JPS632505B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a satellite communication system, and particularly to a satellite communication system using narrowband communication, such as the SCPC system, which uses one carrier wave for each telephone channel.

In satellite communication systems using narrowband communication, such as the SCPC system, pilot signals are used for the following purposes. One is used as a reference frequency signal for AFC control performed by each earth station to correct frequency deviations due to frequency fluctuations and Doppler shift of the satellite repeater's local oscillator, and to match the received signal with the center frequency of the demodulator. is to do,
Another method is to use it as a reference level signal for AGC control to set the received signal level to the optimal operating level of the demodulator. One pilot signal is normally used for one communication system consisting of a plurality of earth stations, and conventionally, an unmodulated continuous wave signal has been used. This signal is the AFC and
It is used only for AGC and consumes a certain frequency band and satellite power, and there is still room for improvement from the perspective of effective use.

The purpose of the present invention is to change the frequency of the pilot signal.
It is an object of the present invention to provide a satellite communication system that improves frequency and satellite power usage efficiency by using pilot signals for AFC/AGC and communication signals for communication purposes in a time-sharing manner.

The satellite communication system of the present invention is a satellite communication system in which a plurality of earth stations communicate via a satellite using a plurality of narrowband carrier waves modulated with a narrowband signal.
By intermittently transmitting a pilot signal that serves as a frequency and level reference in a time-division manner, and performing time-division communication at the same frequency as the pilot signal using time slots where the pilot signal is not transmitted. configured.

Next, the present invention will be explained in detail with reference to the drawings.

Figure 1 shows the control and response signals of the SCPC system operated by the request-assignment multiple access (DAMA) system,
This is a code configuration diagram of an embodiment of the present invention in which a pilot signal is transmitted in a time-division manner. 1 is a pilot signal burst that is intermittently sent from a DAMA control station at time intervals of frame length τ, and 2 is a pilot signal burst that is transmitted following the pilot signal. control signal burst sent from the control station,
3, 4, and 5 are response signal bursts such as response/calling signals sent from each controlled station. Frequency fluctuations in the satellite transponder local oscillator are mainly due to temperature and power supply fluctuations, and rapid changes are not expected due to the satellite's thermal control and stabilized power supply system, and the Doppler shift is small for geostationary satellites, so such changes are unlikely. Very little. In addition, with regard to loss fluctuations in the propagation path, large interfering fading does not occur except in extremely low elevation angle propagation, and since rain attenuation is the main factor, very rapid changes do not occur. Therefore, AFC and
Even if the pilot signal for AGC is transmitted not continuously but in a time-division manner, the purpose can be sufficiently achieved. If the frame length τ in Figure 1 is 50 ms, which is the same as the frame length of the common signal channel (CSC) that transmits SPADE control signals and exchange signals using time division multiple access (TDMA), then The above-mentioned frequency/propagation loss fluctuation information is transmitted at the sampling frequency,
Fluctuations such as when a satellite enters an eclipse of the Earth or during a shower can also be sufficiently transmitted. According to this method, the control signal of the DAMA system can be transmitted at the frequency of the pilot signal, and a dedicated frequency for the control signal is not required, so that the frequency can be used effectively. A frequency bandwidth is required for the pilot signal frequency depending on the amount of information such as control signals to be transmitted, but compared to the conventional method of transmitting both on separate frequencies,
This can be easily understood if you consider that when transmitting both at the same frequency, there is no need for a guard band between adjacent carrier waves, which is required due to frequency stability, receiver selectivity, etc. In addition, in the case of conventional continuous wave pilot signals, even if the noise bandwidth of the receiver is generally selected to be large considering conditions such as stability and initial acquisition/reacquisition of the signal, the required signal A large pilot signal power is transmitted to obtain a power-to-noise ratio. Therefore, even though time-division transmission requires carrier wave power for the pilot signal frequency, it does not need to be increased compared to the conventional total power for the two frequencies of the pilot signal and the control signal. Furthermore, there is the advantage that a portion of the receiving device can be shared between the pilot and the control signal.

Figure 2 is a block diagram of one embodiment of the earth station used in the present invention.
The case of a control station is shown. In the figure, 6 is an antenna used for both transmission and reception, 7 is a low-noise amplifier, 8 is a down converter that converts the received signal to an intermediate frequency, 9 is an intermediate frequency amplifier with AGC function, 10 is a distributor that branches the output, and 11 is a a TDMA receiving device that detects and demodulates pilot signals and control signals; 12 is a receiving channel unit that demodulates communication signals; 13;
is a pilot holding control unit that holds the pulsed pilot signal detection output of the TDMA receiver 11 for a certain period of time and generates continuous AFC and AGC signals;
14 uses the pilot signal oscillator 15 as a carrier wave source.
The output of the DAMA control device 16 is used to phase modulate the first
A TDMA transmitting device 1 that transmits pilot signal burst 1 and control signal burst 2 in a time-division manner as shown in the figure.
7 is a combiner that combines the output of this TDMA transmitter 14 and the output of the transmission channel unit 18 modulated by the communication signal, 19 is an up converter that converts the output of the combiner 17 into a radio frequency, and 20 is an up converter that converts the output. This is a transmission power amplifier that amplifies the transmission power.
The DAMA control device 16 sends control signals and receives response signals from each controlled station, and sets the frequency of the synthesizer local oscillators of the transmit channel unit 18 and the receive channel unit 12.

Figure 2 shows an example of a DAMA control station, but in the case of a controlled station, the pilot signal oscillator 15 is removed from the block diagram of Figure 2 and the DAMA control device 16 is replaced.
It can be configured by replacing it with a DAMA slave station device.

In the embodiment of FIG. 1, pilot signal burst 1
Although control signal burst 2 and control signal burst 2 are sent out continuously, 1 and 2 may not be consecutive, but may have a guard time in between, and the order of 1 and 2 may be reversed. Also, the pilot signal sending station
DAMA control stations do not necessarily have to be the same,
Signals that are transmitted in time division with the pilot signal
The signal is not limited to a DAMA system control signal, but may be a broadcast format or mutual communication format signal sent from any earth station. Furthermore, pilot signal bursts are transmitted from two earth stations, one of which is always used as the main pilot signal, the other one is configured as a backup pilot signal that can be immediately switched and used in the event of a failure in the main pilot signal, and the remaining It is also possible to improve the reliability of the pilot signal by communicating in time slots. In addition,
The pilot signal burst does not necessarily have to consist only of unmodulated carrier bursts;
It is also possible to use a part or all of the reference burst signal for frame synchronization, which consists of an unmodulated carrier burst for carrier reproduction and a phase-modulated burst for bit synchronization reproduction and synchronization confirmation, as a pilot signal. be.

The present invention is based on the DAMA control explained in the embodiment.
Not only SCPC method but also fixed chain assignment
Of course, it can be applied to the SCPC method, but it also uses a large number of carrier waves to make 2 to 3 calls per carrier.
It can also be applied to cases where pilot signals for AFC/AGC are required in narrowband communication satellite communications that transmit channels or equivalent data, music programs, etc.

As explained in detail above, according to the satellite communication system of the present invention, by time-divisionally transmitting communication signals at the same time at the frequency of the pilot signal, a system with improved frequency usage efficiency and power usage efficiency is provided. There is an effect that can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a code configuration diagram of an embodiment of the present invention, and FIG.
The figure is a block diagram of an embodiment of an earth station used in the present invention. 1... Pilot signal burst, 2... Control signal burst, 3, 4, 5... Response signal burst,
6...Antenna, 7...Low noise amplifier, 8...Up converter, 9...Intermediate frequency amplifier, 10...
...Distributor, 11...TDMA receiving device, 12...
Reception channel unit, 13...Pilot holding control unit, 14...TDMA transmitter, 15...
Pilot oscillator, 16...DAMA control device,
17...Synthesizer, 18...Transmission channel unit, 19...Up converter, 20...Transmission power amplifier.

Claims (1)

[Claims] 1 In a satellite communication system in which multiple earth stations communicate via satellite using multiple narrowband carrier waves modulated with narrowband signals, the pilot signal, which serves as the frequency and level reference, is transmitted intermittently in a time-sharing manner. 1. A satellite communication system characterized in that time-division communication is performed at the same frequency as the pilot signal using a time slot in which the pilot signal is transmitted and the pilot signal is not transmitted.