JPH05191370A - Burst signal demodulator and demodulation control method - Google Patents

Abstract

PURPOSE:To obtain the inexpensive small sized burst signal demodulator controller coping with all frequency fluctuation including that on a satellite for a burst signal demodulator single body. CONSTITUTION:A dummy burst signal is sent continuously from a dummy burst transmission section 2 for many times with an instruction from a control section 1 at the initial acquisition and the section 2 receives by itself via a satellite, a demodulator 7 sweeps a local oscillation frequency 13 and stops sweeping when a frequency fluctuation error is not included in a signal at a reproduction intermediate frequency band and implements demodulation. In the steady-state, while the burst signal is being received, an AFC circuit 20 is operated. Furthermore, when the burst signal is not received for a prescribed period, the dummy burst signal is sent for self-check and when the signal is not normally received, the operation is restored to the operation of the initial acquisition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulator control method, and more particularly to a burst signal demodulator and demodulation control method for demodulating a burst signal used in satellite communication.

[0002]

2. Description of the Related Art There is a multiple access satellite communication system in which communication is performed between stations installed at physically different places using a common channel via a communication satellite. For example, the well-known Time Division Multiple Access (Time Division)
The multiple access (TDMA) communication method, the quasi-Aloha communication method, the slotted Aloha communication method, and the like. These communication systems require a demodulator that faithfully reproduces digitally modulated burst (intermittent) signals from geographically widely distributed earth stations.

In these satellite communications, due to variations in the performance of the hardware provided for each earth station, in addition to the frequency error that occurs individually at each earth station, the frequency that occurs due to the drift of the frequency converter mounted on the satellite. There is an error. Further, the causes of the frequency error individually generated in each earth station are divided into those caused by the frequency conversion of the transmission system and those caused by the frequency conversion of the reception system.

In the above-mentioned communication system, when the above-mentioned frequency fluctuation is observed on the receiving side for demodulating a burst signal,
The frequency error on the satellite and the frequency error that occurs in the receiving system are the "frequency fluctuations that appear in common" in each burst signal individually transmitted from each earth station, and the frequency error that occurs in the transmitting system of the burst signal. Is a “frequency error appearing as an inter-station deviation” that differs depending on each burst signal.

Among these, the "frequency error appearing as an inter-station deviation" is captured by the carrier recovery circuit inside the demodulator,
The tracking of the “common frequency fluctuation” is performed by a pilot reception AFC device that constantly monitors the pilot signal on the receiving side and compensates for this.

[0006]

The above-mentioned "common frequency fluctuation" is much larger than the "frequency error appearing as an inter-station deviation" and cannot be captured by the carrier recovery circuit inside the demodulator. is there.

Further, the pilot reception AFC device for following the above-mentioned "commonly appearing frequency fluctuation" requires a down converter and a demodulator for receiving the pilot signal, and the entire system is required. In the case of consideration, a pilot signal generator for generating a pilot signal is required. Also, when a burst signal demodulator is used at the base station of the system, it is common to have a backup device in case of emergency, but these devices are very expensive. Therefore, it is not preferable from the viewpoint of reducing the cost of equipment and also from the viewpoint of downsizing of the apparatus.

[0008]

A burst signal demodulating device, which is a first solution of the present invention for solving the above-mentioned problems, includes a dummy burst transmitting section and a dummy burst transmitting section for outputting the dummy burst transmitting section. A burst signal demodulation device comprising a control unit for controlling transmission / stop of a burst signal and a demodulator, wherein the dummy burst transmission unit includes a dummy data generator for generating dummy data, and the dummy data. Unique word synthesizer that generates and adds a unique word to the
A preamble synthesizer for generating and adding an amble,
The demodulator is composed of a modulator that modulates and transmits dummy data created by combining the unique word and the preamble as a dummy burst signal,
A variable frequency type local oscillator that can change the local oscillation frequency according to the frequency control signal, a mixer that converts the received burst signal into an intermediate frequency band signal according to the output signal of the variable frequency type local oscillator, and the output of the mixer. A demodulation unit that receives and demodulates data using a carrier signal regenerated by a built-in carrier regeneration circuit, a unique word detection unit that determines a unique word detection state from the demodulation signal of this demodulation unit, and the variable frequency Type local oscillator A local oscillator frequency sweeping unit for outputting a sweep signal for sweeping the local oscillator frequency of the local oscillator stepwise and cyclically in burst cycle units, and captured according to frequency error information from the carrier recovery circuit of the demodulator An AFC circuit for performing a tracking process with respect to a frequency fluctuation within a range, a sweep signal of the local oscillation frequency sweep unit, and the AFC circuit And wherein this constituted an adder for superimposing the power signal.

A second solving means of the present invention for solving the above-mentioned problem is to use the burst signal demodulation control method of the burst signal demodulating device according to the solving means 1 as a dummy method for the initial acquisition process for starting the demodulator. A burst signal is continuously transmitted, and the unique word detection unit
The local oscillation frequency is swept stepwise and cyclically until a word is detected, and when the unique word is detected by the unique word detection unit, the dummy burst transmission unit is sent a dummy burst signal. When the demodulator is stopped and the normal operation process is performed, and it is identified by the unique word detection signal from the unique word detection unit that no unique word is detected during the constant period of the normal operation process. , The control unit causes the dummy burst transmission unit to transmit a predetermined number of dummy burst signals,
The unique word detection unit determines whether or not a unique word has been detected. If a unique word is detected, the steady operation process is maintained. If no unique word is detected, the initial acquisition is performed. It is characterized in that processing is performed by the demodulator.

[0010]

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

FIG. 1 is a block diagram showing an embodiment of the present invention. Here, the dummy burst transmission unit 2, which is controlled by the signal 9 indicating the initial acquisition process output from the control unit 1, inputs the output of the dummy data generator 3 to the unique word synthesizer 4, The output of the unique word synthesizer 4 is input to the preamble synthesizer 5, and the output of the preamble synthesizer 5 is input to the modulator 6.

The demodulator 7 receives the input signal 8 to the demodulator 7.
Is input to one terminal of the mixer 14, and the mixer 14
The output signal 13 of the variable frequency local oscillator 12 is input to the other terminal of the. And the output signal 1 of the mixer 14
5 is input to the demodulation unit 16, and the demodulation signal 17 which is the output of the demodulation unit 16 is input to the unique word detection unit 18 and is output to the outside of the demodulator 7. Unique word detection signal 1 of the unique word detection unit 18
9 is input to the AFC circuit 20, the local oscillation frequency sweeping unit 10 and the control unit 1. Frequency error information 22 output from the carrier recovery circuit of the demodulation unit 16 is also input to the AFC circuit 20. Local oscillation frequency sweep unit 10
The signal 9 of the control unit 1 is also input to the input terminal, and the output signal of the local oscillation frequency sweeping unit 10 is input to the adder 21 together with the output signal of the AFC circuit 20. The frequency control signal 11 output from the adder 21 is connected to the variable frequency local oscillator 12 so as to be input.

The operation of the above arrangement will be described below.

At the initial acquisition of the demodulator 7, the controller 1 issues a command to the dummy burst transmitter 2 to continuously output a plurality of dummy burst signals. Receiving this, the dummy burst transmission unit 2 starts transmitting a dummy burst signal. At this time, the unique word synthesized by the unique word synthesizer 4 into the dummy burst is the same as the unique word used in normal communication.

The dummy burst signal transmitted by the dummy burst transmitter 2 is input to the demodulator 7 via the satellite. The input signal 8 of the demodulator 7 includes "frequency error appearing as inter-station deviation" and "frequency fluctuation appearing in common", which is captured by the demodulator 7 alone.

The signal 9 indicating the initial acquisition is input from the control unit 1 to the local oscillation frequency sweeping unit 10, and the local oscillation frequency sweeping unit 10 adds the frequency control signal 11 to perform periodic sweeping. It outputs to the variable frequency type local oscillator 12 via 21. However, at this time, it is necessary to sweep stepwise so as not to exceed the pull-in frequency range during the burst period. This state is shown in FIG. 2, and the sweep range needs to be a range that can include the frequency fluctuation 31 that is considered in advance. By sweeping the local oscillation frequency, the local oscillation frequency for compensating for the frequency fluctuation error included in the input signal 8 of the demodulator 7 becomes a variable frequency type local oscillator 12.
When it is given to the mixer 14 by the output signal 13 of
The output signal 15 of the mixer 14 is converted into an intermediate frequency band signal from which the frequency fluctuation error is removed. In addition, in FIG.
The frequency width 33 indicates a frequency width equal to or less than the pull-in range of the demodulation unit, and the time width 32 indicates an example of burst cycle.

The demodulation section 16 receives the signal 15 in which the frequency fluctuation error is compensated at this point and demodulates it. At this time, it is well known that even if the frequency error is not completely zero, demodulation can be completely performed within the frequency range in which the carrier recovery circuit of the demodulator 16 can be pulled. The demodulation signal 17 demodulated by the demodulation unit 16 is input to the unique word detection unit 18, the unique word is detected, and the unique word detection signal 19 is output. Local oscillation frequency sweep unit 10
Then, upon receiving the unique word detection signal 19 and recognizing that the frequency variation error has been compensated, the frequency control signal 11 is held constant in order to immediately stop the frequency sweep. Further, the control unit 1 also receives the unique word detection signal 19 at the same time, stops the transmission of the dummy burst, and starts the steady operation. That is, a normal burst signal is received and communication is performed.

In this steady state, the AFC circuit 20 outputs the frequency error information 2 output from the carrier recovery circuit of the demodulator 16.
Follow frequency fluctuations according to 2. However, AFC circuit 2
0 is operated only during the period when the burst signal is being received. Since the length of the burst signal is known in advance, the length of the data portion following the unique word is also known.
Therefore, only when the unique word is detected, the AFC circuit 20 may be operated during the fixed period corresponding to the data portion. Further, the control unit 1 operates the timer in the steady state, and if the unique word cannot be detected during a certain predetermined period, it is possible that the burst signal could not be received. self·
Check. It instructs the dummy burst transmission unit 2 to send N dummy burst signals, and if this dummy burst signal can be received via the satellite, the unique burst signal that follows the dummy burst signal is received. When the word is detected by the unique word detection unit 18,
If the AFC circuit 20 operates normally, it means that the demodulation operation is functioning normally based on the local oscillation frequency of the demodulator 7.

If the unique word due to the dummy burst signal cannot be detected, it means that the dummy burst signal for self-check cannot be received, and it is judged that the local oscillation frequency has moved due to some abnormality. Then, it returns to the initial acquisition operation and restarts the sweep of the local oscillation frequency.

[0020]

As described above, according to the present invention, as a burst signal demodulation control device, a number of dummy burst signals are continuously transmitted at the time of initial acquisition, and the dummy burst signals are self-received via a satellite. By changing the local oscillation frequency generated inside the demodulator, the fluctuation of the frequency generated on the satellite and the error of the frequency generated in the receiving system in the local station are compensated. And, in the steady state, only when the burst signal is received, A
The FC circuit is operated to follow the frequency fluctuation, and when no burst signal is received for a certain period, a dummy burst signal for self-check is sent to confirm the steady operation. When it is determined that the self-unique word following the self-check dummy burst signal cannot be received, the initial acquisition operation for correcting the local oscillation frequency is returned to. With the above-described functional operations, the pilot reception AFC device and the like which have been conventionally required are not required, and there is an effect that the demodulator can be significantly downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram illustrating how frequencies are swept.

[Explanation of symbols]

 1 control section 2 dummy burst transmission section 3 dummy data generator 4 unique word synthesizer 5 preamble synthesizer 6 modulator 7 demodulator 8 input signal 9 signal indicating initial acquisition process 10 local oscillation frequency sweep Part 11 Frequency control signal 12 Variable frequency type local oscillator 13 Output signal of variable frequency type local oscillator 14 Mixer 15 Mixer output signal 16 Demodulator 17 Demodulated signal 18 Unique word detector 19 Unique word detection signal 20 AFC circuit 21 adder 22 frequency error information

Claims (2)

[Claims] 1. A dummy burst transmission unit and the dummy burst transmission unit.
What is claimed is: 1. A burst signal demodulation device comprising: a control unit for controlling transmission / stop of a dummy burst signal output from a burst transmission unit; and a demodulator, wherein the dummy burst transmission unit is a dummy for generating dummy data. A data generator; a unique word synthesizer for generating and adding a unique word to the dummy data; a preamble synthesizer for generating and adding a preamble necessary for demodulation;・ A modulator that modulates / transmits dummy data created by synthesizing a word and the preamble as a dummy burst signal, and the demodulator changes the local oscillation frequency according to the frequency control signal. The variable frequency type local oscillator that can be used and the received burst signal are converted into signals in the intermediate frequency band according to the output signal of the variable frequency type local oscillator. A mixer to be exchanged, a demodulator that receives the output of the mixer and demodulates data using a carrier signal regenerated by a built-in carrier regenerating circuit, and a unique word detection state is determined from the demodulated signal of this demodulator. A unique word detection unit, a local oscillation frequency sweeping unit that outputs a sweep signal for sweeping the local oscillation frequency of the variable frequency type local oscillator stepwise and periodically in burst cycle units, and the demodulation unit It is composed of an AFC circuit for performing a tracking process for a frequency fluctuation within a capture range according to frequency error information from a carrier wave regenerating circuit, and an adder for superimposing a sweep signal of the local oscillation frequency sweep unit and an output signal of the AFC circuit. A burst signal demodulating device characterized by the above. 2. An initial acquisition process in which the demodulator starts up,
A dummy burst signal is continuously transmitted, and the local oscillation frequency is swept stepwise and cyclically until a unique word is detected by the unique word detector, and the unique word detector is unique. When the word is detected, the dummy burst transmission unit stops the output of the dummy burst signal and causes the demodulator to perform the steady operation process, and the unique word is detected during a certain period of the steady operation process. When the absence is detected by the unique word detection signal from the unique word detection unit, the control unit causes the dummy burst transmission unit to transmit a predetermined number of dummy burst signals, and the unique word detection unit To determine whether a unique word has been detected,
If the word is detected, maintain the normal operation process,
2. The burst signal demodulation control method of the burst signal demodulation apparatus according to claim 1, wherein the demodulator is caused to perform the initial acquisition processing when no unique word is detected.