JPH0453331B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] Phase uncertainty detection that detects the minimum phase shift of a received signal by setting the initial phase of a Doppler buffer in satellite communication based on the minimum number of syndrome pulses output from an error correction decoder. This is done by the output of the circuit.

[Industrial application field]

The present invention relates to a Doppler buffer control system for satellite communications, and more particularly to an improvement in an initial phase setting system for a Doppler buffer for satellite communications.

In the conventional initial phase setting method of the Doppler buffer for satellite communication, the initial phase setting is performed when the device is powered on, so when communication actually starts, the phase is already shifted and good communication cannot be performed.

[Conventional technology]

It is well known that there are two types of satellite communication communication methods: multiplex communication method and single communication method.The single communication method transmits one piece of information using one radio carrier wave, so it is called SCPC (single channel per carrier). It is said that there are many earth stations that use one satellite,
Suitable for fixed communications where the number of lines used per earth station is extremely small.

SCPC uses the PCM-PSK method (audio information is transferred to PCM
There are many systems that use PSK modulation of the carrier wave.

In such communication devices, the initial phase setting for Doppler buffer control was conventionally performed when the power of the communication device was turned on.

A Doppler buffer for satellite communication is a buffer provided to remove phase distortion caused by the movement of a satellite, and is written using the receiving clock and read using the earth station clock.

A Dotsupura buffer normally has a capacity of about 1mS. Therefore, if the communication speed is 25 Mbit/s, it has a capacity of about 25 Kbits. Since the writing speed and reading speed of this Doppler buffer do not necessarily match, its operating point always moves, but it is desirable to always operate at the center of its capacity.

Therefore, conventionally, control has been performed such that the initial phase is set to operate at approximately the center of the Doppler buffer.

[Problem that the invention seeks to solve]

However, since the initial phase setting of the conventional Doppler buffer is performed when the device is powered on, there is a drawback that the phase shifts when communication actually starts.

[Means for solving problems]

The above problem is related to satellite communications, as shown in the figure, the initial phase setting of the Doppler buffer 4 that absorbs the Doppler signal from the satellite increases as the number of errors in the received code output from the error correction decoder 3 increases. Due to the increased number of syndrome pulses, the output signal of the phase uncertainty detection circuit 6 detects the minimum phase shift of the received signal.

[Effect]

According to the present invention, the phase uncertainty detection circuit 6 sets the initial phase of the Doppler buffer using the detection signal outputted every time it detects that the number of syndrome pulses from the error correction decoder 3 becomes the minimum. It is possible to set the initial phase of , which has the effect of improving reliability compared to the conventional method.

〔Example〕

The figure is a diagram showing an embodiment of the Doppler buffer control method according to the present invention.

In the figure, 1 is a MODEM, 2 is a phase uncertainty removal circuit, 3 is an error correction decoder, 4 is a Doppler buffer, 5 is a Doppler buffer control circuit, and 6 is a phase uncertainty detection circuit.

As mentioned in the conventional technology section, in SCPC
Many use the PCM-PSK method.

In a communication device that uses the PSK modulation method, a phase uncertainty removal circuit 2 is used to search for a phase that minimizes the number of syndrome pulses (error correction codes) in the error correction decoder 3 in a phase uncertainty detection circuit 6. is spinning in a free running state.

What is free run state? (I, Q) → (I,) →
(,Q)→(,)→(I,Q) are output in a cyclic manner, and for each phase state, the error correction decoder 3 outputs a syndrome pulse, and the phase uncertainty detection circuit 6 outputs a syndrome pulse. examines these syndrome pulses, detects the smallest one, determines that its phase state is optimal, fixes the phase uncertainty removal circuit 2 in that state, and performs communication.

Communication devices that use the PSK modulation method have conventionally performed the above operations before communicating.

The present invention is an improvement plan that focuses on the above matters.

That is, in the present invention, instead of setting the initial phase when the power is turned on as in the conventional system, the phase uncertainty detection circuit 6 detects the minimum phase of the syndrome pulse output from the error correction decoder 3 and removes the phase uncertainty. At the time when the circuit 2 is fixed, a detection signal is sent from the phase uncertainty detection circuit 6 to the Doppler buffer control circuit 5 to generate a control signal, and the initial phase of the Doppler buffer 4 is set.

As described above, in the present invention, when a PSK-modulated transmission signal with an error correction code is sent from the transmitting side and demodulated on the receiving side, the phase uncertainty detection circuit 6 detects the output of the error correction decoder 3. Each time the minimum phase of the syndrome pulse is detected, the Doppler buffer control circuit 5 sets the initial phase of the Doppler buffer 4, so that the initial phase setting of the Doppler buffer 4 is always guaranteed.

〔Effect of the invention〕

As described in detail above, according to the present invention, the initial phase setting of the Doppler buffer is always guaranteed, so there is a great effect that good communication conditions can always be obtained in satellite communication.

[Brief explanation of drawings]

The figure is a diagram showing an embodiment of the Doppler buffer control method according to the present invention. In the figure, 1 is a MODEM, 2 is a phase uncertainty removal circuit, 3 is an error correction decoder, 4 is a Doppler buffer, 5 is a Doppler buffer control circuit, and 6 is a phase uncertainty detection circuit.

Claims (1)

[Claims] 1. In the control method of the Doppler buffer 4, which absorbs the Doppler shift in which the phase of the received signal of the earth station changes due to the irregular movement of the satellite, errors in the code of the received signal are corrected by using a transmitted signal with an error correction code added in advance on the transmitting side. An error correction decoder 3 that statistically judges and corrects errors in the error correction code in the received signal when receiving and demodulating it on the receiving side, and a pulse that is sent out as the number of code errors in the received signal output from the error correction decoder 3 increases. A phase uncertainty detection circuit 6 detects that the phase of the received signal deviates from the normal value and becomes uncertain when the number of syndrome pulses that increase in number becomes greater than a predetermined number of pulses. a phase uncertainty removal circuit 2 that removes uncertainty in the phase of the received signal by locking a demodulator to the phase of the received signal when the number of syndrome pulses is the smallest; A Doppler buffer control system characterized in that when the uncertainty in the received phase is removed, a control signal is simultaneously generated to set the initial phase of the Doppler buffer 4.