JPH0567997A - Data synchronization system for mobile body satellite communication system - Google Patents

Abstract

PURPOSE:To allow a center station to reproduce correctly an out-bound signal sent from a network control station via an asynchronization line. CONSTITUTION:A control section 10 of a network control station generates an out-bound signal S1 in response to a frame timing signal F1 generated by a frame timing generating circuit 11 and sends it to a MODEM section 20 of the center station via an asynchronization line 30 as a packet signal S2 by a data output circuit 13. A data reception circuit 21 of the MODEM section 20 latches once data by one packet. A frame detection circuit 22 detects a head of a frame from the packet signal S2 to output a frame detection signal D. A timing generating circuit 23 generates a clock signal C and a frame timing signal F2 synchronously with the frame detection signal D. The data reception circuit 21 outputs the latched data in response to the timing signal C to reproduce an out-bound signal S3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data synchronization system for a mobile satellite communication system.

[0002]

2. Description of the Related Art Generally, a mobile satellite communication system comprises a large number of mobile stations, a central station which communicates with the mobile stations via a communication satellite, and a network control station which controls the entire system.

The central station time-division-multiplexes time information, control information for communication, and other communication texts with all mobile stations, and transmits them in a continuous broadcast mode. This signal is commonly referred to as the outbound signal. The type of information to be put on the outbound signal differs depending on the system, but it often includes time information such as universal time. This time information is used for various purposes such as time display on the mobile station side. Further, as shown in FIG. 3, the outbound signal has a frame structure on the time axis, a control field is provided at the beginning of the frame, and control information including time information is inserted. The format of inserting in the data field part is often used.

Now, the central station comprises a transmitting / receiving section for satellite communication, a modulation / demodulation section, and a control section for controlling these. Here, the modulator / demodulator is provided with a modulator for an outbound signal, and sends a modulated output of the outbound signal including time information sent from the controller. In addition, the control unit is provided with a high stable frequency oscillator and a frame timing generation unit that generates a frame timing signal using the output of this oscillator as a clock signal in order to create accurate time information. Is generated as a time reference, and an outbound signal including time information is generated and sent to the modulator / demodulator together with the clock signal.

By the way, in order to match the time indicated by the time information received by the mobile station with the actual time, the delay time in the modulator and the round-trip propagation time to the communication satellite (about 24
(0 msec), the frame timing signal is offset earlier by the delay time.

[0006]

As described above, conventionally, the central station generates time information of practically sufficient accuracy and provides it to the mobile station. However, as a system configuration, a system in which a control unit provided in a central station is installed in a network control station, a modulation / demodulation unit and a transmission / reception unit are installed in the central station, and both stations are connected by an asynchronous line is considered. By configuring such a system, the control system can be centralized in the network control station, so the configuration of the control system equipment can be rationalized, and a general public telephone line can be used as an asynchronous line, so a new line can be added. There are many merits, such as that it is not necessary to lay, and an inexpensive MODEM can be used for the interface. Therefore, it will be introduced in the future.

However, when a general public telephone line is used, the clock signal cannot be transmitted as it is. Therefore, it is possible to prepare an oscillator separately for the modulation / demodulation unit of the central station.In this case, however, the oscillator of the modulation / demodulation unit of the central station side and the oscillator of the control unit of the network control station are asynchronous, so this is However, there is a problem in that errors such as data loss and repetition occur periodically, frame desynchronization occurs in the mobile station, and frequent line interruptions occur.

It is an object of the present invention to transmit an outbound signal generated by a control unit of a network control station to a modulation / demodulation unit of a central station via an asynchronous line without causing an error such as data loss or repetition. SUMMARY OF THE INVENTION It is an object of the present invention to provide a data synchronization method for a mobile satellite communication system capable of correctly transmitting an outbound signal to a mobile station.

[0009]

According to the data synchronization method of a mobile satellite communication system of the present invention, a network control station which governs the system generates an outbound signal having a frame structure including time information and the like and transmits it via an asynchronous line. In the mobile satellite communication system in which the central station receives the received outbound signal and transmits it to the slave station via the communication satellite in the broadcast mode, the central station detects the frame timing of the received outbound signal. A detecting unit; a data holding unit that temporarily holds the received one-frame data of the outbound signal; a unit that generates a timing signal in synchronization with the frame timing detected by the detecting unit; And means for sequentially transmitting the held data in accordance with the timing signal. Further, the means for generating the timing signal is configured to include a phase locked loop (PLL) having a voltage controlled oscillation circuit, a phase comparison circuit and the like.

[0010]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, showing a modulation / demodulation unit of a central station and a control unit of a network control station. FIG. 2 is a timing chart of signals of each circuit.

Now, the control unit 10 of the network control station
Is a frame timing generation circuit 11 for generating a frame timing signal F1 and a frame timing signal F1.
Each time when is input, one frame of outbound signal S1
And a data output circuit 13 for sending the outbound signal S1 to the modulation / demodulation unit 20 of the central station via the asynchronous line 30. here,
Time information such as universal time is inserted at the beginning of the frame forming the outbound signal S1.

By the way, since the clock signal cannot be transmitted through the asynchronous line 30, the data output circuit 13 sets the data of the outbound signal for one frame as one packet and adds the header to the data transmission system such as start-stop synchronization. Thus, one frame of each frame is transmitted as a packet signal S2. In this case, the transmission rate is higher than the satellite line rate.

On the other hand, the modulation / demodulation unit 20 of the central station receives the packet signal S sent from the control unit 10 of the network control station.
2 through the asynchronous line 30 to reproduce the outbound signal S3, and the frame detection circuit 22 for recognizing the head of the frame by using the header of the packet signal S2 and transmitting the frame detection signal D. When,
A timing generation circuit 23 that generates a clock signal C and a frame timing signal F2 in synchronization with the frame detection signal D, and a modulator 24 that receives and modulates the outbound signal S3 and the frame timing signal F2 are provided.

Although not shown, the timing generating circuit 23 is a phase locked loop (PLL) including a voltage controlled oscillator circuit (VCO), a frequency divider for counting frame periods, a low pass filter (LPF) and a phase comparison circuit. ), The clock signal C and the frame timing signal F2 are generated in phase synchronization with the frame detection signal D.

By the way, the data generation circuit 1 of the control unit 10
2 and the data output circuit 13 generally perform signal processing by software, the frame timing signal F1
There is a variation in the processing time from the reception of the signal and the output of the outbound signal S1. Further, since the propagation time also varies due to the asynchronous line 30, the detection signal D
Deviation occurs in the timing of. However, this timing deviation can be absorbed by the PLL of the timing generation circuit 23.

Now, the data receiving circuit 21 of the central station temporarily holds the data for one packet in accordance with the frame timing signal F2, and after a predetermined time has passed, the data once held is sequentially held from the beginning. The outbound signal S3 is reproduced by outputting according to the clock signal C. Here, the predetermined time is a processing time until packet data of about several bytes is input and output preparation is completed.
Further, when the transmission of the outbound signal for one frame is completed, the data of the next frame starts to be input, so that the outbound signal S3 can be similarly transmitted as a continuous signal. In this way, the data receiving circuit 21 executes the reception processing of the packet signal S2 and the reproduction processing of the outbound signal S3 in parallel.

The modulator 24 receives the outbound signal S3 reproduced by the data receiving circuit 21 and the frame timing signal F2 from the timing generating circuit 23, modulates the signal and sends it to the communication satellite as an outbound signal S4.

Next, the relationship between signal timing and time information will be described.

As shown in FIG. 2, the data generation circuit 12
Processing time t1 at the modem 2 via the asynchronous line 30
The transmission time t2 required for transmission to 0, the processing time t3 in the data receiving circuit 21 of the modulation / demodulation unit 20, the delay time t4 in the modulator 24, the propagation delay time t5 required for propagation to the mobile station via the communication satellite, etc. In consideration of the above, the frame timing signal F1 is generated by offsetting this time earlier. By doing so, the time when the mobile station receives the outbound signal and the time indicated by the time information included in the received outbound signal can be matched. It should be noted that the deviation of the reception timing due to the geographical position of the mobile station on the earth can be ignored.

[0021]

As described above, according to the present invention, in the central station, the frame timing of the outbound signal transmitted from the network control station via the asynchronous line is detected, and the phase locked loop (PLL) is detected at this frame timing. Controls the clock signal and rereads the outbound signal input using this clock signal, so that even if data with timing deviation is input through the asynchronous line, , The correct outbound signal without error such as data loss or repetition can be reproduced, and no obstacle such as momentary interruption is given to the mobile station. Therefore, a rational system can be realized in which all control systems are integrated in the network control station and a general public telephone line can be used.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, showing a modulation / demodulation unit of a central station and a control unit of a network control station.

FIG. 2 is a timing chart of signals of each circuit shown in FIG.

FIG. 3 is a diagram showing an example of a frame structure of an outbound signal.

[Explanation of symbols]

 10 control unit of network control station 12 data generation circuit 13 data output circuit 20 modulation / demodulation unit of central station 21 data reception circuit 22 frame detection circuit 23 timing generation circuit 30 asynchronous line S1, S3 outbound signal F1, F2 frame timing signal C clock signal D frame detection signal

Claims (2)

[Claims] 1. A network control station that controls the system generates an outbound signal having a frame structure including time information and sends it to a central station via an asynchronous line, and the central station receives the signal and transmits it via a communication satellite. In a mobile satellite communication system for transmitting to a slave station in a broadcast mode, the central station temporarily holds detection means for detecting a frame timing of the received outbound signal and data for one frame of the received outbound signal. Data holding means, means for generating a timing signal in synchronization with the frame timing detected by the detecting means, and means for sequentially sending the data held in the data holding means in accordance with the timing signal A data synchronization system for mobile satellite communication systems characterized by. 2. The means for generating the timing signal comprises:
2. The data synchronization system for a mobile satellite communication system according to claim 1, further comprising a phase locked loop (PLL) having a voltage controlled oscillation circuit, a phase comparison circuit and the like.