JPH0728252B2 - Redundant switching device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a redundancy switching device for a demodulator in digital satellite communication.

[Conventional technology]

FIG. 3 is a block diagram showing a conventional redundant switching system,
In the figure, 1 is an input terminal of a reception IF signal, 2 is N online digital demodulators, 3 is one standby digital demodulator, 4 is a redundant switching controller, 5 is a baseband switch circuit, and 6 is N. This is an output terminal for each demodulated digital signal.

Next, the operation will be described.

Input from terminal 1, digital modulation (eg PSK modulation)
The frequency-division-multiplexed received IF signals of the N waves are demultiplexed into N online demodulators 2 and one standby demodulator 3, and then frequency-divided by each online demodulator 2. The generated waves are demodulated and are output as baseband digital data. The redundant switching controller 4 constantly monitors the operating conditions of the N online demodulators 2, and when any of the online demodulators 2 fails and a fault signal is input, the standby demodulator 3 receives the fault signal. After setting the frequency channel of the wave received by the online demodulator 2 to the synthesizer of the demodulator, the baseband switch circuit 5 is switched to replace the digital data output of the online demodulator 2 with the standby demodulator. The digital data output of the device 3 is output.

[Problems to be Solved by the Invention]

Such digital demodulators, especially those operating in continuous mode with low C / N, usually use the synchronous detection method.The carrier frequency of the received modulated wave and the voltage controlled crystal oscillator for carrier recovery in the demodulator When the initial frequency difference from the output frequency of (VCXO) is large, it takes time to synchronize the carrier wave. Especially, when the operation at low bit rate and low C / N is required, it is necessary to narrow the band of the carrier recovery loop, and it usually takes several tens of seconds to several minutes to synchronize the carrier frequency. Met. Therefore, when the above-mentioned redundancy switching is performed using such a digital demodulator, the reception frequency channel set in the standby demodulator is the nominal value of the frequency, and a large frequency is generated between it and the input reception modulated wave. Since there is a deviation, there is a problem that it takes time to capture the frequency and the line is disconnected during that time.

The present invention has been made to solve the above-mentioned problems, and when redundancy switching is performed, the synchronization acquisition time of the standby demodulator is shortened and the time of line disconnection is shortened, resulting in extremely high reliability. It is an object to obtain a redundant switching device for a high digital demodulator.

[Means for Solving the Problems]

The redundancy switching device according to the present invention is provided with a circuit for measuring the output frequency of the VCXO for carrier recovery of each online demodulator in each demodulator, and transmits the measurement results to the redundancy switching controller for storage and redundancy switching. When performing, the failed online frequency is set in the standby demodulator as the center frequency of the standby carrier recovery VCXO by the redundant switching controller.

[Action]

The redundancy switching method in the present invention, by setting the frequency of the reproduced carrier of the online demodulator before the failure to the center frequency of the VCXO of the standby demodulator, the input carrier of the standby demodulator and the VCXO output reproduced carrier are Since the frequency deviation between the two can be made extremely small, it is possible to shorten the acquisition time of the reproduced carrier wave of the standby demodulator.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, the same reference numerals as in FIG. 3 indicate the same parts,
21 is a means for measuring the frequency of the carrier regeneration VCXO of the online demodulator 2, 22 is a storage circuit (memory circuit) in the redundancy switching controller 4, and 23 is the center frequency of the carrier regeneration VCXO of the standby demodulator 3. It is a means of setting.

Next, the operation will be described.

In FIG. 1, the output frequency of the carrier regeneration VCXO of each on-line demodulator 2 measured by the measuring means 21 is, for example, a method of directly counting the VCXO output frequency or a method of measuring the input control voltage of the VCXO. As one of the monitoring signals, it is periodically sent from each online demodulator 2 to the storage circuit 22 in the redundancy switching controller 4, and is stored separately for each online demodulator 2. The stored frequency value is updated to the latest value each time the measurement result from the online demodulator 2 is sent.

Next, if any of the online demodulators 2 fails,
A fault signal is input from the online demodulator 2 to the redundancy switching controller 4. At this time, the redundancy switching controller 4 sets the frequency of the synthesizer for the demodulator 3 of the standby system to the frequency of the synthesizer of the online demodulator 2 that has failed, and also the storage circuit 22.
The output frequency of the VCXO for carrier recovery of the defective online demodulator 2 stored in (1) is set as the center frequency of the VCXO for carrier recovery of the standby demodulator 3 by the frequency setting means 23. The means 23 for setting this frequency is
It consists of a latch circuit that temporarily stores the frequency data from the means 22 that stores the frequency, and a D / A converter that converts the output of the latch circuit into an analog value, and the output of the D / A converter is the voltage of the carrier recovery circuit. It is applied to the control crystal oscillator.

In this embodiment, the frequency can be captured quickly,
Therefore, the time for disconnecting the line is shortened, and a highly reliable redundant switching system can be obtained.

In the above embodiment, the case of the 1: N redundancy switching system in which the number of online demodulators is N and the number of standby demodulators is one is shown. However, N online demodulators and M standby standby demodulators are shown. The present invention is also applicable to the case of M: N (M> 1), which is the number of 2: N in the second embodiment in which M = 2.
The redundant switching system is shown in FIG.

〔The invention's effect〕

As described above, according to the present invention, the output frequency of the carrier regeneration VCXO of the online demodulator that failed during redundancy switching is set as the center frequency of the carrier regeneration VCXO of the standby demodulator. Can be quickly captured, the time for disconnecting the line can be shortened, and a highly reliable redundant switching system can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a redundancy switching device according to an embodiment of the present invention, FIG. 2 is a block diagram showing a redundancy switching device according to another embodiment of the present invention, and FIG. 3 is a conventional redundancy switching system. It is a block diagram. 1 is an input terminal of a reception IF signal, 2 is an online digital demodulator, 3 is a standby digital demodulator, 4 is a redundant switching controller, 5 is a baseband switch circuit,
6 is an output terminal for the demodulated digital signal, 21 is means for measuring the frequency of the reproduced carrier wave, 22 is means for storing the frequency, and 23 is
Is a means for setting the frequency. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A redundancy switching device for a demodulator in digital satellite communication, means for measuring the frequency of a reproduced carrier wave of each online demodulator, means for storing each frequency, and the online system that has failed at the time of redundancy switching. Redundancy switching means for sending the frequency of the demodulator to the standby demodulator, and in the standby demodulator, the frequency sent from the redundancy switching means is set as the center frequency of the frequency acquisition of the carrier wave regenerating circuit. And a redundant switching device.