JPH0728255B2 - Earth station communication equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used for an earth station communication device for satellite communication. In particular, the SCPC method (Single Channel P) that performs frequency multiplexing of multiple channels and communicates with multiple earth stations via communication satellites.
er Carrier method) earth station communication device.

〔Overview〕

The present invention, in an earth station communication device, transmits an unmodulated carrier for a short period of time at a predetermined cycle, compares the frequencies of the unmodulated carrier returned by a communication satellite and the transmitted unmodulated carrier, and based on this comparison result. By correcting the frequency on the receiving side, the scale is small, the cost is low, the channel efficiency is good, and good channel separation is possible.

[Conventional technology]

Conventionally, the earth station communication device has performed channel separation using a frequency converter and a filter. For this reason, when the radio frequency is extremely large compared to the band of the channel,
A frequency converter or the like requires extremely high frequency accuracy.
In order to meet this requirement, various conventional AFC methods (Automatic
ic Frequency Compensation method) has been used.

As an example, there is a method using a pilot carrier. This is a system in which an unmodulated carrier is transmitted to a specific channel among a large number of channels, and stations other than the transmitting station use the unmodulated carrier as a frequency reference. Especially in satellite communications, frequency fluctuations due to the frequency fluctuations of the satellite transponder and the Doppler effect of the satellite itself are large, and the pilot carrier method is indispensable to suppress the frequency stability of the entire line to the required value. It was

[Problems to be solved by the invention]

However, in such a conventional earth station communication device, since it is an AFC system using a pilot carrier, a transmission device and a reception device dedicated to the pilot carrier are required, and the device scale is large. Has a drawback that is not negligible and expensive.

Also, the frequency band is usually set to 1 for the pilot carrier.
There is a drawback that the number of channels used for the original communication is reduced because the channels are occupied.

The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide an earth station communication device that is small in scale, inexpensive, has good channel efficiency, and can perform good channel separation.

[Means for solving problems]

The present invention provides a modulation means for modulating each frequency of a plurality of channels based on an input transmission baseband signal, a transmission means for transmitting an output signal of the modulation means to a communication satellite, and an output signal of the communication satellite. Receiving means for receiving, demodulating means for demodulating the output signal of the receiving means for each of the channels to output a received baseband signal, the modulating means and frequency control means for performing frequency division control of the demodulating means. In the earth station communication device provided, the frequency control means interrupts the application of the transmission baseband signal to the modulation means for a short period of time at a predetermined cycle and sends out an unmodulated carrier during the period, and the sending means. Means for inputting from the demodulation means a signal in which the unmodulated carrier is returned by the communication satellite, and detecting a frequency fluctuation of the signal; Based on the detection result of the means for output, characterized in that it comprises a means for controlling the output frequency of said receiving means.

[Action]

The frequency control means interrupts the application of the short-time transmission baseband signal to the modulation means at a predetermined cycle, and causes the non-modulated carrier to be transmitted during that period. Further, a signal returned from the unmodulated carrier sent out via the communication satellite is input from the demodulation means, and the frequency of the signal is compared with the frequency of the unmodulated carrier when sent out to detect the frequency fluctuation. Further, based on this detection result, the output frequency of the receiving means is controlled during the period until the next non-modulated carrier is transmitted. By the above operation, the scale is small, the cost is low, the channel efficiency is good, and the good channel separation can be performed.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings. First
FIG. 1 is a block diagram of an earth station communication device according to an embodiment of the present invention. In FIG. 1, the earth station communication device includes a transmitter-side synthesizer circuit 6 and a modulator 7 as a modulator that modulates respective frequencies of a plurality of channels based on an input transmission baseband signal, and an output of the modulator 7. A transmission frequency converter 3, a part of the feeder circuit 2 and a part of the antenna 1 as transmission means for transmitting a signal to a communication satellite;
As a receiving means for receiving the output signal of the communication satellite, a part of the antenna 1, a part of the feeder circuit 2, the reception frequency converter 4, and the output signal of the reception frequency converter 4 are demodulated and received for each channel. The receiving side synthesizer circuit 9 and the demodulator 8 are provided as demodulation means for outputting a baseband signal, and a part of the frequency control circuit 11 is provided as frequency control means for performing frequency division control of the modulator 7 and the demodulator 8.

Here, the feature of the present invention is that the frequency control means is switched as a means for interrupting the application of the transmission baseband signal to the modulator 7 for a short period of time at a predetermined cycle and transmitting an unmodulated carrier during that period. A part of the frequency control circuit 11 and the frequency control circuit 11 and a frequency control circuit as means for inputting from the demodulator 8 a signal in which the transmitted unmodulated carrier is returned by the communication satellite and detecting the frequency fluctuation of the signal.
11 and a part of the voltage control oscillator 5 and the frequency control circuit 11 as a means for controlling the output frequency of the reception frequency converter 4 based on the detection result of the detecting means.

The operation of the earth station communication device having such a configuration will be described. FIG. 2 is a diagram showing the transmission / reception timing of the unmodulated carrier of the earth station communication apparatus of the present invention. In FIG.
When transmitting communication data, a transmission signal input from the transmission baseband device is modulated by the modulator 7 after passing through the switch 10. Next, a radio channel is selected by the transmitting side synthesizer circuit 6 and then transmitted to the communication satellite via the transmitting frequency converter 3, the feeder circuit 2 and the antenna 1.

On the other hand, when receiving communication data, it is demodulated by the demodulator 8 after passing through the antenna 1 and the feeder circuit 2 and then through the receiving frequency converter 4. Here, the receiving channel is selected by the receiving side synthesizer circuit 9. The output of the demodulator 8 is output to the receiving baseband device.

Although only one modulation / demodulation unit is shown in this embodiment for simplicity, frequency modulation can be performed by connecting a large number of modulation / demodulation units to a frequency converter.

On the other hand, the frequency control circuit 11 provided in this embodiment includes a transmitter side synthesizer circuit 6 and a receiver side synthesizer circuit 9.
It has a means to control the frequency. It also has means for transmitting the unmodulated carrier by controlling the switch 10.
Further, it has a counting means for inputting the output signal of the reception frequency converter 4 and counting the frequency. It also has means for detecting the difference between the frequency obtained by the counting means and the original frequency and controlling the voltage controlled oscillator 5 to compensate for it.

Next, a method of automatic frequency compensation by folding back in the own station according to the present invention will be described. The frequency control circuit 11 controls the switch 10 at every predetermined cycle to forcibly make an unmodulated carrier. This non-modulated carrier sending time may be a short time, and may be a time such that the counting means of the frequency control circuit 11 can count. Also, the transmission cycle of the unmodulated carrier is
Considering that the communication satellite and the transmission / reception frequency converter are the dominant elements of the frequency fluctuation and they are long-term fluctuations rather than short-term fluctuations, they are selected for a long time, for example, about one hour period.

Next, the frequency correction by the loopback of the own station is performed by the tanning shown in FIG. In FIG. 2 (a), T _N represents the non-modulated carrier transmission time. In order to receive the unmodulated carrier, the receiving side synthesizer circuit 9 is switched to the same channel as the transmitting side, and the timing is shown in FIG. 2 (b). That is, the transmission and reception are on the same channel only after the delay time T _D due to the communication satellite and the unmodulated carrier transmission time T _N. Upon reception of an unmodulated carrier, the gate of the counting means of the frequency control circuit 11 instantly opens and counts the frequency. As a result, the voltage corresponding to the frequency difference is applied to the voltage controlled oscillator 5 by comparison with the original frequency.

With the above, the frequency correction in the own station is completed, and upon completion, the normal data transmission / reception state is set. In this case, the voltage controlled oscillator 5
The control voltage is stored by the frequency control circuit 11 and the same control voltage is used until the next frequency correction.

By performing the above-described in-station frequency correction by each earth station, it is possible to suppress the frequency fluctuation of the satellite transponder and the frequency fluctuation of the receiving system high frequency circuit.

Since the frequency correction is performed by the return of the own station in this embodiment, the frequency is not corrected in the communication between the respective earth stations because each transmission system is different from that at the time of the return of the own station. Therefore, it is necessary to reduce the frequency deviation of the transmitting side high frequency circuit of each earth station, that is, the transmission frequency converter 3 to eliminate the frequency error between the earth stations.

〔The invention's effect〕

As described above, the present invention is excellent in cost because accurate control can be performed with a small-scale and inexpensive control circuit without using an expensive pilot carrier system. Further, there is an advantage that it is unnecessary to control the voltage controlled oscillator with high frequency accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram of an earth station communication device according to an embodiment of the present invention. FIG. 2 is a diagram showing a transmission / reception timing of an unmodulated carrier of the earth station communication device of the present invention. 1 ... Antenna, 2 ... Feeder circuit, 3 ... Transmission frequency converter, 4 ... Reception frequency converter, 5 ... Voltage controlled oscillator, 6 ... Transmitting side synthesizer circuit, 7 ... Modulator,
8 ... Demodulator, 9 ... Receiving side synthesizer circuit, 10 ...
Switching device, 11 ... Frequency control circuit.

Claims (1)

[Claims] 1. A modulation means for modulating each frequency of a plurality of channels based on an input transmission baseband signal, a transmission means for transmitting an output signal of the modulation means to a communication satellite, and an output signal of the communication satellite. Receiving means, a demodulating means for demodulating an output signal of the receiving means for each channel to output a received baseband signal, a modulating means and a frequency control means for performing frequency division control of the demodulating means. In the earth station communication device provided with, the frequency control means, means for interrupting the application of the transmission baseband signal to the modulation means for a short period of time at a predetermined period, and sending an unmodulated carrier during the period, Means for inputting from the demodulation means a signal in which the transmitted unmodulated carrier is returned by the communication satellite, and detecting a frequency fluctuation of the signal; Detection for earth station communication apparatus characterized by comprising means for controlling the output frequency of said receiving means based on a detection result of means.