EP0052655A4 - Procede et dispositif de brouillage et de decodage de signaux de television. - Google Patents

Procede et dispositif de brouillage et de decodage de signaux de television.

Info

Publication number
EP0052655A4
EP0052655A4 EP19810901828 EP81901828A EP0052655A4 EP 0052655 A4 EP0052655 A4 EP 0052655A4 EP 19810901828 EP19810901828 EP 19810901828 EP 81901828 A EP81901828 A EP 81901828A EP 0052655 A4 EP0052655 A4 EP 0052655A4
Authority
EP
European Patent Office
Prior art keywords
signal
television
time delayed
television signal
delayed signals
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19810901828
Other languages
German (de)
English (en)
Other versions
EP0052655A1 (fr
Inventor
Lawrence H Ragan
Clinton S Hartmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
RF Monolithics Inc
Original Assignee
RF Monolithics Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by RF Monolithics Inc filed Critical RF Monolithics Inc
Publication of EP0052655A1 publication Critical patent/EP0052655A1/fr
Publication of EP0052655A4 publication Critical patent/EP0052655A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
    • H04N7/169—Systems operating in the time domain of the television signal

Definitions

  • This invention relates to methods and apparatus for preventing a television signal from being acceptably received by an unauthorized television receiver while maintaining the television signal recoverable by an authorized receiver.
  • Subscription television is now in wide and growing use in both cable television and over-the-air systems.
  • over-the-air systems preventing unauthorized receivers from receiving the transmission is a major problem for subscription services, but even cable television systems might desire to have different classes of customers which can be serviced over the same cable. For instance, a special rate might be charged for customers who want to view certain sporting events or first run movies.
  • many systems have been developed for preventing the reception of an acceptable television signal by unauthorized receivers.
  • Synchronization pulse modification or suppression and video signal superposition are expensive to perform in the decoder function, requiring demodulation of the received coded signal, and in the case of a set top decoder, the remodulation of the signal after it has been restored to viewable condition.
  • interfering carrier systems do not require demodulation and remodulation, they have other disadvantages. Such systems can be easily defeated by persons with only modest means and effort. Extra transmitter power must be devoted to the interfering carrier. This is detrimental in cable systems, not so much for the slight penalty in consumed energy, but for the care and expense that is involved in maintaining linearity in all the amplifiers that must amplify the signals. The linearity problem becomes especially severe in over-the-air transmission systems because of the high transmitter power involved.
  • a method for preventing a television signal from being acceptably received by an unauthorized television receiver while maintaining the television signal recoverable by an authorized receiver includes passing the television signal through at least one linear filter of the type that produces multiple time delayed signals of different time delays.
  • the multiple time delayed signals are then transmitted and received. They are then passed through at least one receiver linear filter of the type that produces multiple time delayed signals of different time delays.
  • the time delays of the multiple signals of the receiver are spaced in time so that they reinforce the received multiple time delayed signals, creating one output signal which is reinforced significantly more than the remaining output signals.
  • the transmitting linear filter in different embodiments either shifts the phase of at least one of the multiple time delayed signals with respect to at least one other of the multiple time delayed signals, which can include inverting the phase of at least one of the multiple time delayed signals with respect to others, or varies the amplitude of the multiple time delayed signals with frequency or varies the time delay with frequency.
  • the receiver includes a linear filter which compensates for the function of the linear filter in the transmitter so that the final reinforced signal is a substantially true representation of the original video signal.
  • the at least one linear transmitter filter is in the signal path, but it can be in the video path prior to the video being modulated by the carrier or in the modulated carrier part of the path or right before transmission after mixing with the output of the transfer oscillator.
  • the at least one linear receiver filter can be located in various parts of the receiver's signal path.
  • a linear filter is in the video part of the signal path, then a preferred embodiment is of the charge coupled device or digital approximation type, when the linear filter is elsewhere, one preferred embodiment includes Surface Acoustic Wave devices known as SAW devices. At extremely high frequencies, a preferred embodiment of the linear filter includes ferromagnetic materials so that the signal takes on the nature of magnetostatic waves. Such linear filters can also be recursive in nature in the various embodiments.
  • FIGURE 1 is a block diagram of a system according to the present invention, including a transmitter and a receiver, for preventing a television signal from being acceptably received by an unauthorized television receiver while maintaining the television signal recoverable by an authorized receiver;
  • FIGURE 2 is a pictorial representation and schematic diagram of a linear filter of the type that produces multiple time delayed signals of different time delays for use in the transmitter of the system of Figure 1;
  • FIGURE 3 is a linear filter of the type that produces multiple time delayed signals of different time delays for use in the receiver of the system of Figure 1;
  • FIGURE 4 is a block diagram representation of another linear filter for -use in the transmitter of the system shown in Figure 1;
  • FIGURE 5 is a block diagram representation of another embodiment of a linear filter for use in the transmitter of the system of Figure 1.
  • System 10 includes an apparatus 12 for preventing a television signal from being transmitted for acceptable use by an unauthorized television receiver while maintaining the television signal recoverable by an authorized receiver and an apparatus 14 for receiving and decoding such a signal.
  • Apparatus 12 includes a means for generating a television signal, having an input 16 for a video signal, an output 18 to a transmission network 20, a signal path connecting the input to che output, a carrier oscillator 22 for generating a carrier signal, a first mixer 24 for modulating the carrier signal with the video signal, a transfer oscillator 26 and a second mixer 28 for mixing the modulated carrier signal with the output of transfer oscillator 26.
  • Transmission network 20 might typically comprise, for example, at least two antennas and associated feed lines for transmitting and receiving the signals through space, or a cable transmission system, or satellite transmission paths, or other transmission means.
  • Apparatus 12 also includes at least one linear filter in the signal path through which the signal must pass, of the type that produces multiple time delayed signals of different time delays, each time delayed signal representative of the corresponding signal at the input of the linear filter, in this case linear filter 30 located in the signal path between input 16 and first mixer 24, linear filter 32 located in the signal path between first mixer 24 and second mixer 28, and linear filter 34 located in the signal path between second mixer 28 and output 18.
  • the signal path thus includes input 16, a video frequency amplifier 36, linear filter 30, a video frequency amplifier 38, mixer 24, an intermediate frequency amplifier 40, linear filter 32, another intermediate frequency amplifier 42 , second mixer 28, a radio frequency amplifier 44, linear filter 34 and a radio frequency amplifier 46. All of the described linear filters will not be required in most systems. Apparatus 12 as shown represents three possible locations for linear filters in a transmitter which could be used singly or in concert.
  • Apparatus 14 After the signal from output 13 is transmitted tnrough transmission network 20, it is received by apparatus 14 which is a means for receiving the transmitted signals.
  • Apparatus 14 includes an impulse noise blanking circuit comprising delay line 48 which is in the signal path, impulse detector 50 which ovpasses delay line 48, and blanking switch 52 which is in the signal path, but responsive to impulse detector 50.
  • Apparatus 14 also includes means for producing a video signal from a television signal, including a local, oscillator 54 and a mixer 56 for mixing th e output of local oscillator 54 with a television signal converting the frequency of the signal to the intermediate frequency, demodulator 58 for converting the intermediate frequency to video frequency, input 60 for receiving the television signal from the transmission network, and output 62 for the video signal.
  • Apparatus 14 also includes at least one linear filter, in this case linear filter 64 located in the signal path between input 60 and mixer 56, linear filter 66 located in the signal path between mixer 56 and demodulator 58 and linear filter 68 located in the signal path between demodulator 58 and output 62.
  • the signal path through apparatus 14 thus includes input 60, delay line 48, blanking switch 52, a radio frequency amplifier 70, linear filter 64, a radio frequency amplifier 72, mixer 56, an intermediate frequency amplifier 74, linear filter 66, another intermediate frequency amplifier 76, demodulator 58, a video frequency amplifier 78, linear filter 68, another video frequency amplifier 80 and output 62.
  • Apparatus 14 represents three possible locations for linear filters in a receiving apparatus.
  • a linear filter in the present invention must include delays approximately as long as the sweep time necessary to define features of interest in the resultant picture. For example, with television systems in widespread use today, the smallest sweep time is in the horizontal direction and is approximately 50 microseconds long. If it i s desired to prevent unauthorized viewers from distinquishing features of the order of 10 percent of the sjcreen width, total delay in the linear scrambling filter set must be approximately 5 microseconds in length, disregarding delay required for spectral weighting which may be necessary to provide distortion free reconstruction of the coded signal in the unscrambling filter set.
  • the intermediate frequency output of amplifier 40 is fed to linear filter 32 by means of bond wire 82 to pad 84.
  • Pad 84 distributes the signal to metal fingers 86 which excite a surface wave in piezoelectric material substrate 88.
  • a pad 90 connects the complementary fingers of finger pairs 86 to ground return 92. The surface wave traverses the substrate and is intercepted by metal fingers 94.
  • a pad 96 connected to one of the metal fingers 94 is also connected to ground return 92 while a pad 98 connected to the complementary fingers provides input to intermediate frequency amplifier 42 by bond wire 100.
  • the output signal in this example would consist of the input signal and two replicas of the input signal at different time delays determined by the spacing between the metal finger pairs 86.
  • the three signals in the output are of equal strength, causing appearance on the television screen of an unauthorized viewer not equipped with a correct unscrambling filter, of a picture with two ghosts so strong as to deny identification of the intended picture.
  • the lengths or amount of overlap between the various finger pairs can be varied so that the output signals are not of equal strength.
  • spacing between the pairs can be varied so that the time delays are unequal in length.
  • linear filter 66 in apparatus 14 includes a bond wire 102 for transmitting the output of intermediate frequency amplifier 74 to a pad 104 and metal fingers 106.
  • a pad 108 is connected to the complementary fingers of pairs 106 as well as to receiver ground 110.
  • the scrambled signals then traverse a piezoelectric substrate 112 to metal finger pairs 114.
  • the ground side of metal finger pairs 114 is connected to ground 110 through a pad 116.
  • a bond wire 118 connects a pad 120 for the complementary fingers of pairs 114 to the input of intermediate frequency amplifier 76.
  • Metal finger pairs 106 and 114 are designed to have the reverse effect of transmitter metal finger pairs 94 and 86.
  • the three signals transmitted from metal finger pairs 106 are all received at a single time by the pairs 114 so as to reinforce the signal. There are also unwanted side lobe signals, but the side lobe signals are not as strongly reinforced.
  • An ST cut of quartz crystal is workable for the substrate.
  • the width of the substrate must take into account beam spreading and the packaging available, but will typically be between .2 inches and .25 inches.
  • the thickness will normally be as thin as possible for economic reasons, but will typically be .025 inches. For a delay in the order of 10 microseconds, the length will be in the range of 1.20 and 1.30 inches.
  • one transducer will have several tens of finger pairs and the second will have several hundred.
  • Spectral weighting will be typically included in the transmitter apparatus in systems with few transmitters and many receivers, since longer time delays are required in linear filters which include weighting.
  • a typical linear filter included in a transmitter apparatus would have up to several thousand fingers in one transducer and several tens in the other.
  • the .phase and amplitude of the scrambling filters and the descrambling filters will be typically complementary in the sense that the product of the amplitudes of their frequency responses will be essentially constant with frequency, and the total of their phase responses will be linear over the information band of interest. When these conditions are met, distortion free reconstruction of the scrambled signal is assured.
  • Linear filters which pass the signal through the delay paths one time are called transversal, while those with feedback paths such that the signal passes through the delay path multiple times are called recursive. Both types are applicable in television scrambling, and are within the scope of the invention.
  • Recursive filters are typically realized in digital and CCD form.
  • linear filter 30 includes an analog to digital converter 122 for converting the video output of video amplifier 36 into digital form, a digital filter 124 for creating multiple time delayed digital signals of different time delays, each representative of the original digital signal at the output of analog to digital converter 122, and a digital to analog converter 126 for converting the multiple time delayed digital signals at the output of digital filter 124 into multiple time delayed analog signals acceptable for input to video amplifier 38.
  • a specific embodiment 128 of linear filter 30 includes analog to digital converters 130 and 132 for converting the output of video frequency amplifier 36 into digital form, but the conversion is accomplished with clock wave forms that are 90 degrees out of phase which is known as "phase quadrature.”
  • the digital outputs of these converters is then converted to multiple time delayed outputs by digital filters 134 and 136.
  • the multiple time delayed outputs of digital filters 134 and 136 are converted back into multiple time delayed analog signals by digital to analog converters 138 and 140 respectively.
  • the multiple time delayed outputs of digital to analog converters 138 and 140 are added by means of summing network 142.
  • Rendering the signal unviewable can be accomplished in a number of ways.
  • the signal can be coded in such a way that many images appear on the screen, making the picture confusing and unpleasant to watch. If the images are placed close enough together the picture appears smeared beyond recognition.
  • Other choices of code for the scrambling filter result in the failure of the unequipped receiving set to acquire horizontal or vertical sychronization, so that the picture "tears" or "rolls", making it unacceptable.
  • Some choices of code result in transmission system efficiency improvement. Those codes for which the frequency spectra exhibits lower amplitude near the carrier frequencies in a television signal lower the average power required from the transmitter for acceptable signal to noise performance in the receiver equipped, with the corresponding descrambling filter. Other choices of code result in reductions in peak power required in the transmitter for equivalent results. These economies may in some cases outweigh the cost of the scrambling and descrambling filters, resulting in systems coded and decoded solely for transmission efficiency and economic reasons, rather than for the purpose of denying utilization by unauthorized receivers of the video information. Obviously, the scrambling could also be used in a system to achieve both signal security and transmission efficiency.
  • the system Since scrambling the television signal results in spreading it in time, the system demonstrates immunity to impulse noise, such as automobile ignition noise, picked up in the transmission path anywhere between the scrambling filter set and the descrambling filter set. Short interfering impulses are spread in time in the decoding filter set, reducing their amplitude in the output video.
  • impulse noise blanking system comprising delay line 48, impulse detector 50 and blanking switch 52 practical.
  • Impulse noise blanking for television systems in the past was of little use, since typically blanking a noise pulse would simply change a white area of the screen to a black area of the screen or vice versa, but with the present invention there is redundancy so that blanking the noise will simply create a slightly lighter patch on the screen which may not even be noticeable.
  • This same smoothing characteristic is useful in combining linear filter scrambling techniques with signal switching scrambling methods which might otherwise prove unpractical.
  • a switching scrambler added to the transmitter apparatus after the first linear filter and a switching descrambler added to the receiver before the last linear filter could be included to further scramble the signal.
  • switching can be accomplished asynchronously to the sweep rate without visible effects in the reconstructed signal when the systems are combined. Scrambling with asynchronous switching waveforms is much more difficult to defeat than scrambling with switching waveforms synchronized to the video sweep rate.
  • Asynchronous switching is not commonly used because imprecision in the descrambling apparatus which reconstructs the video results in unacceptable visible effects in the video output.
  • linear filter 30 is a linear filter of the charge coupled device type.
  • a suitable linear filter for extremely high frequency, such as linear filters 34 and 64 comprises ferromagnetic materials in the signal path and through which a signal must pass.
  • the multiple time delayed signals in such a linear filter are in the form of magnetostac ⁇ c waves of differing time delays.
  • Receiver 14 does not, of course, have to be a single unit or in a single "box". It is contemplated that in some applications, a receiver linear filter and its accompanying descrambling apparatus will be a separate unit for use in combination with a conventional television set.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)
  • Television Systems (AREA)

Abstract

Procede et dispositif permettant le brouillage et le decodage de signaux de television de maniere a empecher la reception de signaux acceptables par un recepteur de television non autorise tout en maintenant le signal de television decodable par un recepteur autorise. La presente realisation peut aussi etre utilisee pour reduire la puissance necessaire d'un signal porteur d'un emetteur de television. Un emetteur (12) envoie un signal de television au travers d'au moins un filtre lineaire (30, 32 et 34) du type produisant des signaux multiples retardes dans le temps presentant des retards de temps differents. Un recepteur (14) capte les signaux multiples retardes dans le temps provenant de l'emetteur et les envoie au travers d'au moins un filtre lineaire (64, 66 et 68) permettant d'additionner ces signaux de maniere a renforcer un signal representatif du signal a l'origine ce qui permet une reception acceptable par un poste de television autorise. Dans un mode de realisation, les filtres lineaires sont composes de dispositifs SAW. Dans un autre mode de realisation, les filtres lineaires sont du type utilisant des dispositifs a couplage de charge et dans un troisieme mode de realisation, les filtres lineaires sont du type digital. Dans un quatrieme mode de realisation, les filtres lineaires de haute frequence sont du type ferromagnetique. Differents codes de brouillage sont ainsi obtenus.
EP19810901828 1980-05-27 1981-04-06 Procede et dispositif de brouillage et de decodage de signaux de television. Withdrawn EP0052655A4 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US15316480A 1980-05-27 1980-05-27
US153164 1980-05-27

Publications (2)

Publication Number Publication Date
EP0052655A1 EP0052655A1 (fr) 1982-06-02
EP0052655A4 true EP0052655A4 (fr) 1986-01-07

Family

ID=22546033

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19810901828 Withdrawn EP0052655A4 (fr) 1980-05-27 1981-04-06 Procede et dispositif de brouillage et de decodage de signaux de television.

Country Status (3)

Country Link
EP (1) EP0052655A4 (fr)
JP (1) JPS57500908A (fr)
WO (1) WO1981003593A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1338158C (fr) * 1982-07-15 1996-03-12 John D. Lowry Chiffrement et dechiffrement (brouillage et debrouillage) de signaux video
DE3485639D1 (de) * 1983-10-31 1992-05-14 Rf Monolithics Verfahren und apparat zur fernsehverschleierung und -entschleierung.
US4682224A (en) * 1983-10-31 1987-07-21 R. F. Monolithics, Inc. System, method, and apparatus for television signal scrambling and descrambling
EP0140704A3 (fr) * 1983-10-31 1987-05-20 R F Monolithics, Inc. Procédé et appareil pour embrouillage et désembrouillage de télévision
US4682223A (en) * 1983-10-31 1987-07-21 R. F. Monolithics, Inc. Descrambler unit method and apparatus for television signal descrambling

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3936749A (en) * 1961-06-23 1976-02-03 The United States Of America As Represented By The Secretary Of The Army Matched filter communication systems
US4170757A (en) * 1977-12-30 1979-10-09 The United States Of America As Represented By The Secretary Of The Army Method of and apparatus for transmitting clandestine radio signals

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2972008A (en) * 1956-04-23 1961-02-14 Paramount Pictures Corp Coding methods and system
US4002825A (en) * 1973-07-25 1977-01-11 Summit Systems, Inc. System for encoding and decoding amplitude modulated signals
SU656239A1 (ru) * 1975-07-28 1979-04-05 Рязанский Радиотехнический Институт Устройство дл передачи и приема телевизионных сигналов
JPS5931241B2 (ja) * 1975-11-12 1984-08-01 松下電器産業株式会社 ゴ−ストジヨキヨソウチ
US4060833A (en) * 1976-04-26 1977-11-29 Rca Corporation Transducer arrangement for a surface acoustic wave device to inhibit the generation of multiple reflection signals

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3936749A (en) * 1961-06-23 1976-02-03 The United States Of America As Represented By The Secretary Of The Army Matched filter communication systems
US4170757A (en) * 1977-12-30 1979-10-09 The United States Of America As Represented By The Secretary Of The Army Method of and apparatus for transmitting clandestine radio signals

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO8103593A1 *

Also Published As

Publication number Publication date
JPS57500908A (fr) 1982-05-20
EP0052655A1 (fr) 1982-06-02
WO1981003593A1 (fr) 1981-12-10

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Inventor name: RAGAN, LAWRENCE H.

Inventor name: HARTMANN, CLINTON S.