JPH0730595A - Modulation control system in satellite communication - Google Patents

Abstract

PURPOSE:To prevent deterioration in quality of a transmission line and the reliability between earth stations in satellite communication and to increase the transmission capacity. CONSTITUTION:A transmission station A adds an error correction code to a transmission signal (102), a changeover device 107 selects one of plural modulation system modulators 103-106 for the transmission. A reception station B uses a changeover device 207 to select one of plural different modulation systems 203-206 and measures an error number from its demodulation signal to obtain an error rate (210). The error rate is sent to the transmission station A via a telephone line T and when the error rate is a predetermined rate or over, the changeover device 107 is used to select a modulator. A reception station B extracts a synchronizing signal from a demodulation signal (209) and uses a changeover device 207 to select the demodulator when the synchronizing signal is not extracted. The modulator whose transmission capacity is switched sequentially from a larger system to a smaller system and the transmission capacity is increased without deteriorating the quality of the transmission line and its reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in digital communication between earth stations using satellites, does not reduce the quality and reliability of the transmission line in response to changes in the transmission loss of the transmission line due to factors such as rainfall. The present invention relates to a modulation control method that maximizes the efficiency of information transmission capacity.

[0002]

2. Description of the Related Art Conventionally, in digital communication between earth stations using satellites, the transmission loss of a transmission line may change due to factors such as rainfall, and the quality and reliability of the transmission line may deteriorate. For this reason, conventionally, there has been proposed a method of detecting the transmission loss in the transmission line and ensuring the quality and reliability of the transmission line based on the detection result. For example, JP-A-63
In Japanese Patent Laid-Open No. 173426 and Japanese Patent Laid-Open No. 63-42447, a transmission error is measured by measuring a bit error rate at a receiving station, the transmission loss is notified to the transmitting station, and the transmission power at the transmitting station is controlled. Prevents the quality and reliability of the transmission line from deteriorating.

[0003]

By the way, in this kind of communication, the transmission capacity is closely related to the modulation system, and the quality and reliability of the transmission line are easily influenced by the modulation system. Therefore, if a certain modulation method is adopted for the purpose of increasing the transmission capacity, the quality and the reliability are likely to be deteriorated due to the transmission loss of the transmission path. On the other hand, in order to ensure quality and reliability above a certain level regardless of the transmission loss of the transmission line, it is unavoidable to adopt a modulation method with a small transmission capacity. For this reason, conventionally, measures have been taken to adopt a modulation method that maximizes the transmission capacity and reduce the information transmission capacity and enhance the error correction function when the transmission loss of the transmission line increases due to factors such as rainfall. However, there is a limit to maintaining constant quality and reliability with this measure. It is an object of the present invention to provide a modulation control method that increases the transmission capacity while preventing the quality and reliability of the transmission line from decreasing.

[0004]

According to the modulation control method of the present invention, an error correction encoder for adding an error correction code to a transmission signal and a plurality of modulations for modulating the transmission signal in a transmission station are provided in a transmission station. And a modulation method switching device that selects these modulators. The receiving station also includes a plurality of demodulators that demodulate the received signals by different demodulation methods, a demodulation method switch that selects these demodulators, and an error correction code that is decoded from the demodulated signals And an error correction decoder that measures the error rate, a synchronization signal extractor that extracts the synchronization signal from the demodulated signal, and an error rate monitor that determines the error rate from the measured number of errors and transmits this error rate to the transmitting station. Equipped with. Then, the transmitting station is configured to switch the modulation method switch based on the transmitted error rate, and the receiving station is configured to switch the demodulation method switch depending on whether or not the synchronization signal is extracted. Here, in the transmitting station, when the error rate is larger than a predetermined value, the plurality of modulators are sequentially switched from a modulation system having a large transmission capacity to a modulation system having a small transmission capacity. For example, the plurality of modulators and demodulators are polyphase DPSK modulators and demodulators having different multivalues, and are configured to sequentially switch from a modulation method having a large multivalue to a modulation method having a small multivalue.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram of satellite communication to which the present invention is applied. A transmitting station A adds an error correction code to a transmission signal and multiphase DPSK-modulates the transmission signal before transmission. The receiving station B receives the signal via the satellite S, decodes the error correction code in the received signal, and monitors the error rate. Further, the two stations A and B are connected by a telephone line T, the error rate monitored by the receiving station B is sent to the transmitting station A through the telephone line T, and the modulation system in the transmitting station A is switched.

FIG. 2 is a block diagram of each of the transmitting station A and the receiving station B. The transmitting station A includes an error correction encoder 102 that adds an error correction code to a digital signal input from a transmission side signal input terminal 101, and a plurality of modulators of different modulation systems connected in parallel. DP
SK modulator 103, 4-phase DPSK modulator 104, 8-phase D
4 of PSK modulator 105 and 16-phase DPSK modulator 106
It has one modulator, a modulation method switch 107 for selectively switching these modulators, and a transmitter 108. That is, the modulation system switching unit 107 determines that the receiving station B
From one of the four modulators based on the error rate transmitted from the telephone line T to the error rate input terminal 109, and the signal modulated by the selected modulator is a modulated signal. Output to the output terminal 110. The modulated signal output to the output terminal 110 is transmitted by the transmitter 108.
It goes without saying that the signal is converted into a high frequency signal and transmitted to the satellite S.

On the other hand, the receiving station B receives a signal from a satellite, and a plurality of receivers 201 and a plurality of demodulators that individually demodulate the modulated signals that have been converted into intermediate frequencies by the receiver 201 and are input to an input terminal 202. Demodulator, here 2-phase DPSK demodulator 203, 4-phase DPSK demodulator 204, 8
Phase DPSK demodulator 205, 16-phase DPSK demodulator 206
4 demodulators, a demodulation method switch 207 that selects a signal demodulated by each demodulator, an error correction code of the demodulated signal from the selected demodulator, and error correction and bit error Decoder 208 for obtaining the number and sync signal extractor 209 for extracting the sync signal from the demodulated signal
And an error rate monitor 210 for obtaining the error rate Pe based on the difference between the number of bit errors from the error correction decoder 208 and a predetermined reference. Then, the error rate Pe obtained by the error rate monitor 210 is sent from the error rate output terminal 211 to the telephone line T and sent to the transmitting station A. Also, it goes without saying that the demodulated signal is output from the signal output terminal 212 and is subjected to reception processing.

[0008] The transmitting station A and the receiving station B configured as described above
The control operation of the modulation method between and will be described with reference to the flowchart of FIG. In the transmitting station A, the signals to which the error correction code is added by the error correction encoder 102 are modulated by the four modulators 103 to 106, respectively. In the modulation method switch 107, first, a modulation method having a large transmission capacity, in this example, the 16-phase DPSK modulator 1
Select the signal modulated at 06 and send it to transmitter 1
08 to send.

In the receiving station B, the signals received by the receiver 201 are demodulated by the four demodulators 203 to 206, respectively, and the signal demodulation method switch 207 is first transferred to the 16-phase DPSK demodulator 206 having a large transmission capacity. The error correction decoder 208 decodes an error correction code from the demodulated signal selected by switching and from the selected demodulator, performs error correction, obtains the number of bit errors, and outputs the error rate monitor 210.
Send to. At the same time, the sync signal extractor 209 extracts the sync signal from the demodulated signal. Then, when the sync signal can be extracted, the demodulation signal switch 207 is held in the selected state for the time being, and a signal capable of extracting the sync signal is output to the error rate monitor 210, and the error rate monitoring is performed at this timing. The device 210 compares the number of input bit errors with a reference value and sends the difference as an error rate Pe to the transmitting station A through the telephone line T. Then, at this time, the error rate P
When e is smaller than the predetermined value R, the modulation method switch 107 of the transmission station A holds the current switching state. As a result, the transmission capacity between the transmission station A and the reception station B is 1
Communication by the 6-phase DPSK modulation method will be continued.

On the other hand, when the error rate Pe is larger than the predetermined value R, the modulation scheme switch 107 is switched in the transmitting station A based on this error rate, and this time the 8-phase DPSK whose transmission capacity is one step smaller. The modulator 105 is selected and the signal modulated by this modulator is transmitted. Therefore, at the receiving station B, 16
Since the synchronization signal cannot be extracted from the signal demodulated by the phase DPSK demodulator 206, the synchronization signal extractor 2
09 outputs a signal incapable of extracting the synchronizing signal, operates the demodulation method switching device 207, and lowers the 8-phase DPSK demodulator 20 by one stage.
Switch to 5. Then, the error correction decoder 208 obtains the number of bit errors from the demodulated signal from the switched demodulator and outputs it to the error rate monitor 210, and at the same time, the synchronization signal extractor 2
If 09 can extract the synchronization signal, the demodulation method switch 2
07 is kept in that state, and a signal capable of extracting the synchronizing signal is output to the error rate monitor 210. The error rate monitor 210 obtains the error rate from the number of bit errors from the error correction decoder 208 at that timing, and transmits it to the modulation system switch 107 of the transmitting station A through the telephone line T.

At this time, when the error rate is equal to or less than the predetermined value, the modulation method switch 107 of the transmitting station A holds the current switching state. As a result, the transmission capacity is the second largest.
Communication by the phase DPSK modulation method will be continued. On the other hand, when the error rate is less than or equal to the predetermined value, the modulation scheme switch 107 is switched in the transmitting station A based on the error rate, and the 4-phase DPSK modulator 10 having a further smaller transmission capacity is provided.
4 is selected and the signal modulated by this modulator is transmitted. By repeating the same procedure below, depending on the transmission loss of the transmission line due to factors such as rain on the transmission line at that time, the transmission line should be transmitted as much as possible after ensuring quality and reliability above a certain level. It becomes possible to improve the efficiency of the information transmission capacity by performing communication with a modulation method having a large capacity.

In the above-mentioned embodiment, a configuration example in which four modulation systems are switched is shown, but it goes without saying that the number and modulation systems are not limited. However, it goes without saying that the plurality of modulators and demodulators arranged in the transmitting station and the receiving station correspond to each other on a one-to-one basis.

[0013]

As described above, according to the present invention, based on the error rate obtained at the receiving station, the transmitting station switches a plurality of modulators of different modulation systems, and
By configuring the receiving station to switch between demodulators with different demodulation methods depending on whether or not the synchronization signal is extracted, the error rate is higher than a predetermined value depending on the change in transmission loss of the transmission line due to factors such as rainfall. When it becomes large, for example, by sequentially switching a plurality of modulators from a modulation system having a large transmission capacity to a modulation system having a small transmission capacity, it is possible to improve the efficiency of the information transmission capacity without degrading the quality and reliability of the transmission path. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of satellite communication to which the present invention is applied.

FIG. 2 is a block diagram of an embodiment of the present invention.

FIG. 3 is a flowchart showing an example of the operation of the modulation control method.

[Explanation of symbols]

 A transmitting station B receiving station S satellite T telephone line 102 error correction encoder 103 to 106 DPSK modulator 107 modulation method switch 108 transmitter 201 receiver 203 to 206 DPSK demodulator 207 demodulation method switch 208 error correction decoder 209 Sync signal extractor 210 Error rate monitor

Claims (3)

[Claims] 1. In communication between a transmitting station and a receiving station using a satellite, the transmitting station uses an error correction encoder for adding an error correction code to the transmitting signal and the transmitting signal by different modulation methods. A plurality of modulators for modulating, and a modulation method switching device for selecting these modulators, the receiving station,
A plurality of demodulators that demodulate the received signals by different demodulation methods, a demodulation method switch that selects these demodulators, and an error correction decoder that decodes the error correction code from the demodulated signals and measures the number of errors A sync signal extractor for extracting a sync signal from the demodulated signal; and an error rate monitor for obtaining an error rate from the measured number of errors and transmitting this error rate to the transmitting station. In the station, the switching operation of the modulation method switching device based on the transmitted error rate,
A modulation control method in satellite communication, wherein the receiving station is configured to switch the demodulation method switch depending on whether or not a synchronization signal is extracted. 2. The satellite communication according to claim 1, wherein the transmitting station is configured to sequentially switch the plurality of modulators from a modulation system having a large transmission capacity to a modulation system having a small transmission capacity when the error rate is larger than a predetermined value. Modulation control method in. 3. A plurality of modulators and demodulators are polyphase DPSK modulators and demodulators having different multi-values, and are configured to sequentially switch from a modulation system having a large multi-value to a modulation system having a small multi-value. Modulation control method in satellite communication of 2.