in the slot, since 42 × 3 = 126, synchronization for up to three units can be secured in one frame.

  Next, in FIG. 3, the PHS base station 10 transmits synchronization information through the slot 1, and the PHS base station 20 receives the synchronization information of the PHS base station 10 through the slot 1. The PHS base station 20 transmits synchronization information to the PHS base station 30 through the slot 5 corresponding to the same channel position after 4 slots. The PHS base station 30 receives the synchronization information of the PHS base station 20 through the slot 5 and transmits the synchronization information to another PHS base station through the slot 1 after 4 slots. Thereafter, the PHS base station repeats the above operation.

  In the above embodiment, slot 1 and slot 5 are used as synchronization slots for transmitting synchronization information, but any slot other than the control slot (slot 2, 6 or slot 3, 7) is used. Also good.

  FIG. 5 is a flowchart showing the operation of the inter-base station synchronization system and method according to the present invention.

  Next, the operation of the PHS base station will be described with reference to FIG. 2, FIG. 3, and FIG.

  Immediately after starting a CS (Cell Station) which is a PHS base station (here, PHS base station 20) (step S1), the base station management unit 105 first searches for a control channel and then searches for CSIDs of neighboring CSs ( Cell Station Identifier) and a list of reception levels thereof are created (step S2).

  FIG. 6 is a diagram showing the correspondence between the CSID of the PHS base station and the reception level.

  FIG. 6 shows a correspondence list between the CSID of the PHS base station on the local station side and its reception level, and the synchronization destination is shown based on this list.

  Here, CS indicates a PHS base station, and CSID indicates an identification number inherent to each PHS base station. Next, the base station management unit 105 determines whether the list is empty (step S3). If the list is empty, the base station management unit 105 takes the timing with the free-running internal clock (step S10), proceeds to step S11, controls the transmission unit 103, and starts control channel transmission. If the list is not empty, the base station management unit 105 transmits a request for synchronization slot position information to the CS (for example, PHS base station 10) having the highest reception level in the list by the transmission unit 103 (step S4). . Here, the synchronization slot position information indicates the synchronization slot number in FIG. 3 (slot 1 in the case of FIG. 3).

  Next, the base station management unit 105 determines whether or not there is a response to the synchronization slot position information (step S5). If there is no response to the synchronization slot position information at step S5, the CSID of the target (PHS base station 10) is selected from the list. Delete (step S8) and return to step S3.

  When there is a response of the synchronization slot position information in step S5, the base station management unit 105 receives the synchronization information from the synchronization slot (step S6), and does the synchronization information include the CSID of the own station (PHS base station 20)? It is determined whether or not (step S7).

  In step S7, when the CSID of the local station is included in the synchronization information, the base station management unit 105 deletes the CSID of the CS (PHS base station 10) that has responded to the synchronization information from the list. That is, in order to delete this CS item from the list and change the synchronization target CS, the process returns to step S3 (step S8). The reason for this operation will be described later with reference to FIG.

  If the CSID of the own station is not included in step S7, the base station management unit 105 sends this information to the synchronization determination timing correction unit 106, and the synchronization determination timing correction unit 106 receives the synchronization slot (the slot in FIG. 3). In 1), the timing is corrected for each frame (step S9). Next, control channel transmission is started (step S11).

  Thereafter, step S3 to step S11 are repeated for each frame between the PHS base stations 10 and 20 as shown in FIG. 3, thereby establishing synchronization by slot 1 for each frame.

  FIG. 7 is a diagram illustrating a synchronization state between PHS base stations.

  By synchronizing with a base station whose own CSID is included in the synchronization information, a synchronization loop (following the synchronization destination can be reached) (FIG. 7 (a)). In this state, synchronization is not stable, and a plurality of synchronization groups may be formed. The reason why the synchronization is not stable is that when the own station is erroneously synchronized such as false lock, all other stations are erroneously synchronized. In FIG. 7A, the synchronization between group A and group B is not achieved. In principle, it is necessary for all PHS base stations to perform radio synchronization. In this case, the synchronization state is a tree (branching state) as shown in FIG. 7B.

  Here, determination of whether or not the synchronization destination is appropriate will be described. As a condition for performing a stable service in PHS, “the wireless timing is synchronized in all PHS base stations in the service area”. The fact that all PHS base stations have radio timing means that the synchronization state is in a tree shape (FIG. 7B).

  As a method for realizing this, it is conceivable to manage the synchronization state externally. To that end, it is necessary to prepare a device (synchronization management server) for managing the synchronization state for each service area. The method of the present invention does not require an external device for managing the synchronization state, each PHS base station autonomously selects the synchronization destination PHS base station, and maintains the correct synchronization state (= synchronization loop) Avoid).

  When each PHS base station independently selects a synchronization destination, it is necessary to avoid the generation of a synchronization loop as shown in FIG.

  In the present invention, in order to avoid the above-mentioned synchronization loop, in the determination process at the time of synchronization destination selection (step S7 in FIG. 5), it is checked whether the CSID of the local station is included in the synchronization information received from the synchronization destination. To do. If the PHS base station is selected, the PHS base station is deleted from the synchronization destination candidates because a circle of synchronization is created when the PHS base station is selected as the synchronization destination (step S8 in FIG. 5).

Since the synchronization destination PHS base station can stably receive synchronization information when the distance is short (that is, the reception level is large), it basically synchronizes with the closest PHS base station. If the distance is far away, a transmission error occurs and the possibility of missing the synchronization information increases. Therefore, in step S4 in FIG. 5, it is checked whether or not synchronization is possible from the list with the highest reception level.
In step S4 of FIG. 5, a request for synchronization slot position information is transmitted to the CS having the highest reception level in the list, and the synchronization information of the target CS is received from the response. When the CSID of the local station is included in the synchronization information (step S7 in FIG. 5), the item of this CS is deleted from the list (step S8 in FIG. 5), and the target is changed to the next CS.

  On the other hand, if the synchronization information does not include the CSID of the local station, the CS that has transmitted the synchronization information is determined as the synchronization destination CS, and the TDMA frame of the local station is synchronized with the transmission timing of the synchronization slot for each frame. The timing is corrected (step S9 in FIG. 5).

  Note that “synchronization slot information” and “synchronization destination CSID information” are used for confirming the synchronization state so far from the synchronization destination PHS base station. That is, it is used to determine whether or not it is possible to synchronize with this PHS base station.

  As described above, since the TDMA frame timing is corrected for each frame, even when the reception quality is temporarily deteriorated, the shift width at the time of timing correction can be reduced.

  Further, since the synchronization information of the synchronization destination PHS base station can always be acquired from the synchronization slot, the synchronization destination CS can be selected reliably and easily.

  Furthermore, since all of the operations are completed within the PHS base station, there is no need to perform processing related to synchronization in an externally connected PBX or other server.

  By adding the synchronization information plus the CSID of the synchronization destination PHS base station to the synchronization slot and transmitting it, the PHS base station that received the information is the base station to which the other station that sent the synchronization information as the synchronization destination is suitable. Since it can be easily determined whether or not the station is a station, the PHS base station can independently realize a stable wireless synchronization state.

  In addition, this invention is not limited to the above-mentioned embodiment, For example, it can apply also to the normal PHS base station which is not LAN connection.

  In addition, the present invention is not limited to the PHS communication system as long as it is a time division multiplexing (TDMA) system and performs transmission / reception using signals composed of a plurality of slots.

[BRIEF DESCRIPTION OF THE DRAWINGS] It is a block diagram which shows one Embodiment of the synchronization system between base stations of this invention, and its method. It is a detailed block diagram of the PHS base station of FIG. It is a figure of the frame format which shows reception and transmission of synchronous information. FIG. 4 is a diagram showing a slot configuration in the frame format of FIG. 3. It is a flowchart which shows operation | movement of the synchronization system between base stations of this invention, and its method. It is a figure which shows a response | compatibility with CSID of a PHS base station, and a reception level. It is a figure which shows the synchronous state between PHS base stations, (a) is a figure which shows the ring | wheel of synchronization, (b) is a figure which shows the correct synchronous state.

Explanation of symbols

10, 20, 30 PHS base station 11, 21, 31 PHS cordless handset 40 Ethernet (registered trademark) LAN
50 PBX
101 LAN Interface Unit 102 Slave Unit Interface Unit 103 Transmitting Unit 104 Receiving Unit 105 Base Station Management Unit 106 Synchronization Determination Timing Correction Unit 107 Timer

Claims (16)

  Synchronizing means for transmitting and receiving synchronization information between base stations for each frame using at least one slot in one frame and performing synchronization between base stations in a synchronization system between base stations using a frame signal by time division multiplexing A synchronization system between base stations, comprising:   In a synchronization system between base stations using a frame signal by time division multiplexing, a first base station that transmits synchronization information using at least one slot in one frame, and a first base station that receives the synchronization information from the slot 2, and the second base station performs a timing correction for correcting the frame timing of the local station after determining that the first base station is appropriate as a synchronization destination from the received synchronization information. Means for synchronizing between base stations.   3. The inter-base station synchronization system according to claim 2, wherein the first and second base stations acquire the synchronization information and correct the frame timing for each frame.   The second base station receives the synchronization information transmitted from the first base station, confirms that the identification number of the own station is not included in the synchronization information, and then sets the reference to the first base station. 3. The inter-base station synchronization system according to claim 2, wherein frame timing correction is performed and the synchronization information is transmitted to another base station.   3. The inter-base station system according to claim 2, wherein when there is a deviation from the timing of the second base station, the timing correction unit corrects using a timer held by the first base station. Synchronous system. The base station synchronization system according to any one of claims 1 to 5, wherein the base station is a PHS (Personal Handyphone System) base station. In a base station that performs inter-base station synchronization using a frame signal by time division multiplexing,
A transmission unit and a reception unit that transmit and receive synchronization information;
The presence / absence of the identification number of the local station is determined in the synchronization information received from the counterpart station, the identification number of the counterpart station is deleted when the identification number of the local station is present, and the identification number of the local station is absent. A base station manager that determines the other station as the synchronization destination;
A synchronization determination timing correction unit for comparing the reception timing from the partner station with the timing of the timer of the own station and performing synchronization determination and timing correction after determining the partner station as a synchronization destination;
A base station characterized by comprising:   The base station according to claim 7, wherein the base station management unit creates a list of the identification numbers and reception levels of neighboring base stations.   9. The base station according to claim 7, wherein the base station is a PHS (Personal Handyphone System) base station.   In a base station synchronization method using a frame signal according to time division multiplexing, base information is transmitted and received between base stations using at least one slot in one frame, and base station synchronization is performed. Inter-station synchronization method. In the synchronization method between base stations using frame signals by time division multiplexing,
The first base station transmits synchronization information using at least one slot in one frame, the second base station receives the synchronization information from the slot, and receives the synchronization information from the received synchronization information. A synchronization method between base stations, wherein after the station determines that it is appropriate as a synchronization destination, the frame timing of the local station is corrected.   12. The inter-base station synchronization method according to claim 11, wherein the first and second base stations perform acquisition of the synchronization information and frame timing correction every frame.   The second base station receives the synchronization information transmitted from the first base station, confirms that the identification number of the own station is not included in the synchronization information, and then sets the reference to the first base station. 12. The inter-base station synchronization method according to claim 11, wherein frame timing correction is performed and the synchronization information is transmitted to another base station.   12. The inter-base station correction according to claim 11, wherein the frame timing correction is corrected using a timer held by the first base station when there is a deviation from the timing of the second base station. Synchronization method. In the synchronization method between base stations using frame signals by time division multiplexing,
Searching for a control channel when the base station is activated, and creating a list of unique identification numbers of neighboring base stations and their reception levels;
Transmitting a request for synchronization slot information to the base station having the highest reception level in the list, and receiving the synchronization information of the target base station from the response;
Determining whether or not there is a response to the synchronization slot information, and deleting the identification number of the target base station from the list if there is no response to the synchronization slot information;
If there is a response to the synchronization slot information, receiving synchronization information from the synchronization slot and determining whether the synchronization information includes an identification number of the own station;
Deleting the identification number of the target base station from the list when the synchronization information includes an identification number of the own station;
When the synchronization information does not include the identification number of the local station, performing timing correction for each frame and starting control channel transmission;
A synchronization method between base stations, comprising: The inter-base station synchronization method according to any one of claims 10 to 15, wherein the base station is a PHS (Personal Handyphone System) base station.

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