JPH0472825A - Reception system for satellite communication - Google Patents

Abstract

PURPOSE:To obtain a voice signal without noise by deciding the presence of noise in each voice signal received, and demodulated by a vice waveform shaping adapter to select the voice signal in which no noise is in existence. CONSTITUTION:A digital processing signal A/D-converted and outputted by A/D converters 131-134 is inputted respectively to high speed digital arithmetic units such as digital signal processors DSP1, DSP2. The digital signal processor DSP1 compares and supervises two digitally processed voice signals and images it that noise due to a bit error is generated from any waveform when the difference of them is much and it is judged that a waveform changed rapidly in a differentiating way from a preceding waveform is subjected to the effect of noise and a digital processing signal of the voice signal corresponding to the waveform not affected by noise is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a receiving system for satellite communication equipped with an audio waveform shaping adapter.

[Prior art 1] Recently, a large number of communication satellites for private use have been launched, and inter-company communications using these communication satellites is becoming common. This inter-company communication is generally transmitted from a transmitting station on the ground to a communication satellite, and after this transmitted signal is amplified by a microwave amplifier such as a TWT on the communication satellite, it is transmitted again from the communication satellite to the ground. By being done.

This transmission area generally covers a wide area, for example, all of Japan. Secondary goals such as information being transmitted to sales offices and factories within the same company and unification of intentions within the company can be achieved.

In such inter-company communications, in order to transmit confidential company information, a scrambled signal is inserted so that the general public cannot understand it even if it is received, and it cannot be demodulated without a special discable unit. is common.

Overseas, there are scramble systems such as Maycom's Cyber ■ and B-MAC systems, and in Japan, there are scramble systems such as M system.

[Problems to be Solved by the Invention] Generally, a large amount of control information is sent together for scrambling and for turning on/off the discable unit attached to the address of each individual tuner for reception and demodulation. Among the various scrambling systems, there are those that eliminate or greatly simplify the error correction part for the transmission system of the digitized audio signal (PCM) for transmitting the control information.

In such a simplified transmission system without error correction, if the C/N deteriorates even slightly due to rain, bit errors will occur due to noise.

There is a problem in that pulse noise is superimposed on the waveform of the reproduced audio signal, producing a crackling sound, which is extremely unpleasant. A similar problem also occurs in facsimile communication (for example, GIII), which uses the same frequency band as the voice signal.

The present invention has been made in view of these problems, and its purpose is to prevent unpleasant noises from occurring even when there is a slight deterioration of C/N, and to prevent facsimile communications from producing unpleasant sounds. To provide a receiving system for satellite communication which is free from errors.

[Means for Solving the Problem] In order to achieve the above-mentioned object, the invention according to claim 1 provides a method for transmitting the same digital data simultaneously transmitted on two transmission channels in a transmission system with poor transmission quality such as a satellite line. The device is equipped with a receiving means for receiving a converted audio signal and demodulating the audio signal, and an audio waveform shaping adapter that simultaneously determines the presence or absence of noise in each demodulated audio signal and selects an audio signal free of noise. be.

The invention according to claim 2 is the invention according to claim 1,
An A/D converter that A/D converts each demodulated audio signal from the receiving means, and an A/D converter that monitors both the A/D converted and digitized signals and determines that there is no noise in the corresponding audio signal waveform. Output one of the digitized signals,
A signal processing means for switching to and outputting a noise-free digitized signal when it is determined that there is noise in the audio signal waveform corresponding to the digitized signal being output, and a digitized signal output from the signal processing means. The audio waveform shaping adapter is composed of a D/A converter that performs D/A conversion, and a low-pass filter that passes the D/A converted audio signal.

The invention according to claim 3 is the invention according to claim 1,
An A/D converter that A/D converts each demodulated audio signal from the receiving means, and one of the A/D converted digitized signals is monitored and outputted, and the waveform of the digitized signal is free from noise. signal processing means for switching to and outputting the other digitized signal for a certain period of time when it is determined that there is a digitized signal;
The digitized signal output from this signal processing means is
The audio waveform shaping adapter is composed of a D/A converter that performs A conversion, and a low-pass filter that passes the D/A converted audio signal.

[Operation] According to the present invention, the receiving means reproduces the same digitized audio signal transmitted simultaneously through two channels separately, and the audio waveform shaping adapter determines the presence or absence of noise in each received and demodulated audio signal. Since the noise-free audio signal is selected by using the noise control method, even if there is some C/N deterioration and spike-like noise is superimposed on the waveform of each audio signal, it will not be superimposed on the same phase of the waveform of each audio signal at the same time. Since the probability of this occurring is low, a noise-free audio signal is obtained and does not cause discomfort. Furthermore, no errors occur in facsimile communication. This is particularly effective in transmission systems where the transmission format does not have sufficient error correction capability.

[Example] The present invention will be explained below with reference to Examples.

FIG. 3 shows the overall configuration of an inter-company communication system using an embodiment of the present invention. For example, a ground transmitting station 1 installed at a location such as a head office transmits audio signals collected by a microphone 3. After A/D conversion in the machine 4, encoding and multiplexing with a PCM encoder, for example, PSK modulation, and then using a synthesis circuit (not shown) to combine the resulting video signal with the video signal captured by the video camera 2. synthesized, then FM modulated to 1
4. A carrier wave of GHz is transmitted from the antenna 5 toward the communication satellite 6.

In general, transmission systems using communication satellites transmit one image,
It is now possible to send two voices and two more voices or data (facsimile communication), and normally one channel is sufficient for voice and one channel for data in intercompany communications. However, in accordance with the satellite communication receiving system of the present invention, one voice signal (or facsimile signal) is simultaneously transmitted on two channels.

Therefore, at ground stations 7 such as factories and sales offices nationwide that receive transmission signals from communication satellites 6, the received signals are received by antennas 8 and converted to IGz band by converters 9, as shown in FIG. Further, the signal is received and demodulated by a tuner 10 serving as a receiving means. At this time, the audio signals transmitted through the two channels are demodulated separately and taken into the audio waveform shaping adapter 12 via the descramble unit 11.

The waveforms of the two audio signals input to the audio waveform shaping adapter 12 are the same as shown in FIG. As shown, spike-like noise NS is generated.

2. The audio waveform shaping adapter 12 is an A/D converter corresponding to the two channels of audio signals inputted via the descramble unit 11 as shown in FIG. 2 after being reproduced by the tuner 10. ．． 13□ and an A/D converter 131, 1 corresponding to two channels of facsimile signals.
34 are provided respectively. Here, A/D converter 1B,
At step 132, the simultaneously transmitted, received and demodulated audio signals are digitally converted.

Similarly to audio signals, for example, a GL facsimile signal consisting of a signal of a single frequency (2400 Hz) transmitted simultaneously on two channels is simultaneously demodulated by the tuner 10 and input via the descramble unit 11. /D converters 133 and 134 are for A/D conversion.

These A/D converters 1.35, 132.133, 134
The digitized signals outputted after A/D conversion are input to high-speed digital processing units such as digital signal processors DSP, DSP2, respectively.

Here, the digital signal processor DSP compares and monitors the two digitized audio signals as shown in Figure 5, and if there is a large difference between the two, it determines that one of the waveforms has generated noise due to a bit error. At the same time, it is determined that the waveform that has differentially changed rapidly from the previous waveform is affected by noise (C-), and the digitized signal of the audio signal corresponding to the waveform that is not affected by noise is selected and output. do.

In this case, a digitized signal corresponding to one audio signal is normally output, and when there is an influence of noise, the digitized signal corresponding to the other audio signal is switched and output.

This output digitized signal is D/A converted by the D/A converter 141 and returned to an analog audio signal, and this audio signal is further passed through the low-pass filter 15 to the monitor television 1.
6, etc.

Fig. 4(c) shows the output state, and this Fig. 4(c)
As shown in Fig. 4(a), normally the audio signal of the channel ■ is output as shown in Fig. 4(a), but if it is determined that noise NS is superimposed, (b
) Switches and outputs the audio signal of channel ■ shown in ( ).

Similarly to the voice signal, the digital signal processor DSP2 determines whether or not there is noise in the facsimile signal and switches the signal to be output. The D/A converter 142 is for D/A converting the digitized signal output by the digital signal processor DSP2, and the low-pass filter 152 is a filter that passes this D/A converted analog facsimile signal. It is. The facsimile signal thus output is sent to the facsimile machine 17.

By the way, in the above embodiment, the signals of two channels are monitored to determine the presence or absence of noise, but it is possible to monitor one of the signals and detect the presence of spike-like noise caused by a bit error. When the determination is made, the other signal may be output for a certain period of time in the same manner as described above.

Since facsimile signals (for example, GIII) use a single frequency, noise may be cut using a filter that passes a single frequency. After demodulating the QAM of formats 1 to 1, it may be re-modulated and output.

Also, if there is a time delay between the received and demodulated signals of the two channels, it is necessary to perform processing in the digital signal processor DSP or DSP2 so that there is no time delay, or to eliminate the time delay by adding a delay time element. There is.

[Effects of the Invention] According to the present invention, the same digitized audio signal transmitted simultaneously on two channels is reproduced separately by the receiving means, and the presence or absence of noise in each received and demodulated audio signal is determined by the audio waveform shaping adapter. Since the noise-free audio signal is selected based on the judgment, even if there is some C/N deterioration and spike noise is superimposed on the waveform of each audio signal, the audio signal will be in the same phase as the waveform of each audio signal at the same time. Since the probability of superimposition is low, a noise-free voice signal is obtained, and no unpleasant sound is generated, or errors do not occur in facsimile communication, and the transmission format has sufficient error correction ability. This is particularly effective in transmission systems that do not have the following characteristics.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an embodiment of the present invention, Figure 2 is a configuration diagram of the audio waveform shaping adapter same as above, Figure 3 is an overall configuration diagram of an inter-company communication system using the same, and Figure 4 is the operation of the same as above. The explanatory waveform diagram and FIG. 5 are flowcharts for explaining the same operation. 8 is an antenna, 9 is a converter, 10 is a tuner, 11 is a descramble unit, 12 is an audio waveform shaping unit, 1-116 is a monitor television, 17 is a facsimile device,
131... is an A/D converter, DSPL... is a digital signal processor, 14. ... is a D/A converter,
151... is a low-pass filter. Agent Patent Attorney Ishi 1) Choshichi

Claims (3)

[Claims] (1) In a transmission system with poor transmission quality such as a satellite line, a receiving means that receives the same digitized audio signal transmitted simultaneously on two transmission channels and demodulates the audio signal, and each audio signal demodulated at the same time. 1. A reception system for satellite communication, comprising: an audio waveform shaping adapter that determines the presence or absence of noise in a signal and selects an audio signal free of noise. (2) The audio waveform shaping adapter includes an A/D converter that A/D converts each demodulated audio signal from the receiving means, and monitors both of the A/D-converted digitized signals to produce a corresponding audio signal. Either one of the digitized signals whose signal waveform is determined to be noise-free is output, and if it is determined that the audio signal waveform corresponding to the output digitized signal has noise, a noise-free digitized signal is output. a D/A converter that converts the digitized signal outputted from the signal processing means, and a low-pass filter that passes the D/A converted audio signal. A receiving system for satellite communication according to claim 1, characterized in that said receiving system is configured as follows. (3) The audio waveform shaping adapter includes an A/D converter that A/D converts each demodulated audio signal from the receiving means, and monitors and outputs one of the A/D converted digitized signals. , signal processing means that switches to and outputs the other digitized signal for a certain period of time when it is determined that there is noise in the waveform of this digitized signal, and D/A converts the digitized signal output from this signal processing means. 2. The receiving system for satellite communication according to claim 1, comprising a D/A converter and a low-pass filter that passes the D/A converted audio signal.