JPH03114312A - Automatic frequency control method - Google Patents

Abstract

PURPOSE:To eliminate a frequency fluctuation component of an equipment on a satellite without use of a pilot signal by using reception frequency deviation information to control the oscillating frequency of a voltage controlled oscillator, thereby deciding the frequency of frequency conversion of the reception signal. CONSTITUTION:A demodulator 10 and a 1st band pass filter 11 limiting the reception band of the demodulator 10 are provided to the method. Then a voltage controlled oscillator 7 is controlled by using reception frequency deviation information detected at every demodulation of the reception signal by the synchronization detection system to decide the frequency of the frequency conversion of the reception signal. Thus, the frequency control is implemented by using an optional communication signal received continuously. Thus, a reference station sending a pilot signal and installation receiving the signal are not required, and the entire system cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of commercial application] The present invention relates to an automatic frequency control method that follows the frequency of a received signal in satellite communications.

[Conventional technology]

As an example of an automatic frequency control method in a conventional satellite communication receiving station, the following pilot signal is transmitted from the reference station and is received.
There is a phase-locked loop (PLL) system that detects the frequency and phase error between this signal and a reference oscillator of the receiving station, and controls the reference oscillator of the frequency converter of the receiving station based on the detected frequency and phase errors.

Fig. 2 is a diagram showing the conventional automatic frequency control method. In Fig. 9, fi+ is the receiving antenna of the satellite communication receiving station, (2
) is a frequency converter (down converter).

(3) is a power divider, (4) is a first bandpass filter, (6) is a reference oscillator, (7) is a phase comparator, and (7) is a phase comparator.
) is a voltage controlled oscillator, and (8) is a second bandpass filter.

(9) is a demodulator.

Next, the operation will be explained. The satellite communication receiving station receives the pilot signal h (unmodulated signal) sent from the reference station and the signal f2 (modulated signal) for the purpose of communication via the antenna (RI), but the frequency within the satellite is Depending on the frequency variation Δf of the converter, f1+Δf, f
2+Δf.

These received signals are converted by the frequency converter (2) based on the frequency tfI number conversion signal f5 from the voltage controlled oscillator +71, and are converted into 9 (f1+Δf)-f3 and (f2+Δf).
)-f3 and after being divided by the power divider (31), it is sent to the bandpass filter (4) of the cylinder 1 and the second bandpass filter (81).

The first bandpass filter (4) selects the frequency band of the pilot signal, and the phase comparator (5) inputs (f1+Δ
Only the frequency components of f)-fs are sent.

In the phase comparator (5ν, the frequency difference Δ between the received signal f1 + Δf-f and the reference signal f1-fs from the reference oscillator (6)
It detects f and sends out a psychic voltage value to the voltage controlled oscillator (7) according to one frequency difference.

The voltage controlled oscillator (7) changes the oscillation frequency from fs to f3+Δf using this control voltage and sends it to the frequency converter (2). By repeating the above control, the conversion frequency of the frequency converter (2) is changed to f3 by following the frequency fluctuation of the satellite.
+Δδ can be maintained.

By the above frequency control, the second bandpass filter (
8), the 7tf1 and f2 signals from which the Δf acid component has been removed are always sent, and after the frequency band of the target communication signal f2 is selected by this second bandpass filter (8),
The communication data is reproduced by a demodulator (9)K.

[Problem to be solved by the invention]

Conventional automatic frequency control systems consist of the above-mentioned equipment and a reference station that transmits the pilot signal. Therefore, if the pilot signal is not transmitted to the satellite communication receiving station due to a failure of the reference station or weather conditions in the area of the reference station. If reception becomes impossible, frequency fluctuations Δf at the satellite cannot be removed.

As a result, a frequency deviation Δf occurs in the intended communication signal f2, so that it takes a very long time for the demodulator to initially acquire the frequency. Especially burst signals (PTT signals, TDMA, etc.)
In the case of communication using the above method, since it takes time for initial acquisition each time a line is connected, there is a problem that data during that time is lost and information throughput is reduced.

This invention was devised to solve the above-mentioned problems, and an object of the present invention is to provide an automatic frequency control method that can remove frequency fluctuation components in a satellite without using a pilot signal.

[Means to solve the problem]

The automatic frequency control method according to the present invention provides one new demodulator, controls a voltage controlled oscillator using reception frequency deviation information detected when demodulating a reception signal using a synchronous detection method, and converts the frequency of the reception signal. It is designed to determine the frequency of

[Effect]

In the present invention, the frequency variation Δf of the intra-satellite frequency converter can be determined from received frequency deviation information detected by a newly installed demodulator.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention, (1) to f
31. +71 to (91 are completely the same as the above conventional example. αα is a newly provided demodulator, and aD is a first bandpass filter that limits the reception band of this demodulator αG.

Automatic station 'tft! configured as above! In the second control method, the satellite communication receiving station receives a signal f2 (modulated signal) for the purpose of communication and a signal f4 (modulated signal) for the purpose of frequency control via the satellite at antenna +11. f4
As long as it can be received continuously, any communication signal transmitted by any earth station can be used for communication even though it is intended for single frequency control. As in the conventional example, each received signal becomes f2+Δf and f4+Δf, respectively, due to the frequency fluctuation Δf of the frequency converter in the satellite. These received signals are converted by the frequency converter (2) based on the frequency conversion signal f3 from the stain pressure control oscillator (7), and (
f2+Δf)-fs and (f4+Δf)-f, which are divided by the power divider (2) and then sent to the first band-pass filter αD and the second band-pass filter (8). The first bandpass filter aD selects the frequency band of the received signal for use on the frequency side, and sends a signal of (f4+Δf)−f to the demodulator tiα. Demodulator+I
In G, when demodulating received data using a synchronous detection method, a received frequency deviation is detected and a voltage value corresponding to one frequency difference is sent to a voltage controlled oscillator (7). The voltage controlled oscillator (7) changes the oscillation frequency from fs to f3+Δf using this control voltage and sends it to the 9 frequency converter a2).

By repeating the above control, the conversion frequency of the frequency converter (2) can be maintained at f5+Δf by following the frequency fluctuation of the satellite. Due to the frequency control described above, the second bandpass filter (8) always receives ∆f acid component removed f.
After the frequency band of the target communication signal f2 is selected by the second bandpass filter (81), the communication data is recirculated by the demodulator (9).

The received signal f2 is a burst signal (PTT signal or TDMA signal)
etc.), the frequency control is performed using the continuous α recipient signal fa' and the frequency fluctuation Δf due to the general satellite is removed, so that the shortening of the initial acquisition time is maintained.

〔Effect of the invention〕

As described above, according to the present invention, nine-frequency control can be performed using any communication signal that can be received continuously.
A reference station for transmitting pilot signals and equipment for receiving them are not required, making the entire system inexpensive. Furthermore, since there is no need to rely on a single reference station for frequency control signals, system reliability is significantly improved.

In Figures 1 and 2, if the demodulator is capable of detecting reception frequency deviation using a synchronous detection method, it is PSK;
FM etc. may be collapsed.

Furthermore, it goes without saying that the receiving station may have a larger number of demodulators, and that the present invention can also be applied to the case where the signal is input via the same satellite.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional frequency control method. In the figure, (1) is an antenna, and (2) is a frequency converter. (3) is a power divider, and C4+ is a bandpass filter. (5) is a phase comparator, CB) is a reference oscillator, (7) is a voltage controlled oscillator, (8) is a bandpass filter, (9) α
α is a demodulator. Al with αna bandpass filter. Note that the same reference numerals in the two figures indicate the same or corresponding parts.

Claims (1)

[Claims] In an automatic frequency control circuit for correcting frequency fluctuations of a frequency converter in a satellite in satellite communication, the received frequency deviation information detected when demodulating a received signal using a synchronous detection method is used to control the voltage controlled oscillator. An automatic frequency control method characterized by controlling an oscillation frequency and determining a frequency for frequency conversion of a received signal.