JP4996717B2 - Time synchronization system and time synchronization method - Google Patents

Description

  Embodiments described herein relate generally to a time synchronization system and a time synchronization method for supplying a synchronization signal to a wireless system.

  In a time division multiple-duplex radio system, it is necessary to synchronize the transmission / reception timing of uplink (terminal → radio unit) and downlink (radio unit → terminal) radio signals. If transmission / reception timing is shifted between adjacent base stations, signals interfere with each other, resulting in a decrease in communication quality or inability to communicate. Therefore, a GPS (Global Positioning System) 1 pulse / second reference signal (1 second signal) is used as a highly accurate clock that can be commonly referred to throughout the entire wireless system.

JP 2008-182385 A JP 2005-520447 A JP 2004-150892 A

  However, in the above method, it is necessary to receive radio waves transmitted by GPS satellites, and the GPS reference signal may not be used depending on the location of the wireless base station, which has been a problem in widespread use of wireless systems.

  An object of the present embodiment is to provide a time synchronization system and a time synchronization method that can keep a synchronization state between radio base stations stable.

  The time synchronization system according to the present embodiment is connected to the parent device via a parent device that supplies a first synchronization signal for synchronizing wireless base stations, and a transmission path having a first channel and a second channel. A time synchronization system including a slave device, wherein the slave device receives a GPS (Global Positioning System) reference signal, and the reference signal is transmitted to a first channel of an upstream signal to the parent device. And a transmitter for transmitting the uplink signal via the transmission path, and the master device multiplexes the delay measurement signal on the second channel of the downlink signal to the slave device. A transmission unit that transmits the downlink signal via the transmission path, a separation unit that separates the first channel and the second channel from the uplink signal from the slave device, and a delay measurement signal of the second channel On the basis of Corrected by a delay measurement unit that measures a delay time of the transmission path, a first phase correction unit that corrects the phase of the reference signal of the first channel based on the delay time, and the first phase correction unit And an output unit that outputs the first synchronization signal based on a reference signal.

  The time synchronization method according to the present embodiment is connected to the parent device via a parent device that supplies a first synchronization signal for synchronizing wireless base stations and a transmission path having a first channel and a second channel. The slave device receives a GPS (Global Positioning System) reference signal and transmits the reference signal to the first channel of the upstream signal to the parent device. And transmitting the uplink signal via the transmission path, the master device multiplexes a delay measurement signal on the second channel of the downlink signal to the slave device, and the downlink signal is transmitted to the slave device. Transmitting through the transmission line, separating the first channel and the second channel from the upstream signal from the slave device, measuring the delay time of the transmission line based on the delay measurement signal of the second channel, and the delay Based on time The phase of the reference signal of the first channel is corrected, and the first synchronization signal is output based on the corrected reference signal.

The figure which shows the radio | wireless system provided with the time synchronization system which concerns on this embodiment. The figure which shows the other structural example of a radio | wireless system. The block diagram which shows the structure of a GPS receiver. The block diagram which shows the structure of a control apparatus. It is a figure which shows the signal form in the subscriber line of an ISDN basic rate interface. The figure which shows the measuring method of the transmission delay of a 1 second signal. The figure which shows the phase relationship of a 1 second signal.

  Hereinafter, a time synchronization system and a time synchronization method according to the present embodiment will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a wireless system including a time synchronization system according to the present embodiment. In the radio base station, the radio units 7a and 7b and the radio control unit 8 are separated and connected between them by optical fibers 9a and 9b. The time synchronization system includes a GPS (Global Positioning System) receiver 1, a GPS antenna 2, a control device 4 that controls the GPS receiver 1, and a transmission path 3 that connects between the GPS receiver 1 and the control device 4. The radio control unit 8 synchronizes the radio units 7 a and 7 b based on the first synchronization signal 6 supplied from the control device 4, and transmits uplink (terminal → radio unit) and downlink (radio unit → terminal) radio signals. It is designed to be able to send and receive in a time division multiple-duplex communication system. The radio units 7a and 7b and the radio control unit 8 may be integrated without being limited to the separated radio base station.

  As an example in which GPS cannot be used indoors, there is a case where the radio control unit 8 is installed by borrowing a communication station building of a carrier. Since the station building is owned by another company, for example, even if the GPS receiver 1 can be installed on the rooftop, there is a case where wiring for transmitting a signal for 1 second cannot be laid. However, since the station building is a place for collecting subscriber lines, telephone lines are laid out in various places outside the building. In the present embodiment, the first synchronization signal 6 is supplied from the GPS receiver 1 installed outdoors to the wireless control unit 8 by using a subscriber line as the transmission path 3.

  FIG. 2 shows a configuration when radio base stations in two stations are adjacent to each other. The first station and the second station are connected by a communication network NW. A second synchronization signal 5 synchronized with the communication network NW is input to the control devices 4-1 and 4-2. When the delay time of the transmission line 3-1 and the delay time of the transmission line 3-2 are different, transmission / reception is performed between the adjacent wireless units 7a-1 and 7b-1 and the wireless units 7a-2 and 7b-2. Timing may shift and interference may occur. Therefore, the present embodiment proposes a method for eliminating the delay times of the transmission lines 3-1 and 3-2 and providing the first synchronization signals 6-1 and 6-2 synchronized with the 1-second signal.

  In the present embodiment, as an example, an ISDN (Integrated Services Digital Network) basic rate interface is used for the transmission path 3. The ISDN basic rate interface has two B channels (first channel and second channel) of 64 kbps and one D channel of 16 kbps.

  FIG. 3 is a block diagram showing the configuration of the GPS receiver 1. The GPS receiver 1 includes a GPS receiving unit 11, a demultiplexing unit 12, and a DSU (Digital Service Unit) unit.

  The GPS receiving unit 11 generates a 1-second signal as a synchronization signal from the signal received by the GPS antenna 2. The demultiplexing unit 12 separates each channel from the downlink frame from the control device 4 and multiplexes the 1-second signal on the first channel of the uplink frame to the control device 4 as described later. The DSU unit is a connection interface with the transmission path 3 and transmits an upstream frame to the control device 4 installed in the station building.

  FIG. 4 is a block diagram illustrating a configuration of the control unit 4. The control unit 4 includes an OCU (Official Channel Unit) unit 41, a demultiplexing unit 42, a delay measurement unit 43, a first phase shifter 44, a PLL circuit 45, a phase shift comparison unit 46, a second phase shifter 47, and a driver. 48.

  The OCU unit 41 provides a subscriber line interface function of the ISDN basic interface. The demultiplexer 42 demultiplexes each channel of the ISDN basic rate interface. The demultiplexing unit 42 extracts a 1-second signal from the first channel and outputs it to the terminal B, or transmits and receives a delay measurement signal using the second channel. The delay measuring unit 43 measures a delay time until the signal inserted from the terminal C returns to the terminal D. The first phase shifter 44 outputs a 1-second signal whose phase is corrected based on the delay time so as to cancel the transmission delay of the circuit and the transmission line 3 with respect to the 1-second signal output from the terminal B. Output to.

  A PLL (Phase-Locked Loop) circuit 45 generates a 1-second signal based on the second synchronization signal 5 synchronized with the communication network NW and outputs it to the terminal G. The second synchronization signal 5 is a highly available signal that is not affected by eclipse or the like than the 1-second signal supplied by GPS, and supplies a clock with a frequency of 8 kHz or 64 kHz, for example. The 1-second signal output (terminal G) generated by the PLL circuit 45 is input to the second phase shifter 47 and output to the wireless control unit 8 via the driver 48. On the other hand, the output (terminal F) branched from the second phase shifter 47 is input to the phase comparison unit 46 and is compared in phase with the 1-second GPS signal passed through the first phase shifter 44 until the phase difference disappears. The phase is adjusted by the second phase shifter. In this way, a highly available and phase corrected 1 second signal is obtained.

  Next, details of the transmission delay measurement operation in the present embodiment will be described.

  FIG. 5 is a diagram showing a signal form in the subscriber line of the ISDN basic rate interface. The 1-second signal is transmitted using the B1 channel of the upstream frame, and the B2 channel of the upstream frame and the downstream frame is used for delay measurement.

  FIG. 6 is a diagram illustrating a transmission delay measurement method. The terminal C is set to the logical value 1 at the time when the delay measurement is started. Since the B2 channel upstream frame and downstream frame are connected inside the GPS receiver 1, the signal of logical value 1 appearing at the terminal C 'is input to the terminal D' as it is. The signal of logical value 1 that is turned back through the communication circuit 3 appears at the terminal D. The delay time (t) between the GPS receiver 1 and the control device 4 is a half of the time (2t) required for the change from 0 to 1 at the terminal C to 0 to 1 at the terminal D. .

  Therefore, the 1-second signal obtained by subtracting the delay time (t) in the control device 4 cancels the delay time of the transmission path 3 and the like, and is equal to the GPS 1-second signal received at the place where the control device 4 is installed. Become. FIG. 7 shows the phase relationship of the 1-second signal. A delay time (t) is generated from terminal A on the GPS receiver 1 side to terminal B on the control device 4 side. A signal whose delay is corrected by the phase shifter 44 is output from the terminal E. In this way, even when a GPS receiver is installed at a location away from the radio base station, a GPS reference signal (1 second signal) can be used as a timing source.

  Furthermore, since the 1-second signal is recreated based on the second synchronization signal 5 synchronized with the communication network NW, the first synchronization signal 6 can be stably supplied even when the radio wave transmitted from the GPS satellite cannot be received. It becomes like this. In such a case, since the signal at the terminal E disappears, the operation of the phase comparator 46 is temporarily stopped.

  As described above, according to the above embodiment, even when GPS signals cannot be received, the synchronization state between the radio base stations can be kept stable, and a radio system with stable communication quality can be constructed. It is not always necessary to select a location where GPS can be seen, and there is an advantage that flexibility is created in network construction because there is no restriction on the location where the radio base station is installed.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... GPS receiver, 2 ... GPS antenna, 3 ... Transmission path (subscriber line), 4 ... Control apparatus which controls GPS, 5 ... 2nd synchronizing signal, 6 ... 1st synchronizing signal, 7a. 7b: Radio unit, 8: Radio control unit, 9a, 9b ... Optical fiber, 11a, 11b ... Terminal, NW ... Communication network, 11 ... GPS receiver unit, 12 ... Demultiplexing unit, 13 ... DSU unit, 41 ... OCU unit , 42 ... demultiplexing unit, 43 ... delay measuring unit, 44 ... first phase shifter, 45 ... PLL circuit, 46 ... phase comparison unit, 47 ... second phase shifter, 48 ... driver.

Claims (4)

A time synchronization system comprising: a parent device that supplies a first synchronization signal for synchronizing radio base stations; and a child device that is connected to the parent device via a transmission path having a first channel and a second channel. There,
The child device is
A GPS receiver that receives a GPS (Global Positioning System) reference signal;
A multiplexing unit for multiplexing the reference signal on the first channel of the upstream signal to the parent device;
A transmission unit for transmitting the uplink signal via the transmission path,
The parent device is
A multiplexing unit for multiplexing the delay measurement signal on the second channel of the downstream signal to the slave device;
A transmission unit for transmitting the downlink signal via the transmission path;
A separation unit that separates the first channel and the second channel from an upstream signal from the slave device;
A delay measuring unit that measures a delay time of the transmission path based on a delay measurement signal of the second channel;
A first phase correction unit that corrects the phase of the reference signal of the first channel based on the delay time;
An output unit that outputs the first synchronization signal based on the reference signal corrected by the first phase correction unit;   The parent device further includes a second phase correction unit that corrects the reference signal corrected by the first phase correction unit based on a second synchronization signal supplied from a communication network. Item 2. A time synchronization system according to item 1. A time synchronization system comprising: a parent device that supplies a first synchronization signal for synchronizing radio base stations; and a child device connected to the parent device via a transmission path having a first channel and a second channel A method used,
The child device is
Receives GPS (Global Positioning System) reference signal,
Multiplexing the reference signal on the first channel of the upstream signal to the parent device;
Transmitting the upstream signal via the transmission path,
The parent device is
Multiplexing a delay measurement signal on the second channel of the downstream signal to the slave device;
Transmitting the downlink signal via the transmission path;
Separating the first channel and the second channel from the upstream signal from the slave device;
Measuring the delay time of the transmission line based on the delay measurement signal of the second channel;
Correcting the phase of the reference signal of the first channel based on the delay time;
A time synchronization method comprising: outputting the first synchronization signal based on the corrected reference signal.   The time synchronization method according to claim 3, wherein the parent device further includes correcting the corrected reference signal based on a second synchronization signal supplied from a communication network.

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