JPH0357325A - Earth station communication equipment - Google Patents

Abstract

PURPOSE:To miniaturize a scale, to reduce the cost, to improve the channel efficiency and to attain excellent channel separation by providing a means sending a no-modulation carrier and a means detecting a frequency fluctuation or the like. CONSTITUTION:A frequency control circuit 11 controls a switch 10 at every prescribed period to form a no-modulation carrier forcibly, which is sent for a time when a counting means is able to count and the transmission period is selected to a long time e.g. one hour period or so. Moreover, a gate of the counting means of the circuit 11 is opened momentarily at the reception of no-modulation carrier, the frequency is counted. Thus, a voltage corresponding to the frequency difference is given to a voltage controlled oscillator 5 through the comparison with a substantial frequency. Thus, the correction of the frequency of its own station is finished and normal data transmission/reception state is attained simultaneously with the completion. In this case, the control voltage of the oscillator 5 is stored by the circuit 11 and the same control voltage is used till the succeeding frequency correction. Thus, accurate reception is attained with the inexpensive control circuit with a small scale is attained and channel separation is attained in an excellent manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is applied to an earth station communication device for satellite communication. In particular, the SCPC method (Single
The present invention relates to an earth station communication device based on the Channel Per Carrier method.

〔overview〕

The present invention uses an earth station communication device to transmit a short-time unmodulated carrier at a predetermined period, compare the frequencies of the unmodulated carrier returned by the communication satellite and the transmitted unmodulated carrier, and based on the comparison result, By correcting the frequency on the receiving side, it is possible to achieve small scale, low cost, high channel efficiency, and good channel separation.

[Conventional technology]

Conventionally, earth station communication equipment has used frequency converters and filters to separate channels. For this reason, when the radio frequency is extremely large compared to the channel band,
Frequency converters and the like require extremely high frequency accuracy.

In order to meet this demand, various AFC methods (Au
tomatic Frequency CoITIp
ensation method) has been used.

One example is a method using a pilot carrier. This is a system in which a non-modulated carrier is sent to a specific channel among a large number of channels, and stations other than the sending station use the non-modulated carrier as a frequency reference.

In particular, in satellite communications, there are large frequency fluctuations due to frequency fluctuations of the satellite transbonder and the Doppler effect of the satellite itself.
In order to suppress the frequency stability of the entire line to the required value,
The pilot carrier system had become indispensable.

"Problems to be Solved by the Invention" However, since such conventional earth station communication equipment uses an AFC method that uses a pilot carrier, it requires a transmitter and a receiver dedicated to the pilot carrier, resulting in a large equipment scale. However, in small-capacity communication stations, their proportion could not be ignored, and they also had the disadvantage of being expensive.

Also, one frequency band is usually allocated for the pilot carrier.
This has the disadvantage that the number of channels used for actual communication is reduced because the number of channels is occupied.

The present invention solves the above-mentioned drawbacks, and aims 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 the frequency of each 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 a transmission means for transmitting an output signal of the communication satellite. a receiving means for receiving;
Earth station communication comprising a demodulator for demodulating the output signal of the receiving means for each channel and outputting a received baseband signal, and a frequency control means for frequency division control of the modulating means and the demodulating means. In the apparatus, the frequency control means includes 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 transmitting an unmodulated carrier during the period; means for inputting a signal returned by the communication satellite from the demodulating means and detecting the frequency fluctuation of the signal; and means for controlling the output frequency of the receiving means based on the detection result of the detecting means. It is characterized by containing.

[Effect]

The frequency control means interrupts supplying the transmission baseband signal to the modulation means for a short time at a predetermined period, and causes the unmodulated carrier to be transmitted during that period. Further, a signal obtained by returning the transmitted non-modulated carrier via a communication satellite is manually inputted from a demodulating means, and the frequency of the signal is compared with that of the transmitted non-modulated carrier to detect frequency fluctuations. Furthermore, based on the result of this field detection, the output frequency of the receiving means is controlled for a period until the next non-modulated carrier is sent out. The above operation makes it possible to achieve small scale, low cost, high channel efficiency, and good channel separation.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings. 1st
The figure 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 transmitting side synthesis circuit 6 and a modulator 7 as modulating means for modulating the frequencies of each of a plurality of channels based on an input transmitting baseband signal, and an output of the modulator 7. Transmission frequency converter 3 as a transmission means for transmitting signals to a communication satellite
, a part of the feeder circuit 2, a part of the antenna i, a part of the antenna 1, a part of the feeder circuit 2, a reception frequency converter 4, and a reception frequency converter as receiving means for receiving the output signal of this communication satellite. A receiving side synthesizer circuit 9 and a demodulator 8 serve as demodulators to demodulate the output signal of the converter 4 for each channel and output a received baseband signal.
and a part of a frequency control circuit l1 as frequency control means for performing frequency division control of the modulator 7 and demodulator 8.

Here, the feature of the present invention is that the frequency control means interrupts supplying the transmission baseband signal to the modulator 7 for a short time at a predetermined period, and switches the frequency control means to transmit an unmodulated carrier during that period. 10 and a part of the frequency control circuit 11, and a part of the frequency control circuit 11 as a means for inputting a signal from the demodulator 8 into which the transmitted non-modulated carrier is reflected by the communication satellite and detecting the frequency fluctuation of the signal. and a part of the voltage controlled oscillator 5 and the frequency control circuit 11 as means for controlling the output frequency of the receiving frequency converter 4 based on the detection result of the detecting means.

The operation of the earth station communication device having such a structure will be explained. FIG. 2 is a diagram showing the transmission and reception timing of an unmodulated carrier in the earth station communication device of the present invention. In Figure 1,
When transmitting communication data, the transmission signal input from the transmission baseband device passes through the switch 10 and then the modulator 7.
Modulated by

Next, after a radio channel is selected by the transmitting side synthesizer circuit 6, the signal is 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, the data passes through the antenna 1 and the feeder circuit 2, passes through the reception frequency converter 4, and is then demodulated by the demodulator 8. Here, the receiving channel is selected by the receiving synthesizer circuit 9. The output of the demodulator 8 is output to the receiving baseband device.

In this embodiment, only one modulation/demodulation section is shown for simplicity, but it is also possible to connect multiple modulation/demodulation sections to a frequency converter to perform frequency multiplexing.

On the other hand, the frequency control circuit 11 provided in this embodiment has means for controlling the frequencies of the transmitting synthesizer circuit 6 and the receiving synthesizer circuit 9.

It also has means for transmitting unmodulated carriers by controlling the switch 10. Furthermore, it has a counting means for inputting the output signal of the receiving 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 the difference.

Next, a method of automatic frequency compensation by loopback within the local station according to the present invention will be explained. The frequency control circuit 11 controls the switch 10 at predetermined intervals to forcibly create a non-modulated carrier. This unmodulated carrier sending time may be short,
Further, the time may be long enough to be counted by the counting means of the frequency control circuit l1.

In addition, the transmission period of the unmodulated carrier should be set to a period of about one hour, for example, considering that the dominant elements of frequency fluctuation are communication satellites and transmitting/receiving frequency converters, and these fluctuations are long-term rather than short-term fluctuations. selected at the time.

Next, frequency correction by local station loopback is performed at the timing shown in FIG. In FIG. 2(a), Tx indicates the unmodulated carrier exit time. In order to receive an unmodulated carrier, the receiving side synthesizer circuit 9 is switched to the same channel as the transmitting side, and the timing thereof is shown in FIGS. In other words, the delay time TIll due to the communication satellite
After a delay of 1 minute, the same channel is used for transmission and reception only during the non-modulated carrier transmission time T1. When a non-modulated carrier is received, the gate of the counting means of the frequency control circuit 11 is instantaneously opened, the frequency is counted, and as a result, a voltage corresponding to the frequency difference is applied to the voltage controlled oscillator 5 by comparison with the original frequency.

With the above steps, the internal frequency correction is completed, and at the same time, the normal data transmission/reception state is established. In this case, the voltage controlled oscillator 5
The control voltage is stored by the frequency control circuit l1, and the same control voltage is used until the next frequency correction.

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

Note that in this embodiment, since frequency correction is performed by returning to the own station, in communication between each earth station, each transmission system is different from when returning to the own station, so frequency correction is not performed. For this purpose, 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, and eliminate the frequency error between each earth station.

〔Effect of the invention〕

As described above, the present invention is advantageous in that it does not use an expensive pilot carrier system and can perform accurate reception with a small scale and inexpensive control circuit.

Another advantage is that it is not necessary to control the voltage controlled oscillator with high frequency accuracy.

[Brief explanation 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 the transmission and reception timing of an unmodulated carrier in the earth station communication device of the present invention. l...Antenna, 2...Feeder circuit, 3...Transmission frequency converter, 4...Reception frequency converter, 5...
Voltage controlled oscillator, 6... Transmission side synthesizer circuit, 7
... Modulator, 8 ... Demodulator, 9 ... Receiving side synthesizer circuit, 10 ... Switch, l1 ... Frequency control circuit. Embodiment: Transmission and reception timing of non-modulated CASSOYA Figure 2

Claims (1)

[Claims] 1. A modulating means for modulating the frequency of each of a plurality of channels based on an input transmission baseband signal, and a transmitting means for transmitting an output signal of the modulating means to a communication satellite;
A receiving means for receiving the output signal of the communication satellite, a demodulating means for demodulating the output signal of the receiving means for each channel and outputting a received baseband signal, and frequency division control of the modulating means and the demodulating means. In the earth station communication device, the frequency control means interrupts providing the transmission baseband signal to the modulation means for a short time at a predetermined period, and transmits the unmodulated carrier during that period. means for transmitting the unmodulated carrier, a means for inputting a signal obtained by returning the transmitted unmodulated carrier by the communication satellite from the demodulating means and detecting the frequency fluctuation of the signal; An earth station communication device comprising: means for controlling the output frequency of the receiving means.