Abstract: A method of operating a multi-standard noise immune sync pulse recovery system establishes a time window during which a sync pulse is expected. The count of a counter is stored when a sync pulse occurs as expected, the counter is reset and a sync output is generated. Successive sync pulses occurring as expected are verified by comparison with the stored counts. When a first predetermined number of successive sync pulses occur as expected, a state of periodicity is established for the signal. The window is progressively narrowed to optimize the system noise immunity responsive to a second predetermined number of sync pulses occurring as expected. Sync outputs are generated in the place of expected sync pulses that do not occur during the window when the system is in the state of periodicity. The state of periodicity is lost when a third predetermined number of sync pulses do not appear as expected and the window is progressively widened.

Abstract: A method of operating a pay per view television system in which the television signal includes a program tag and an IPPV tag identifying memory locations in subscriber authorization memories. A subscriber can self-authorize his terminal decoder to unscramble a pay per view program with a password that inputs a "1" to the memory location identified by the IPPV tag. The program tag is changed to indicate the memory location identified by the IPPV tag, thus enabling subscribers who bought the program to unscramble the signal. The head-end periodically polls each subscriber terminal to determine the status of the second memory location and to reset it to "0" after the pay per view event.

Abstract: A bit packet communication system includes a head-end having a software implemented 16 bit shift register with a plurality of feed-forward taps and a different plurality of feedback taps for simultaneously dividing and multiplying the input data bit packet to provide an output bit packet that is both encrypted and error protected. Dynamic encryption is provided by utilizing an initial preset for the software corresponding to a preset encryption key for the shift register. Authorized subscriber terminals are provided with memories and decryption keys are downloaded. The bit packets are assembled with a global bit packet encrypted with a global encryption key and subsequent individually addressed bit packets encrypted with address keys. The address keys and terminal addresses are permanently stored in the subscriber terminal memories. The global encryption keys are changed periodically.

Abstract: A bit packet communication system includes a head-end having a software implemented 16 bit shaft register with a plurality of feed-forward taps and a different plurality of feed-back taps for simultaneously dividing and multiplying the input data bit packet to provide an output bit packet that is both encrypted and error protected. Dynamic encryption is provided by utilizing an initial preset for the software corresponding to a preset encryption key for the shift register. Authorized subscriber terminals are provided with memories and decryption keys are downloaded. The bit packets are assembled with a global bit packet encrypted with a global encryption key and subsequent individually addressed bit packets encrypted with address keys. The address keys and terminal addresses are permanently stored in the subscriber terminal memories. The global encryption keys are changed periodially.

Abstract: A television signal scrambling system scrambles by suppressing horizontal syncs and changing the phase of the video carrier during the horizontal intervals. Data is transmitted by using two different widths for the horizontal intervals. Framing code information is sent by means of long pulses of two different durations during the vertical blanking interval. Three filters are utilized for dynamic scrambling, with filters A and B defining one scrambling mode and A and C defining a second scrambling mode. Corresponding descrambling filters are included in subscriber terminals and the subscriber microprocessor controllers have information downloaded as to the filter pairs to be used for descrambling based upon the receipt of the first or second framing code and a mode definition. The mode definitions are in the form of encrypted data and are dynamically changed by downloading to the subscriber terminals.

Abstract: A bit packet communication system includes a head end having a software implemented 16 bit shift register with a plurality of feed-forward taps and a different plurality of feedback taps for simultaneously dividing and multiplying the input data bit packet to provide an output bit packet that is both encrypted and error protected. Dynamic encryption is provided by utilizing an initial preset for the software corresponding to a preset encryption key for the shift register. Authorized subscriber terminals are provided with memories and decryption keys are downloaded. The bit packets are assembled with a global bit packet encrypted with a global encryption key and subsequent individually addressed bit packets encrypted with address keys. The address keys and terminal addresses are permanently stored in the subscriber terminal memories. The global encryption keys are changed periodically.