JP2013048328A - Base station and communication control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base station capable of suppressing a synchronization shift between the base station and a neighboring base station even when the base station and a public network or the like are connected by a communication cable which is not a leased line.SOLUTION: A base station comprises: a wireless communication unit 1 which performs wireless communication between itself and a communication terminal MS; a wired communication unit 6 which performs wired communication between itself and a public network NW; a control unit 9 which performs synchronous processing on the basis of a synchronous signal included in transmission data transmitted from a host device 100 via the public network NW; and a synchronization unit 2 which performs synchronous processing based on a high-precision synchronous signal having higher precision than a synchronous signal from the host device 100. If synchronous processing in the synchronization unit 2 is disabled, the control unit 9 instructs the host device to increase priority so that the transmission data can preferentially pass the public network and transmit the data. The control unit determines whether synchronization adjustment is required based on whether a difference between a first timing based on the synchronous signal from the host device 100 and a second timing based on a clock of the own machine exceeds a prescribed value.

Description

  The present invention relates to a base station and a communication control method in wireless communication, and more particularly to a base station and a communication control method that can maintain high timing accuracy.

  Since PHS (Personal Handyphone System) uses TDMA (Time Division Multiple Access) -TDD (Time Division Duplex) as a communication method, high timing accuracy is required. If there is a base station that transmits and receives at a different timing from the neighboring base stations, uplink radio communication with weak radio waves from the communication terminal and downlink radio communication with high output radio waves from the base station are performed simultaneously. In this case, a large interference wave is generated for uplink wireless communication from the communication terminal. In addition, if the timing is shifted when performing a handover, the communication terminal searches for a base station having a different timing, which causes a hindrance to the handover.

  The base station before the communication terminal can be connected (before operation) can detect the timing by receiving the radio waves of the surrounding base stations in the same manner as the communication terminal. Because it transmits at the same timing as the station, it cannot receive radio waves from other base stations.

  In general, the accuracy of the internal clock of the base station is not high, and if all the base stations operate based on the internal clock, the timing is shifted and an interference wave is generated as described above. Therefore, the same clock source is required between adjacent base stations.

  The current PHS base station and the public network such as the Internet are connected by a dedicated line such as an optical line cable or ISDN line, and these can send a highly accurate synchronization signal simultaneously with data. The PHS base station is controlled so as not to cause a synchronization error with the surrounding base stations by synchronizing the synchronization signal transmitted from the circuit switch via the public network and the clocks of each part in the base station. ing.

  Here, although not an example of PHS, Patent Document 1 discloses that a clock is extracted from data input to a network repeater, and the data output from the network repeater is synchronized with the timing of the extracted clock. By transmitting transmitted data, a configuration is disclosed in which devices using a communication path having a network repeater can perform processing synchronously.

JP 2010-200033 A

  As described above, high timing accuracy is required in the PHS base station, and the PHS base station and the public network such as the Internet are connected by a dedicated line so that a high-accuracy synchronization signal can be transmitted. . However, the dedicated line is expensive, and in terms of cost reduction, it is desirable that a communication line such as a LAN cable generally used in a personal computer or the like can be used.

  On the other hand, since an inexpensive communication line cannot send a highly accurate synchronization signal, there is a problem that it cannot be used for a PHS base station.

  The present invention has been made to solve the above-described problems. Even when a base station and a public network are connected by a communication cable that is not a dedicated line, a synchronization shift between neighboring base stations is prevented. An object is to provide a suppressed base station and a communication control method.

  In order to solve the above problems, a base station according to the present invention includes a wireless communication unit that performs wireless communication with a communication terminal, a wired communication unit that performs wired communication with a public network, and the public network. A control unit that performs synchronization processing based on a synchronization signal included in transmission data transmitted from the host device, and synchronization that performs synchronization processing based on a high-precision synchronization signal that is more accurate than the synchronization signal from the host device. And the control unit prioritizes the transmission data so that the transmission data can preferentially pass through the public network when the synchronization process in the synchronization unit becomes impossible. Whether or not the difference between the first timing based on the synchronization signal from the host device and the second timing based on the own clock exceeds a predetermined value Whether synchronization adjustment is necessary To determine.

  In one aspect of the base station according to the present invention, the control unit calculates a difference between the first timing and the second timing a plurality of times in a predetermined period, and a minimum value thereof exceeds the predetermined value. If so, adjust the synchronization.

  One aspect of the base station according to the present invention is that the difference between the first timing and the second timing is calculated a plurality of times in a predetermined period in a state where the synchronization processing is possible in the synchronization unit, and the minimum value thereof To obtain the predetermined value.

  One aspect of the base station according to the present invention is such that the control unit can preferentially pass the transmission data through the public network to the host device in a state where the synchronization processing in the synchronization unit is possible. The minimum value is acquired by instructing to transmit with higher priority.

  In one aspect of the base station according to the present invention, the high-accuracy synchronization signal is received and acquired from GPS.

  In one aspect of the base station according to the present invention, when the control unit is in a state where the synchronization processing in the synchronization unit is impossible, so as to shorten the interval of transmitting the transmission data from the host device, An instruction is issued to the host device.

  In one aspect of the base station according to the present invention, the control unit calculates a difference between the first timing and the second timing a plurality of times in a predetermined period, calculates a variance of those values, When the value exceeds a predetermined threshold, it is not determined whether synchronization adjustment is necessary.

  The communication control method according to the present invention includes a base station that performs wireless communication with a communication terminal and performs wired communication with a public network, and exchange of data between the base station via the public network. A communication control method in a communication system comprising: a base station, wherein the base station performs synchronization processing based on a synchronization signal included in transmission data transmitted from the host apparatus; and When the base station has a function of performing synchronization processing based on a high-precision synchronization signal with higher accuracy than the synchronization signal, and the base station is in a state where the synchronization processing based on the high-precision synchronization signal is impossible (A) instructing the host device to transmit the transmission data with a higher priority so that the transmission data can preferentially pass through the public network; and (b) the host device from the host device. First timing based on the synchronization signal And determining whether or not synchronization adjustment is necessary based on whether or not the difference between the second timing and the second timing based on the own clock exceeds a predetermined value.

  According to the base station of the present invention, when the synchronization process in the synchronization unit becomes impossible, the priority is increased so that transmission data can preferentially pass through the public network to the higher-level device. Since an instruction to transmit is issued, the delay of transmission data can be suppressed, and the difference between the first timing based on the synchronization signal from the host device and the second timing based on the own clock Since it is determined whether or not synchronization adjustment is necessary depending on whether or not exceeds a predetermined value, it is possible to suppress synchronization deviation with other base stations.

  According to the communication control method of the present invention, when the synchronization processing based on the high-precision synchronization signal becomes impossible, the transmission data can preferentially pass through the public network to the host device. Since an instruction to transmit at a higher priority is issued, transmission data delay can be suppressed, and the first timing based on the synchronization signal from the host device and the first timing based on the own clock Since it is determined whether or not synchronization adjustment is necessary based on whether or not the difference with the timing of 2 exceeds a predetermined value, synchronization deviation with other base stations can be suppressed.

It is a figure which shows typically the structure of the communication system in which the base station which concerns on this invention is integrated. It is a block diagram which shows the structure of the base station which concerns on this invention. It is a block diagram which shows the structure of a circuit switch. It is a figure which shows typically the synchronous operation | movement of the base station which concerns on this invention. It is a figure which shows an example of a structure of a synchronous packet. 3 is a flowchart showing a synchronization operation of a base station according to the present invention. It is a figure explaining application when a clock speed differs. It is a figure which shows typically the synchronous operation | movement of the base station which concerns on this invention. It is a figure explaining the synchronous operation of the base station which concerns on this invention. It is a figure explaining the modification of the synchronous operation of the base station which concerns on this invention. It is a figure which shows an example of a structure of a synchronous packet.

<Embodiment>
<Configuration of communication system>
FIG. 1 is a diagram illustrating an example of a communication system in which a base station according to the present embodiment is incorporated. A communication system shown in FIG. 1 includes a plurality of communication terminals MS, a plurality of base stations BS, a public network NW such as the Internet, a hub device HB that connects base stations to each other, and a circuit switch 100 such as an OLT (Optical Line Termination) Device) and an upper network TN such as a telephone network. The plurality of base stations BS include those connected to the circuit switch 100 via the public network NW and those connected to the circuit switch 100 via the hub device HB. The base station BS and the communication terminal MS Is wirelessly connected. The hub device HB and the base station BS are connected by a dedicated line such as an optical line cable or ISDN line, and the public network NW and the base station BS are connected with a general communication such as a LAN cable. Assume that they are connected by a line.

  The circuit switch 100 is a device that relays between the public network NW or the hub device HB and the upper network TN.

<Base station configuration>
FIG. 2 is a block diagram showing the configuration of the base station BS. In FIG. 2, only the configuration according to the invention is shown, and other configurations are omitted.

  As shown in FIG. 2, the base station BS is connected to a transmission / reception antenna AT1 and is based on a wireless communication unit 1 that performs wireless communication and a synchronization signal received and acquired from a GPS (Global Positioning System) via a GPS antenna AT2. A synchronization unit 2 that performs synchronization processing, a clock unit 4 that measures its own clock, an instruction unit 5 that instructs the circuit switch 100 to perform priority control of packets to the public network, A wired communication unit 6 that receives a synchronization signal and the like, a wired synchronization unit 7 that acquires a synchronization signal on the public network side from a synchronization signal received by the wired communication unit 6, a wireless communication unit 1, a synchronization unit 2, and a clock unit 4 And a comparison unit 3 that is connected to the wired synchronization unit 7 and compares the synchronization timings of the synchronization unit 2, the clock unit 4, and the wired synchronization unit 7.

  The synchronization unit 2, the comparison unit 3, the clock unit 4, the instruction unit 5, and the wired synchronization unit 7 are included in the control unit 9 that controls the entire base station BS including synchronization processing.

  Here, the base station BS performs synchronization processing based on a synchronization signal received and acquired from GPS (Global Positioning System). This synchronization signal is highly accurate and does not pass through a public network such as the Internet. So it does not include fluctuations.

  Therefore, when the synchronization signal from the GPS can be acquired, synchronization between the base stations is established, but when the synchronization signal from the GPS cannot be acquired, for example, when the GPS signal is interrupted due to the influence of the weather, etc. The synchronization is established based on the synchronization signal from the circuit switch 100.

  In the above description, the synchronization unit 2 has been described as performing the synchronization process based on the synchronization signal received and acquired from the GPS. However, the synchronization unit 2 can supply a highly accurate synchronization signal comparable to the synchronization signal from the GPS. The base station BS may include a precision oscillator or the like, and the synchronization unit 2 may perform synchronization processing by receiving a synchronization signal therefrom.

  In the base station BS, a reception signal received by the transmission / reception antenna AT1 is input to a reception unit (not shown) of the wireless communication unit 1, subjected to amplification processing and down-conversion, converted into a baseband signal, and output. A signal received by the transmission / reception antenna AT is modulated by a BPSK (Binary Phase Shift Keying) modulation method, a QPSK (Quadrature Phase Shift Keying) modulation method, or the like.

  In addition, the wireless communication unit 1 transmits a wireless signal modulated by a BPSK modulation method, a QPSK modulation method, or the like. In addition, although control of each part of base station BS, such as transmission / reception control in the wireless communication part 1 and transmission / reception control in the wired communication part 6, is performed by the control part comprised by CPU (Central Processing Unit) etc., The description is omitted.

<Configuration of circuit switch>
FIG. 3 is a block diagram showing the configuration of the circuit switch 100. In FIG. 3, only the configuration according to the invention is shown, and other configurations are omitted.

  As shown in FIG. 3, the circuit switch 100 includes a wired control unit 101 that controls connection to the base station BS and the upper network TN, an instruction receiving unit 104 that receives an instruction from the base station BS, and a reception from the base station BS. If the received instruction is an instruction to perform priority control of packet processing for the public network, the priority setting unit 105 for setting priority and the instruction received from the base station BS perform priority control of packets for the public network. If it is an instruction to perform, a synchronization packet creation unit 103 that creates a synchronization packet including priority information, and a clock unit that generates and counts a high-accuracy clock and sets a transmission interval of the synchronization packet 102, and a control unit 106 that controls communication information given from the base station BS or the upper network TN via the wired control unit 101.

<Synchronous operation example 1>
Next, a first synchronization operation example of the base station BS according to the present invention will be described with reference to FIGS. In the following, the state in which the synchronization process is performed based on the synchronization signal received and acquired from the GPS is the normal operation state, the synchronization signal from the GPS cannot be acquired, and the synchronization signal sent from the circuit switch 100 is used. The operation when it is necessary to synchronize based on this will be described.

  FIG. 4 schematically shows the synchronization operation of the base station BS according to the present invention. In FIG. 4, the timing at which the synchronization signal from the GPS is given is 1 pps (precise positioning service) timing of GPS, and the interval Is every second.

  In addition, the clock count number in the circuit switch 100 (described as OLT in FIG. 4) is also shown, and the count number at 1 pps timing of GPS is shown as 10,000 counts.

  The base station BS and the circuit switch 100 operate at 100 clock / sec, and the clock count in the circuit switch 100 increases by 100 counts every 1 second.

  Here, when synchronization processing is performed based on a synchronization signal received and acquired from GPS (during normal operation), the clock of the base station BS has neither delay nor delay time fluctuation. On the other hand, the public network NW and the base station BS are connected by a general communication line such as a LAN cable, and the delay time fluctuates. Therefore, when the synchronization signal from the GPS cannot be acquired and synchronization is performed based on the synchronization signal sent from the circuit switch 100, the synchronization signal includes delay and fluctuation of the delay time. If the fluctuation of the delay time is large, it becomes impossible to synchronize with the neighboring base stations, so it is necessary to acquire the fluctuation of the delay time.

  Therefore, first, the delay time between the circuit switch 100 and the base station BS is measured periodically during normal operation or when the base station BS is activated.

  Here, the problem is the time spent for packet processing on the public network. In other words, when a service that does not require high time responsiveness via a public network, such as a web service, is used, even if packet communication that requires high time responsiveness is performed, Packet processing is performed only after completion. The same applies to the case where the synchronization signal is received from the circuit switch 100 by packet communication, and as a result, the fluctuation of the synchronization signal transmitted increases.

  Therefore, when measuring the delay time between the circuit switch 100 and the base station BS during normal operation, the shortest delay time is measured by preferentially performing packet processing on the public network. .

  For this purpose, prior to the measurement of the delay time, an instruction is sent from the instruction unit 5 (FIG. 2) of the base station BS to the circuit switch 100 so as to increase the priority of packet processing for the public network.

  In the circuit switch 100, when the instruction receiving unit 104 receives an instruction from the base station BS and this is an instruction to increase the priority of packet processing for the public network, the priority setting unit 105 sets the priority. Set. In this case, the priority is set to be, for example, the highest value, but a certain effect can be obtained if the priority is not the lowest value (corresponding to normal first-come-first-served processing).

  Then, the synchronization packet creation unit 103 includes a synchronization packet including the count number at the GPS 1 pps timing obtained by counting the clock generated by the clock unit 102 and the priority set by the priority setting unit 105. Create Here, FIG. 5 shows an example of the synchronization packet.

  A synchronization packet 10 shown in FIG. 5 has a payload 14 including a MAC header 11 at the head, an IP header 12, a UDP header 13, and clock count information in the OLT. In the synchronization packet 10, the priority is stored in the IP header 12. More specifically, for example, in IPv6, it is stored in the traffic class field of the IP header 12 or the like. The priority can also be specified using DiffServ (Differentiated Services) or IntServ (Integrated Services).

  The synchronization packet 10 has a UDP header 13, which means that the synchronization packet 10 is a UDP (User Datagram Protocol) packet. UDP is a protocol that does not check whether a packet has arrived at the other party (does not perform retransmission control), and enables high-speed communication.

  Returning to the description of FIG. When an instruction is sent from the base station BS to the circuit switch 100 to increase the priority of packet processing for the public network, the circuit switch 100 transmits, for example, the synchronization packet 10 as shown in FIG. 5 to the public network NW (FIG. 1). To the base station BS. In the relay device on the public network NW, since the priority of the synchronization packet 10 is high, the synchronization packet 10 is processed in preference to the processing of other services. Therefore, the synchronization packet 10 arrives at the base station BS with the shortest delay time.

  In FIG. 4, first, the information (message) of the clock count number at the GPS 1pps timing (0.0000 seconds) of the circuit switch 100 is the count number in the clock unit 4 (FIG. 2) in the base station BS. Reached when reached.

  Here, if the number of times the message is sent from the circuit switch 100 is set to 3 (this number can be arbitrarily set), the count of the clock at the GPS 1pps timing is 1.0000 seconds and 2.0000 seconds. Number of information (message) will arrive. In the example of FIG. 4, this is reached when the counts at the clock unit 4 (FIG. 2) in the base station BS reach 20100 and 20200, respectively.

  The above-described synchronization packet 10 from the circuit switch 100 is received by the wired communication unit 6 of the base station BS, and information on the clock count in the circuit switch 100 is given to the wired synchronization unit 7. Further, it is given to the comparison unit 3 and compared with the count number of the own device counted by the clock unit 4.

  In the example of FIG. 4, the clock count in the circuit switch 100 at a GPS 1 pps timing of 0.0000 seconds is 10,000, and when the information reaches the base station BS, the clock unit 4 (FIG. 2) Since the count number is 20000, the difference is 10,000.

  Further, the count number of clocks in the circuit switch 100 at 1 pps timing of 1.000 seconds of GPS is 10100, and the count number in the clock unit 4 (FIG. 2) when the information reaches the base station BS is 20100. Therefore, the difference is 10,000.

  Similarly, the count number of the clock in the circuit switch 100 at 1 pps timing 2.000 seconds of GPS is 10200, and when the information reaches the base station BS, the count number in the clock unit 4 (FIG. 2) is Since it is 20200, the difference is 10,000.

  Thus, the delay time between the circuit switch 100 and the base station BS measured during normal operation is 10,000 counts in terms of clock count, and there is no fluctuation (fluctuation) even after multiple measurements. As a result, the minimum delay time obtained by these three measurements is 10,000 counts. Thereafter, the presence or absence of synchronization deviation is determined using the minimum value of the delay time during normal operation as an index.

  After the measurement of the delay time, the packet processing priority for the public network is set to the normal priority (for example, a value corresponding to the first-come-first-served processing) from the instruction unit 5 (FIG. 2) of the base station BS to the circuit switch 100. Send instructions to return to

  In this way, the normal priority is returned to the base station that needs communication with a higher priority if all the base stations keep the higher priority, including the base station capable of normal operation. This is because the request will not be accepted.

  Next, a case will be described in which a synchronization signal from GPS cannot be acquired and synchronization needs to be performed based on a synchronization signal sent from the circuit switch 100.

  In FIG. 4, it is assumed that it has been detected that the GPS synchronization signal cannot be used at the GPS 1 pps timing of 12.0000 seconds. That is, the synchronization unit 2 (FIG. 2) of the base station BS performs synchronization processing based on the synchronization signal received and acquired via the GPS antenna AT2 (FIG. 2), but the GPS synchronization signal is interrupted. The synchronization unit 2 (FIG. 2) detects it. Then, the information is given to the instruction unit 5 (FIG. 2), and the instruction unit 5 sends an instruction to the circuit switch 100 to increase the priority of packet processing for the public network.

  This instruction is sent before the timing at which the next synchronization signal is sent, here, the GPS 1 pps timing 13.0000 seconds.

  In the circuit switch 100, priority is set based on an instruction from the base station BS, a synchronization packet including the count number and priority at the GPS 1pps timing 13.0000 seconds is created, and the public network NW (see FIG. 1) to the base station BS.

  First, the information (message) of the clock count number at the GPS 1pps timing (13.000 seconds) of the circuit switch 100 is reached when the count number in the clock unit 4 (FIG. 2) in the base station BS reaches 21300. To do.

  Here, if the number of messages sent from the circuit switch 100 is set to 3 (this number can be arbitrarily set), the GPS count of 1pps is 14.0000 seconds and 15.0000 seconds. Number of information (message) will arrive. In the example of FIG. 4, this is reached when the counts at the clock unit 4 (FIG. 2) in the base station BS reach 21420 and 21500, respectively.

  The above-described synchronization packet 10 from the circuit switch 100 is received by the wired communication unit 6 of the base station BS, and information on the clock count in the circuit switch 100 is given to the wired synchronization unit 7. Further, it is given to the comparison unit 3 and compared with the count number of the own device counted by the clock unit 4.

  In the example of FIG. 4, the clock count in the circuit switch 100 at the GPS 1 pps timing of 13.0000 seconds is 11300, and when the information reaches the base station BS, the clock unit 4 (FIG. 2) Since the count number is 21300, the difference is 10,000.

  Further, the count number of the clock in the circuit switch 100 at the GPS 1pps timing of 14.0000 seconds is 11400, and the count number in the clock unit 4 (FIG. 2) when the information reaches the base station BS is 21420. Therefore, the difference is 10020.

  Similarly, the count number of the clock in the circuit switch 100 at the GPS 1pps timing 15.0000 seconds is 11500, and when the information reaches the base station BS, the count number in the clock unit 4 (FIG. 2) is Since the difference is 21500, the difference is 10,000.

  Since the delay time obtained by the second measurement is 10020 counts, the delay time is larger than the minimum value of the delay time during normal operation, and it can be said that the delay time fluctuates.

  However, the minimum delay time obtained by three measurements is 10,000, which is the same as the minimum delay time during normal operation. Therefore, during the three measurement periods, it is determined that there is no synchronization shift, and synchronization adjustment (resynchronization) is not performed.

  After this, if the state in which the synchronization signal from the GPS cannot be acquired further continues, the circuit switch 100 uses the count number at the GPS 1pps timing 16.0000 seconds and the priority (first received from the base station). The synchronization packet including the priority is maintained and sent to the base station BS via the public network NW (FIG. 1).

  First, the information (message) of the clock count at the GPS 1pps timing (16.0000 seconds) of the circuit switch 100 is reached when the count at the clock unit 4 (FIG. 2) in the base station BS reaches 21620. To do.

  Here, if the number of messages sent from the circuit switch 100 is set to 3 times (this number can be arbitrarily set), the clock count at 17.0000 seconds and 18.0000 seconds for the GPS 1pps timing is further provided. Number of information (message) will arrive. In the example of FIG. 4, this is reached when the count numbers in the clock unit 4 (FIG. 2) in the base station BS reach 21720 and 21840, respectively.

  Then, the comparison unit 3 of the base station BS performs comparison with the count number of the own device counted by the clock unit 4.

  In the example of FIG. 4, the clock count in the circuit switch 100 at the GPS 1pps timing of 16.0000 seconds is 11600, and when the information reaches the base station BS, the clock unit 4 (FIG. 2) Since the count number is 21620, the difference is 10020.

  Further, the count number of the clock in the circuit switch 100 at the GPS 1pps timing of 17.0000 seconds is 11700, and the count number in the clock unit 4 (FIG. 2) when the information reaches the base station BS is 21720. Therefore, the difference is 10020.

  Similarly, the count number of the clock in the circuit switch 100 at the GPS 1pps timing 18.0000 seconds is 11800, and the count number in the clock unit 4 (FIG. 2) when the information reaches the base station BS is Since it is 21840, the difference is 10040.

  Since the delay time obtained by the first measurement and the second measurement is 10020 counts, and the delay time obtained by the third measurement is 10040 counts, the delay time is less than the minimum value during normal operation. It can be said that the fluctuation of the delay time is large.

  The minimum value of the delay time obtained by three measurements is 10020, which is larger than the minimum value of the delay time during normal operation. Therefore, it is determined that the fluctuation of the delay time is large and the synchronization shift has occurred.

  In this case, for example, the comparison unit 3 uses the information (message) of the clock count when the GPS 1 pps timing is 18.0000 seconds included in the synchronization packet used in the third measurement to adjust synchronization ( Resynchronize). In this case, information on the number of clock counts included in the synchronization packet for which the largest delay time is calculated may be used.

  The synchronization adjustment can be realized, for example, by inputting a predetermined value based on the above message to an FPGA (Field Programmable Gate Array) included in the wireless communication unit 1 (FIG. 2).

  As described above, when the synchronization signal from the GPS cannot be obtained and synchronization is performed based on the synchronization signal sent from the circuit switch 100, the delay included in the synchronization signal and the fluctuation of the delay time are measured. Since the synchronization is adjusted when the time fluctuation is large, the synchronization shift can be suppressed even when the public network NW and the base station BS are connected by a general communication line.

  FIG. 6 is a flowchart showing the synchronization operation of the base station BS described above. Hereinafter, the flow of the synchronization operation of the base station BS will be described with reference to FIG.

  In FIG. 6, in the synchronization operation of the base station BS, first, acquisition of a GPS signal is started (step S1), and whether or not the GPS signal is acquired is checked (step S2). This operation is performed by the synchronization unit 2 (FIG. 2) of the base station BS.

  If it is confirmed in step S2 that the GPS signal has been successfully acquired, the synchronization unit 2 performs synchronization processing based on the GPS synchronization signal (step S14).

  Next, the delay time between the circuit switch 100 and the base station BS is measured during normal operation. For this purpose, first, an instruction is sent to the circuit switch 100 to increase the priority of packet processing for the public network (step S15). This operation is performed by the instruction unit 5 (FIG. 2) of the base station BS.

  In response to this, the circuit switch 100 creates a synchronization packet with a higher priority and sends it to the base station BS via the public network NW (FIG. 1).

  The wired communication unit 6 of the base station BS receives the synchronization packet (step S16), and the comparison unit 3 (FIG. 2) counts the clock count in the circuit switch 100 and the clock unit 4 (FIG. 2). Comparison is made with the count number of the own device (step S17).

  The operations of steps S15 and S16 are repeated a specified number of times (step S18), and the minimum value of the obtained measurement results is used as a timing difference (delay time) during normal operation, which is used as an index of synchronization deviation (step S19).

  Thereafter, the instruction unit 5 (FIG. 2) of the base station BS sends an instruction to the circuit switch 100 to return the packet processing priority to the public network to the normal priority (for example, a value corresponding to the first-come-first-served processing) (Step S20), it returns to Step S2 and waits for the acquisition of the GPS signal at the next timing. In addition, you may make it perform the process from said step S14 to step S20 intermittently at a predetermined space | interval.

  On the other hand, if it is confirmed in step S2 that the acquisition of the GPS signal has failed, the predetermined period waits for the GPS signal to return (step S3). If the GPS signal returns, the process proceeds to step S14, and the predetermined period If the GPS signal does not return even after elapses, the process proceeds to step S4.

  In step S4, the instruction unit 5 (FIG. 2) of the base station BS sends an instruction to the circuit switch 100 so as to increase the priority of packet processing for the public network.

  In response to this, the circuit switch 100 creates a synchronization packet with a higher priority and sends it to the base station BS via the public network NW (FIG. 1).

  The wired communication unit 6 of the base station BS receives the synchronization packet (step S5), and the comparison unit 3 (FIG. 2) counts the clock count in the circuit switch 100 and the clock unit 4 (FIG. 2). Comparison with the count number of the own device is performed (step S6).

  The operations in steps S5 and S6 are repeated a specified number of times (step S7), and the minimum value of the timing difference of the measurement results obtained (obtained in step S8) is compared with the timing difference in the normal operation obtained in step S18. (Step S9).

  Then, it is determined whether or not resynchronization is necessary depending on whether the minimum value of the measurement result is the same as the timing difference during normal operation (step S10). If resynchronization is required, it is included in the synchronization packet used in the measurement Using the information (message) of the clock count number, synchronization adjustment (resynchronization) is performed (step S11), and the synchronization operation is terminated.

  On the other hand, if it is determined in step S10 that resynchronization is not necessary, it is confirmed whether or not the GPS signal has been successfully acquired (step S12). If the GPS signal has been successfully acquired, the packet processing priority for the public network is determined. Is returned to normal priority (for example, a value corresponding to the first-come-first-served processing), the instruction unit 5 (FIG. 2) of the base station BS sends an instruction (step S13), and the synchronization operation is terminated.

  If it is confirmed in step S12 that the GPS signal has not been successfully acquired, the operations in and after step S5 are repeated.

<Apply when the clock speed is different>
In the above description, the base station BS and the circuit switch 100 are assumed to operate at 100 clock / sec and transmit synchronization packets at regular intervals, but for example, the circuit switch 100 is 1000 clk / sec. The present invention is effective even when the base station BS operates at 150 clk / sec and the transmission of the synchronization packet is not at regular intervals.

  FIG. 7 shows the count value of the clock in the circuit switch 100 (described as OLT in FIG. 7) in the above case, the obtained value of the count number of the clock at the base station BS, and the count number of the clock at the base station BS. A difference between the assumed value and the obtained value of the clock count number at the base station BS and the assumed value is shown as a list.

  In FIG. 7, the acquired values of the clock counts at the base station BS are 2000, 2150, and 2450 for the clock counts 10000, 11000, and 13000 in the circuit switch 100 during normal operation. Using this value, an expected value of the clock count at the base station BS is calculated, and used after the GPS signal is interrupted and switched to synchronization by a synchronization packet.

  That is, as shown in FIG. 7, even when the GPS signal is interrupted and the synchronization packet is switched to synchronization, the difference between the acquired value of the clock count at the base station BS and the assumed value is 0 immediately after switching. However, as time goes on, the difference widens, and the acquired values of the clock counts at the base station BS are 5100, 2250, and 2400 compared to the clock counts 30000, 31000, and 32000 in the circuit switch 100. In this case, the difference between the acquired value of the clock count at the base station BS and the assumed value is 100, indicating that a synchronization error has occurred.

  In this way, even when the clock speed is different between the base station BS and the circuit switch 100 and the transmission of the synchronization packet is not at a constant interval, the information on the clock count in the circuit switch 100 is acquired, and the base station BS By obtaining the difference between the acquired value of the clock count number and the assumed value, the occurrence of synchronization loss can be detected.

<Synchronous operation example 2>
Next, with reference to FIG. 8, a description will be given of a synchronization operation example 2 of the base station BS according to the present invention. It should be noted that measuring the delay time between the circuit switch 100 and the base station BS in the normal operation state in which the synchronization processing is performed based on the synchronization signal received and acquired from the GPS is the synchronization operation shown in FIG. Since it is the same as that of Example 1, description is abbreviate | omitted.

  The difference from the synchronization operation example 1 is that the synchronization signal from the GPS cannot be acquired, and when synchronization needs to be performed based on the synchronization signal sent from the circuit switch 100, the transmission interval of the synchronization signal is shortened. It is a point that is configured.

  That is, as shown in FIG. 8, the packet processing priority for the public network is returned to the normal priority from the instruction unit 5 (FIG. 2) of the base station BS to the circuit switch 100 (denoted as OLT in FIG. 8). It is assumed that after sending the instruction, it is detected that the GPS synchronization signal has become unavailable at the GPS 1 pps timing of 12.0000 seconds.

  The instruction unit 5 of the base station BS sends an instruction to the circuit switch 100 to increase the priority of packet processing for the public network and shorten the transmission interval of the synchronization packet.

  This instruction is sent before the timing at which the next synchronization signal is sent, here, the GPS 1 pps timing 13.0000 seconds.

  In the circuit switch 100, priority is set based on an instruction from the base station BS, a synchronization packet including the count number and priority at the GPS 1pps timing 13.0000 seconds is created, and the public network NW (see FIG. 1) to the base station BS. At this time, based on an instruction from the base station BS, the transmission timing is set at 0.25 second intervals. Note that the transmission timing is set by the clock unit 102 of the circuit switch 100.

  As shown in FIG. 8, first, the information (message) of the clock count number at the GPS 1pps timing (13.000 seconds) of the circuit switch 100 is the count number in the clock unit 4 (FIG. 2) in the base station BS. Reached when 21300 is reached.

  Here, when the number of times the message is sent from the circuit switch 100 is set to 3 times (this number can be arbitrarily set), the information on the clock count when the GPS 1pps timing is 13.2500 seconds and 13.5000 seconds ( Message). In the example of FIG. 8, it reaches when the count numbers in the clock unit 4 (FIG. 2) in the base station BS reach 21345 and 21350, respectively.

  The comparison with the count of the own device counted by the clock unit 4 of the base station BS is the same as in the synchronous operation example 1, and in the example of FIG. 8, the circuit switch 100 at the GPS 1 pps timing 13.0000 seconds. The count number of the clock is 11300, and when the information reaches the base station BS, the count number in the clock unit 4 (FIG. 2) is 21300, so the difference is 10,000.

  Further, the count number of the clock in the circuit switch 100 at the GPS 1pps timing 13.2500 seconds is 11325, and the count number in the clock unit 4 (FIG. 2) when the information reaches the base station BS is 21345. Therefore, the difference is 10020.

  Similarly, the count number of the clock in the circuit switch 100 at the GPS 1pps timing 13.5000 seconds is 11350, and when the information reaches the base station BS, the count number in the clock unit 4 (FIG. 2) is Since this is 21350, the difference is 10,000.

  Since the delay time obtained by the second measurement is 10020 counts, the delay time is larger than the minimum value of the delay time during normal operation, and it can be said that the delay time fluctuates.

  However, the minimum delay time obtained by three measurements is 10,000, which is the same as the minimum delay time during normal operation. Therefore, during the three measurement periods, it is determined that there is no synchronization shift, and synchronization adjustment (resynchronization) is not performed.

  After this, if the state in which the synchronization signal from the GPS cannot be acquired further continues, the circuit switch 100 uses the GPS count number at the 1pps timing 13.7500 seconds and the priority (first received an instruction from the base station). The synchronization packet including the priority is maintained and sent to the base station BS via the public network NW (FIG. 1). In this case, the transmission timing is maintained at an interval of 0.25 seconds.

  First, the information (message) of the clock count at the GPS 1pps timing (13.7500 seconds) of the circuit switch 100 is reached when the count at the clock unit 4 (FIG. 2) in the base station BS reaches 21395. To do.

  Here, when the number of times the message is sent from the circuit switch 100 is set to 3 times (this number can be arbitrarily set), the information of the clock count at the GPS 1pps timing of 14.0000 seconds and 14.2500 seconds ( Message). In the example of FIG. 8, it reaches when the count numbers at the clock unit 4 (FIG. 2) in the base station BS reach 21420 and 21465, respectively.

  Then, the comparison unit 3 of the base station BS performs comparison with the count number of the own device counted by the clock unit 4.

  In the example of FIG. 8, the clock count in the circuit switch 100 at the GPS 1pps timing of 13.7500 seconds is 11375, and when the information reaches the base station BS, the clock unit 4 (FIG. 2) Since the count number is 21395, the difference is 10020.

  Further, the count number of the clock in the circuit switch 100 at the GPS 1pps timing of 14.0000 seconds is 11400, and the count number in the clock unit 4 (FIG. 2) when the information reaches the base station BS is 21420. Therefore, the difference is 10020.

  Similarly, the count number of the clock in the circuit switch 100 at the GPS 1pps timing 14.2500 seconds is 11425, and when the information reaches the base station BS, the count number in the clock unit 4 (FIG. 2) is Since the difference is 21465, the difference is 10040.

  Since the delay time obtained by the first measurement and the second measurement is 10020 counts, and the delay time obtained by the third measurement is 10040 counts, the delay time is less than the minimum value during normal operation. It can be said that the fluctuation of the delay time is large.

  The minimum value of the delay time obtained by three measurements is 10020, which is larger than the minimum value of the delay time during normal operation. Therefore, it is determined that the fluctuation of the delay time is large and the synchronization shift has occurred. After this, synchronization adjustment (resynchronization) is performed.

  As described above, when the synchronization signal from the GPS cannot be obtained and synchronization is performed based on the synchronization signal sent from the circuit switch 100, the delay included in the synchronization signal and the fluctuation of the delay time are measured. Since the synchronization is adjusted when the time fluctuation is large, the synchronization shift can be suppressed even when the public network NW and the base station BS are connected by a general communication line.

  In addition, when it is necessary to synchronize based on the synchronization signal sent from the circuit switch 100, the synchronization signal transmission interval cannot be obtained because the transmission interval of the synchronization signal is shortened. In this case, it is possible to shift to a state of synchronization based on a synchronization signal sent from the circuit switch 100 in a relatively short time.

  FIG. 9 shows the number of clock counts in the circuit switch 100 (described as OLT in FIGS. 8 and 9), the acquired value of the clock count number at the base station BS, and the clock at the base station BS in the synchronous operation example 2. The table shows the difference between the assumed value of the count number, the acquired value of the clock count number in the base station BS, and the clock count number in the circuit switch 100.

<Modification 1>
In the synchronous operation examples 1 and 2 described above, when the synchronization signal from the GPS cannot be acquired and synchronization is performed based on the synchronization signal sent from the circuit switch 100, the number of times of detecting the fluctuation of the delay time is 3 times. In the case where the number of detections is further increased, the variance of the delay time fluctuation (clock count difference) is calculated, and the value exceeds a predetermined threshold, It is determined that the credibility of the detection result is low, and it is not used for synchronization adjustment regardless of the acquired value.

  FIG. 10 shows the count value of the clock in the circuit switch 100 (denoted as OLT in FIG. 10) when the number of detections is 11, the acquired value of the count number of the clock at the base station BS, and the clock at the base station BS. The difference between the assumed value of the count number and the acquired value of the clock count number at the base station BS and the assumed value is shown as a list.

  In FIG. 10, for example, when the clock count in the circuit switch 100 is 11300 and 11350, the difference between the acquired clock count value in the base station BS and the clock count in the circuit switch 100 is 10,000. Therefore, in the synchronous operation examples 1 and 2, it is determined that the value is the same as the minimum value of the delay time in the normal operation, but other detection values are larger than the minimum value of the delay time in the normal operation. It is off.

  In this way, when the detection results vary, it is determined that the reliability of the detection results is low. On the other hand, when the variation in the detection result is small, it is used for synchronization adjustment as in the synchronous operation examples 1 and 2.

<Modification 2>
In the synchronous operation examples 1 and 2, it has been described that the synchronous packet 10 shown in FIG. 5 is used. However, the synchronous packet 20 shown in FIG. 11 may be used.

  The synchronization packet 20 shown in FIG. 11 includes a payload 25 including downlink communication data to the communication terminal in addition to the payload 24 including the IP header 22, the UDP header 23, and the clock count information in the OLT, with the MAC header 21 at the head. Have.

  By using such a synchronization packet 20, downlink communication data can be sent simultaneously.

<Modification 3>
In the synchronous operation examples 1 and 2, if the delay time fluctuation is detected as a result of the detection of the delay time and does not include the minimum value of the delay time in the normal operation, the synchronization adjustment is performed. Although described as being performed, even in the above case, the synchronization adjustment may not be performed if the magnitude of the fluctuation is within an allowable value.

  Here, as the allowable value, for example, 41.7 μsec may be considered. This value is a time corresponding to the guard time of PHS.

DESCRIPTION OF SYMBOLS 1 Wireless communication part 2 Synchronization part 6 Wired communication part 9 Control part 100 Circuit switch BS Base station MS communication terminal NW Public network

Claims (8)

A wireless communication unit that performs wireless communication with a communication terminal;
A wired communication unit that performs wired communication with the public network;
A control unit that performs synchronization processing based on a synchronization signal included in transmission data transmitted from the host device via the public network;
A synchronization unit that performs synchronization processing based on a high-accuracy synchronization signal that is more accurate than the synchronization signal from the host device, and
The controller is
When the synchronization process in the synchronization unit becomes impossible,
Instruct the higher-level device to transmit the transmission data with a higher priority so that the transmission data can preferentially pass through the public network,
Determining whether or not synchronization adjustment is necessary based on whether or not a difference between a first timing based on the synchronization signal from the host device and a second timing based on the clock of the own device exceeds a predetermined value. Feature base station. The controller is
2. The base station according to claim 1, wherein the difference between the first timing and the second timing is calculated a plurality of times in a predetermined period, and synchronization adjustment is performed when the minimum value exceeds the predetermined value. .   The difference between the first timing and the second timing is calculated a plurality of times in a predetermined period in a state where the synchronization processing is possible in the synchronization unit, and the minimum value is obtained and set as the predetermined value. Item 1. The base station according to Item 1. The controller is
In a state where the synchronization processing is possible in the synchronization unit, the upper unit is instructed to transmit the transmission data with a higher priority so that the transmission data can pass through the public network with priority. The base station according to claim 3, wherein a value is acquired. The high-precision synchronization signal is
The base station according to claim 3, which is received and acquired from a GPS (Global Positioning System). The controller is
The base station according to claim 1, wherein when the synchronization processing in the synchronization unit becomes impossible, the base station issues an instruction to the host apparatus so as to shorten an interval for transmitting the transmission data from the host apparatus. The controller is
The difference between the first timing and the second timing is calculated a plurality of times in a predetermined period, the variance of those values is calculated, and if the value exceeds a predetermined threshold value, The base station according to claim 1, wherein the necessity of adjustment is not determined. A base station that performs wireless communication with a communication terminal and performs wired communication with a public network;
A communication control method in a communication system comprising a host device that exchanges data with the base station via the public network,
The base station
A function of performing a synchronization process based on a synchronization signal included in transmission data transmitted from the host apparatus, and a synchronization process based on a high-accuracy synchronization signal having a higher precision than the synchronization signal from the host apparatus;
The base station
When the synchronization process based on the high-accuracy synchronization signal becomes impossible,
(a) instructing the host device to transmit the transmission data with a higher priority so that the transmission data can preferentially pass through the public network;
(b) Whether synchronization adjustment is necessary is determined based on whether or not the difference between the first timing based on the synchronization signal from the host device and the second timing based on the own clock exceeds a predetermined value. A communication control method comprising the steps of:

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