JPH02121591A - Catv transmission system - Google Patents

Abstract

PURPOSE:To transmit and receive PCM sounds suitable for the already existing broadcasting system by using the same sound subcarriers as that of the already existing broadcasting system and, at the same time, reducing the transmitting speed by applying a compress-processing on PCM sound signals so that the signals can be made suitable for a narrowed sound band. CONSTITUTION:A BS tuner decoder 11 outputs video signals 15 and PCM digital sound signals 14. The video signals 15 are inputted to the video input of a TV modulator 13 and the PCM digital sound signals 14 are signal-compressed from 14 bits to 8 bits by means of a PCM encoder 12 by using a sub- instantaneous compressing DPCM system. In addition, error noise caused by cut-off bits is compensated with differential data obtained from an original signal the bit of which is cut off in accordance with a range bit. The output of the PCM encoder 12 is a signal QPSK-modulated with a 4.5MHz subcarrier. The ouptut is inputted to the sound subcarrier input of the TV modulator 13 and outputted as a TV RF signal.

Description

[Detailed description of the invention] Industrial applications The present invention applies to NTSC in CATV systems.

The present invention relates to a CATV transmission system that is compatible with existing broadcasting systems such as PAL.

2. Description of the Related Art Conventionally, in a CATV system using a coaxial cable as a transmission path, audio signals are transmitted and received as analog signals.

This is because the frequency band assigned to voice is a narrow band in each existing transmission method.

The conventional CATV transmitter/receiver 7 system will be explained using FIG. 1 is a parabolic antenna that receives broadcast radio waves from a communication satellite; 2 is a BS tuner decoder that demodulates the satellite broadcast signal into a baseband signal; the BS tuner decoder 2 outputs a baseband video signal 3 and audio signal 4; do.

Reference numeral 5 denotes a television modulator, which inputs the baseband video signal 3 and audio signal 4 and outputs a television RF signal of an arbitrary TV channel frequency. Line amplifiers 6a and 6b are used to compensate for transmission loss due to transmission through the coaxial cable 7a and the other cables. 8
A, 8b, and 8c are branchers for branching television RF signals. 9 is a television receiver.

As shown in Figure 7, the frequency band of satellite broadcasting is 4.5M) for video signals, and 6.73M for audio signals.
) h as a subcarrier. The audio signal is a PCM audio signal for high quality sound.

Problems to be Solved by the Invention However, PCM audio signals cannot be transmitted using existing broadcasting systems. That is, in the audio band of the existing broadcasting system, since the PCM audio signal is a high-speed digital signal, it cannot be transmitted in the band conventionally allocated, and furthermore, interference with the video signal occurs. As shown in FIG. 8, the frequency band of the NTSC system, which is an existing broadcasting system, uses subcarriers of 4.2M)-1z for video signals and 4.5M)h for audio signals. Furthermore, FIG. 9 shows the RF frequency array of the NTSC system, which is an existing broadcasting system, where fV is the video 1ψ carrier wave of the own station, and fA is the audio carrier wave. Furthermore, fv. is a video carrier wave of an adjacent station. As is well known, fV and fV.

has a frequency difference of eMI-b, and fV- and fA are 1
．． The relationship is such that there is a frequency difference of 5 MH. As described above, it can be seen that the band allocated to the audio signal in the existing broadcasting system is narrow, and as a result, it is insufficient for transmitting the PCM audio signal. Therefore, in a CATV system that receives satellite broadcasting and uses a coaxial cable as a transmission path, the only means available is to demodulate the audio signal to baseband and transmit it using a television modulator, which impairs high-quality PCM audio.

The present invention solves the above problems and aims to provide a CATV transmission system that can transmit and receive PCM audio that is compatible with existing broadcasting systems.

Means for Solving the Problems In order to achieve the above object, the CATV transmission system of the present invention uses the same audio subcarrier as the existing broadcasting system, and further uses a PCM audio signal to adapt to the narrowing of the audio band. The transmission speed is reduced by performing compression processing.

Function: By compressing the 5PCM audio signal using the above transmission method, the transmission speed of the PCM audio can be lowered so that the PCM audio signal can be transmitted in the narrow audio band of existing broadcasting, and the transmission speed of the PCM audio can be reduced. There is no interference and it can be adapted to existing broadcasting systems.

Embodiment Hereinafter, a CATV transmission system according to an embodiment of the present invention will be explained with reference to FIGS. 1 to 4. FIG. 1 is a block diagram showing the configuration of a CATV transmission system according to an embodiment of the present invention. In FIG. 1, the same components as those of the conventional example shown in FIG. 6 are designated by the same reference numerals, and detailed explanation thereof will be omitted. In FIG. 1, 1 is a parabolic antenna that receives broadcast waves from a communication satellite, and 2 is a BS tuner decoder that demodulates satellite broadcast signals. The BS tuner decoder 2 outputs a baseband video signal 15 and a PCM digital audio signal 14.

The video signal 15 is input to the video input of the television modulator 13. On the other hand, the PCM digital audio signal 14 is a 14-bit digital signal, and the PCM encoder 12 compresses the signal from 14 bits to 8 bits. For compression, quasi-instantaneous compression D
Using the PCM method, 4 bits are rounded down to 8 bits using the range bit. Further, error noise due to bit truncation is dealt with by obtaining differential data between the original signal and the original signal in which the bits of the original signal are truncated according to the range bit, and performing full compensation for the difference data. PCM encoder 1
The output of 2 is 4. This is a QPSK modulated signal using the rsMh subcarrier. The output of this PCM encoder 12 is input to the audio subcarrier input of the television modulator 13,
It is output as a television RF signal. ea and eb are line amplifiers that compensate for cable losses of the coaxial cables 7a and 7b. 8a, 8b, 8c TV R
This is a branching device that branches the F signal. 17 is a reception decoder, which outputs baseband video signals, audio signals, and R.
is output. Each baseband signal is input to a television receiver 9.

The internal configuration of the PCM encoder 12 will be explained in more detail. The PCM digital audio signal 14, which is the output of the BS tuner decoder 11, is a digital signal with 14 bits as a unit, and is outputted to the DPCMPCM encoder to generate 32KH.
Quasi-instantaneous compression DPCM of 8 pino 1- at sampling frequency of z
converted into a signal. At this time, 14 bits requires a bandwidth of approximately 570 kHz, which cannot be applied using existing broadcasting systems, but by compressing it to 8 bits, the bandwidth becomes approximately 380 Kh, which can be transmitted within the TV audio band. can.

Figure 2 shows the frame format (#) 32 lines x 48
It has a column structure, and the first bit of each row is part of the header, and part of the header is a 12-bit frame synchronization code.
It consists of 4 bits of control code, 14 bits of range bits (7 bits each for L and R), and 2 bits of audio mode identification code. Furthermore, since each frame includes 64 samples for L and R, the transmission time for one frame is 2 hours, and the transmission rate is 788 Kbpg, which allows narrow bandwidth. Figure 3 shows the frequency band of the existing NTS
It conforms to the C format. Now, D.P.
The CMPCM encoder 20 is input to a scramble circuit (scrambler) 21, and the DPCM signal is scrambled by a Varnu noise (PN) code addition (pseudorandom signal addition method) K. In the output signal QPSK modulation circuit 22 of the scrambled PCM encoder 2Q, the output signal from the oSC 23 is 4.5MHz (7).
QPSK modulation is performed on the reference subcarrier.

Next, the configuration of the reception decoder 17 will be explained.

The broadcast signal outputted via the PCM encoder 12 and television modulator 13 is tuned by a tuner circuit 26, and the video signal is demodulated into a baseband signal by a VIF demodulation circuit 26. On the other hand, the PCM audio signal is detected by the SIF synchronous detection circuit 27.
, input the video carrier wave from the VIF demodulation circuit 26,
It performs synchronous detection and demodulates to a 4.5M 0PSK signal.

The QPSK signal is reproduced into a PCM audio signal by the QPSK demodulation circuit 28. Note that since the output of the QPSK demodulation circuit 28 remains scrambled on the transmitting side, it is descrambled by the descrambling circuit 29. Furthermore, the descrambled DPCM audio signal is DPCMPC
The M echoder decodes it into L and H digital audio signals. The decoded PCM audio is converted into analog audio by 31 D/A converters.

As described above, according to this embodiment, it is possible to provide high-quality PCM audio from satellite broadcasting to viewers while supporting the signal format of the current broadcasting system.

Furthermore, Figure 4 shows the C/N and bit error rate characteristics of the system according to the present invention, which shows that the system has performance with a large margin for the error rate of 3×1o, which is the limit for detecting noise in reproduced sound. I can understand that.

FIG. 5 shows an embodiment of the present invention. To explain only the difference from the first embodiment described above, it shows a case where the sampling frequency of the PCM signal sent by satellite broadcasting is different, and the PCM encoder 40
The sampling frequency is converted by a sampling frequency conversion circuit 41 provided in the 1. ．． Add a circuit to convert to a 32KHz digital audio signal.

In the embodiment, the PCM audio of satellite broadcasting has been described, but it goes without saying that similar effects can be obtained even when an AV source is used by adding A/D conversion to the input of the PCM encoder.

Further, in the embodiment, NTSC was described, but similar effects can be obtained in other systems by adding a subcarrier frequency conversion circuit.

Effects of the Invention As is clear from the above explanation, the present invention provides high-quality PCM broadcasting that conforms to the format of existing broadcasting systems while maintaining the high-quality PCM audio signal of satellite broadcasting without deterioration. We can submit an 0ATV transmission method that can realize this.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a CATV transmission system according to an embodiment of the present invention, FIG. 2 is a diagram showing a signal format of the CATV transmission system, and FIG. 3 is a frequency band diagram of the CATV transmission system. FIG. 4 is a characteristic diagram showing C/N and pit error characteristics according to the present invention, and FIG. 6 is a CA of another embodiment of the present invention.
Figure 6 is a block diagram showing the configuration of the transmitting side of the TV transmission system, Figure 6 is a block diagram showing the configuration of a conventional CATV transmission system, Figure 7 is a frequency band diagram of satellite broadcasting, and Figure 8 is the existing N
Frequency band diagram of the TSC system. FIG. 9 is an RF frequency band diagram of the existing NTSC system. 12...PCM encoder, 17...
PCMf coder, 2o...DPCMPCM encoder...Scrambler, 22...QP
SK modulation circuit, 23...O20, 28...QP
SK demodulation circuit, 29... descrambler, 30
...DPCM decoder, 31...D/A
converter. Name of agent: Patent attorney Shigetaka Awano and 1 other person 2nd
Figure 3 Figure 4, Z 4S (,, Hl)

Claims (1)

[Scope of Claims] A BS tuner decoder that receives and demodulates satellite broadcasting, a PCM encoder that converts the output digital audio signal of the BS tuner decoder to conform to a predetermined broadcasting system, and a PCM encoder that converts the output digital audio signal of the BS tuner decoder to conform to a predetermined broadcasting system. The PCM encoder is a DPCM encoder that differentially compresses the digital audio signal. The reception decoder includes a scrambling circuit that scrambles the output of the DPCM encoder circuit, and a QPSK modulation circuit that modulates the scrambled PCM signal with PSK. A VIF demodulation circuit that demodulates, an SIF detection circuit that detects the SIF signal on the video carrier,
QP demodulates the output of this SIF detection circuit into a PCM signal
The present invention includes an SK demodulation circuit, a descrambling circuit for unscrambling the PCM signal, a DPCM decoding circuit for reproducing the PCM signal into a digital signal, and a D/A conversion circuit for converting the digital signal into an analog signal. Characteristic CATV transmission method.