JPS63267084A - Digital data transmission system - Google Patents

Abstract

PURPOSE:To attain excellent transmission and effective scramble even when the level of a carrier is low by superimposing FSK modulated digital data on the sound signal carrier of a television broadcasting signal and transmission. CONSTITUTION:The sound signal is converted into the digital data in an A/D converter 2, mixed with a pseudo noise signal in a mixer for scrambling to have scramble signal, supplied to an FM modulator 6 through a roll off filter 5 and the FSK modulated digital signal is supplied to the sound signal input terminal of a mixer 7 for mixing a video and a sound. In such a way, the FSK modulated data is superimposed on the sound signal carrier and transmitted, thereby, an FSK modulating modulator and demodulator can use the FM modulator and an FM demodulator for the sound signal of the television broadcasting equipment to simplify a constitution. Even when the level of the sound signal carrier like a CATV is low, the data can be effectively transmitted and further, when it is scrambled and transmitted, it is difficult to tap.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital data transmission system suitable for use in cable broadcasting such as CATV.

[Summary of the invention]

In a digital data transmission system suitable for use in cable broadcasting such as CATV, the present invention transmits FSK-modulated digital data by superimposing it on an audio signal carrier wave of a television broadcast signal. The receiver has a simple configuration and can satisfactorily transmit audio signals of television broadcasting, and can also reliably scramble the audio signals to prevent eavesdropping.

[Prior Art] In recent years, a cable broadcasting system for television broadcasting called CATV has been put into practical use. In the case of this CATV,
The number of channels that can be transmitted through one transmission line is large,
In addition to normal television broadcasting, various services such as paid broadcasting of movies and the like are provided.

[Problem that the invention seeks to solve]

However, in the case of CATV with a large number of channels, the carrier wave level of the audio signal must be set higher than that of a normal wireless television broadcast signal in order to prevent the broadcast signals of each channel from interfering. It is set low. For this reason, television broadcasting by CATV has the disadvantage that the sound quality is lower than that of normal television broadcasting.

In addition, when performing paid broadcasting on CATV, the video signal is scrambled and transmitted on the transmitting side, and this video signal is descrambled (
Generally, settings are made so that the scrambled signal can be recovered (II). By doing this, receiving households that do not pay fees receive the video signal of this pay channel in a scrambled state, making it impossible for them to view normal images.

However, even in the case of such paid broadcasting, the audio signal is not scrambled at all, or is only scrambled using a simple method, so even households that do not pay the fee can only hear the audio, or Even if it was scrambled, there was a risk that it could be easily descrambled and eavesdropped on. In order to solve this problem, it has been proposed to convert audio signals into digital signals and transmit them, as shown in US Pat. No. 3,504,286, for example, but there are various problems in transmitting digital signals together with video signals. was there.

In view of these points, it is an object of the present invention to provide a data transmission system that can perform good transmission even when the level of a carrier wave is low, and can also reliably scramble data.

[Means for solving problems]

In the digital data transmission system of the present invention, for example, as shown in FIG. 1, FSK-modulated digital data is transmitted by being superimposed on the audio signal carrier wave of a television broadcast signal.

[Effect]

According to the digital data transmission system of the present invention, for example, an audio signal is converted into digital data and then subjected to FSX modulation, and this FSK transformed data is superimposed on an audio signal carrier wave and transmitted. The FM modulator and FM demodulator for audio signals of ordinary television broadcasting equipment can be used as the demodulator and the FM modulator for audio signals, so that the configuration is simple. In addition, since it is transmitted as digital data, it is possible to reliably transmit good data even when the level of the audio signal carrier wave is low as in CATV, and furthermore, since it is digital data, it is difficult to eavesdrop if it is transmitted after being scrambled. be.

〔Example〕

An embodiment of the digital data transmission method of the present invention will be described below.
Let me explain with reference to the attached drawings.

The digital data transmission method in this example is commonly used as the audio signal transmission method for CATV, which is cable television broadcasting. First, see Figure 1 for the configuration of the transmitter installed at the CATV center on the transmitting side. and explain.

This Figure 1 is a diagram showing the configuration of the transmitter. In the figure, (1) indicates the audio signal input terminal of TVILAN broadcasting, and this input terminal (1) is used to receive the audio signal of the channel transmitted by this transmitter. is obtained. The audio signal obtained at this input terminal (1) is supplied to an analog-to-digital converter (hereinafter referred to as A/D converter) (2), and is converted into digital data by this A/D converter (2). The converted digital data is then supplied to one mixed signal input terminal of the scramble mixer (3).

Further, the pseudo noise signal outputted from the pseudo noise generator (4) is supplied to the other mixed signal input terminal of the scrambling mixer (3). Then, the scramble mixer (3) mixes this digital data and the pseudo-noise signal to produce a scramble signal, and the mixed signal, which is the scramble signal, is passed through the roll-off filter (5) to the FM modulator (6).
). This FM modulator (6) is a normal FM modulator used when converting an audio signal into a carrier wave.
The mixed signal is subjected to FM modulation by the M modulator (6). Here, since the mixed signal supplied to the FM modulator (6) is a digital signal, FSK (Frequency 5-hift) which is FM modulation of the digital signal is used. Key
lng) modulation is performed.

Then, the FSX modulated digital signal is supplied to the audio signal input terminal of the video/audio mixing mixer (7).

In Fig. 1, (8) indicates a video signal input terminal, and after the video signal obtained at this input terminal (8) is converted into a digital signal by an A/D converter (9), it is stored in a frame memory (10). supply The video signal supplied to this frame memory (10) and once stored is outputted after changing the order of each horizontal scanning line, and this output video signal is sent again to a digital-to-analog converter (hereinafter referred to as a D/A converter). )
(11) into an analog video signal, and the video signal output from the D/A converter (11) is converted into an analog video signal by the AM converter 11.
3 (12). This AM modulator (12) converts the video signal into an AM modulated signal for transport, and supplies this AM modulated signal to the video signal input terminal of the video/audio mixer (7).

Then, the mixer (7) mixes the FSK modulated audio signal supplied to the audio signal input terminal and the AM modulated video signal supplied to the video signal input terminal as described above, and outputs the mixed signal from the output terminal (13). Output. And this output terminal (
The output signal obtained in step 13) is converted into a signal in a frequency band of a predetermined channel, and then supplied to each receiving household via a CATV transmission line.

By configuring the transmitter in this way, for example, the audio signal converted into digital data by the A/D converter (2) is
If the pseudo noise signal outputted by the pseudo noise generator (4) is the signal shown in FIG. 2B,
The scrambled mixed signal output from the mixer (3) becomes a pulse signal in which both are added together as shown in Fig. 2C, and this pulse signal is passed through a roll-off filter (5) to differentiate the rising and falling edges of the signal. This becomes a gentle signal, and the signal as shown in the second diagram is converted into FSK by an FM converter (6). Then, the mixer (7) converts the audio signal and the video signal into a composite video signal of 4.5 MHz, which lowers the level of the carrier wave a of the audio signal A by 15 dB than the level of the carrier wave V of the video signal ■. This prevents the audio signal from affecting the video signal of an adjacent channel. The bandwidth of the audio signal A is approximately the same as that when transmitting a normal analog signal. The signal sent out from the transmitter in this way is a scrambled signal with pseudo noise mixed in after the audio signal is digitized, and the video signal has a different order of horizontal scanning lines than usual. Both the audio and video become scrambled signals.

Next, a description will be given of the configuration of a receiver that receives the television broadcast signal supplied from the transmitter to each receiving household via the CATV transmission line in this manner.

Figure 4 is a diagram showing the configuration of this receiver, and in the figure (21)
indicates a broadcast signal input terminal to which the above-mentioned television broadcast signal is supplied from the CATV transmission line, and the broadcast signal obtained at this input terminal (21) is supplied to the television tuner (22). This television tuner (22
) selects the transmission signal of a predetermined channel, demodulates it to baseband, and supplies the audio signal superimposed on the audio signal carrier of the demodulated transmission signal to the FM demodulator (23). This FM demodulator (23) converts the supplied audio signal into F
M demodulates and descrambles the demodulated signal (24
) to one of the mixed signal input terminals. Further, the pseudo noise signal output from the pseudo noise generator (25) is supplied to the other mixed signal input terminal of this mixer (24). The mixer (24) then mixes the demodulated signal with the pseudo-noise signal to obtain an unscrambled original signal, and supplies this mixed signal to the D/A converter (26). This D/
The A converter (26) converts the supplied mixed signal from a digital signal to an analog signal, and supplies the converted signal to the audio signal output terminal (27).

With this configuration, the digital signal of the audio signal that is superimposed on the audio signal carrier wave and FSK-modulated and supplied from the transmitter as described above is demodulated and becomes a pulse signal.
The mixer (24) mixes the pseudo-noise signal output from the pseudo-noise generator (25), which is the opposite of the one used during transmission, and decripples the signal to obtain the original digital audio signal as shown in FIG. 2A. This digital audio signal is sent to a D/A converter (26
), the original audio signal can be obtained by converting it into an analog signal. Then, by supplying this audio signal obtained at the output terminal (27) to the audio reproducing device, the audio is reproduced.

Then, the video signal of the broadcast signal demodulated by the television chainer (22) is supplied to the AM demodulator (28). This AM demodulator (28) performs AM demodulation on the supplied video signal, converts the demodulated signal into a digital signal with an A/D converter (29), and then supplies it to a frame memory (30). 30) to be memorized once. The video signal once stored in this frame memory (30) is read out in the original order, with the order of each horizontal scanning line being reversed from the time of transmission, and the read video signal is sent via the D/A converter (31). It is converted into an analog signal again and supplied to the video signal output terminal (32).

With this configuration, the scrambled video signal by changing the order of the horizontal scanning lines during transmission is descrambled into the original video signal, and this video signal obtained at the output terminal (32) is sent to the receiver. By supplying the signal, normal image reception is performed.

By configuring the CATV transmitter and receiver in this way, both the video signal and the audio signal are scrambled and transmitted, and unless this receiver is installed, the scrambled channel cannot be viewed or eavesdropped. It becomes difficult. In particular, since the audio signal is a digital signal mixed with pseudo-noise, equivalent audio cannot be obtained by simply performing FM demodulation with a normal receiver.

Since the audio signal is transmitted as FSK-modulated digital data superimposed on the audio signal carrier wave, CAT
Even though the level of the audio signal carrier wave is set low because of V, as long as the digital data can be received accurately, the sound quality will not deteriorate, and the audio will be of good quality without affecting the video. can get. In addition, in order to transmit digital data with FSX modulation, a normal FM modulator and FM demodulator for audio signals can be used as the modulator and demodulator provided in the transmitter and receiver. Configuration becomes easier.

In the above embodiment, FSK modulation is simply used as the modulation method for the digital audio signal, but various FSX modulations such as MSK modulation and GMSK modulation using a Gaussian filter can be used. Further, although the digital data superimposed on the audio signal carrier wave is only the audio signal, various data such as data related to scrambling can be transmitted together with the audio signal. Further, in the above embodiment, CA
Although the present invention is configured as a TV, it goes without saying that the present invention can be applied to television broadcasting that performs wireless transmission. moreover,
The present invention is not limited to the above-described embodiments, and may take various other configurations without departing from the gist of the present invention.

〔Effect of the invention〕

According to the digital data transmission method of the present invention, the transmitter and the receiver can transmit audio signals of television broadcasts with a simple configuration, and can also reliably scramble the audio signals to prevent eavesdropping. There are benefits that can be made.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a transmitter according to an embodiment of the digital data transmission system of the present invention, and FIGS.
FIG. 4, which is a diagram for explaining the illustrated example, is a configuration diagram showing a receiver according to an embodiment of the present invention. (2) is an analog-to-digital converter, (6) is an FM modulator, (23) is an FM demodulator, and (26) is a digital-to-analog converter.

Claims (1)

[Claims] A digital data transmission system characterized in that FSK-modulated digital data is transmitted by being superimposed on an audio signal carrier wave of a television broadcast signal.