JPH0353685A - Satellite broadcast reception system - Google Patents

Abstract

PURPOSE:To reduce noise in a video signal apparently by counting the number of detection of code errors for each line when an audio signal is demodulated, interrupting a video signal of a line sent simultaneously with the audio signal when the count reaches a prescribed value, sending the video signal for each line and interpolating the video signal. CONSTITUTION:When an audio signal is demodulated, the number of times of error detection is counted by a counter 12, the counter 12 is reset for each line, the frequency of occurrence of errors for each line is recognized. When an error is detected in one line or errors of a number or over are detected, it is regarded that noise is also superimposed on the video signal with a probability, the video signal of the line is interrupted and the video signal of one preceding line stored in a line memory 8 is outputted. Thus, the noise in the video signal is reduced apparently by a simple method.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a satellite broadcast receiving system that receives radio waves of television signals sent from a broadcasting satellite or a communication satellite and sends them to a television receiver. This is to reduce noise in the video signal caused by deterioration of the CN ratio.

[Conventional technology]

Satellite broadcasting is a system that can efficiently cover the entire country as a broadcast area, and because the angle of arrival of radio waves is high, it is not affected by terrain, and by using a receiving antenna with sharp directivity, it eliminates ghosts caused by buildings. It is a medium that enables uniform, high-quality broadcasting nationwide, without being influenced by other sources.

Furthermore, since it uses a new frequency band that is different from conventional terrestrial broadcasting, it is possible to broadcast new media and meet the needs of a diversified society. Satellite broadcasting based on the NTSC system currently carried out in Japan uses a 120H2 main carrier that is frequency-modulated (
FM) method is used. The frequency shift due to the video signal is the frequency 760 of the relative amplitude OdB of the emphasis characteristic.
kHz is 17 MHzp-P, and the polarity of the modulation is positive to give a frequency shift so that the frequency of the main carrier wave at the white level of the video signal is higher than that of the synchronizing signal. In addition, the audio signal is PCML and then time-division multiplexed for several channels, resulting in a total of 5.727272M}
PC with DPSK (differential phase keying) for Iz subcarrier
The M subcarrier system is used.

(Problem to be solved by the invention) As mentioned above, the modulation method for satellite broadcasting uses the FM method, so if the CN ratio (received carrier power to noise power ratio) deteriorates, the degree of FM improvement is rapidly lost. As a result, truncation noise similar to medaka noise appears in video signals, and code errors increase in audio signals, resulting in deterioration of audio quality.

Since the audio signal is a PCM signal, it is designed to ensure sufficient sound quality to some extent even if the CN ratio deteriorates and the video quality deteriorates by performing error correction of the transmission code and bit interleaving. Since the video signal is an analog signal, it is not subjected to such processing.

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

[Means for Solving the Problems] The present invention provides for receiving and demodulating a television signal sent from a broadcasting satellite or a communication satellite, and transmitting the signal to a television receiver by adding an error correction code to the digital signal. The number of code errors in the audio signal sent as a signal is counted at regular intervals, and when the counted value reaches a predetermined value, the video signal on the line that is sent at the same time is cut off and the signal is sent first. The video signal of the previous line is transmitted, and the noise of the video signal is apparently reduced.

[For production]

When a television signal is sent from a broadcasting satellite or a communication satellite, the frequency-multiplexed video signal and audio signal are separated and demodulated. Since the audio signal is sent as a PCM signal with an error correction code added, the audio signal is demodulated based on this error correction code. When a code error is detected when demodulating an audio signal, the number of detections is counted for each line, and when the count reaches a predetermined value, noise is stochastically superimposed on the video signal due to deterioration of the CN ratio. It determines that the video signal of the line sent at the same time as the audio signal is cut off, and sends out the video signal of the previous line for interpolation. By doing so, the noise in the video signal can be reduced in appearance.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a satellite broadcast receiving system according to the present invention.

In FIG. 1, the output of an outdoor unit consisting of a BS antenna 1 and a BS converter 2 is input to a tuning demodulator 4 of a BS tuner 3, which is an indoor unit, via a connecting cable. The channel selection demodulation section 4 selects the signal of the desired channel, separates the video signal and audio signal of the selected channel, and sends the video signal to the video signal processing section 5 and the audio signal to the audio signal demodulation section 6. Output.

The video signal processing section 5 performs de-emphasis processing, energy diffusion signal removal processing, etc. on the input video signal, restores it to the original video signal, and outputs the restored video signal. The demodulated video signal is input to one side of the switching circuit 7, and after being temporarily stored in the line memory 8, is input to the other side of the switching circuit 7. The switching circuit 7 is connected to the video signal processing unit 5 in the steady state.
However, when a switching signal SW, which will be described later, is generated, it is switched to the line memory 8 side. The output of the switching circuit 7 is output to an NTSC receiver (not shown).

The audio signal selected by the channel selection demodulator 4 is sent to the audio signal demodulator 6.
is input. The audio signal demodulator 6 is composed of a 4-phase DPSK demodulator 9, a PCM demodulator 10, and a DA converter 1l. In the DPSK demodulation section 9, the input signal is detected by two phase detection circuits using subcarriers with a phase difference of 90', and the two phase detection outputs are reliably identified by a discriminator circuit and sent to a difference circuit. The difference between the input signal and the 1-bit delayed signal is taken and reproduced into a digital signal with the same code sequence as the modulation input on the transmitting side. In the PCM demodulation section 10, DP
The digital signal reproduced by the SK demodulator 9 is subjected to descrambling processing, deinterleaving processing, etc., the scrambling and interleaving added on the transmitting side are canceled, and then the error correction/error detection circuit corrects a 1-bit error. 2
Bit errors are interpolated using previous and subsequent sample values. P
The output digital signal from the CM demodulator 10 is converted into an audio analog signal by the DA converter 1l, and sent to the NTSC receiver as an audio output signal from the BS tuner 3.

When a code error is detected in the PCM demodulator 10, an error signal ER is generated and input to the counter l2. counter 1
2, the number of occurrences of this error signal ER is counted, and when it reaches a certain value or more, a switching signal SW is sent to the switching circuit 7.
is output and the switching circuit 7 is switched to the line memory 8 side.

The count value of the counter 12 is reset for each line by the output of a synchronization detector 13 that detects and separates a horizontal synchronization signal from the output of the video signal processing section 5. Therefore, the error signal ER is counted line by line in the counter 12.

In this precept, NTS from broadcasting satellites or communication satellites
When C broadcast radio waves arrive, these radio waves are sent to BS antenna 1.
The received signal in the 12 GHz band is converted to an intermediate frequency signal in the 12 GHz band as an FM signal by the BS converter 2, and then amplified to the required level and sent to the tuning demodulator 4 of the BS tuner 3. is input.

The channel selection demodulator 4 extracts the signal of the desired channel from the IGHz band FM signal sent from the BS converter 2 and sends it to the 4.5 MHz low-pass filter and the
．． The video signal and the audio signal are separated by a band pass filter of approximately 500 KHz.

The separated video signal is demodulated by the video signal processing section 5, outputted to the NTSC receiver via the switching circuit 7, and temporarily stored in the line memory 8.

The audio signal demodulated by the channel selection demodulator 4 is sent to the audio signal demodulator 6.
DPSK demodulator 9 and PCM demodulator 10
After being demodulated into the original digital signal, the DA converter 11
is converted to an analog signal and output. When a code error is detected in the PCM demodulator 10, an error signal ER is generated and input to the counter l2. The counter 12 counts the number of occurrences of this error signal ER for each line, and when it reaches a certain value, generates a switching signal SW to switch the switching circuit 7 and cut off the video signal sent from the video signal processing section 5. and outputs the video signal of the previous line stored in the line memory 8, and corrects the blocked video signal.

The audio signal is multiplexed as shown in FIG. 2(a), and one frame consists of 2048 bits. Frame frequency is IK
In H2, the transmission speed is 2.048 Mb/s.

The first frame of one frame is a 16-bit synchronization signal to facilitate pit clock recovery on the receiving side, the next 16 bits are a switching control code for the mode being transmitted, and then a 32-bit range bit is sent. . The range bits are allocated to 4 channels of audio data (described later), with 8 bits per channel.

Next, 4 channels of audio data 1280 (=1 0X
3 2x4) bits and independent data 480 (=15x32)
) bits, plus 22 bits for correction of all bit errors.
A code of 4 (=7×32) bits is sent. BCH (63.56) code is used as the error correction method.

BCH (63.56) code has a bit length of 56 out of 63
(=1+10X.4+15) bits are information bits and the remaining 7 bits are used for error correction. This makes it possible to correct a 1-bit error out of 56 bits and detect a 2-bit error.

In digital code transmission, in order to reduce the influence of continuous burst-like errors, one information bit is not sent consecutively, but is sent in a different order. This is called interleaving, and Figure 2 (b) shows a matrix for sorting. That is, signals are generated from left to right, but when transmitted, they are read from top to bottom. Therefore, even if there is an error in three successive bits during transmission, for example, by rearranging it on the receiving side, it becomes a one-bit error in one line, and perfect reproduction is possible using the error correction code.

Error correction is performed at 1/3 2 as shown in Figure 2 (c).
It is performed once every ms, that is, every 32KHZ, and
line (15.75 KHz) every second time. The number of times this error is detected is counted by a counter l
2 and reset the counter l2 for each line, the frequency of error occurrence for each line can be determined. When an error is detected within one line, or when more than a certain number of errors are detected, it is assumed that noise is superimposed on the video signal, and the video signal of the line is cut off, and the line memory 8 Outputs the video signal stored in the previous l line.

〔Effect of the invention〕

According to the present invention, the number of occurrences of a code error detection signal generated when demodulating a digital audio signal is counted, and when the counted value exceeds a predetermined value, the CN ratio of the transmission path deteriorates and the S
By determining that the N ratio has decreased and assuming that noise is stochastically superimposed on the video signal sent at the same time, the video signal from one line before is sent. It becomes possible to reduce signal noise in appearance.

[Brief explanation 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 an audio signal transmission format diagram. 6...Audio signal demodulation section, 7...Switching circuit, 8...
Line memory, 12...Counter, 13...Synchronization detector.

Claims (1)

[Claims] In a satellite broadcast reception system that receives and demodulates television signals sent from broadcasting satellites or communication satellites and sends them to a television receiver, the code of the audio signal that is sent as a digital signal with an error correction code added. The number of errors is counted at regular intervals, and when the counted value reaches a predetermined value, the video signal of the line that is sent at the same time is cut off and the video signal of the previous line that is sent first is sent. A satellite broadcasting reception system characterized by: