JPH10145274A - Satellite communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and correctly supervise transmission quality at a receiving station in a satellite communication system which digitizes a video signal and transmits and receives it. SOLUTION: In a transmitting station 1, a code generator 107 sends a test signal, together with a main signal and a synthesizer 105 synthesizes them and transmits them. A receiver 112 receives the test signal that returns from a satellite station 3, and a demodulator 111 demodulates it and calculates its BER(bit error rate). A transmitting power variable device 109 controls transmitting power of the test signal, so that a calculated value may be a fixed value that has been preliminarily defined. At the same time, the fixed value is added to the test signal and sent. In a receiving station 2, a separator 202 separates the test signal from the fixed value information, a bit error rate calculator 207 calculates the BER of the test signal, the calculated value is compared with the fixed value and an alarm is generated based on the compared result. In this case, as for a fixed value, even if the state of a transmission path is satisfactory, the value is preliminarily selected so that a BER can easily be calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite communication system, and more particularly to a method for digitizing video information and the like, adding an error correcting code redundant bit having a high coding gain, and transmitting the digital information from a transmitting station to a space station. The present invention relates to a satellite communication system which is adapted to be received by a satellite communication system.

[0002]

2. Description of the Related Art In recent years, satellite communication systems for digitizing video signals and transmitting / receiving the digital signals through a satellite line have been increasing. For example, there are a digital SNG (Satellite News Gathering) system for transmitting a camera image from an imaging site to a broadcast station, and a satellite communication system such as digital satellite broadcasting and digital broadcasting.

FIG. 2 is a system block diagram showing a conventional example of such a typical satellite communication system. In the transmitting station 1, an input signal (a video signal or the like) is digitized by a digital encoder 101, and an error correction redundant bit is added by an error correction encoder 102. Thereafter, digital modulation is performed in the digital modulator 103, and the signal S13 is transmitted to the space station (satellite) 3 via the transmitter 106.

FIG. 2 shows two typical configurations of receiving stations. First, in the receiving station 2, the frequency of the transmission signal S 32 from the space station 3 is tuned in the receiving station 201 and demodulated in the digital demodulator 203. Thereafter, error correction is performed by an error correction decoder 204, and the digital video signal is converted to an original video signal by a digital decoder 205. The bit error rate calculator 207 obtains transmission quality information from the bit error information from the error correction decoder 204.

[0005] In the receiving station 6, the transmission signal S 33 from the space station 3 is frequency-tuned by the receiver 601, demodulated by the digital demodulator 602, and then decoded by the error correction decoder 603.
Perform error correction. Then, the digital video signal is converted by the digital decoder 604 into the original video signal. In the receiver 601, the normal A
GC (automatic gain control) is performed, and from the AGC control voltage information, the reception level measuring device 605 determines the transmission quality,
In particular, reception level information is obtained.

As another example of monitoring the reception state,
As disclosed in Japanese Patent Application Laid-Open No. 5-102875, there is a technique for monitoring a reception state by converting a reception level into a sound, and a technique for controlling power of a transmission station based on a bit error rate and a reception level of the reception station. It is disclosed in Japanese Unexamined Patent Publication No. Sho 62-178024.

[0007]

FIG. 3 shows the transmission quality of the satellite communication system shown in FIG. 2, that is, the relationship between C / N (carrier to noise power ratio) and bit error rate (BER). The digitized video has a property that when the transmission quality deteriorates to some extent, the video quality rapidly changes. In addition, powerful error correction is often performed to reduce the transmission path error rate.

FIG. 3 shows a BER when Viterbi decoding and Reed-Solomon decoding are performed for error correction. FIG.
It can be seen that BER rapidly deteriorates when C / N falls below a certain value as shown in FIG.

In communication using a satellite line, rain attenuation becomes a problem. Therefore, as in the receiving station 2 of FIG. 2, it is difficult to monitor the quality of the video and the degree of deterioration of the transmission quality in terms of the bit error rate. In the method of monitoring the reception level at the receiving station 6 in FIG.
There is a drawback that the accuracy of quality monitoring is low, largely depending on the characteristics of the reception level detector and the antenna direction adjustment.

The above-mentioned JP-A-5-102875 and JP-A-62-178024 have the same disadvantages as described above.

An object of the present invention is to provide a satellite communication system capable of easily and accurately monitoring transmission quality at a receiving station.

[0012]

According to the present invention, there is provided a satellite communication system for transmitting from a transmitting station to a receiving station via a space station, wherein the transmitting station digitizes a main signal to be transmitted. Means for adding and outputting an error correction code, a modulating means for modulating the output, a first power amplifying means for power amplifying the modulated output, and a test signal generator for generating a predetermined digital test signal. Means for modulating the test signal, and a second means for power amplifying the modulated output.
Power amplifying means, transmitting means for combining the outputs of the first and second power amplifying means and transmitting the output to the space station, receiving a signal from the space station and demodulating the test signal Demodulating means, calculating means for calculating a bit error rate of the demodulated output, and control means for controlling an amplification rate of the second power amplifying means so that the bit error rate becomes a predetermined value. Is obtained.

[0013] The control means controls an amplification rate of the second power amplification means in accordance with a difference between the bit error rate and the predetermined value. , The amplification factor of the first power amplifying means is controlled in accordance with the difference, whereby the transmission quality of the main signal is maintained constant.

[0014] Further, the transmitting station is characterized in that information indicating the predetermined value is also added to the test signal and transmitted, and the receiving station includes: a receiving unit for receiving a test signal; Means for calculating the bit error rate of the received test signal; and comparing means for comparing the calculated bit error rate with information indicating a predetermined value added to the received signal. And an alarm output is generated.

The operation of the present invention will be described. First, the transmitting station transmits a predetermined test signal in addition to the main signal while controlling the transmission power so that the bit error rate is constant,
The bit error rate information indicating the value of the constant bit error rate is also transmitted. The receiving station determines the bit error rate of the test signal received through the space station, determines the magnitude of the received bit error rate from the bit error rate and the received bit error rate information, and generates an alarm. .

At this time, at the transmitting station, the transmission power of the main signal is similarly controlled and transmitted by the transmission test signal power control signal, thereby improving the transmission quality of the transmission path from the transmitting station to the space station. Keep it constant. This makes it possible to easily and accurately monitor the state of the transmission path from the space station to the receiving station.

[0017]

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

FIG. 1 is a system block diagram of an embodiment of the present invention, and the same parts as those in FIG. 2 are denoted by the same reference numerals. Referring to FIG. 1, in a transmitting station 1, an input signal such as a video is digitized by a digital encoder 101,
The error correction encoder 102 adds redundant bits for error correction, and the digital modulator 103 performs digital modulation.

The modulation output is converted to a first transmission power variable
4 (variable power amplifier), and transmits it from the transmitter 106 to the space station 3 via the combiner 105 (S
13).

In the code generator 107, a test signal using a carrier different from the main signal is generated.
The test signal is a predetermined digital pattern signal. This test signal is transmitted to the digital modulator 10
8, the power is amplified by the second transmission power variable unit 109, and the signal is combined with the main signal by the combiner 105.
This is also transmitted to the space station 3.

The test signal can be received by the own station 1 via the space station 3 by providing the receiver 112 (S31). The received signal is demodulated by a digital demodulator 111, and the obtained signal is compared with a signal from a code generator 107, so that a bit error rate (BER) is calculated by a bit error rate calculator 110. .

Based on the calculation result, the second transmission power varying unit 109 is controlled. That is, the transmission power of the test signal is controlled by the second transmission power variable unit 109 so that the calculated bit error rate becomes a predetermined value obtained in advance.
Specifically, a predetermined constant value is compared with the calculated bit error rate, and the difference between the calculated bit error rate and the constant value is set to zero (that is, both are equal). Thus, the transmission power control (power amplification degree control) of the second transmission power variable device 109 is performed by the control signal 101.

In this case, the constant value of the bit error rate is the number of errors (for example, 10 bits) for which the bit error rate can be easily calculated.
^-6 ). The information S103 indicating the constant bit error rate is added to the test signal, combined with the main signal, and transmitted.

The control of the first transmission power variable unit 104 for controlling the power of the main signal is also performed by the control signal S 102 from the bit error rate calculator 110. That is, the control signal S such that the difference between the calculated bit error rate (the bit error rate of the received test signal) and the constant value becomes zero.
By 102 (equivalent to S101), power control (control of power amplification) of the first transmission power variable device 104 is performed.
By doing so, the control is performed so that the transmission quality from the transmitting station 1 to the space station 3, that is, the C / N of the uplink (S13) becomes constant.

In the receiving station 2, in addition to the main signal receiving, demodulating and decoding blocks 201 to 205 of the receiving station 2 shown in FIG. 2, a block for separating a test signal and calculating its bit error rate is added. Have been. That is, the test signal is separated from the output of the receiver 201 by the separator 202, the separated test signal is demodulated by the digital demodulator 206, and the bit error rate is calculated by the bit error rate calculator 207.

In this case, the test signal is controlled by the second transmission power variable unit 109 in the transmitting station 1 so that the bit error rate becomes a transmission power set in advance to a value that can be easily calculated. That is, even when the transmission path is in a good state, the transmission power is controlled by the transmitting station 1 so that a certain error occurs.

The calculated bit error rate and the transmission station 1
Is compared with a constant value of the bit error rate of the transmitting station 1 which is added to the test signal and transmitted, and an alarm output is generated according to the comparison result. That is, if the calculated value exceeds a certain value by a certain threshold or more, an alarm is issued.

FIG. 4 shows an example of the relationship between the transmission quality (C / N) of the main signal, the BER (bit error rate) of the main signal, and the BER of the test signal. As shown in the figure, even when the C / N ratio is good to some extent, the deterioration of the BER can be clearly confirmed. Further, the BER value can be transmitted to the receiving station 2 by superimposing the BER information of the test signal on the transmitting side on the test signal baseband.

In this case, the BER on the receiving side can be easily converted by the receiving station alone from the antenna gain and the thermal noise of the receiver 201 when the transmission quality (rain attenuation etc.) is neglected. By comparing the BER of the signal, the reception quality can be sent to the outside step by step. Further, there is an advantage that it can be used for fine adjustment of the antenna direction adjustment work.

[0030]

As described above, according to the present invention, a transmitting station transmits a test signal that gives a predetermined constant BER and information indicating this constant BER, together with a main signal, The receiving station has an effect that the transmission path can be monitored by comparing the BER of the reception test signal with the constant BER information.

At this time, by controlling the transmission power of the main signal to be constant, C / C, which is the transmission quality from the transmitting station to the space station, is controlled.
By keeping N constant, the receiving station can easily and accurately determine the case where the reception quality changes slowly.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a conventional satellite communication system.

FIG. 3 is a diagram illustrating a relationship between reception quality and a bit error rate.

FIG. 4 is a diagram illustrating a relationship between a bit error rate of a test signal and a main signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmitting station 2 Receiving station 3 Space station 101 Digital encoder 102 Error correction encoder 103, 108 Digital modulator 104 First transmission power variable device 105 Synthesizer 106 Transmitter 107 Code generator 109 Second transmission power Variable device 110, 207 Bit error rate calculator 111, 203, 206 Digital demodulator 112, 201 Receiver 202 Separator 205 Digital decoder

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04L 1/00 H04L 1/00 C

Claims (5)

[Claims] 1. A satellite communication system for transmitting a signal from a transmitting station to a receiving station via a space station, wherein the transmitting station digitizes a main signal to be transmitted, adds an error correction code thereto, and outputs the digitized signal. Means, modulating means for modulating the output, first power amplifying means for power amplifying the modulated output, test signal generating means for generating a predetermined digital test signal, and modulation for modulating the test signal Means, second power amplifying means for power amplifying the modulated output, transmitting means for combining the outputs of the first and second power amplifying means and transmitting the combined output to the space station, Demodulating means for receiving the signal and demodulating the test signal, calculating means for calculating a bit error rate of the demodulated output, and amplifying the second power amplifying means so that the bit error rate becomes a predetermined value. Control means for controlling the rate And a satellite communication system. 2. The apparatus according to claim 1, wherein said control means controls an amplification rate of said second power amplification means according to a difference between said bit error rate and said predetermined value. Satellite communication system. 3. The control means is configured to control an amplification factor of the first power amplifying means in accordance with the difference, whereby the transmission quality of the main signal is maintained constant. 3. The satellite communication system according to claim 2, wherein: 4. The satellite communication system according to claim 1, wherein the transmitting station adds information indicating the predetermined value to the test signal and transmits the test signal. 5. The receiving station includes: a receiving unit that receives a test signal; a unit that calculates a bit error rate of the received test signal; and the calculated bit error rate and a predetermined value added to the received signal. The satellite communication system according to any one of claims 1 to 4, further comprising comparison means for comparing information indicating a value, and generating an alarm output according to a result of the comparison.