FR2501948A1 - DEVICE FOR INTERFERENCE AND RESTITUTION AFTER INTERFERENCE OF A TELEVISION VIDEO SIGNAL - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS BOTH A DEVICE FOR JAMMING A TELEVISION VIDEO SIGNAL AND A DEVICE FOR RESTITUTING THE VIDEO SIGNAL AT THE RECEPTION LEVEL WHERE THE JAMMING IS ELIMINATED. THE JAMMING DEVICE CONSISTS OF A VIDEO PROCESSING UNIT 13 RECEIVING THE VIDEO SIGNAL, AND MODULATION 12 AND AMPLIFICATION UNITS 16 WHICH INTRODUCE THE SIGNAL INTO A PARASITING FILTER 18 WHICH ALLOWS THE JAMMING. THIS FILTER INTRODUCES A FREQUENCY DEPENDENT DELAY IN THE VIDEO SIGNAL. THE RECEPTION RESTITUTION DEVICE INCLUDES SIGNAL PROCESSING ELEMENTS AS WELL AS A DELAY DEVICE HAVING A CHARACTERISTIC DEPENDING ON THE FREQUENCY ESSENTIALLY REVERSE FROM THAT OF THE PARASITING FILTER 18. APPLICATION TO VIDEO SIGNAL JAMMING TO OPERATE THE VIDEO SUBSCRIPTION TYPE.

Description

The present invention relates to scrambling and restitution after

  interference with television video signals and in particular the application to the video signal of a frequency-dependent delay while at the receiver

  the opposite of such a delay to the video signal.

  The main subject of the present invention is a video interference transmitter and receiver of the type indicated where the delay characteristics are introduced.

by a parasitic filter.

  Another object of the present invention is a video scrambling system in which the filter of

  interference works as a band-pass device.

  Yet another object of the present invention is a video scrambling system in which the filter

  interference works as a low-pass device.

  An object of the present invention is also

  a video scrambling system in which the characteristics

  delay devices are variable either by the delay device itself or by using

several such devices.

  Finally, another object of the present invention is a video scrambling system in which the delay is applied to the video signal by coupling devices.

charge.

  Other features of the present invention

  will appear in the following description of

  embodiments of the present invention which are given by way of non-limiting example and shown in the drawings, in which: Figure 1 is a block diagram of a

  exciter modulator of television comprising the arrangement

  delay device with interference filter according to the present invention;

  FIG. 2 is a schematic block diagram of a

  positive feedback after interference used with the transmitter of Figure 1; FIG. 3 is a diagram illustrating an alternative embodiment of the interference filter.

  FIG. 4 is a schematic diagram similar to FIG.

  bling to that of Figure 1 and showing the implementation of

  interference interference filter interference of Figure 3, in the case of a television transmitter; FIG. 5 is a block diagram of a scrambling playback device operable with the scrambling device of FIG. 4; and - Figure 6 is a block diagram showing

  a variant of the present invention.

  As a result of the significant progress in television equipment and given the different types of programs available, an important market has developed over the last twenty years in the direction of television.

  pay television or television by subscribing.

  During the same period, an almost unlimited number of scrambling and restaging systems after scrambling video signals have also been developed. The scrambling systems having a certain complication are thus more reliable but have the disadvantage of a high cost price. while the temptations!

  have the disadvantage of allowing looting of the signals.

  The present invention provides a scrambling system

  which is both a low price and reliable.

  An interference filter with frequency-dependent delay characteristics is used as the primary component determining interference and restitution after interference. The characteristics of the interference filter can be fixed; it is possible to have several such interference filters connected in parallel as well as switching devices for connecting different filters at different times, or the characteristics of the interference filter may themselves be variable on a time basis and

ordered way.

  If we first consider the application of a

  the only interference filter with

  variable, the frequency function of said filter is given by the equation: H (jw) = exp [-x (WW) 2 + j 2 (-w 22] so + exp [-x (t)> 2 _ jy ( *) 2] (oo (1) ox and y are paramters of the desired mode of scrambling

  and w0 is the nominal carrier frequency of the modu-

  in radians per second. Restitution after scrambling is accomplished by essentially providing an inverse filter applied to the receiver of an individual subscriber, the frequency function of the filter at the receiver being given by: H (jw) = exp [-x (<- W) 2 _ jy (w -_ ()] doo + exp [-x (+ w-) 2 + jyQtJ0>] (2) When Hd and Hs are cascaded, as in

  the case where they apply to the video signal under conditions

  interference and restitution after interference, the resulting mathematical expression of the wave is as follows: Hd (j,) H (I) = exp [2x (t-w) 2] + exp (-2x (tW + ) 2] dsoo + 2exp rx (there-w) 2] exp [- <(w) 2] exp [2jy (i + tW)) 2 2

0 0 '

  (3) The last term of equation (3) is essentially zero when x and wo are chosen to make Hd and Hs passband filters. Thus, the bandwidth of Hd and Hs is of the order of 1, which indicates

  that if x is small enough compared to reciprocal

  As the modulated video bandwidth, the cascading of scrambling and scrambling filters leaves unchanged the final video signal. Since usually a video signal needs a bandwidth of 4 MHz, as shown below in more detail, x will have an amplitude of 7.9 x 1016

  Figure 1 shows a particular implementation

  particular of the interference filtering principle according to the present invention. A carrier generator 10 provides the usual modulation carrier wave and is connected to an input of a field effect transistor video modulator 12. The input video signal is applied to an

  video processor 13 which feeds the other input of the

  12. The output of the modulator 12 is connected to a medium frequency shaping circuit 14 whose output is connected to the buffer amplifier 16. The output of this buffer amplifier 16 constitutes the input of an interference filter. 18 having the characteristics set forth in equation (1). Such filters are well known in the art and do not have specific component designations, but are manufactured according to the requirements of the

  prospective customer. In this application,

  In particular, surface acoustic wave (SAW) devices are the most effective type of interference filter. The output of the interference filter 18 is

  connected to the medium frequency amplifier 20 whose output

  tie, in turn, is connected to a high converter

visual 22.

  A UHF (microwave) generator 24 is connected to a multiplier 26 whose output is connected to an automatic level control circuit 28 which works in conjunction with a detector 30 and a broadband power amplifier and doubler 32. The output of the doubler 32 is connected to a splitter device 34 whose output, in turn, is connected to the visual converter 22. This circuit is particularly suitable for a UHF television channel for subscription. Thus, the output of the converter 22 is the video signal modified by the delay characteristics of the interference filter and raised

  at the frequency of the particular UHF channel.

  As in most subscription television systems, the sound can also be scrambled. The sound does not have to be scrambled

  however, a sound processing unit is exposed here.

  The sound input is connected to a sound processor 36 which is applied to an input of a sound modulator 38 whose other input is fed by a carrier generator 40. The output of the modulator 38 is connected to a series of filters not granted indicated in 42 and whose exit

  of the last filter is connected to the buffer amplifier 44.

  An interference filter 46 having the same characteristics as the interference filter 18 is connected to the output of the amplifier 44 and its output is in turn connected to the medium-frequency amplifier 48. The amplifier 48 is connected to a converter 50 which receives the other output of the splitter 34 for the purpose of raising the output signal to that of a conventional UHF channel. Thus, the output of the transmitter is constituted by the video signals and its raised to a suitable UHF level if this must be the transmission medium, the two sound and video signals being then delayed according to a frequency-dependent process by the application of modulated sound and video carrier waves to

  interference with the characteristics of the equa-

tion (1).

  To restore the video after jamming, the subscriber's receiver must understand the illustrated circuit

  In FIG. 2, a mixer 52 has a received input

  video signal and another input receiving a

  sinusoidal wave of a frequency selected so as to provide

  a mixer output with an intermediate frequency

  f0. A buffer amplifier can also be inserted at this point if necessary. The scrambled video signal

  at frequency fo is applied to the inverse filter of para-

  54 having the characteristics described by the equation

  tion (2). Thus, the output of the interference filter 54 will be a video signal no longer including the delay applied at the transmitter. The unaltered video signal is then ready for processing and use in the subscriber's receiver. The output of the interference filter 54 is applied to a second mixer 56 which receives a sinusoidal wave having a frequency of fx-f0, so that f is chosen so that the output frequency can be used in a subscriber receiver , normally on a channel where one does not diffuse locally. The output of the mixer 56 is applied to the amplifier 58 and then to a resistive combination network 60 which is conventional and which is used to supply all the local broadcast channels to the input of the receiver.

television.

  The determination of x and y in the above equations

  depends on the degree to which it is necessary to

  twist or render unusable the video signal for a conventional receiver. The impulsional response of a interference interference filter of the type described is given by the inverse Fourier transform H sj) which is shown to be essentially the following: h (t) = exp-! - l cos (1t + ---- t01 x [+ y) e4 (x + 2 +) (4) It should be noted that: tan 20 = y (5) y As the cascade of interference filters, scrambling and restitution after interference, must let the video signal of 4 MHz without alteration, it follows from equation (3) that for a loss of 2dB signal at the edge of the bandwidth of 4 MHz: 2x (4 x 106 x 2) 2 = 1 6) (6) or x = 7 9 x o1016 (7)

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  At the moment when the interfering filter causing the interference receives a step variation which may be for example a sudden change from a very dark image to a very white one, the delay characteristics of the interference filter make sure that what is normally an abrupt change becomes substantially a mixture of hues ranging from deep darkness to white to gray. In fact, the smoothness of the video> the normal state becomes a blur in the state of

  distortion. To allow a reinforcement of the

  When the interference filter receives a pulse of this type, it is appropriate to make it react during

  about 60 microseconds or during the duration of a line.

  This has the advantage of providing streaks in the bar zone.

  where there is a change in the hues of the color. Thus, for the iipu.sioni response to go down to - at 60 microseconds x (60 x 10-6) 2 (8) 4 (x '+ y or y = 8.4 x 10-6) (9) It should be noted that the parameter y is substantially larger than the parameter x as explained above in equation (7), in this way the parameters of the interference filters are chosen, and they can be modified according to the distortion characteristics

of the video signal that we are looking for.

  In practice, a more realistic form of the interference filter could be that where the response to a pulse would be a reaction lasting about 30 microseconds. The interference filter described in connection with FIGS. 1 and 2 is a band-pass filter. You can also have a noise filter using low pass characteristics. Such an embodiment specifically involves the separation of the video signal into in-phase and quadrature components, the separate filtration of such coroepsantes and then the reconstitution of the video signal with application of a modulation carrier wave. With reference to FIG. 3, it can be seen that the input baseband video signal is applied to a mixer 62 which receives a CosO0t modulation carrier wave. A second mixer 64 is in contact with a modulating carrier wave sin w0t. Each of the products resulting from the mixers is applied to filters of

  interference in phase and in quadrature with the characteristics

  following ticks H (ja) = ej CoYos V 10 (l 0) H (jw) = exw sinyu32 (II) The interference filter in phase connected to the mixer 62 is designated by the reference number 66 and its output is applied to one of the addition circuit inputs 68. The quadrature interference filter 70 connected to the

  mixer 62 has its output connected to the addition circuit 72.

  Likewise, the quadrature filter 74 connected to the output of the mixer 64 has its output connected to the addition circuit 68, while the interference filter 76 connected in phase

  at the mixer 64 has its output connected to the addition circuit 72.

  The in-phase and quadrature components of the implementation of the low-pass filter illustrated in FIG. 3 are respectively connected to the mixers 78 and 80 which, again, receive modulating carrier waves Cos w0t and sin w0t. The outputs of the two mixers are combined by addition into an adder 82 whose resultant output will be the video signal having the characteristics of equations (10) and (11) and to which the waveform is applied.

Modulation carrier cot.

  FIG. 4 illustrates the implementation of the low-pass filter structure of FIG.

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  transmitter. Since most of the components of FIG. 4 are identical to those of FIG. 1, the same reference numbers have been assigned to them. The interference filter structure is illustrated at 84 and receives its input from the buffer amplifier 16. A timing device 86 receives an input of the carrier wave from the carrier wave generator 10. The phase shift device 86 provides a quadrature carrier wave to the low pass interference filter to be used as shown

  Figure 3. The carrier wave in phase is provided directly

  Also, a low-pass interference filter 88 and a phase shift device 90 are connected to the audio side of the transmitter circuit. The transmitter of Figure 4 operates in all respects from the

  same way as the transmitter of Figure 1.

  Fig. 5 illustrates the scramble rendering device for use in conjunction with the low pass interference filter transmitter type of Fig. 4. 92 designates a high frequency input circuit; it provides a modified video wave output at a frequency f0. A carrier detector 94 is connected to a phase shifter 96 to provide carrier signals in

  phase and in quadrature to a filter structure of para-

  low-pass sink 98 which is substantially the opposite of the structure shown in FIG. 3 and used in the transmitter system of FIG. 4. The high-frequency input circuit 92 supplies a modified video wave to another input of FIG. interference filter 98. The output of the interference filter 98 is applied to a mixer 100 which receives at an input a sinusoidal wave of a frequency fx-f in order to provide a video signal output at the frequency fx which will usually be a channel no

  used locally. This signal is applied to a combination

  resistor 102 similar to that of FIG.

  putting in to provide a set of television signals

to the receiver of the subscriber.

  While the interference filters of FIGS. 1 and 2 may be surface acoustic wave type devices, the low-pass filter structure of the

  Figure 3 is best implemented in use.

  reading charge-coupled devices.

  The various embodiments described,

  designed to apply the technique of interference filters, provided for a single interference fiiter

  providing the video signal with frequency-varying delays.

  Fig. 6 illustrates a configuration in which a plurality or a series of interference filters are used with a pre-established command determining u-3l.

  Interference filter is in circuit at a given moment.

  A buffer amplifier 104, cili may for example be the same as the buffer amplifier 16 of Figures I and 4, is connected to three bandpass interference filters 106, 108 and 110 which represent the filter n iv n 2 and born m from the Serie. The outputs of the fi.ltres are each connected

  pin-shaped diode switches, respectively

  112, 114 and 116. Each of the diode converters receives on the inputs indicated by arrows filter control signals which are implemented at a given time. The outputs of the switches

  diodes are connected to a resistive combiner 118.

  As the order type corresponding to the

  Figure 6 requires the same configuration at the receiver, it is necessary to provide a data path between the transmitter and the receiver, so that variations in the implementation of

  Interference filters can be tracked by the receiver.

  These data paths are well known in the art in question; they may be a normally unused part of a video signal, video subcarrier, sound subcarrier or other available transmission path. If we look in particular at the low-pass filter configuration of FIG. 3, it will be seen, as indicated above, that it can be implemented most suitably by means of charge-coupled devices. Preferably, the signal will be sampled by

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  for example, at three or four times the chroma frequency (saturation), the samples being supplied to two filter-shaped charge-coupled devices which are equivalents, for sampling, of time-delay lines. With regard to the two filters, the tap weights are respectively samples of function Hp or Hq whose parameters are given by the following equations

1 0X 60 X 1-G 2.

  (12) 4 (x '+ y 2) y = 8.4 x 1 (13) The analog samples can then pass through a hold circuit and be filtered at the video bandwidth. Each will be remodulated on phase-shifted carriers

  of 90, as indicated specifically in Figure 3.

  It is also possible to apply

  in digital process the principle of scrambling in phase and in quadrature. The samples can be paced as above, for example at three or four times the chroma frequency, but then are quantized at 12 bits, a number chosen to ensure an adequate ratio

  between the signal and the quantization noise power.

  The interference filter is then implemented using

  classical digital processes, in a

programmable digital positive.

  It is obvious that the present invention has been described and illustrated only in the form of nonlimiting exemplary embodiments and that variants may be

  introduced without departing from its scope.

Claims (13)

  1. Device for effecting a jamming of a   television video signal, characterized in that   takes a delay device (18) whose characteristic is dependent on the frequency, and a device (13) for applying a video signal to said delay device (18); Interference device according to Claim 1, characterized in that the delay device (18) has   a characteristic according to the frequency corresponding to   to the following formula: H (jt) = exp [-x (-wo) 2 + jy (.-. <32 s oo + exp [- (, W * o -jy (* io) 2] ox and y are parameters of the delay device and o corresponds to the nominal carrier frequency of the wave modulated in radians per second.   3. Apparatus for effecting a scrambling of a television video signal, characterized in that it comprises   a device (18) for filtering the video signal, this   positive having filters having a characteristic   delay that depends on the frequency.   4. Interference device according to the claim   3, characterized in that the delay characteristic of the filters corresponds to the following formula: H (ji) = exp [-x (wn) 2 + jy (iW) 2] soo + exp [-x (o 2 _ ijy (-w) t 3 3 ox and y are parameters of the filters and wo corresponds to the nominal carrier frequency of the modulated wave in radians per second.   Interference device according to claim 3, characterized in that the filters are devices surface acoustic wave.   6. Jamming device according to the claim   3, characterized in that the filters comprise in-phase (66) and quadrature (70) filters having the following formulas: ## EQU1 ##   o x and y are parameters of the filters.   7. Interference device according to the claim   6, characterized in that the modulation carrier wave is applied to the video signal both as a cosine function and as a sine function, the filters   in phase (66, 74) and in quadrature (70, 76) being applied   each of the video signal products and the functions   of cosine and sinus carriers respectively.   8. Interference device according to the claim   3, characterized in that it comprises a plurality of frequency-dependent filters (106, 108, 110) connected in parallel, as well as devices (112, 114, 116) for selecting   one of the filters at any particular time.   9. Device for reproducing after scrambling a scrambled television video signal by the application of a frequency dependent delay, characterized in that it comprises a delay device <54, 98) dependent on the frequency, whose characteristic depending on the frequency is essentially the inverse of the frequency-dependent delay device that has performed the scrambling.   10. Device for rendering according to the   cation 9, characterized in that the delay device has a characteristic as a function of frequency which corresponds to the following formula: Hd (JW) = ex [-xt (-) 2 _ iy (_-mo)] - O   + ex [--X (+ FiL,) t -iv + e) 7] where x and y are parameters of the delay device and <0 corresponds to the nominal carrier frequency of the wave modulated in radians per second.   11. Device for rendering according to the claim   9, characterized in that the delay device   is in the form of a filter (54, 98) having   Frequency dependent delay schemes.   12. Restitution device according to the claim   11, characterized in that the filter is a device surface acoustic wave.   13. Restitution device according to the   11, characterized in that the filter comprises in-phase and quadrature filter elements (96, 98) corresponding to the following formulas: -Xi2 H (jc) =, e q (jH = -e-2 sin v w2 q