JP2725492B2 - Satellite communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite communication system, and more particularly to a DAMA (Deman) system employing a frequency division multiplexing system.
d Assign Multiple Access)
The present invention relates to a satellite communication system having an AFC function for forming a communication line at an early stage.

[0002]

2. Description of the Related Art Conventionally, in this type of satellite communication system, the frequency fluctuation of a satellite is relatively large compared to the transmission speed, and cannot be received by an ordinary satellite receiver. As a first method to remedy this, as shown in the frequency allocation diagram used by the satellite in FIG.
In addition to a plurality of carrier signals 22 used on a satellite transponder, a system pilot signal 21 is set up, and an AFC is transmitted to a receiver of an earth station based on the pilot signal 21 based on the pilot signal 21.
And a method in which the received signal input to the demodulator is a signal from which the satellite frequency fluctuation has been removed.
As a method of (1), there has been a method in which an AFC function is provided to a carrier recovery circuit of a demodulator so as to follow a frequency fluctuation of a satellite.

[0003]

The first conventional method described above requires a system pilot signal, and the AFC function based on the pilot signal must be added to the receiver of the earth station. It is also expensive. The second method has a disadvantage that it is difficult to set up a line in a short time because the AFC operation of the earth station must follow the frequency fluctuation of the satellite.

[0004]

The satellite communication system according to the present invention is a DAMA system employing a frequency division multiplexing system.
In a satellite communication system of an earth station having a demodulator performing FC operation, the earth station inputs free line information from external satellite line management information and outputs a transmission control signal for transmitting a transmission signal of its own transmission unit. And a line control means for outputting a control signal for causing the demodulator to release AFC holding, and a signal obtained by converting a transmission signal of the transmission unit into a reception signal by a satellite and returning the signal by the demodulator. Means for holding a frequency variation of a received signal received from the satellite after the synchronization is established.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. The embodiment of FIG. 1 shows an earth station 7 and a satellite 8 constituting an FDMA / DAMA system.

Next, the configuration and operation of the earth station 7 will be described.

The line control unit 1 receives line control information 18 from a device which separately manages the entire line, judges the use state of the line, and if the line is not used, transmits the signal at a predetermined transmission frequency. The transmission control signal 11 is output to the modulator 2 so as to output the transmission signal of No. 3. The transmission output signal 14 of the transmission unit 3 becomes a transmission wave 16 radiated from the antenna 6 and is transmitted to the satellite 8. The satellite 8 converts this transmission wave to the satellite 8
Becomes a received wave 17 including the frequency fluctuation of the antenna 6 again.
, And becomes a received signal 15. The received signal 15 is input to the demodulator 4 via the receiving unit 5. At the same time as the transmission control signal 11 from the line control unit 1, the demodulator 4 adjusts the reception frequency and the reception control signal 1 for releasing the AFC holding.
Receiving 2, it receives a received signal 15 and sends out a synchronization establishment signal 13 to the line controller 1. In response to this, the line control unit 1 performs AFC holding control on the demodulator 4 in accordance with the reception control signal 12, and causes the demodulator 4 to hold the frequency fluctuation information of the satellite 8. Thereafter, a transmission control signal 11 is output to the transmission unit 3 to stop the transmission, and the communication unit 3 waits for a communication request. Thus D
When the AMA communication method is adopted, A
FC holding control operation is indispensable, and early line setting is possible.

[0009]

As described above, according to the present invention, since the demodulator holds the satellite frequency fluctuation in advance, when a communication request occurs, the AFC function is operated after receiving a received signal from the satellite. You can receive without letting it go. Therefore, it is possible to set up a line in a short time, and it is possible to provide an inexpensive satellite communication system.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a frequency allocation diagram of a conventional satellite communication system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Line control part 2 Modulator 3 Transmitting part 4 Demodulator 5 Receiving part 6 Antenna 7 Earth station 8 Satellite

Claims (2)

(57) [Claims] 1. A DAMA employing a frequency division multiplexing method
In a satellite communication system of an earth station having a demodulator that performs an AFC operation by inputting a received signal from a satellite after a call request is generated, the earth station inputs free line information from external satellite line management information. A line control means for outputting a transmission control signal for transmitting a transmission signal of the own station transmission unit and for outputting a control signal for causing the demodulator to release AFC holding; Means for holding a frequency variation of a received signal received from the satellite after the demodulator receives the signal converted and returned by the demodulator and synchronization is established. 2. The line control unit stops the transmission signal of the transmission unit after the demodulator transmits a synchronization establishment signal to the effect that the frequency variation of the satellite is held to the line control unit. Item 2. A satellite communication system according to item 1.