Subscriber-limited reception television broadcast security encoder-decoder system

For use in a subscription television system, a method for scrambling and unscrambling of standard television signals having horizontal scan lines that include horizontal synchronizing signals, vertical synchronizing signals, and video signals, and accompanying audio signals to enable reception of the video and audio signals in an intelligible manner only by authorized subscribers, said method comprising the steps of:

• scrambling video signals by inversion of the video signals of some horizontal scan lines on a line-by line fashion in a pseudo-random basis to produce a picture having some video signals inverted and others not inverted which is unpleasant to view and virtually unintelligible;
• scrambling audio signals by conversion of analog audio signals to coded digital audio signals;
• generating a plurality of unique pulse coded control signals serving to identify individual subscribers which are authorized to unscramble the scrambled video and audio signals;
• transmitting the scrambled video and audio signals together with the control signals, said control signals being transmitted separately and simultaneously during each of the horizontal scan lines to determine whether or not the video portion of the next successive horizontal scan line is to be inverted;
• receiving the transmitted scrambled video and audio signals together with the control signals;
• storing a unique address code to identify a particular subscriber;
• comparing each of the pulse coded control signals with the stored address code;
• unscrambling of the video and audio signals by means of decoding pulses converted from said control signals in the same sequence as used for scrambling when the step of comparing indicates a match to provide restored video and audio signals without degradation in picture and sound qualities;
• and
• enabling continuously the unscrambling step at each individual subscriber's unit on a selective basis so that if there is no match by the comparing step before a pre-selected time interval has elapsed the step of unscrambling is automatically disabled.

For use with receivers in a subscription television system, a method for unscrambling of standard television signals scrambled by inversion of video signals of some horizontal scan lines on a line-by-line fashion in a pseudo-random basis to enable reception to transmitted scrambled video signals in an intelligible manner only by authorized subscribers, said method comprising the steps of:

• receiving the transmitted scrambled video signals together with a plurality of unique pulse coded control signals which are transmitted separately and simultaneously during each of the horizontal scan lines to determine whether or not the video portion of the next successive horizontal scan line is to be inverted, said control signals identifying individual subscribers which are authorized to unscramble the scrambled video signals and providing information needed to unscramble the transmitted scrambled video signals;
• storing a unique address code to identify a particular subscriber;
• comparing each of the pulse coded control signals with the stored address code;
• unscrambling of the video signals by means of decoding pulses converted from said control signals in the same sequence as used for scrambling when the step of comparing indicates a match to provide restored video signals without degradation in picture quality;
• and
• enabling continuously the unscrambling step in response to said plurality of control signals on a selective basis so that if there is no match by the comparing step before a pre-selected time interval has elapsed the unscrambling means is automatically disabled.

For use with receivers in a subscription television system, an apparatus for unscrambling of standard television signals scrambled by inversion of standard television signals scrambled by inversion of video signals of some horizontal scan lines on a line-by-line fashion in a pseudo-random basis to enable reception of the video signals in an intelligible manner only by authorized subscribers, said apparatus comprising:

• means for receiving the transmitted scrambled video signals together with a plurality of unique pulse coded control signals which are transmitted separately and simultaneously during each of the horizontal scan lines to determine whether or not the video portion of the next successive horizontal scan line is to be inverted, said control signals identifying individual subscribers which are authorized to unscramble the scrambled video signals and providing information needed to unscramble the transmitted scrambled video signals;
• means for storing a unique address code to identify a particular subscriber;
• means for comparing each of the pulse coded control signals with the stored address code;
• means responsive to said comparing means when there is a match for unscrambling of the video and audio signals by means of decoding pulses converted from said control signals in the same sequence as used for scrambling to provide restored video signals without degradation in picture quality;
• and
• controlling means responsive to said plurality of control signals for continuously enabling each of the individual unscrambling means at a particular subscriber receiving means on a selective basis so that if there is no comparison by the comparing means of an individual subscriber before a pre-selected time interval has elapsed the unscrambling means is automatically disabled.