Cryptography – Video cryptography – Video electric signal modification
Reexamination Certificate
1998-07-07
2001-03-27
Peeso, Thomas R. (Department: 2767)
Cryptography
Video cryptography
Video electric signal modification
C380S210000, C380S274000, C380S205000
Reexamination Certificate
active
06208737
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of audio-visual signal transmission and reception. More particularly, the present invention relates to a method and apparatus for scrambling an audio-visual signal during transmission in order to control reception and use of the signal.
BACKGROUND OF THE INVENTION
Cable and pay-per-view television programming are extremely popular and widely available in modern society. Those firms providing such programming are frequently lucrative and successful. This success comes from the ability to prevent those who have not purchased the service from receiving and using the audio-visual signals transmitted by the service provider.
In general, it is common for a cable company or other service provider to scramble its signals to prevent their use by unauthorized parties. This scrambling is intended to make the signals unintelligible to typical television sets which are not authorized to receive and use the scrambled signal. When the signal is scrambled, a conventional television will not recognize the signal, or at best, display a distorted image from the signal.
Cable companies which provide a number of channels over a cable connection may only scramble certain channels so that cable subscribers can be required to pay additional fees for receiving these “premium” channels. The premium channels are typically movie or adult channels.
Those subscribers who have paid the service provider for reception of the scrambled signal will be given equipment for use with their television sets which unscrambles the signal. With this equipment, the authorized user can unscramble and receive the service provider's signals and view the programming contained in the transmission.
A well-known conventional method of scrambling a signal to prevent its unauthorized reception is to reverse the spectral positions of the audio and video portions of the signal. Typically, an audio-visual signal will have an audio carrier signal at a first frequency and a video carrier signal at a second frequency. The carrier signals are modulated to carry the respective video and audio data of the transmitted programming.
If, however, the audio carrier signal is transmitted at the second (video carrier) frequency, and the video carrier signal is transmitted at the first (audio carrier) frequency, the signal is scrambled. A television tuner will be attempting to receive the audio signal at the first frequency and the video signal at the second frequency, and will be unable to receive the reversed signal properly.
Many other methods of scrambling audio-visual signals during transmission are known in the art. However, all are subject to various deficiencies. For example, many scrambling methods are only partially effective. Thus, while the scrambled signal is not received clearly, the image and audio may still be intelligible.
Accordingly, there is a need in the art for an improved and more effective means and method of scrambling an audio-visual signal.
SUMMARY OF THE INVENTION
It is an object of the present invention to meet the above-described needs and others. Specifically, it is an object of the present invention to provide a method and apparatus for scrambling an audio-visual signal and for receiving and unscrambling the scrambled signal that is highly effective.
Additional objects, advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The objects and advantages of the invention may be achieved through the means recited in the attached claims.
To achieve these stated and other objects, the present invention may be embodied as a method of transmitting a scrambled electronic audio-visual signal by generating a digital audio signal component of the audio-visual signal having a time base which is common to a synchronization signal of a video signal component of the audio-visual signal and a color sub-carrier signal of the video signal. Prior to generating this audio signal, the method of the present invention includes removing the synchronization signal from the video signal. The color sub-carrier signal is also preferably removed prior to broadcast of the scrambled audio-visual signal.
In conjunction with the creation of the common time base of the audio signal, the method of the present invention includes inserting a fixed digital message into a vertical interval of the video signal which is used to reintegrate the synchronization signal with the video signal.
When the scrambled audio-visual signal is received, the method of the present invention includes reconstructing the synchronization signal and the color sub-carrier signal from the common time base of the audio signal. Specifically, the steps of this inventive method may be broadcasting the video signal and the audio signal in composite; receiving the composite signal; obtaining the common time base from the audio signal; and reconstructing the color sub-carrier and the synchronization signal from the common time base.
Following reconstruction of the signal components necessary to properly display the audio visual signal, the method includes reintegrating the reconstructed synchronization signal and the reconstructed color sub-carrier signal with a video signal component of the received composite signal.
The present invention also encompasses the circuitry necessary to apply the foregoing method. Specifically, the present invention encompasses an audio-visual signal scrambler having: a synchronization separator for receiving a clear video signal and removing therefrom a synchronization signal; and an oscillator and phase locked loop circuit for receiving the synchronization signal and using the synchronization signal to generate a time base common to the synchronization signal, a color sub-carrier signal and an audio signal of the audiovisual signal.
The scrambler of the present invention also includes an audio encoder for generating the audio signal by encoding input audio signals to an audio carrier signal having the common time base; and a video encoder for inserting a fixed digital message into a vertical interval of the video signal which is used to reintegrate the synchronization signal with the video signal.
The oscillator and phase locked loop circuit includes a first reference oscillator regulated by the synchronization signal; a second reference oscillator; and a phase comparator for comparing signals from the first and second reference oscillators. The second reference oscillator is regulated by a signal output by the phase comparator and low pass filtered through a low pass filter.
A first divider circuit is provided for dividing the output of the first oscillator to generate a reference signal on which the fixed message is based; and a second divider circuit is provided for dividing the output of the first oscillator before the output of the first oscillator is input to the phase comparator.
The present invention also encompasses a descrambler for descrambling a scrambled audio-visual signal. Such a descrambler includes a tuner for receiving the scrambled audio-visual signal; a QPSK demodulator for removing a common time base from an audio carrier signal of the audio-visual signal; a clock and timing recovery circuit for receiving the common time base and generating therefrom a vertical time frame reference signal and a color sub-carrier signal phase locked to the audio carrier signal; and a video decoder connected to a synchronization and color burst reconstruction circuit for unscrambling a video signal component of the audiovisual signal using the color sub-carrier signal and the vertical time frame reference signal.
Preferably, the descrambler of the present invention also includes a video demodulator connected between the tuner and the video decoder; and an audio decoder for decoding an audio component of the audio-visual signal.
REFERENCES:
patent: 4336553 (1982-06-01), Den Toonder et al.
patent: 5161188 (1992-11-01), Pires
patent: 56
General Instruments Corporation
Jack Todd
Kananen Ronald P.
Peeso Thomas R.
Rader Fishman & Grauer
LandOfFree
Method and apparatus for television signal scrambling using... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for television signal scrambling using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for television signal scrambling using... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2501444