Sync suppression scrambling of television signals for subscription TV
First Claim
1. The method of sync suppression scrambling of TV signals having video signals with horizontal and vertical sync pulses and audio signals for subscription TV programs which comprises the steps of generating sync suppression pulses in overlapping time relationship with at least the horizontal sync pulses, generating timing pulses in selected time relationship with said sync suppression pulses such that each of said timing pulses and each of said suppression pulses have a selected delay with respect to each other, said selected time relationship being less than the duration between successive horizontal sync pulses selected from a plurality of different delays and a dynamically variable delay, suppressing in amplitude said horizontal sync pulses with said suppression pulses to scramble said TV signals, modulating said audio signals with said timing pulses to encode said TV signals, transmitting said scrambled and encoded TV signals from a transmitting station to receiving stations, deriving said timing pulses at said receiving stations, delaying said derived timing pulses with said selected delay to provide delayed timing pulses, generating restoring pulses in overlapping time relationship with said horizontal sync pulses upon occurrence of said delayed timing pulses, and restoring said horizontal sync pulses in amplitude with said restoring pulses to descramble said TV signals at those of said receiving stations which are authorized to receive subscription TV.
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Accused Products
Abstract
In order to provide higher efficiency of security in sync suppression scrambling of subscription TV signals, the signals are encoded with a timing pulse having a selected time delay relationship with the suppressed horizontal sync intervals of the TV signals. The timing can be implemented digitally by selecting a plurality (e.g., 12) of different timings. The timing can also be dynamically varied. The TV signals are descrambled by restoring the sync pulses at only those receiving stations authorized to receive the premium subscription programming which have circuits for generating restoring pulses with the selected time relationship upon reception of the timing signals. Accordingly, the use of unauthorized descramblers, which are insensitive to the timing signals or do not provide the restoring pulses in proper time relationship, is discouraged.
170 Citations
40 Claims
- 1. The method of sync suppression scrambling of TV signals having video signals with horizontal and vertical sync pulses and audio signals for subscription TV programs which comprises the steps of generating sync suppression pulses in overlapping time relationship with at least the horizontal sync pulses, generating timing pulses in selected time relationship with said sync suppression pulses such that each of said timing pulses and each of said suppression pulses have a selected delay with respect to each other, said selected time relationship being less than the duration between successive horizontal sync pulses selected from a plurality of different delays and a dynamically variable delay, suppressing in amplitude said horizontal sync pulses with said suppression pulses to scramble said TV signals, modulating said audio signals with said timing pulses to encode said TV signals, transmitting said scrambled and encoded TV signals from a transmitting station to receiving stations, deriving said timing pulses at said receiving stations, delaying said derived timing pulses with said selected delay to provide delayed timing pulses, generating restoring pulses in overlapping time relationship with said horizontal sync pulses upon occurrence of said delayed timing pulses, and restoring said horizontal sync pulses in amplitude with said restoring pulses to descramble said TV signals at those of said receiving stations which are authorized to receive subscription TV.
- 6. The method of scrambling and encoding TV signals containing video signals with horizontal and vertical sync signals in horizontal and vertical intervals in each line and frame respectively of the picture represented by said video signals, and also containing audio signals which comprises the steps of generating sync suppression pulses occurring in said horizontal intervals and attenuating said video signals with said pulses to remove the horizontal sync pulses from said video signals to scramble said TV signals, generating timing pulses each with a selected delay with respect to said suppression pulses, said selected delay being less than the duration between successive horizontal sync signals selected from a plurality of different delays and a dynamically variable delay, and modulating said audio signal with said timing pulses to encode said TV signal with information representing the scrambling thereof.
- 14. The method of decoding and descrambling TV signals which have been scrambled by suppression of said TV signals during intervals overlapping the horizontal sync signals thereof and encoded with timing signals on the aural carrier thereof having a selected delay with respect to said horizontal sync signals, said selected delay being less than the duration between successive horizontal sync signals selected from a plurality of different delays and a dynamically variable delay, which comprises the steps of detecting said timing signals, generating restoring pulses each have said selected delay with respect to said timing signals, and restoring said TV signals to normal amplitude during intervals including said horizontal sync signals with said restoring pulses.
- 21. A sync suppression scrambler subscription TV system which comprises means for generating at a transmission point, repetitively, a timing signal and a sync suppression signal which have a selected time delay relationship, said selected time relationship being less than the duration between successive horizontal sync pulses selected from a plurality of different delays and a dynamically variable delay, means for locating both said signals in time with respect to successive intervals of said TV signal each having a horizontal sync pulse thereof such that said suppression signal and horizontal sync intervals are coincident, means for suppressing said TV signal in amplitude during said interval with said suppression signal to suppress said horizontal sync signals, means for transmitting said TV signal with said horizontal sync signals suppressed and with said timing signal on the aural carrier of said TV signal to receiving stations, means for use at said receiving stations responsive to said timing signals for generating restoring signals which have said selected time delay relationship with said timing signals such that said restoring signals are coincident with at least a portion of said horizontal sync intervals which contain said horizontal sync signals, and means responsive to said restoring signals for increasing the amplitude of said TV signals in said portion of said horizontal sync interval to restore the amplitude of said horizontal sync signals so that, at those of said receiving stations which are authorized, subscription TV programs can be displayed.
Specification