JP2015154107A - Tdma radio communication system using common radio channel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication system not requiring a frequency changeover in handover processing.SOLUTION: An AP (radio access point) 1-1, upon receiving a synchronous start instruction command from a communication control device 2, radio-transmits a synchronous signal to be an overall synchronous source. An AP 1-2 adjacent to the AP 1-1: is slave-synchronized with the received synchronous signal; and radio transmits a duplicated signal of the synchronous signal in synchronization with the received synchronous signal. Then, after the slave synchronization is similarly established for all APs 1, radio communication using a common CH which is common to the all APs 1 is started. A radio terminal 4, after a handover also, performs TDMA (Time Division Multiple Access) communication using the same time slot.

Description

  The present invention relates to a wireless communication system including a communication control device that executes control related to communication via an external line or an extension, and a plurality of wireless access points that relay communication data between the communication control device and a wireless terminal. In particular, the present invention relates to a radio communication system to which a TDMA (Time Division Multiple Access) system is applied.

  As a general technique of a private cordless telephone system using a micro cell or a pico cell, there is a technique related to a wireless communication system to which a TDMA (Time Division Multiple Access) system such as a DECT (Digital Enhanced Cordless Telecommunications) system is applied (for example, Patent Document 1).

  Here, a cell is a range covered by one base station (in the present invention, a wireless access point), and is a micro cell (radius several tens to several hundreds of meters) or a pico cell (radius several meters to several tens of meters). When the cell range is narrow as in (), the output of radio waves transmitted from the base station can be reduced, and a plurality of base stations can be installed to flexibly secure a desired call area. For this reason, in a local cordless telephone system, it is common to apply a wireless communication system using a micro cell or a pico cell. In order to effectively use radio resources, it is common to use radio channels with different frequencies between adjacent base stations and repeatedly use radio channels with the same frequency as remote base stations. .

  In this case, handover processing (base station switching) is required when moving between cells of a plurality of base stations while making a call. Since radio channels between adjacent cells have different frequencies, a switching time associated with frequency switching is required during the handover process (for example, several msec), and there is a possibility that the call quality may deteriorate due to a momentary interruption.

JP-A-8-289359

  Accordingly, an object of the present invention is to provide a wireless communication system that does not require frequency switching during handover processing.

  In order to solve the above-described problems, the present invention provides a communication control apparatus that accommodates an external line and an internal line and executes control related to communication, and one or more wireless terminals that are connected to the communication control apparatus and belong to the own wireless access point And a plurality of wireless access points that perform wireless communication based on TDMA (Time Division Multiple Access), wherein the communication control device includes a plurality of time slots based on the TDMA Synchronous signal transmission instructing means for transmitting a command for instructing wireless transmission of a synchronization signal related to frame synchronization of a TDMA frame to one of the wireless access points, and communication data between the external line or extension and the wireless access point A relay means for relaying, wherein the wireless access point is configured to wirelessly generate the synchronization signal from the communication control device. A synchronization signal transmitting means for wirelessly transmitting a synchronization signal related to frame synchronization of the TDMA frame when receiving a command for instructing the wireless communication or when a synchronization signal transmitted wirelessly by another wireless access point is received; and Wireless communication means for performing wireless communication based on the TDMA, and relay means for relaying communication data between the wireless terminal and the communication control device, wherein the wireless access point wirelessly communicates with the wireless terminal. The signal to be communicated is a signal modulated with a carrier wave having a frequency corresponding to a predetermined radio channel common to all of the wireless access points, and the time slot used by the wireless terminal is any of the plurality of wireless access points. Both are the same predetermined time slot.

  According to the present invention, since the wireless terminal 4 communicates with each wireless access point 1 using the same frequency and the same time slot, the frequency switching process and the time slot changing process used in the handover process. Is not required, the processing required for handover is extremely simple and quick, and it is possible to provide a radio communication system that is unlikely to deteriorate call quality during handover.

1 is an overall configuration diagram of a wireless communication system according to an embodiment of the present invention. It is an example of the basic sequence of the radio | wireless communications system which concerns on embodiment of this invention. It is the figure which showed the structural example of the time slot which concerns on embodiment of this invention. It is a block block diagram of the wireless access point which concerns on embodiment of this invention. It is an operation | movement flowchart of the communication control apparatus which concerns on embodiment of this invention. 5 is an operation flowchart of the wireless access point according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall configuration diagram of a wireless communication system according to an embodiment of the present invention, which includes a wireless access point 1, a communication control device 2, a wireless terminal 4, and an extension terminal 6.

  A wireless access point (hereinafter sometimes abbreviated as AP) 1 is a wireless base station that forms a wireless communication area (hereinafter also referred to as a cell) 5 of a micro cell or a pico cell. The wireless access point 1 performs wired communication with the communication control device 2 via the extension 3 and also performs wireless communication with the wireless terminal 4 existing in the wireless communicable area 5, and the communication control device 2 and the wireless terminal 4. Relay communication data to and from. There are a plurality of wireless access points 1 in order to expand a wireless communication possible area as a wireless communication system. The connection between the wireless access point 1 and the communication control device 2 is not limited to the extension 3, and may be a wired or wireless local connection that directly connects the communication control device 2 and each wireless access point 1.

  Each wireless access point 1 performs wireless communication based on TDMA with each wireless terminal 4. In this wireless communication based on TDMA, a predetermined specific CH among a plurality of wireless channels (hereinafter also abbreviated as CH) is used as a common CH. The internal configuration and operation flow of the wireless access point 1 will be described later.

  The communication control device 2 is, for example, a main device of a private branch exchange or a button telephone system in a private cordless telephone system. The communication control device 2 relays communication data between the extension line 3, the outside line 7, and each wireless access point 1. The operation flow of the communication control device 2 will be described later.

  The wireless terminal 4 is an extension terminal that can move during communication, and is, for example, a DECT-standard private cordless phone. The wireless terminal 4 belongs to one of the wireless access points 1 and operates as a local cordless phone, and communicates with the communication destination of the outside line 7, the other wireless terminals 4, and the extension terminal 6 via the communication control device 2.

  The extension terminal 6 is a general extension terminal accommodated in the communication control device 2, and communicates with the communication destination of the external line 7, the wireless terminal 4, and other extension terminals 6 via the extension 3 and the communication control device 2. To do.

  The extension 3 is a wiring for connecting the communication control device 2 to various extension terminals including the extension terminal 6 and the wireless access point 1, and the communication method is an analog communication method, a digital communication method, or an IP (Internet Protocol). ) Any communication method may be used. In the case of the IP communication method, general LAN (Local Area Network) wiring can be applied as the extension 3.

  The external line 7 is a line for accessing a WAN (Wide Area Network) 8 such as a telephone network or the Internet network, and the communication method may be any of an analog communication method, a digital communication method, and an IP communication method.

  In the present embodiment, the adjacent wireless access points 1 exist in the wireless communication possible area 5 of each other. For example, AP1-2 exists in the cell 5-1 of AP1-1. This is to catch the radio wave of a signal (for example, a beacon signal) including a synchronization signal transmitted from the adjacent access point 1 to the subordinate wireless terminal. The synchronization timing is extracted from the caught radio wave and is adjacent. The TDMA communication is executed in synchronization with the access point 1. For example, the AP 1-1 designated by the communication control device 2 wirelessly transmits a synchronization signal as a synchronization source, the AP 1-2 receives the synchronization signal and performs subordinate synchronization with the AP 1-1, and the AP 1-2 Duplicate the received synchronization signal and send it wirelessly. In the same manner, dependent synchronization is established in the order of AP1-1 → AP1-2 → AP1-3 →.

  This wireless slave synchronization method is particularly effective when the extension 3 is a LAN. That is, when the communication control device 2 distributes the synchronization signal to each wireless access point 1 via the extension 3 as the LAN, the timing of the synchronization signal arriving at each wireless access point 1 varies due to the transmission delay peculiar to the LAN. Since it fluctuates, the correction is necessary. On the other hand, the wireless dependent synchronization method has a small transmission delay and is constant, so that correction for the transmission delay is unnecessary or easy.

  FIG. 2 is a sequence example of the wireless communication system according to the embodiment of the present invention. The sequence until the subordinate synchronization of all APs is established with the AP 1-1 as the parent AP, and the wireless terminal 4 becomes the AP 1-1. This shows a sequence for handing over to AP1-2 after belonging, a sequence in which the common CH becomes full and the new wireless terminal 4-X is not allowed to belong. A sequence line indicated by a solid line indicates that the sequence is based on wired communication via the extension line 3, and a sequence line indicated by a broken line indicates that the sequence is based on wireless communication.

  First, synchronization establishment of each AP will be described. When communication control device 2 transmits a synchronization signal transmission instruction command for instructing AP 1-1 to start transmission of a synchronization signal via extension 3 (S200), it starts dependent synchronization to instruct AP 1-2 to start dependent synchronization. When the instruction command is transmitted via the extension 3 (S201), the AP 1-1 wirelessly transmits a synchronization signal that is the source of the overall synchronization, and the AP 1-2 receives the synchronization signal from the AP 1-1 (S202). Then, the AP 1-1 transmits a synchronization signal and transmits a synchronization completion notification indicating that the synchronization of the own AP 1-1 has been established to the communication control device 2 (S203). Note that the wireless access point 1 that is the transmission destination of the synchronization signal transmission instruction command transmitted by the communication control device 2 is arbitrary, and may be set in advance or selected at random.

  When the AP 1-2 adjacent to the AP 1-1 receives the synchronization signal wirelessly transmitted by the AP 1-1 (S202), the AP 1-2 subordinately synchronizes the own AP 1 with the received synchronization signal, and the received synchronization signal The copy is transmitted wirelessly in synchronization with the received synchronization signal (S204), and the communication control apparatus 2 is notified of the completion of synchronization indicating that the slave synchronization has been performed (S205). In the same manner, dependent synchronization is established in the order of AP1-1 → AP1-2 → AP1-3 →.

  Note that the synchronization signals S202 and S204 periodically transmitted by each AP1 may be beacon signals that notify the nearby wireless terminal 4 of the presence of the own AP. That is, the synchronization signal received by the own AP 1 from the adjacent other AP 1 is an interception of the beacon signal transmitted from the other AP 1 to the wireless terminal 4 existing in the cell of the other AP 1.

  Here, when the beacon signal transmitted wirelessly by each AP1 is a wireless signal having the same frequency as that of the adjacent other AP1, the wireless terminal 4 located in the area where the cells of both AP1 overlap each other from both AP1 Since the beacon signal is simultaneously received in the interference state, it is difficult to extract the ID information and the like in the beacon signal. For this reason, it is reasonable that the beacon signal transmitted wirelessly by each AP1 is wirelessly transmitted alternately at a timing different from that of the adjacent AP other than the common CH.

  That is, for example, when AP1-2 transmits a synchronization signal (beacon signal) in S204, the presence or absence of a synchronization signal from another AP1 (for example, synchronization signal S202 transmitted by AP1-1) is monitored. The synchronization signal may be transmitted wirelessly at a timing at which AP1 does not transmit the synchronization signal (not shown). In this case, the wireless transmission of the synchronization signal is intermittent, but the frame synchronization interval is only slightly increased, so that the possibility of loss of frame synchronization is not great.

  By the way, in the process of establishing synchronization between adjacent APs 1 in the order of AP 1-1 → AP 1-2 → AP 1-3 →..., Radio signal propagation delay and synchronization signal replication and transmission at each AP 1. However, since the transmission timing of the beacon signal is periodic, there is no problem if the replicated synchronization signal is transmitted wirelessly at the transmission timing of the next and subsequent beacon signals.

  Next, the attribution process between the wireless terminal 4 and AP1 will be described. After the synchronization of all the APs 1 is established, each AP 1 periodically (intermittently) transmits a beacon signal having a common CH frequency at a predetermined timing. The beacon signal includes frame synchronization information and additional information such as ID information for identifying the own AP (not shown).

  The wireless terminal 4 sequentially switches each CH (5CH in the case of DECT) and periodically monitors the beacon signal wirelessly transmitted by the nearby AP1, and when detecting the beacon signal, the wireless terminal 4 wirelessly transmits the beacon signal. Is sent to the AP 1-1 existing at the beacon signal frequency (common CH) (S210). When beacon signals from a plurality of APs 1 are detected, an attribution request may be wirelessly transmitted to the AP 1 on the side where the received radio wave intensity is high.

  Upon receiving the attribution request, the AP 1-1 determines whether or not the wireless terminal 4 is affiliated (whether it is a terminal that is permitted and registered), and if it is a registered terminal that is permitted to belong, it indicates that a new attribution request has been accepted. An attribution request notification is transmitted to the communication control apparatus 2 via the extension 3 (S211). It should be noted that the determination as to whether or not belonging may be performed by the communication control device 2.

  The communication control device 2 manages the usage status of each time slot in TDMA communication, and if there is an empty time slot, an attribution condition including information specifying any of the empty time slots is given to the AP 1-1. The AP 1-1 notifies the wireless terminal 4 of the attribution permission including the notified time slot information (S213).

  The same processing as S210 to S213 described above is executed between each AP1 and each wireless terminal 4, and N (up to 12 in the case of DECT) wireless terminals 4 corresponding to the upper and lower N time slots It belongs to AP1 (not shown). Then, relay of communication data is started between each of the outside line 7, the communication control device 2, AP1-1, and the associated wireless terminal 4 by wireless communication using the common CH (S220).

  In S220, the communication data of each AP1 and each wireless terminal 4 is modulated with the frequency (carrier frequency) of the common CH, so there is a concern about communication data interference in the area where the cells of each AP1 overlap. There is no problem because wireless transmission is not performed in a period other than the time slot used by the wireless terminal belonging to the own AP. That is, in all APs 1, the time slot Tn used by each wireless terminal 4 is unchanged, and only one AP 1 to which the wireless terminal 4 belongs is the AP 1 that transmits and receives a wireless signal at the timing of Tn. Therefore, no interference occurs at the timing of Tn.

  Next, the handover process will be described. When the wireless terminal 4 moves to the AP 1-2 side during communication, the wireless terminal 4 that has determined that the reception intensity of the beacon signal from the AP 1-2 is larger transmits an attribution request to the AP 1-2 (S230).

  Upon receiving the attribution request from the wireless terminal 4 in S230, the AP 1-2 determines whether or not the wireless terminal 4 belongs as in S211, and if it is a registered terminal that is permitted to belong, the AP 1-2 has received a new attribution request. Is sent to the communication control device 2 via the extension 3 (S231). The communication control device 2 that has received the notification of attribution request knows that the wireless terminal 4 has belonged to the AP 1-1, and therefore determines that the notification is an attribution request notification accompanying handover, and An attribution change notification including information relating to the allocated time slot is notified to AP1-1 and AP1-2 via extension 3 (S232, S233).

  Then, the AP 1-2 that has received the attribution change notification in S232 notifies the attribution permission to the wireless terminal 4 (S234), starts exchanging communication data with the wireless terminal 4, and the handover is completed. Further, the AP 1-1 that has received the notification of belonging change in S233 cancels the belonging of the wireless terminal 4 that has belonged so far, sets the time slot used for communication with the wireless terminal 4 to an empty state, and Transmission of the carrier wave (common CH) at the time slot timing is stopped.

  The handover process of S230 to S234 is an example. For example, when the wireless terminal 4 wirelessly transmits an attribution request to the handover destination AP 1-2 in S230, a handover including information on a time slot in use is performed. It is also possible to add the information to the effect and send it. In this case, the AP 1-2 can omit the assignment permission / inhibition determination and can immediately start transmission / reception of communication data with the wireless terminal 4 in the notified time slot in use.

  Further, AP1-2 may notify AP1-1 of the process of releasing the belonging relationship between the original wireless terminal 4 and AP1-1.

  In this handover process, since the CH (common CH) and time slot for transmitting / receiving communication data used before and after the handover by the wireless terminal 4 are unchanged, the process is efficient, and the communication data being communicated may be damaged. Very low.

  Next, the attribution process after the common CH is full will be described. The wireless terminal 4-X transmits an attribution request to any AP (AP1-1 in FIG. 2) in a state where there is no vacant time slot of the common CH (S240), and the AP1-1 requests an attribution request in the same manner as S211. When the notification is transmitted to the communication control device 2 via the extension 3 (S241), the communication control device 2 managing the time slot knows that there is no empty time slot in the common CH, so the wireless terminal 4 -X is reported to the AP 1-1 via the extension 3 (S242), and the AP 1-1 wirelessly transmits to the wireless terminal 4-X that the attribution is not possible (S243).

  Note that the communication control device 2 may notify all the APs 1 that the new wireless terminal 4 cannot be assigned when the time slot of the common CH becomes full.

  FIG. 3 is a diagram illustrating a configuration example of a frame of communication data according to the embodiment of the present invention. A frame of communication data is composed of a plurality of TDMA frames which are a header and a payload. Each TDMA frame is composed of a plurality of downlink time slots (5 msec, 12 slots in the case of DECT) and uplink time slots (5 msec, 12 slots in the case of DECT). The frequency used for the common CH is a predetermined frequency (in the case of DECT, 1895.616 / 1, 897.344 / 1, 899.072 / 1, 900.8 / 1, 902.528 MHz 5CH )

  As the common CH in the present embodiment, an arbitrary CH can be set as the common CH (for example, 1,895.616 MHz). In each time slot, in the case of an empty slot with no data to be communicated, the carrier wave output is stopped in the time slot of the empty slot. Therefore, for example, in FIG. 1, even if the wireless terminal 4 belonging to the AP 1-1 moves to the adjacent AP 1-2 side and enters the range of the communication area 5-2 of the AP 1-2, Since the slot used by the wireless terminal 4 is common, the slot is empty for the AP 1-2 to which the wireless terminal 4 has not yet been assigned, and the output of the carrier remains stopped at the timing of the slot. Then, when the wireless terminal 4 approaches the AP 1-2 and the handover to the AP 1-1 is executed and belongs to the AP 1-2, this time, the slot becomes free for the AP 1-1. The carrier wave output stops at the timing of the slot. That is, there is no radio wave interference due to the carrier of the common CH having the same frequency between the moving wireless terminal 4 and the AP before and after the handover, and the wireless terminal 4 can execute communication with little quality degradation even while moving. .

  FIG. 4 is a block diagram of the wireless access point 1 according to the embodiment of the present invention. The communication control unit 10, the wireless communication unit 11, the extension correspondence unit 12, the synchronization signal extraction unit 13, the synchronization signal generation unit 14, and the channel It comprises a switching unit 15, a wireless terminal attribution processing unit 16, and an belonging wireless terminal information storage unit 17.

  The communication control unit 10 is a means for controlling the entire wireless access point 1, and includes a wireless communication unit 11, an extension corresponding unit 12, a synchronization signal extraction unit 13, a synchronization signal generation unit 14, a channel switching unit 15, a wireless terminal It exchanges and relays communication data with each unit of the belonging processing unit 16 and the belonging wireless terminal information storage unit 17.

  The wireless communication unit 11 is a wireless communication unit with other wireless access points 1 and wireless terminals 4 belonging to the own wireless access point 1, and demodulates the received wireless signal, and communicates with the communication control unit 10. The data is output to the signal extraction unit 13 and the wireless terminal attribution processing unit 16. In addition, the signal input from the synchronization signal generation unit 14 and the wireless terminal attribution processing unit 16 is modulated and wirelessly transmitted to another wireless access point 1 or the wireless terminal 4. Note that this wireless transmission channel is a channel (common CH) instructed by the channel switching unit 15.

  The extension correspondence unit 12 is a connection interface with the extension 3 and relays communication data between the communication control unit 10 and the extension 3.

  The synchronization signal extraction unit 13 monitors a signal received and demodulated by the wireless communication unit 11, extracts a synchronization signal received from another wireless access point 1, and outputs the extracted synchronization signal to the communication control unit 10. And the communication control part 10 which input the synchronizing signal controls each part so that it may be subordinately synchronized with the synchronizing signal.

  The synchronization signal generation unit 14 generates a synchronization signal according to an instruction from the communication control unit 10, and the generated synchronization signal is transmitted as a beacon signal via the wireless communication unit 11 to the nearby wireless terminal 4 and the adjacent wireless access. Called to point 1.

  The channel switching unit 15 is means for switching a plurality of CHs (5CH in the case of DECT) for executing TDMA communication, and in accordance with an instruction from the communication control device 10, the channel used by the radio communication unit 11 to be transmitted is determined. The wireless communication unit 11 is controlled so as to switch to one of the channels designated as the common CH. Note that a CH used as a preset common CH may be stored in the channel switching unit 15 or may be stored in the communication control unit 10.

  The wireless terminal attribution processing unit 16 monitors the wireless signal received and demodulated by the wireless communication unit 11, extracts the attribution request signal transmitted by the wireless terminal 4, and processes the extracted attribution request signal. Is delivered to the communication control unit 10. Further, the response information to the wireless terminal 4 related to the attribution input from the communication control device 2 is delivered to the wireless communication unit 11.

  The belonging wireless terminal information storage unit 17 stores information related to communication with the wireless terminal 4 such as ID information, slot number, and CH information of the wireless terminal 4 belonging to the wireless access point 1.

  FIG. 5 is an operation flowchart of the communication control apparatus 2 according to the embodiment of the present invention. Hereinafter, an operation flow will be described with reference to other drawings. This flow starts in an initial state where synchronization between the APs 1 is not established (S500).

  In the initial state, when the communication control device 2 detects a start event of total synchronization (for example, reset operation of the device 2 or the wireless system) (S501, YES), it is stored as a parent AP that is a predetermined synchronization source. A synchronization signal transmission instruction command (corresponding to S200 in FIG. 2) for instructing transmission of a synchronization signal necessary for frame synchronization is transmitted to extension AP 1 (AP 1-1 in the example of FIG. 2) via extension 3 (S502).

  Here, the synchronization signal transmitted to the parent AP is a signal including timing information of frame synchronization necessary for executing the TDMA communication. For example, the header of the frame shown in FIG. Only the frame and may be the same as the beacon signal transmitted to the wireless terminal 4. Further, the carrier frequency of the synchronization signal transmitted by the parent AP is the frequency of the common CH, and the communication control device 2 may designate CH in the synchronization signal transmission instruction command, or set in advance for each AP1. You may keep it.

  In S503, before a certain time (for example, 1 minute) elapses (S503, NO), a synchronization completion (corresponding to S203 in FIG. 2) is received from the AP1 which is the transmission destination of the synchronization signal transmission instruction command. If received (S503, YES), the process proceeds to S511. When the synchronization completion is not received (S503, NO), and when a time-out occurs (S504, YES), a synchronization signal transmission instruction command is transmitted to another AP1, and the synchronization completion is received from any AP1 until S503 is received. Repeat ~ S505. This loop is a permanent loop. However, if a synchronization completion is not received from any AP 1 even after a predetermined time (for example, 5 minutes) has elapsed, some fatal error occurs. Therefore, an alarm to that effect may be issued and this flow may be terminated (not shown).

  In S511, the communication control device 2 monitors reception of synchronization completion from each AP1 (corresponding to S205, S206,... In FIG. 2), and receives synchronization completion from all AP1 via the extension 3 ( (S511, YES), the process proceeds to S520.

  If no synchronization completion has been received from all the APs 1 (S511, NO) and time-out (for example, T1 = 1 minute) (S512, YES), a synchronization signal transmission instruction command to any AP 1 that has not completed synchronization Is transmitted (S513), and if a higher-level timeout (for example, T2 = 10 minutes) has not been reached (S514, NO), the process returns to S511.

  The processing of S511 to S514 is processing for preventing the synchronization processing of the entire system from being stopped by a part of AP1 that is not subordinately synchronized. That is, there is a high possibility that the AP 1 that has not transmitted the synchronization completion in S511 does not receive the radio wave from the adjacent AP 1. Therefore, in this case, a synchronization signal transmission instruction command similar to S502 may be transmitted to the AP 1 via the extension 3 (S513). However, since the area of AP1 is a local synchronization area by a local parent AP that is out of the overall frame synchronization, when handing over to this area, the wireless terminal 4 is dependent on the frame synchronization system of the local synchronization area. However, since this is similar to a general handover process in which slave synchronization is performed with a beacon signal transmitted by a local parent AP that is a handover destination, there is no major problem.

  If a time-out occurs in S514 (S514, YES), there is an AP that cannot complete the synchronization process, and in this case, there is a high possibility that the AP itself has a problem, so communication within the area is abandoned. Is reasonable. Therefore, in this case, an alarm indicating that there is an inactive AP is notified to a predetermined destination (for example, a system administrator's terminal) via the extension 3 (S515), and the process proceeds to S520.

  In S520, the communication control device 2 is a general communication control device for relaying communication data and for call control (call incoming / outgoing etc.) between each AP 1 and the external line 7 via the extension 3. Start processing and control. Then, after S520, the communication control device 2 monitors the reception of the attribution request notification from each AP1 (S521) and the reception of the attribution cancellation (S522).

  In S522, when a notification to the effect that the wireless terminal 4 belonging to the AP1 has been released from any AP1 is received (S522, YES), the process proceeds to S530, and any AP1 also notifies the removal of the attribution. If not received (S522, NO), the process returns to S521.

  In S521, upon receiving an attribution request notification (corresponding to S211, S231, S241 in FIG. 2) from any AP1 (S521, YES), the belonging wireless terminal stored in the internal memory (not shown) 4 is examined to determine whether the wireless terminal 4 that has requested attribution belongs to another AP1 that is adjacent to the AP1 that has notified the attribution request and belongs to the other AP1. If it is determined that the new wireless terminal 4 is not affiliated (that is, not a handover) (S523, NO), the process proceeds to S524.

  In S523, when it is determined that the request is a membership request from the wireless terminal 4 already belonging to another AP1 (that is, a handover) (YES in S523), the wireless terminal 4 belonging to the memory stored in the internal memory Referring to the information, AP1 that has notified the attribution request of the attribution change information (corresponding to S232 and S233 in FIG. 2) including the information of the time slot used by the wireless terminal 4 and the wireless terminal 4 Notification is made to the belonging AP 1 (S527), and the process proceeds to S530. As a result, the change process (handover process) of the belonging AP 1 of the wireless terminal 4 is performed, and the AP 1 before the handover to which the wireless terminal 4 belonged cancels the belonging of the wireless terminal 4 and the wireless terminal 4 Stop using the time slot used by. In addition, the AP 1 after the handover to which the wireless terminal 4 is attached starts communication with the wireless terminal 4 using the time slot used by the wireless terminal 4.

  In S524, the communication control apparatus 2 refers to the wireless terminal attribution information stored in the internal memory, and determines whether or not the total number of wireless terminals 4 belonging to any one of AP1 is equal to or less than a predetermined value K. This K is a predetermined upper limit number of radio terminals 4 to be assigned to the common CH, and is, for example, the number of time slots in TDMA (12 in the case of DECT).

  If the total number of wireless terminals 4 belonging to any one of AP1 is less than or equal to a predetermined value K (S531, YES), an attribution condition indicating that attribution is included including information designating any of the empty slots (FIG. To the notification source AP (S525), and the process proceeds to S530. As a result, the attribution process between the attribution request source wireless terminal 4 and the AP 1 that has notified the attribution request is performed, and the notified empty slot is being used by the wireless terminal 4.

  If the total number of wireless terminals 4 belonging to any one of AP1 is not less than or equal to the predetermined value K (S524, NO), since the number of terminals that can be accommodated has already been reached (no empty slot), the notification source is not allowed AP1 is notified (S526), and the process proceeds to S530. Note that the state of NO in S524 is a state in which the new wireless terminal 4 cannot be assigned to any AP 1 in this wireless system that performs TDMA communication using only the common CH, and therefore, notification of the non-assignment to all APs 1 is made. You may make it do.

  In S530, the communication control apparatus 2 updates the wireless terminal attribution information stored in the internal memory to the data after the attribution cancellation / new attribution / handover is executed, and returns to S521.

  In addition, although the flow of S521-S530 is an infinite loop, this flow is complete | finished by the predetermined | prescribed end event (For example, the power-off or reset of the own communication control apparatus 2) (not shown).

  FIG. 6 is an operation flowchart of the wireless access point 1 according to the embodiment of the present invention. Hereinafter, an operation flow will be described with reference to other drawings. This flow starts with the power turned on (S600), and monitors reception of a synchronization signal transmission instruction command or a dependent synchronization start instruction command (S601, S602).

  In S601, when a synchronization signal transmission instruction command (corresponding to S200 in FIG. 2) is received from the communication control device 2 via the extension 3 (S601, YES), the own AP1 operates as a parent AP that is a synchronization source. The communication control unit 10 activates the synchronization signal generation unit 14 and starts wireless transmission of a periodic (intermittent) synchronization signal (S611). Then, the communication control device 2 is notified that transmission of a synchronization signal has started (corresponding to S203 in FIG. 2) (S612), and the process proceeds to S630. Note that the periodic (intermittent) synchronization signal wireless transmission in S611 is at a constant interval synchronized with the frame, but when a synchronization signal from the adjacent AP 1 is detected, the transmission is stopped intermittently at that timing. Calling operation.

  In S602, when the slave synchronization start instruction command is received from the communication control device 2 via the extension 3 (S602, YES), the communication control unit 10 activates the synchronization signal extraction unit 13 and generates a synchronization signal from the adjacent AP. When the radio signal is monitored and a synchronization signal (corresponding to S202 and S204 in FIG. 2) is received (S620, YES), the communication control unit 10 controls each unit so as to be subordinately synchronized with the received synchronization signal (S621). ). If dependent synchronization is established (S622, YES), the process proceeds to S623. If dependent synchronization is not established even after a predetermined time (for example, 1 minute) has elapsed (S622, NO), the process returns to S601.

  In S620, if a synchronization signal is not received from the adjacent AP1 even after a predetermined time (for example, 1 minute) has elapsed (S620, NO), if a timeout (for example, 10 minutes) has not occurred (S625, NO), S601 Return to. If timed out (S625, YES), the communication control unit 10 transmits a message notifying that the synchronization signal is not received (synchronization signal reception is impossible) to the communication control device 2 (S626), and returns to S601. In addition, the state of YES in S625 may be a state where the distance from the adjacent AP1 is set at a location that is more than the radio wave arrival distance (for example, 100 m) and the synchronization signal transmitted by the adjacent AP1 cannot be received. Therefore, the process returns to S601, and again waits for reception of a synchronization signal transmission instruction command (corresponding to S513 in FIG. 5). Then, the state in which wireless transmission of the synchronization signal is started in S611 via S626 → S601, YES, the local AP is the local AP and the local AP is the synchronization source.

  In the state of YES in S625, there is a possibility that the own AP1 or an adjacent AP1 is out of order, so this flow may be terminated in S626. In that case, the communication control apparatus 2 that has received the message indicating that the synchronization signal cannot be received displays an alarm to that effect, or notifies a predetermined destination (for example, a system administrator) and leaves it to the system administrator or the like. That's fine.

  In S622, when the dependent synchronization is established (S622, YES), the communication control unit 10 controls the synchronization signal generating unit 14, duplicates the received synchronization signal, and copies the synchronized signal (corresponding to S204 in FIG. 2). The wireless transmission process is periodically started at the timing of frame synchronization with the received synchronization signal (S623). Then, a message notifying that the slave synchronization is completed (corresponding to S205 and S206 in FIG. 2) is transmitted to the communication control device 2 via the extension 3 (S624), and the process proceeds to S630.

  Thereafter, in the standby state of the wireless communication by TDMA, the communication control unit 10 receives the presence request from the wireless terminal 4 (S630), receives the change notification from the communication control device 2 (S640), communication The presence or absence of reception of communication data from the control device 2 or the wireless terminal 4 is circulated and monitored.

  In S630, when an attribution request (corresponding to S210 and S240 in FIG. 2) is received from the wireless terminal 4 (S630, YES), the communication control unit 10 refers to the belonging wireless terminal information storage unit 17 and refers to the wireless terminal 4 It is determined whether or not the terminal permits the attribution. If the wireless terminal 4 is a terminal that is permitted to belong, the communication control unit 10 sends an attribution request (corresponding to S211 and S241 in FIG. 2) of the wireless terminal 4 that has requested the attribution to the communication control device 2. Notification is made (S631), and the process proceeds to S632.

  In S632, when an attribution condition or an attribution change notification is received from the communication control device 2 (S632, YES), attribution permission including information on the time slot to be used (corresponding to S213 and S234 in FIG. 2) is given to the wireless terminal 4. Wireless transmission is performed (S633), and the process proceeds to S650. If NO in 632, S633 is skipped and the process proceeds to S650.

  In S640, when the notification of belonging change related to the handover is received from the communication control apparatus 2 (S640, YES), the communication control unit 10 refers to the belonging wireless terminal information storage unit 17, and the wireless terminal belonging to the own AP1 4, the presence / absence of the wireless terminal 4 that has moved to another AP 1 is determined. If there is, the wireless terminal 4 is a handed over terminal that is already out of the communication area of its own AP 1. The use of the time slot used for communication with the wireless terminal 4 is stopped (S641), and the process proceeds to S650. If NO in S640, S641 is skipped and the process proceeds to S650.

  In S650, when communication data is received from the communication control device 2 or the wireless terminal 4 (S650, YES), the communication control unit 10 transmits communication data (including call control data) between the communication control device 2 and the wireless terminal 4. Relay to each other (S651), and return to S630. If NO in S650, S651 is skipped and the process returns to S630.

  Although the flow from S630 to S651 is an infinite loop, this flow ends (not shown) at a predetermined end event (for example, power-off or reset of the own AP 1).

  The embodiment of the present invention has been described above. According to the present invention, since the wireless terminal 4 communicates with each wireless access point 1 using the same frequency (common CH) and the same time slot, when the wireless terminal 4 moves between cells of the plurality of wireless access points 1. In the handover process, the frequency switching process and the change process of the time slot to be used are not required, and the process required for the handover is extremely simple and quick. In addition, the call quality is less likely to deteriorate.

  Note that the wireless terminal 4 communicating with each wireless access point 1 at the same frequency and in the same time slot means that the number of wireless terminals 4 that can be accommodated as a whole system is limited to the number of time slots. However (12 in the case of DECT), this restriction is less affected if the general office has several tens of employees or less, and the advantage of simplifying the handover process is greater.

  By the way, in the present invention, radio communication areas of the same frequency are adjacent to each other, and there is a concern about radio wave interference. However, each time slot is occupied by a specific radio terminal 4, and each radio access point is accessed by its own radio access. The time slot of the wireless terminal 4 that does not belong to the point is empty, and the wireless access point 1 does not transmit a radio wave (carrier wave) at that timing. Therefore, there is little risk of radio wave interference with adjacent wireless access points in the TDMA frame.

  However, it is necessary to pay attention to the beacon signal that is transmitted wirelessly by the adjacent wireless access point 1. Regarding this beacon signal, it is necessary to cope with a situation in which the wireless terminal 4 located in the middle of both wireless access points 1 receives two beacons simultaneously in addition to worrying about radio wave interference. As a countermeasure, for example, if the wireless transmission timing of the beacon signal is sequentially transmitted with a time shift, simultaneous reception (interference) by the wireless terminal 4 can be prevented.

  In the present embodiment, the wireless dependent synchronization method has been described as an example of the synchronization method between the wireless access points 1, but the present invention is not limited to this. For example, the communication control device 2 or any one of the wireless access points 1 may broadcast the synchronization signal to each wireless access point 1 via the extension 3 (not shown). In this case, an extension communication method based on a synchronous digital communication method such as ISDN (Integrated Services Digital Network) is suitable for the distribution of synchronous signals because there is little variation and fluctuation in propagation delay.

  In this embodiment, the frame structure of communication data between the wireless terminal 4 and the wireless access point 1 includes an uplink time slot (AP1 ← wireless terminal 4) and a downlink time slot (AP1 → wireless terminal 4) in the TDMA frame. However, the present invention is not limited to this. For example, an uplink-dedicated uplink common CH and a downlink-dedicated downlink common CH having different frequencies may be provided. In this case, the wireless access point 1 needs to simultaneously execute two wireless communications with different frequencies, but the number of wireless terminals 4 that can be accommodated as a wireless communication system can be doubled while maintaining the simplicity of the handover process. .

DESCRIPTION OF SYMBOLS 1 ... Wireless access point which concerns on this invention 2 ... Communication control apparatus which concerns on this invention 3 ... Extension 4 ... Wireless terminal 5 ... Wireless communication possible area of each access point 6 ... Extension Terminal 7 ... Outline 8 ... WAN
DESCRIPTION OF SYMBOLS 10 ... Communication control part 11 ... Wireless communication part 12 ... Extension corresponding | compatible part 13 ... Synchronization signal extraction part 14 ... Synchronization signal generation part 15 ... Channel switching part 16 ... Wireless terminal Attribution processing unit 17 ... Attribution wireless terminal information storage unit

Claims (3)

A communication control apparatus that accommodates external lines and internal lines and executes control related to communication, one or more wireless terminals that are connected to the communication control apparatus and belong to the own wireless access point, and based on TDMA (Time Division Multiple Access) A wireless communication system including a plurality of wireless access points for performing wireless communication,
The communication control device includes synchronization signal transmission instruction means for transmitting a command for instructing wireless transmission of a synchronization signal related to frame synchronization of a TDMA frame including a plurality of time slots based on the TDMA to any one of the wireless access points. Relay means for relaying communication data between the external line or extension line and the wireless access point,
When the wireless access point receives a command for instructing wireless transmission of the synchronization signal from the communication control device, or when receiving a synchronization signal wirelessly transmitted by another wireless access point, the wireless access point performs frame synchronization of the TDMA frame. Synchronization signal transmitting means for wirelessly transmitting the synchronization signal, wireless communication means for performing wireless communication based on the TDMA based on the wireless terminal, and relay for relaying communication data between the wireless terminal and the communication control device Means,
A signal for wireless communication between the wireless access point and the wireless terminal is a signal modulated by a carrier wave having a frequency corresponding to a predetermined wireless channel common to all of the wireless access points, and is a time slot used by the wireless terminal. Is a TDMA radio communication system using a common radio channel, which is the same predetermined time slot as any of the plurality of radio access points. The wireless communication system according to claim 1,
The synchronization signal transmitting means provided in the wireless access point receives the synchronization signal transmitted from another wireless access point in a state where the command for instructing wireless transmission of the synchronization signal is not received. A TDMA radio communication system using a common radio channel, wherein a synchronization signal obtained by duplicating a synchronization signal is transmitted wirelessly in synchronization with the received synchronization signal. The wireless communication system according to claim 1 or 2,
If the synchronization signal transmitting means provided in the wireless access point detects a synchronization signal wirelessly transmitted by another wireless access point before a predetermined time before the wireless access point transmits the synchronization signal wirelessly, A TDMA radio communication system using a common radio channel, wherein radio transmission of the synchronization signal is stopped.

Images