JP5063756B2 - COMMUNICATION SYSTEM, BASE STATION DEVICE, AND COMMUNICATION CONTROL METHOD - Google Patents

Description

  The present invention relates to a communication system, a base station apparatus, and a communication control method that have a large number of base stations and communicate with a mobile station at transmission timings and reception timings synchronized with the base stations.

  In a mobile communication system such as a portable wireless device, a communication line using radio waves is set between a wireless base station and a mobile station, and communication is performed by transmitting and receiving voice, data, etc. wirelessly. Since then, digital cellular phone systems based on TDMA and CDMA (Code Division Multiple Access) have been widely used. The base station and mobile station of this TDMA system operate so as to receive a reception slot assigned to the own station, transmit in the transmission slot assigned to the own station, and repeat transmission / reception intermittently. . In addition, CDMA base stations and mobile stations transmit and receive digital signals modulated by spreading codes assigned to the CDMA system. In these digital mobile communication systems, base stations and mobile stations must synchronize and transmit and receive at the same timing.

  In the TDMA scheme, in order to synchronize the base station and the mobile station, the mobile station that has received the signal from the base station transmits / receives its own station based on the synchronization signal (synchronization word) included in the signal from the base station. Synchronize the frames and start transmission from the mobile station. In addition, in order to absorb the frame timing shift caused by the distance between the base station and the mobile station, a guard time is provided at the beginning of each reception slot so that reception is not affected even if a transmission slot enters. .

  In such a mobile communication system, communication is continued by switching the base station of the connection destination as the mobile station moves. Therefore, the transmission timing and the reception timing of each base station must match. If there is a difference in transmission timing and reception timing between base stations, the transmission slot and the reception slot interfere with each other and normal reception cannot be performed.

  In particular, in the TDMA-TDD system that performs time-division bidirectional transmission, an uplink signal to the base station and a downlink signal to the mobile station are mixed at the same frequency. The signal and the downstream signal collide.

  Specifically, in the PHS system (Personal Handyphone System) that employs the TDMA-TDD system, as shown in FIG. 8, four reception slots and four transmission slots are arranged in one TDD / TDMA frame. The transmission / reception slots are repeated with a millisecond cycle. At this time, if the transmission / reception timing (frame timing) between the base station 1 and the base station 2 is shifted, the transmission slot and the reception slot interfere with each other between the base stations. That is, while the mobile station transmits an uplink signal to the base station 1 (RX4), the base station 2 transmits a downlink signal to the mobile station (TX1), and the uplink signal (RX4). And the downstream signal (TX1) collide with each other. In many cases, the transmission output of the base station is larger than that of the mobile station, and the base station 1 cannot receive the upstream signal in the reception slot RX4.

  Various methods have been proposed for synchronizing frame timing between base stations in a mobile communication system. For example, there is a method in which each base station autonomously establishes synchronization in accordance with a base station having the strongest electric field strength among surrounding base stations. However, in this method, a base station is generated that deviates greatly from the frame timing of the reference station due to an infinite chain of synchronization. In addition, since there are a plurality of base stations serving as a reference for synchronization, a plurality of synchronization groups are formed, and frame timing is shifted between the synchronization groups, so that interference occurs between the synchronization groups.

  In addition, since each base station is connected by a wired line, there is a method of establishing synchronization by distributing a reference signal via this wired line. However, since a standard interface such as ISDN cannot distribute a reference signal, and a special interface is required to distribute the reference signal, it is not suitable for a large-scale public network. In addition, it is difficult to synchronize base stations across a plurality of exchanges in consideration of the effect of transmission delay caused by the exchanges.

  Further, since each base station is controlled by a center facility that comprehensively controls the communication network, there is a method of correcting the frame timing according to an instruction from the center facility. However, this method requires an instruction from the center facility by the operator, resulting in an operation cost. In addition, complicated processing is required, for example, the synchronization instruction must be given again when adding base stations.

  An object of the present invention is to provide a communication system that establishes synchronization of transmission timings and reception timings between a plurality of base stations in a simple and reliable manner.

The first invention is a communication system including a plurality of base stations, and a control of the network side can control a plurality of base stations, the base station identification information and synchronization hierarchy of its own station indicating the own station and means for transmitting the base station information including the information indicating the level to the control device, characterized in that.

The base station may notify the other base station apparatus of the base station information when the base station is initialized.

2nd invention is the said base station in the communication system containing a some base station and the network side control apparatus which can control these some base stations, Comprising: The identification information which shows a self station, and the synchronization of a self station And means for transmitting base station information including information indicating the hierarchical level to the control device .

A third invention is a communication control method in a communication system including a plurality of base stations and a network-side control device capable of controlling the plurality of base stations, wherein the base station includes identification information indicating its own station and its own information. Transmitting base station information including information indicating a hierarchical level of station synchronization to the control device .

  In addition, the other first mobile communication system has a plurality of base stations, and the mobile station selectively connects to one or two or more of the base stations and performs transmission / reception at a predetermined timing. In the mobile communication system, the plurality of base stations are composed of a base station having a GPS receiver and a base station having no GPS receiver, and the base station having the GPS receiver Based on the signal from the GPS satellite received by the machine, the transmission timing and reception timing of its own station are determined, and the base station not having the GPS receiver is hierarchically centered on the base station having the GPS receiver. Synchronize to determine transmission timing and reception timing. As a result, a base station having a GPS receiver and a base station not having a GPS receiver are arranged, and the base station having no GPS receiver is hierarchically structured around the base station having a GPS receiver. Since the transmission timing and the reception timing are determined in synchronization with each other, the transmission timing and the reception timing can be synchronized with high accuracy.

  The other second mobile communication system has a plurality of base stations, and the mobile station selectively connects to one or two or more of the base stations and performs communication by transmitting and receiving at a predetermined timing. In a mobile communication system, a base station that generates high-accuracy transmission timing and reception timing among the base stations is set as a reference station at a higher level, and other base stations select a higher-level base station. Then, the transmission timing and the reception timing are determined, and the hierarchy of the own station is set lower than the selected base station, so that synchronization is hierarchically centered on the reference station. As a result, a base station that generates high-accuracy transmission timing and reception timing is set as a reference station at a higher level in the hierarchy, and other base stations select a base station in a higher hierarchy than its own station to transmit and receive timing. Since each base station autonomously selects the optimal synchronization partner base station, there is no need for an operator to perform synchronization control and the operation cost is reduced. Can be reduced.

  In the other third mobile communication system, the signal transmitted by the base station includes a synchronization control code indicating the position in the hierarchy of the own station, and the other base station receives the synchronization control code from the own station. It is characterized by selecting a base station in a higher hierarchy. As a result, the signal transmitted by the base station includes a synchronization control code indicating the status in the hierarchy of the own station, and other base stations select a base station in a higher hierarchy than the own station by the synchronization control code. It is possible to form an autonomous synchronization hierarchy with a simple configuration.

  The other fourth mobile communication system is characterized in that the base station selects a base station having a strong signal strength among base stations of the same layer and determines a transmission timing and a reception timing. As a result, a base station having a strong signal strength is selected from other base stations in the same hierarchy, and the transmission timing and the reception timing are determined. Therefore, synchronization can be reliably performed.

  The other fifth mobile communication system performs communication by the TDD method, and the base station determines frame timing as transmission timing and reception timing. As a result, the base station determines the frame timing based on other base stations, so that the transmission slot and the reception slot do not collide.

  The other sixth mobile communication system has a center facility for overall control of the base station. When the base station synchronizes with another base station, the position in the hierarchy of the own station becomes the center facility. It is characterized by notifying. As a result, when synchronizing with other base stations, the status in the own station's hierarchy is notified to the center equipment that controls the base station in an integrated manner, so the center equipment grasps the position in the synchronization hierarchy of each base station. be able to.

  The other seventh mobile communication system has a center facility for overall control of the base station, and the base station determines its transmission timing and reception timing without synchronizing with other base stations. The center facility is notified. As a result, when the transmission timing and reception timing of its own station are determined without synchronizing with other base stations, it notifies the center equipment that controls the base station in an integrated manner. I can grasp it.

  ADVANTAGE OF THE INVENTION According to this invention, the synchronization between several base stations can be established autonomously simply and reliably.

It is a block diagram of the whole PHS system to which this invention is applied. It is a block diagram of the base station apparatus of embodiment of this invention. It is a block diagram of CSID of embodiment of this invention. It is a table | surface which shows the content of the synchronization control bit of embodiment of this invention. It is a flowchart which shows the operation | movement at the time of power activation of the base station of embodiment of this invention. It is a flowchart which shows the detail of the operation | movement which selects a synchronous other party in the base station of embodiment of this invention. It is a figure which shows the hierarchy of the base station synchronized by embodiment of this invention. It is a figure which shows the transmission / reception timing of the conventional base station apparatus.

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

  FIG. 1 is a configuration diagram of an entire PHS system to which the present invention is applied.

  A PHS terminal (PS) 1, which is a mobile station of the PHS system, establishes a wireless line with the base station apparatus (CS) 2 and performs voice and data communication. Since this PHS method uses a multiple access method (multi-channel access method), the terminal 1 and the base station apparatus 2 exchange information necessary for setting a call channel in the control channel ( Negotiate), set the call channel, and start communication on the call channel.

  The base station apparatus 2 is connected to a subscriber exchange 3, and the subscriber exchange 3 is further connected to an ISDN network 5 via a relay exchange 4. Further, the base station apparatus 2 is connected to the center facility 6 via the exchanges 3 and 4, and the center facility 6 performs overall control of starting, stopping, setting change, and the like of the base station apparatus 2.

  FIG. 2 is a block diagram of the base station apparatus 2 according to the embodiment of this invention.

  The base station apparatus 2 is connected to a subscriber telephone network (ISDN network) 5 through an exchange 3. The signal input from the exchange 3 to the base station apparatus 2 is level-converted by the interface unit 11, encoded by the encoding / decoding unit 12, and modulated, multiplied, amplified, etc. by the baseband unit 13 and the radio unit 14. The processed high frequency signal is transmitted from the antenna 15 as a downstream signal to the PHS terminal 1.

  On the other hand, the upstream signal received from the PHS terminal 1 received by the antenna 15 is subjected to processing such as frequency conversion in the radio unit 14 and sent to the baseband unit 13 for baseband processing such as detection (demodulation). The The encoder / decoder 12 decodes the baseband-processed signal and converts it into an analog signal. The decoded signal is converted to a level that can be input to the exchange 3 by the interface unit 11 and sent to the exchange 3.

  The CPU 17 controls each unit of the base station device 2. The clock unit 16 generates a clock signal, and the CPU 17 instructs the radio unit 14 on the transmission / reception switching timing based on the clock signal. The storage unit 18 stores a control program for the CPU 17 to control the base station apparatus 2 and data necessary for the CPU 17 to operate. The control unit of the base station apparatus 2 is configured by the clock unit 16, the CPU 17, the storage unit 18, and the like.

  Further, some of the base station devices 2 include a GPS receiver 19, which receives a signal from a GPS satellite via a GPS receiving antenna 20, and a clock extraction unit 21 receives time information from the signal from the GPS satellite. To extract. The GPS satellite has an atomic clock and transmits accurate time information. In the base station device 2 including the GPS receiver, the frame synchronization timing signal is generated according to the extracted time information, so that it is possible to generate a timing signal that is extremely accurate (about ± 1 microsecond) and without any error. .

  The GPS receiver 19, the clock extraction unit 21, and the GPS reception antenna 20 constitute a GPS unit and are configured to be detachable from the base station apparatus 2. For this reason, a non-GPS station can be easily changed to a GPS station.

  FIG. 3 is a configuration diagram of an identification code (CSID) according to the embodiment of the present invention.

The base station apparatus 2 transmits its own identification code (CSID) at regular time intervals (100 millisecond intervals) in the control channel. This CSID includes a 3-bit synchronization control code in addition to a 9-bit operator identification code, a general call area number, and an additional ID.
This synchronization control code represents the position of each base station in the hierarchy of the synchronization level, and defines whether it is a base station that is a synchronization partner as viewed from other base stations.

  FIG. 4 is a table showing the contents of the synchronization control code according to the embodiment of the present invention.

The synchronization control code is composed of a 3-bit signal, and in this embodiment, five levels of synchronization are set. The base station (GPS station) provided with the GPS receiver 19 is set to the highest synchronization level (synchronization level 1) and is represented by a synchronization control code of “100”.
“Synchronization level 2” is a station that synchronizes the frame timing of its own station based on a signal from a base station (GPS-equipped station) of synchronization level 1, and the priority that is referenced from other base stations is synchronized. It is next to the base station of level 1 and is represented by a synchronization control code of “101”.
“Synchronization level 3” is a station that synchronizes the frame timing of its own station based on a signal from a base station of synchronization level 2, and the priority that is the reference from other base stations is that of synchronization levels 1 and 2 It is next to the base station and is represented by a synchronization control code of “110”.
“Synchronization level 4” is a station whose frame timing is synchronized based on a signal from a base station of synchronization level 3, and has the lowest priority as a reference from other base stations. This is represented by the synchronization control code.
The “asynchronous station” is a synchronization level of a base station that is not equipped with the GPS receiver 19 and is not synchronized with other base stations, and is represented by a synchronization control code of “000”. A base station that has synchronized frame timing based on a signal from a base station at synchronization level 4 is also set to a synchronization level of “asynchronous station”.

  This synchronization level has the highest priority as a reference for synchronization as viewed from other stations because “sync level 1” has the highest frame timing accuracy. In addition, since “sync level 4” has the lowest frame timing accuracy, the priority as a reference for synchronization is the lowest when viewed from other stations. Further, the “asynchronous station” is provided at the lower level of the synchronization level 4 and the frame timing error of the asynchronous station is estimated to be large, so that it is not used as a reference for synchronization by other base stations.

  In the present embodiment, the synchronization control code is represented by 3 bits, but the number of bits of the synchronization control code may be increased to set a higher-level synchronization level. In this case, it is desirable to set the hierarchy so that the synchronization is lost due to the delay and the line cannot be connected.

  FIG. 5 is a flowchart showing an operation at power-on of the base station apparatus 2 according to the embodiment of the present invention.

  When the base station apparatus 2 is newly started or restarted by a reset signal or the like, the constants are initialized when the power is turned on, and the respective circuits (baseband unit 13, radio unit 14, etc.) are initialized. (S101). The CPU 17 of the control unit detects whether the base station device 2 has the GPS receiver 19 (S102), and if the GPS receiver 19 is mounted, extracts the clock signal from the signal from the GPS satellite. Thus, the frame timing of the own station is synchronized with this time information (S103). Thereafter, the synchronization level of the local station is set to “1” (S104), and transmission on the control channel is started (S109). By using a synchronization control code included in the identification code (CSID) transmitted through this control channel, the base station is notified to the other base station that it is a GPS-equipped station.

  On the other hand, if the GPS receiver 19 is not mounted on the base station apparatus 2 (S102), the control channel is received and CSIDs from surrounding base stations are received (S105). This CSID includes a synchronization control code. Receiving the identification code (CSID) from the surrounding base station, the base station apparatus 2 selects a synchronization partner (S106). The operations in steps S105 to S106 will be described in detail later with reference to FIG.

  Then, in synchronization with the synchronization signal (synchronization word) of the partner station, a synchronization clock of the station is generated, and the frame timing of the station is synchronized with the frame timing of the partner station (S107).

  Thereafter, 1 is added to the synchronization level of the partner station that is the reference for frame synchronization, and it is set at a lower level of the synchronization level of the base station based on the synchronization level of the local station (S108). Then, transmission of the CSID on the control channel is started (S109), and the synchronization level of the own station is notified to other base stations.

Also, the center facility 6 is notified by a wired line that the synchronization level of the own station has been determined (S110). At this time, instead of notifying the center facility 6 unconditionally after synchronization as in the present embodiment, the center facility 6 may be notified only when the station becomes an asynchronous station.
With this configuration, the center facility 6 can grasp only the base station in which an abnormality has occurred.

  FIG. 6 is a flowchart showing details of an operation of selecting a partner base station that synchronizes the frame timing of the own station in the base station according to the embodiment of the present invention. The bases around steps S105 to S106 in FIG. Details of the operation from the reception of the station to the selection of the synchronization partner station are shown.

  The CPU 17 of the control unit of the base station sets a 100 millisecond timer as a time for receiving the control channel, and starts measuring 100 milliseconds (S111). Thereafter, the control channel is continuously received (S113) until the timer expires and 100 milliseconds elapse (S112). In the PHS system, each base station transmits a CSID on the control channel at intervals of 100 milliseconds. Therefore, if the control channel is received continuously for 100 milliseconds, all the base stations that can be received by the base station are received. A CSID can be received.

  If the base station apparatus 2 can receive another base station in any time slot within 100 milliseconds (S114), the base station apparatus 2 receives the received base station CSID, synchronization control code, received field strength (RSSI, Bit error rate and the like) are stored (S115). On the other hand, if the other base station cannot receive (S114), the control channel is continuously received (S112 to S115) until the timer expires and a predetermined time (100 milliseconds) elapses (S112 to S115). Search for nearby base stations.

  When continuous reception of the control channel for a predetermined time (100 milliseconds) is completed, a synchronization partner base station is selected from the received base stations. The CPU 17 of the control unit selects a base station having the lowest synchronization level (higher hierarchy and higher synchronization priority) from the data of neighboring base stations stored in the storage unit 18 (S116). At this time, if a plurality of base stations having the same synchronization level have been received (S117), a base station having the maximum reception level is selected from the base stations having the same synchronization level (S118).

  FIG. 7 is a diagram illustrating a hierarchy of base stations synchronized according to an embodiment of the present invention.

  The base stations shown in the figure are indicated by circles (black circles, white circles). A base station (CS1) indicated by a black circle at the center of the figure is a GPS-equipped station, and is a reference station that is the center of a synchronous group of the illustrated base stations.

  CS1 is a GPS-equipped station and the synchronization level is 1. CS2 and CS3 generate their own frame timing in synchronization with the CS1 frame timing, and the synchronization level of CS2 and CS3 is set to “2” which is one rank lower than the synchronization level of CS1. Since CS4 synchronizes with the frame timing of CS3 and CS5 generates the frame timing of its own station in synchronization with the frame timing of CS2, the synchronization level of CS4 and CS5 is one rank lower than the synchronization level of CS2 and CS3. Set to “3”.

  At this time, CS5 can receive both CS2 and CS4 base stations, but CS2 has a higher synchronization level (CS2 is synchronization level 2 and CS4 is synchronization level 3), so it is a higher-order base station. CS2 is selected, and the frame synchronization clock signal of its own station is generated in synchronization with the frame timing of CS2. Even if CS4 receives CS2 and CS3 having the same synchronization level, CS3 is closer to CS2 and has a stronger received electric field strength, so CS4 selects CS3 and CS3 frame timing. Synchronize with

This GPS-equipped station is appropriately installed so that the order of surrounding base stations is low (the synchronization level is large), and base stations serving as a reference for synchronization do not exist around.
For this reason, the center facility 6 monitors the synchronization level of the base stations, and it is not necessary to arrange many GPS stations. Therefore, the system is flexible and can be configured at low cost.

  In addition, when a plurality of base stations are hierarchized in this way, a plurality of synchronization groups are formed when base stations are arranged in a wide area, but the base station serving as a reference is based on time information from GPS satellites. Therefore, the error between the synchronization groups is small, and a frame timing shift exceeding the guard time does not occur even in a place where different synchronization groups are in contact.

  Asynchronous stations can be configured to receive control channels periodically and to synchronize with the base station to be synchronized by the same procedure as in FIG. it can. In addition, if a CSID from a higher-order base station than the current synchronization partner can be received, the synchronization can be performed again.

  In this way, base stations that do not have GPS receivers are centered on GPS-equipped stations that have GPS receivers, and GPS-equipped stations are set at the top of the hierarchy with reference stations, and other base stations The base station of the higher hierarchy than the own station is selected by the synchronization control code transmitted by the mobile station, the frame timing is determined, and each base station autonomously forms a hierarchy and synchronizes with the GPS-equipped station as the center. Therefore, it is possible to synchronize transmission / reception timing with high accuracy (reference stations are about ± 1 μsec). In addition, there is no need for an operation of synchronization control by the operator, and the operation cost can be reduced.

  Furthermore, because GPS-equipped stations are distributed and installed, even if one GPS-equipped station breaks down, the base station synchronized with this GPS-equipped station only needs to be synchronized with other peripheral stations. The operation of the mobile communication system does not stop, and the resistance to failure is strong.

  Furthermore, since the frame timing is synchronized by selecting a base station having a strong signal strength among other base stations in the same hierarchy, the synchronization can be surely performed.

  In addition, when the synchronization level of the own station is determined by synchronizing with other base stations, the center facility is notified by a wired line that the synchronization level of the own station has been determined. It is possible to grasp the status within.

  1: PHS terminal (PS), 2: Base station apparatus (CS), 3: Subscriber exchange, 4: Relay exchange, 5: ISDN network, 6: Center equipment, 11: Interface unit, 12: Encoding / decoding Conversion unit (CODEC), 13: baseband unit (B / B), 14: radio unit (TRX), 15: antenna, 16: clock unit (CLK), 17: CPU, 18: storage unit (RAM / ROM) , 19: GPS receiver, 20: GPS antenna, 21: Clock extraction unit.

Claims (3)

In a communication system including a plurality of base stations and a network-side control device capable of controlling the plurality of base stations ,
The base station, a communication system, characterized by have a means for transmitting the base station information including the information indicating the synchronization hierarchy level identification information and the own station indicating the own station to the controller. A base station in a communication system including a plurality of base stations and a network-side control device capable of controlling the plurality of base stations,
A base station comprising means for transmitting base station information including identification information indicating the own station and information indicating a hierarchical level of synchronization of the own station to the control device. In a communication control method in a communication system including a plurality of base stations and a network-side control device capable of controlling the plurality of base stations,
The communication control method comprising the step of the base station transmitting base station information including identification information indicating the own station and information indicating a hierarchy level of synchronization of the own station to the control device.

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