JPH0523526B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an automatic frequency control system, and particularly to SCPC (Single Channel Per
The present invention relates to an automatic frequency control method using a received pilot signal of the Carrier method and a signal placed near the received pilot signal.

[Conventional technology]

FIG. 3 is a block diagram of a conventional automatic frequency control system using a received pilot signal. The received pilot signal (TX PILOT) 1 sent from the satellite reference ground station and sent via the satellite and the SCPC signal (SCPC) 2 sent from each ground station via the satellite are sent to a frequency converter 3. The signal is converted to an appropriate frequency, sent to the demodulator, and also input to the narrowband filter 4. The narrowband filter 4 separates the received pilot signal 1 and the SCPC signal 2, improves the carrier-to-noise ratio specific to satellite communications, ensures automatic frequency control operation, and detects the received pilot signal, which will be described later. used to.

The received pilot signal that has passed through the narrowband filter 4 is compared in frequency and phase with a reference signal from a reference oscillator 6 in a subsequent frequency and phase comparator 5. The control signal from the frequency phase comparator 5 includes information on frequency deviations occurring within the satellite and in the receiving system. This control signal is transmitted to a variable frequency oscillator via a low-pass filter 7 that mainly determines the response of the automatic frequency control system and an adder 10 that synthesizes a sweep signal supplied at the time of initial pull-in of the automatic frequency control system, which will be described later. Added to 8. The output signal of the variable frequency oscillator 8 is used as a local signal of the frequency converter 3,
By being controlled by the control signal from the frequency phase comparator 5, frequency deviations occurring in the satellite and the receiving system are compensated for.

Next, the initial pull-in operation of the automatic frequency control system shown in FIG. 3 will be explained. When the automatic frequency control system has not established synchronization, the spectrum of the received pilot signal and SCPC signal at the input of the frequency control system is as shown in FIGS. 4a and 4b in the worst case.

Normally, in the case of satellite communications, the loop band of the automatic frequency control system is selected narrowly, so the pull-in frequency range of the automatic frequency control system is narrow. Therefore, in order to quickly establish synchronization of the automatic frequency control system, a sweep method as shown in FIG. 3 is adopted at the time of initial pull-in. That is, when the received pilot signal does not exist within the band of the narrowband filter 4, a control signal is applied from the controller 9 that detects this to the variable frequency oscillator 8 via the adder 10, Sweep the output signal. When the received pilot signal enters the band of the narrowband filter 4 by sweeping the output signal of the variable frequency oscillator 8, the signal detector in the controller 9 detects the received pilot signal, and the received pilot signal is detected. Then, the detection signal causes the controller 9 to stop sending out the sweep operation signal. After that, the automatic frequency control system starts the standard pull-in operation and synchronization is established.

However, as shown in Figure 4, if an SCPC signal exists near the received pilot signal TX PILOT, and especially if the SCPC signal is an FM modulated wave, has a small frequency deviation, and has a sufficiently high carrier component, this There is a possibility that the sweep operation of the automatic frequency control system described above is stopped by the SCPC signal, and the automatic frequency control system establishes synchronization by the SCPC signal. Therefore, conventionally, in order to prevent the automatic frequency control system from malfunctioning due to this SCPC signal, a guard band is provided on the side near the received pilot signal.

[Problem that the invention seeks to solve]

In the conventional automatic frequency control method described above, a frequency twice as large as the frequency deviation occurring within the satellite and the frequency deviation occurring in the receiving system is required as a guard band on both sides of the received pilot signal, making it difficult for line operation. The disadvantage is that there is a wasted band.

[Means for solving problems]

The present invention attempts to eliminate the above-mentioned drawbacks, and uses a received pilot signal and a signal placed near this signal to determine whether or not the automatic frequency control system is malfunctioning. It is an object of the present invention to provide an automatic frequency control method that can quickly return to normal automatic frequency control operation in case of an automatic frequency control operation.

[Means for Solving the Problems] The present invention uses a received pilot signal sent from a satellite reference ground station and transmitted via the satellite to detect frequency deviations occurring within the satellite and frequency deviations occurring in the receiving system. In an automatic frequency control system that compensates for and a control unit that provides a control signal to the automatic frequency control system based on the automatic frequency control system, and after the automatic frequency control operation is completed, the automatic frequency control system This is an automatic frequency control method characterized by having a function of determining whether or not the frequency control is malfunctioning, and if it is malfunctioning, shifting to normal automatic frequency control operation using a received pilot signal.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an automatic frequency control system to which an embodiment of the present invention is applied, and FIG. Show placement. The frequency arrangement shown in Fig. 2 is used for compandaid FM-SCPC communication, which is used in international satellite communication called STD-D.

As shown in FIG. 1, the automatic frequency control method according to the present invention, similar to the conventional example shown in FIG.
It includes a frequency converter 3, a narrowband filter 4, a frequency phase comparator 5, a reference oscillator 6, a low-pass filter 7, a controller 9, an adder 10, and a variable frequency oscillator 8. In addition to this, the output section of the frequency converter 3 has -90 kHz,
Narrowband filters 11a, 11b, 11c, 11d with center frequencies of -60kHz, +45kHz, +75kHz, these narrowband filters 11a, 11b, 11c, 1
Signal detectors 12a, 12 respectively cascaded to 1d
b, 12c, 12d and a control section 13.

Next, the operation of this embodiment will be explained.

The process of establishing synchronization in the automatic frequency control system is similar to the conventional automatic frequency control system shown in FIG. That is, when there is no received pilot signal within the band of the narrow band filter 4 and the pilot signal is not detected by the signal detector in the controller 9, the output signal of the variable frequency oscillator 8 is It is swept by a control signal via adder 10. When a signal exists within the band of the narrow band filter 4 due to this sweep operation and is detected by a signal detector in the controller 9, the sweep operation of the variable frequency oscillator 8 is performed by the controller 9. It is stopped by a control signal from. Then, the pull-in operation of the automatic frequency control system acts so that the frequency and phase difference between the signal within the band of the narrowband filter 4 and the reference signal of the reference oscillator 6 become zero, and this frequency phase difference When the frequency becomes within the lock-in range of the automatic frequency control system, synchronization of the automatic frequency control system is instantaneously established.

When synchronization is established, the control section 13 starts operating in response to a control signal from the frequency phase comparator 5. The control unit 13 includes narrowband filters 11a, 11b, 11c,
It is determined whether a signal exists within the band 11d based on the output signals from the signal detectors 12a, 12b, 12c, and 12d, and whether the automatic frequency control system is currently synchronized with the received pilot signal. , or placed near the receiving pilot.
It is determined whether synchronization has been established using the SCPC signal. Assuming that the required pull-in range of the automatic frequency control system is ±40kHz, the SCPC signals that may cause the automatic frequency control system to malfunction due to SCPC signals near the received pilot signal are No. 598, No.599, No.602, No.603. However, when the automatic frequency control system malfunctions due to the SCPC signal, the signal detectors 12a, 12b, 1
The outputs of 2c and 12d are the following logical formulas, and the above
The control unit 13 can easily determine which SCPC signal is causing the automatic frequency control system to malfunction.

No.598SCPC signal = D No.599SCPC signal = C Receive pilot signal =... No.602SCPC signal = B... No.603SCPC signal = A... A, B, C, D in the logical formula is the signal detector 12
Output signals of a, 12b, 12c, 12d are “present”
, , , indicates that the output signal is "absent".

When the control unit 13 determines that the automatic frequency control system is malfunctioning due to an SCPC signal near the received pilot signal, it adds a control signal corresponding to the frequency difference between the malfunctioning SCPC signal and the received pilot signal. variable frequency oscillator 8 via the generator 10
The automatic frequency control system is controlled to establish synchronization with the received pilot signal. In this way, a transition is made to normal automatic frequency control operation.

In this embodiment, a plurality of narrowband filters are installed at the output of the frequency converter, but instead of a plurality of narrowband filters, a plurality of narrowband filters are installed at the output of the frequency phase comparator. The same effect can also be obtained by using a low-pass filter and a plurality of sign/negative determiners.

〔Effect of the invention〕

As explained above, the present invention includes a conventional automatic frequency control system including a plurality of bandpass filters, the same number of signal detectors, and a control section, and enables the automatic frequency control system to establish synchronization using a received pilot signal. The control unit following the signal detector detects whether synchronization is established using the SCPC signal near the received pilot signal, and the control unit following the signal detector shifts to establishing normal synchronization of the automatic frequency control system according to the detection signal. By this,
It is possible to eliminate malfunctions in the automatic frequency control system due to the SCPC signal placed near the received pilot signal. In addition, the guard band near the receiving pilot can be reduced, and the satellite frequency band can be used effectively.

[Brief explanation of the drawing]

Fig. 1 shows a block diagram of an embodiment of the present invention, Fig. 2 shows a frequency allocation diagram of the received pilot signal and SCPC signal used in the invention, and Fig. 3 shows the automatic frequency arrangement of the conventional automatic frequency control method. The block diagram of the control section, FIGS. 4a and 4b, are frequency allocation diagrams of the worst-case received pilot signal and SCPC signal, respectively, which are input to the automatic frequency control system. 1... Reception pilot signal, 2... SCPC signal,
3... Frequency converter, 4... Narrowband filter, 5...
...Frequency phase comparator, 6...Reference oscillator, 7...
Low-pass filter, 8... Variable frequency oscillator, 9... Controller, 10... Adder, 11a, 11b, 11
c, 11d... narrowband filter, 12a, 12b,
12c, 12d...Signal detector, 13...Control unit.

Claims (1)

[Claims] 1. In the automatic frequency control system that compensates for frequency deviations occurring within the satellite and frequency deviations occurring in the receiving system using the received pilot signal sent from the satellite reference ground station and transmitted via the satellite, A control system that includes a plurality of bandpass filters with different center frequencies, a plurality of signal detectors connected to each of the bandpass filters, and a control signal that provides a control signal to an automatic frequency control system based on the output signal of the signal detector. After the automatic frequency control operation is completed, the system determines whether the automatic frequency control system is malfunctioning based on the presence or absence of the received pilot signal or a signal placed near the received pilot signal, and determines whether the automatic frequency control system is malfunctioning. 1. An automatic frequency control method characterized by having a function of shifting to normal automatic frequency control operation using a received pilot signal.