JPH01137893A - Synchronization compression scrambling system - Google Patents

Abstract

PURPOSE:To obtain a stable correct scramble release without the disturbance of a picture quality, tone quality, etc., by altering the generating timing of an extended pulse with the combination of two sine waves. CONSTITUTION:The sine waves with different two frequencies, which are in a specific phase relation ship with horizontal synchronizing frequencies and dislocated in time on a transmitting side, AM-modulate a voice intermediate frequencies, and transmit the synchronization compressed position information of a horizontal synchronization signal by making them into the combined condition of the two sine waves. On a receiving side, the two sine waves are obtained from the AM-modulated tone intermediate frequencies by an AM-detection, the combination condition of the two sine waves is decoded, the extended timing of the horizontal synchronization signal is decided, the extended pulse is generated, and the synchronization signal position of the received video intermediate frequencies is level-extended by the extended pulse. Thus, the sine waves as a control signal superimposed on a sound FM signal in an AM form has not the spread of a spectrum, and the picture quality and tone quality are not influenced with an adverse effect. Further, concerning the prevention form furtive glance or wiretapping, sufficient security is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a synchronous compression scrambling method used in a cable television (hereinafter referred to as CATV) system.

(Prior Art) In CATV systems, pay broadcast programs are scrambled and transmitted so that only subscribers who have key data for unscrambling can view them. There are various scrambling methods, and among them, the synchronous compression method is one that can be realized relatively easily. This method is a method in which the synchronization signal section of a video signal is level-compressed and transmitted with respect to the high frequency or intermediate frequency of a broadcast television signal.

A control signal for notifying the timing of level compression is superimposed on the audio FM signal in the form of AM modulation and transmitted to the subscriber terminal. On the receiving side, the control signal is extracted and the level compression portion of the scrambled television signal is expanded based on the timing of the control signal. As a result, the demodulated video signal is displayed normally.

Here, if the transmission timing of the control signal and the horizontal synchronization period match, it is relatively easy for eavesdropping to occur. In order to prevent this eavesdropping, a method has been considered in which the timing of the control signal is shifted from the horizontal synchronization interval (with a delay amount) and transmitted. In the case of such a system, it is possible to make it difficult for eavesdropping to occur by changing the amount of delay from time to time.

(Problems to be Solved by the Invention) According to the scrambling method described above, when the control signal is regenerated on the receiving side, this is used to create an expanded pulse synchronized with the synchronous compression position. If detection is not performed accurately, the phase of the expanded pulse will also be out of order, causing damage to the video signal. In order to accurately detect the control signal, it is better that the control signal is a square wave. However, when a square wave is superimposed on an audio FM signal in the form of an AM signal, there is a problem in that the spectrum spreads greatly and causes interference to video signals and audio signals. Conventionally, there has been a system in which a rectangular wave is superimposed on an FM audio signal in order to notify the receiving side of the synchronous compression position. For reference, an FM audio signal from a conventional system is shown in FIG. 6 (6d). When the control pulses are superimposed and transmitted in this way, and the composite intermediate frequency is descrambled, the FM audio signal becomes as shown in Figure 6 (6e).
, it started to include square waves, and this was sometimes played back as noise. In order to reduce such interference, conventional methods have been considered in which the control signal is passed through a low-pass filter on the transmitting side to form a blunt waveform and then transmitted, but on the receiving side, when extracting the control signal, a slice circuit is used to extract the control signal. Because of this, accurate phase information cannot be obtained because the timing of the expanded pulses deviates from the synchronization signal position. Accurate descrambling (descramble)
The purpose is to provide a synchronous scrambling method that can obtain

[Structure of the Invention] (Means for Solving the Problems) This invention compresses the level of the horizontal synchronization signal position of the video intermediate frequency using a synchronization compression pulse on the transmitting side, expands the level of the synchronization position on the receiving side, and then outputs the signal. In a system that performs scrambling, on the transmitting side, an audio intermediate frequency is AM-modulated with two sine waves of different frequencies that have a specific phase relationship with the horizontal synchronization frequency and are shifted in time, and synchronous compression of the horizontal synchronization signal is performed. Position information is transmitted by a combination of the two sine waves. On the receiving side, the two sine waves are obtained from the AM-modulated audio intermediate frequency by AM waves, and the combination state of the two sine waves is decoded.
The expansion pulse is generated by determining the expansion timing of the horizontal synchronization signal, and the level of the synchronization signal position of the received video intermediate frequency is expanded by the expansion pulse.

(Function) With the above means, the sine wave as a control signal superimposed on the audio FM signal in the form of AM has no spectrum spread and does not adversely affect image quality and sound quality. Furthermore, regarding the prevention of eavesdropping, the configuration is such that the generation timing of the expansion pulse can be changed by the combination of the two sine waves, so that sufficient security can be obtained.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a transmitter encoder in one embodiment of the present invention. An audio signal is supplied to the input terminal 11,
A video signal is supplied to the input terminal 15. The audio signal is
FM modulation is performed in an intermediate frequency modulator 12. The FM audio intermediate frequency is obtained by superimposing the sine wave from the digital-to-analog (D/A) converter 27 in the form of AM in the sine wave superimposition circuit 13, and the FM audio intermediate frequency with the sine wave superimposed is sent to the mixer 14. is mixed with the video intermediate frequency and sent to the high frequency modulator 18.
It is manually converted into a high frequency signal RF.

On the other hand, the video signal is converted into a video intermediate frequency by an intermediate frequency modulator 16. The video intermediate frequency is scrambled in the gain control circuit 17 constituting the level compression means, and the synchronization signal position is level-compressed by the compression pulse from the mono multi-by-break 24, and the scrambled video intermediate frequency is mixed. The signal is mixed with the FM audio intermediate frequency in the device 14, and converted into a high frequency signal in the high frequency modulator 18.

Furthermore, the video signal is supplied to the sync separation circuit 21, and the video signal is vertically,
Horizontal sync signal is separated. The separated vertical and horizontal synchronization signals are supplied to a counter 22. The counter 22 is 1. The count data is given to the decoder 23. The decoder 23 can obtain the synchronous compression timing from the count contents, and supplies the timing pulse to the mono-multivibrator 24, for example. The compressed pulse obtained from the mono multivibrator 24 is supplied to the gain control circuit 17, and the horizontal synchronization signal position of the video intermediate frequency is set to 6, for example.
Compress by dB.

3(3a) shows the video intermediate frequency before being scrambled, FIG. 3(3b) shows the compressed pulse, and FIG. 3(3c) shows the video intermediate frequency after being scrambled.

The explanation will be returned to FIG. 1. The vertical and horizontal synchronization signals separated by the synchronization separation circuit 21 are also supplied to the decoder 25. The decoder 25 provides a frequency switching signal (specifically, f If and 4fl+ switching signals, f II is the horizontal frequency) to the conversion table circuit 26, and the switching timing is synchronized with the separated synchronization signal. . The conversion table circuit 26 constituting the sine wave generation means stores data for sine wave generation, and is driven by the clock from the counter 22. The output data of the conversion table circuit 26 is supplied to the D/A converter 27 and inputted to the sine wave superimposition circuit 13 as an analog sine wave.

Therefore, according to the above encoder, normally 4fl+
When transmitting data to the receiving side by superimposing a sine wave on the FM voice intermediate frequency in the form of AM, when 3 waves of fII waves are superimposed, "0" is generated, and when 6 waves of fH waves are superimposed, "0" is generated. 1"
If such an arrangement is made, data can be freely transmitted to the receiving side.

FIG. 4 (4a) shows an example of a sine wave demodulated on the receiving side. T1 and T3 are the periods of the 4fl+ sine wave, and T2 is the period of the f H sine wave.

In this example, since there are three sine waves of f II, it means that data "1" has been transmitted.

The explanation will be returned to FIG. 1. When transmitting data as described above, the data content is determined by the switching timing of the switching signal output from the decoder 25. Decoder 2
5 is composed of a memory, a power filter, a random number generator, etc., and when transmitting data to be held on the receiving side, for example, data in a predetermined format is transmitted every vertical cycle or every multiple vertical cycles. Transmit. Furthermore, after transmitting the data, the decoder 25 transmits key information necessary for descrambling the data.
It is transmitted by a combination of fH and 4f11 sine waves. This function will be explained with reference to FIGS. 4 and 5 after further explaining the decoder of FIG. 2.

FIG. 2 shows a decoder, in which a high frequency signal introduced into an input terminal 31 is converted into a composite intermediate frequency signal in a tuner 32. The composite intermediate frequency signal includes a video intermediate frequency signal and an audio intermediate frequency signal. The horizontal synchronizing signal portion of the intermediate frequency signal is expanded by an expansion pulse in the gain control circuit 33, and is outputted to the output terminal 34 as a descrambled signal.

On the other hand, a sine wave is extracted from the FM audio intermediate frequency signal in an AM detection circuit 35 constituting a sine wave reproducing means. FIG. 4 (4a) shows an example of an extracted sine wave. The output of the AM detection circuit 35 is supplied to an fH filter 36 that extracts the f II frequency component and a 4f11 filter 37 that extracts the 4 f H frequency component. 4f
The 4fl sine wave extracted by the H filter 37 is supplied to the clock input terminal of the counter 40, and the 4fl sine wave is
1 detection circuit 38. In addition, the counter 40 has
The output of the f I+ filter 36 is also supplied, and the counter 40 receives the f I! When the output of the filter 36 is present, the counting operation is stopped. In addition, 4fl (detection circuit 3
8, when detecting a 4fl+ sine wave, supplies the detection output to the counter 40 and also sends the data separation circuit 39.
supply to. (4b) in FIG. 4 is the f11 filter 36.
(4c) is the output of the 4f11 filter 37,
FIG. 4(d) shows the detection output of the 4fH detection circuit 38.

In FIG. 4, since there are three waves of f I + sine waves, it means that data "1" has been transmitted as in the previous arrangement. This data is determined by the data separation circuit 39, and these three data separation circuits hold a predetermined number of bits in parallel when data is transmitted in a predetermined format during the vertical period. and output.

Next, during periods other than the vertical synchronization period, 4
At the rise of the fH detection signal, descrambling processing is started.

That is, the vicinity of the period TX in FIG. 4 will be enlarged and illustrated in FIG. 5 for explanation. When the 4fH detection circuit 38 detects the 4fl sine wave after the fH sine wave, the 4fH detection circuit 38 detects the detection signal (Fig.
d) Launch ) (time ■).

When this detection signal is input to the counter 40, the output of the fH filter 36 first crosses zero after the elapse of time (2), and the counter 40 first receives 4f1! Counting starts when the signal rises (time point ■), and the count advances every time there is a zero cross. However, in this case, the counter 40 presets the data held in the data separation circuit 39 as initial data.

In this embodiment, the data preset in the counter 40 is 5 (decimal), and the counter 40 is an octal counter. Counter 40 advances to 5°6.7 and counts to 0
Then, the contents of this counter are detected by the decoder 41. When the counter 40 becomes O, the decoder 41
Generates an extension timing pulse and supplies it to the 4th mono multivibrator. When the expansion timing pulse is input, the mono multivibrator 42 generates an expansion pulse of a predetermined width and expands the compressed synchronization signal.
Descrambling will be performed. Figure 5 (5c)
5d shows the counting status of the counter 40, and (5d) shows the extended pulse. Thereafter, if f11 arrives again and the above operation is repeated, or if 4fl+ continues, the counter 40 counts in octal, and an extended pulse is generated every time it reaches 0. .

Furthermore, the output of the 4f11 detection circuit 38 is also supplied to an integration circuit 43. The integrating circuit 43 is a circuit that determines that the current signal is not scrambled when the 4f11 sine wave is not detected for a long time, and stops the operation of the decoder 41.

As described above, the present invention realizes the timing at which an extended pulse should be generated by combining two sine waves in the time axis direction. Further, by combining two sine waves, data transmission as obtained by the data separation circuit 39 is also performed. In the above example, m times C of fH
M-4) and a sine wave with a frequency n times (n-1). With this combination, preset data for the counter 40 is transmitted.

Here, it is clear from the above description that by changing the preset data, the timing of generation of the extended pulse can be changed. The ability to change the generation timing of the expansion pulse means that in the above embodiment, the time interval between the switching point of the f I+ and 4fH sine waves and the synchronous compression position can be changed. Therefore, even if an attempt is made to illegally detect the sine wave of f I+ to create an expanded pulse and descramble it, it is impossible to know the timing of its generation. When changing the preset data, for example, it is possible to transmit and change a combination of two sine waves in a predetermined format during the vertical synchronization period, and when the format is detected, the data separation circuit imports the preset data. .

FIG. 6 is a signal waveform diagram for explaining the influence of the heather system on the FM audio signal. Since the FM audio signal (FIG. 6 (6a)) modulated in AM form by a sine wave is included in the composite intermediate frequency signal, when it passes through the gain control circuit 33 in FIG. (Figure 6 (6b)
), there are extended periods as shown in Figure 6 (6c).

Since synchronous compression was performed only on the video intermediate frequency signal, it is actually only necessary to perform synchronous compression on the video intermediate frequency signal, but in order to do so, it is necessary to must be separated from the frequency.

If such separation were to be performed, the configuration would be complicated, so in this system, synchronous expansion is performed in the composite intermediate frequency state.

As a result, the FM audio signal is as shown in Figure 6 (6c).
However, with this device, the signal superimposed on the FM audio signal is a sine wave, so there is no spectrum spread, and this expanded portion may be reproduced as noise or as a stereo component of the audio signal. will not cause any distortion. Conventionally, when a control pulse as shown in Fig. 6 (6d) is superimposed on an FM audio signal and transmitted, if the composite intermediate frequency is descrambled, the FM audio signal becomes as shown in Fig. 6 (6e).
, it started to include square waves, and this was sometimes played back as noise. However, in this embodiment, there are no problems like the conventional one, and good reproduced sound can be obtained.

[Effects of the Invention] As described above, the present invention can provide a synchronous scrambling method that can obtain stable and accurate descrambling without disturbing image quality, sound quality, etc.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an encoder according to an embodiment of the present invention, FIG. 2 is a block diagram of a decoder according to an embodiment of the invention, and FIG. 3 is a signal diagram for explaining the operation of the encoder. Waveform diagrams, Figures 4 and 5 are signal waveform diagrams shown to explain the operation of the decoder, and Figure 6 is a waveform diagram.
The figure is a signal waveform diagram shown to compare and explain the state on the decoder side of the FM audio signal according to the present invention with the state on the decoder side according to the conventional system. 12... Intermediate frequency modulator, 13... Sine wave superimposition circuit, 14... Mixer, 16... Intermediate frequency modulator, 17
. . . gain control circuit, 18 . . . high frequency modulator, 21.
... Synchronous separation circuit, 22 ... Counter, 23 ... Decoder, 24 ... Mono multivibrator, 25 ...
・Decoder, 26... Conversion table circuit, 27...
D/A converter, 32... Tuner, 33... Gain control circuit, 35... AMI wave circuit, 36... f I+
Filter, 37...4f11 Filter, 38...4
fll detection circuit, 39... data separation circuit, 40...
- Counter, 41... Decoder, 42... Mono multi-by-break. Applicant's agent Patent attorney Takehiko Suzue

Claims (2)

[Claims] (1) On the transmitting side, compression pulse generation means for generating a synchronization compression pulse synchronized with a horizontal synchronization signal, level compression means for level-compressing the horizontal synchronization signal position of a video intermediate frequency by the synchronization compression pulse, and a horizontal synchronization signal. sine wave generating means for generating a combination of two sine waves of different frequencies that are integral multiples of the horizontal frequency in the time axis direction; control means for expressing time difference information between the switching timing of the sine wave and the synchronous compression position by the combination state in the time axis direction, and controlling the switching timing from the one sine wave to the other sine wave. means for notifying that the compressed horizontal synchronization signal is present at a position corresponding to the time difference information; AM modulation means for AM modulating the audio intermediate frequency using the two sine waves; and the level compression means. means for transmitting the output of the AM modulating means;
sine wave reproducing means that obtains two sine waves by AM detection; and reproducing data from the combination of the two sine waves, and the time difference information between the switching timing from the one sine wave to the other sine wave and the synchronous compression position. after detecting the switching point of the regenerated one sine wave to the other, an elongated pulse generating means that determines as the elongated pulse generation timing a time after a lapse of time according to the time difference information and generates the elongated pulse; 1. A synchronous compression scrambling method, comprising: expansion means for level-expanding a synchronization signal of a received video intermediate frequency using the expansion pulse. (2) The elongated pulse generating means has a counter that is preset with the time difference information and counts the other sine wave after the period of the one sine wave has elapsed, and when the value of this counter reaches a predetermined value. A synchronous compression scrambling method characterized in that a decoder sometimes outputs a generation timing pulse of the expansion pulse.