JPH0525235B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scrambling method in a CATV system.

In a terminal device having a circuit configuration as shown in FIG. 3, PLL type tuning is used. That is, the signal sent from the center side is sent from the converter 1 to the TV receiver via the descrambler 2 as a TV signal, and is separated into data signals by the FSK 3. The data signal detected by the FSK 3 and given to the controller 4 is compared with the selected channel number from the channel select key 5 and the address signal from the address 6 to determine whether TV viewing is possible. The controller 4 provides a control signal to the converter 1 using PLL tuning, and the descrambler 2 receives a descramble signal in accordance with the key code extracted from the data signal. In addition,
Reference numeral 7 in the figure is a channel indicator.

A general scrambling method in a CATV system incorporating such a terminal device uses a center side circuit as shown in FIG. Here, a key code is output from the random number generator 8 to the shift register 9. The synchronization detector 10 detects the horizontal synchronization timing of the image signal, and when the key code is "1", the switch 1 is activated via the switch 11.
A switch switching signal is applied to 2, so that the image signal is applied to the modulator 14 via the attenuator 13, and the horizontal synchronization part is compressed. The above key code is for dividing the horizontal synchronization of one field into an appropriate number of blocks, and for each number of blocks, the horizontal synchronization level is encoded in a pattern of "1" or "0" depending on whether or not it is compressed. It is something.

On the other hand, since this code is a correct signal to be restored to its original state on the receiving side, it is sent one field before the field in which the horizontal synchronization is actually compressed by modulation such as frequency multiplexing. As a result, on the receiving side, the code is demodulated by the demodulator 15 in the descrambler 2 and set in the shift register 16, as shown in FIG. When the switch 18 is turned on by the signal from the synchronization detector 17 in the next field, the switch 19 is operated to extend or not extend the horizontal synchronization level. That is, when the signal is "1", the video signal is passed through the amplifier 20. In this way, all horizontal synchronization returns to normal levels. In this case, the number of correct signals is not limited to one type, and different codes may be used for all channels in each field.

The digital scrambling method realized in this way was thought to be a powerful countermeasure to prevent unauthorized viewing because it could use a random key code for each field, but the key code modulation method If this happens, the correct signal can be extracted as is by demodulating accordingly, and the meaning of scrambling is lost.

The present invention has been made based on the above-mentioned circumstances, and is based on the above-mentioned circumstances.
The system aims to provide a scrambling method for CATV systems that uses PLL data to encode key codes and has a strong digital scrambling effect against fraudulent activity.

For this purpose, the present invention provides a method for scrambling in a CATV system using PLL tuning in a terminal, when an image is scrambled by compressing a horizontal synchronization signal portion of a video signal, the tuning used in the channel is The encoded PLL data and key code are encoded by a required linear operation, the encoded signal is superimposed on a signal scrambled with the video signal using the key code, and the encoded signal is transmitted, and the terminal side outputs the tuned PLL data. The method is characterized in that the key code is restored and descrambled by performing an inverse operation on the data and the demodulated encoded signal.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 4 to 7. In addition, in the figures, the same parts as in the previous description are given the same reference numerals, and the description thereof will be omitted. The difference in circuit configuration in this embodiment is that in the terminal device, the PLL data signal in PLL tuning is also given to the descrambler 2, as shown in FIG. The key code applied to the modulator 14 as seen in Figure 4 is input to the exclusive OR gate 21 and
PLL data is also input to the OR gate 21. Here, in the terminal device, as shown in FIG. is input.
Note that the above PLL data is data for determining the tuning frequency sent to the programmable divider in PLL system tuning.

In such a configuration, on the transmitting side, since the PLL data on the terminal side required to tune the channel is known, the required linear operation using this PLL data and random data from the random number generator 8 is performed. is received and encoded. This is extracted as a key code and modulated by the modulator 14.

On the other hand, in horizontal synchronization compression, each block is compressed using random data. On the receiving side,
When the viewer tunes a channel using the channel select key 5, the controller 4
PLL data is output to the PLL built-in converter 1, and the frequency of that channel is received. Therefore, the key code is demodulated by the demodulator 15, and the PLL data is synthesized here. Therefore, the key code for expanding the synchronization signal is obtained by inversely calculating the PLL data and the calculations performed on the transmitting side.

A concrete example of such scrambling will be explained with reference to FIG. 1 field to 8
When divided into blocks, “1” is compressed, “0” is uncompressed, and the random data is “11110000”,
The key code to be sent to the field immediately before that field is determined as follows. If the PLL data for the terminal to receive the A channel is "11001010", the exclusive logical sum of "11110000" and "11001010" is "00111010". This data is modulated using a method such as frequency multiplexing. On the terminal side, the A channel is first tuned, and then demodulated,
Get the data “00111010”. By performing an exclusive OR operation on this with the PLL data 11001010, it becomes possible to reproduce the key code 11110000.
If you affect the horizontal and synchronized parts by setting "1" to expansion and "0" to non-expansion, all horizontal synchronization will return to normal levels and you can normally view the TV screen. Also, considering the B channel, if the same random number is "11110000", the key code to be modulated will be "11101100", which is a completely different code.

In the above embodiment, a one-way CATV system has been described, but it goes without saying that the present invention can also be applied to a two-way CATV system.

As described in detail above, in the present invention, since the key code is encoded by PLL data, a person who attempts to stealth viewing by illegal acts can easily demodulate the horizontal synchronization even if the key code is extracted by demodulating the key code. cannot be restored. Moreover, since the PLL data is all different depending on the channel, the encoded data is also different, and it is almost impossible for someone trying to spy on you to tell which part of the PLL data is being used.
Furthermore, such encoding requires data that corresponds one-to-one to the channels, but in the present invention, the PLL data table is used as is, so there is no need to have a separate table. In this way, in a terminal device that performs PLL tuning, sufficiently high-order and powerful scrambling can be realized with only slight structural changes.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional transmission side scrambling system, Fig. 2 is a block diagram of a terminal side descrambler, Fig. 3 is a block diagram of the same terminal, and Fig. 4 is a transmission side of an embodiment of the present invention. FIG. 5 is a block diagram of the descrambler on the terminal side, FIG. 6 is a block diagram of the terminal, and FIG. 7 is a signal diagram showing the key code generation procedure for each channel. 1...Converter, 2...Descrambler, 3
...FSK, 4...Controller, 5...Channel select key, 6...Address, 7...Channel display, 8...Random number generator, 9...Shift register, 10...Synchronization detector, 11, 12...
Switch, 13... Attenuator, 14... Modulator, 1
6...Shift register, 17...Synchronization detector, 1
8, 19...Switch, 20...Amplifier, 21,
22...Orgate.

Claims (1)

[Claims] 1. PLL tuning is used in the terminal
In a scrambling method in a CATV system, when an image is scrambled by compressing the horizontal synchronizing signal portion of a video signal, the PLL data and key code for tuning used for that channel are encoded by a required linear operation, The coded signal is superimposed on a signal obtained by scrambling the video signal using the key code, and the terminal side receives the tuned signal.
A scrambling method in a CATV system, characterized in that the key code is restored and descrambled by performing an inverse operation on the PLL data and the demodulated encoded signal.