JPH0785583B2 - Satellite broadcasting reception system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a satellite broadcast receiving system for receiving radio waves of a television signal sent from a broadcasting satellite and sending it to a television receiver, and particularly to a CN ratio. This is to reduce the noise of the video signal caused by the deterioration.

[Conventional technology]

Satellite broadcasting is a system that can efficiently cover the entire land area as a broadcasting area. Since the arrival angle of radio waves is high, it is not affected by the topography. It is a medium that enables uniform and high quality broadcasting nationwide without being affected by.

Also, since a new frequency band different from conventional terrestrial broadcasting is used, new media can be broadcast, and it is possible to meet the diversified needs of society.

High-definition television broadcasting is one of the new broadcasting media using satellite broadcasting. High-definition television broadcasting is a system that not only improves image quality and sound quality compared to current television broadcasting, but can also obtain high-level visual psychological effects such as presence and power, and high-definition and HD-MAC methods are available. Proposed.

The signal band of the high-definition system is about 5 times the signal band of the current NTSC system, and a bandwidth of 20 to 25 MHz is required to transmit the high-definition signal as it is. However, one channel of satellite broadcasting is 27MHz, and since the FM method is used as the modulation method, the signal bandwidth should be about 1/3 of the radio wave bandwidth in order to secure sufficient frequency deviation. There must be. Therefore, in order to broadcast a high-definition signal on one satellite channel, the signal bandwidth must be compressed to 9 MHz or less, and the MUSE method has been developed as a band compression method for that purpose.

According to the MUSE method, the signal bandwidth can be compressed to 8.1MHz with a relatively simple method without degrading the image quality of high definition. As shown in Fig. 2, the MUSE system is based on the color line sequential TCI system in which YC signals are time-division multiplexed, and a digital audio signal compressed by quasi-instantaneous companding differential PCM (DANCE) is used in the vertical blanking period. It is multiplexed.

[Problems to be Solved by the Invention]

Since the modulation method of satellite broadcasting adopts the FM method as described above, there is a phenomenon that the FM improvement rate is rapidly lost when the CN ratio (receive carrier power to noise power ratio) deteriorates. As a result, there are disadvantages that medaka noise-like truncation noise appears in the video signal, and code errors increase in the audio signal to deteriorate the audio quality.

Since voice signals are PCM digital signals, by performing error correction of transmission codes and bit interleaving,
It is designed so that the CN ratio deteriorates and the image quality deteriorates to ensure a certain level of sound quality. However, since the video signal is an analog signal, such processing is not performed.

An object of the present invention is to reduce the noise of the video signal caused by the deterioration of the CN ratio.

[Means for Solving the Problems]

The present invention, when receiving and demodulating a television signal in which an audio signal and a video signal are time-division multiplexed for each screen, an error correction code is added to the code of the audio signal transmitted as a digital signal. When the number of errors is counted and the counted value exceeds a predetermined value, the video signal sent later is cut off and the video signal sent earlier or another video signal is sent The noise is apparently reduced.

[Work]

When a television signal such as a MUSE signal in which an audio signal and a video signal are time-division multiplexed for each field is sent, the audio signal is separated from the video signal and demodulated. Since a voice signal is transmitted as a digital signal to which an error correction code is added, when a voice signal is demodulated, it is demodulated based on this error correction code. When a voice signal is demodulated, a code error is detected. , The number of times of detection is counted for each field, and when the count value exceeds a predetermined value, it is determined that noise is probabilistically superimposed on the video signal due to the deterioration of the CN ratio, and the noise signal is continuously detected. The sent video signal of the same field is cut off, and the video signal of the previous screen stored in the memory is sent and interpolated. When the CN ratio continuously deteriorates, the video signal stored in the memory is continuously read and displayed as a still image. In this way, the noise of the video signal is apparently reduced.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a satellite broadcasting receiving system according to the present invention, showing a system for converting a received MUSE signal into an NTSC signal and outputting it.

In FIG. 1, the MUSE baseband signal received by the BS antenna 1 and obtained through the BS converter 2 and the BS tuner 3 is converted into a digital signal by the AD converter 4. The sampling frequency of the AD converter 4 is the MUSE resampling frequency of 16.2 MHz.

The MUSE signal converted into a digital signal by the AD converter 4 is
Then, it is input to the MUSE / NTSC converter (down converter) 5 and the audio decoder 6. Down converter 5 is MU
This is a circuit that generates one line signal from three lines of the SE signal, reduces the number of effective scanning lines of the MUSE signal from 1032 to 344, which is 1/3, and outputs the NTSC signal. The details of the line conversion in the down converter 5 are described in Japanese Patent Application No. 63-242605 (the title of the invention: "MUSE
-NTSC conversion method ").

The signal converted into the NTSC signal by the down converter 5 is input to one of the switching circuits 7, is temporarily stored in the frame memory 8, and is then input to the other of the switching circuits 7.
The switching circuit 7 is connected to the town converter 5 side in a steady state, but is switched to the frame memory 8 side when a switching signal SW described later is generated. Switching circuit 7
The output of is converted into an analog signal by the DA converter 9 and is not shown.
Output to NTSC receiver.

The MUSE signal converted into a digital signal by the AD converter 4 is
Further, it is input to the audio decoder 6. The audio decoder 6 extracts an audio signal from the input MUSE signal, performs deinterleaving, error correction processing, etc., and then demodulates it into an original digital audio signal by a quasi-instantaneous expansion differential PCM decoder. The demodulated digital audio signal is converted into an analog signal by the DA converter 10 and output to an NTSC receiver (not shown).

The error correction process in the audio decoder 6 is performed based on the BCH (82,74) error correction code transmitted with the audio data. This BCH (82,74) code is an 82-bit data obtained by adding an 8-bit error correction code to 74-bit data, and it is possible to correct 1 bit of 82 bits and detect errors up to 2 bits. is there.

When a code error is detected by the audio decoder 6, an error signal
ER is generated and input to the counter 11. In counter 11,
The number of occurrences of this error signal ER is counted, and when it exceeds a certain value, a switching signal SW is output to the switching circuit 7 and the switching circuit 7 is switched to the frame memory 8 side. Counter 11
Is reset for each field by the output of the sync detector 12 which detects and separates the vertical sync signal from the output signal of the down converter 5. Therefore, the counting of the error signal ER in the counter 11 is performed for each field.

In this configuration, when the MUSE signal radio wave arrives from the broadcasting satellite, this radio wave is received by the BS antenna 1, and the BS converter 2 converts the 12 GHz band received signal into an 1 GHz band intermediate frequency signal as an FM signal. , Is amplified to a required level and sent to the BS tuner 3.

In BS tuner 3, 1G sent from BS converter 2
A desired channel is selected from the FM signals in the Hz band, the video signal and the audio signal are demodulated and supplied to the AD converter 4. In the AD converter 4, the sampling signal for MUSE (16.2
Convert the input signal into a digital signal at (MHz).

The video signal of the MUSE signal converted into a digital signal is converted into 3 lines / 1 line by the down converter 5 and output as a digital NTSC signal, and passes through the switching circuit 7.
It is converted into an analog signal by the DA converter 9. The output of the down converter 5 is simultaneously stored in the frame memory 8.

The audio signal of the MUSE signal converted into a digital signal by the AD converter 4 is demodulated into an original digital signal by the audio decoder 6, converted into an analog signal by the DA converter 10, and output.

When a code error is detected by the audio decoder 6, an error signal
ER is generated and input to the counter 11. The counter 11 counts the number of times the error signal ER is generated for each field, and when it reaches a certain value, generates a switching signal SW to switch the switching circuit 7
The switching circuit 7 cuts off the video signal that is subsequently sent, outputs the video signal of the field one screen before stored in the frame memory 8, and interpolates the cut video signal.

As shown in FIG. 2, the audio signal is transmitted in time division for each field prior to the video signal. Therefore, when the code error of the audio signal increases, noise is stochastically superimposed on the video signal. The video signal of the field is cut off and the video signal of the previous screen stored in the frame memory 8 is output. When the CN ratio continuously deteriorates, the storage signal of the frame memory 8 is continuously read and a still image is output. In this case, the screen may be blue backed or a message may be displayed on the screen by superimposing.

In the above-mentioned embodiment, the system for converting the MUSE signal into the NTSC signal has been described, but the present invention is not limited to this and may be applied to a system for directly outputting the MUSE signal.

Further, the present invention can be applied not only to the MUSE system but also to other television systems in which an audio signal and a video signal are time-division multiplexed and transmitted for each field.

〔The invention's effect〕

According to the present invention, the number of times a code error detection signal is generated when demodulating a digital voice signal is counted, and when the count value exceeds a predetermined value, the CN ratio of the transmission line is deteriorated and the SN ratio is decreased. It is judged that the video signal has dropped, and the video signal of the previous screen is sent out assuming that noise is superposed on the video signal that is sent subsequently. It is possible to reduce apparently.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a satellite broadcast receiving system according to the present invention, and FIG. 2 is a format diagram showing a MUSE transmission signal format. 6 ... Voice decoder, 7 ... Switching circuit, 8 ... Frame memory, 11 ... Counter, 12 ... Sync detector.

Claims (2)

[Claims] 1. A satellite broadcast receiving system for receiving and demodulating a television signal in which an audio signal and a video signal are time-division multiplexed for each screen and sent, and an error correction code is added and transmitted as a digital signal. When the number of code errors of the incoming audio signal is counted, and when the count value exceeds a predetermined value, the video signal sent later is cut off and the video signal or other video signal sent earlier is checked. A satellite broadcasting receiving method characterized by transmitting. 2. The satellite broadcast receiving system according to claim 1, wherein the television signal is a MUSE signal for time-division multiplexing and transmitting an audio signal and a video signal for each field.