Abstract: A television system includes a plurality of complementary transmitter and receiver stages for processing an HDTV signal to minimize co-channel interference to and from NTSC signals, thereby facilitating the use of so-called "taboo" channels for the transmission of HDTV signals. The HDTV signals are encoded for transmission in a format exhibiting dominant periodicities equivalent to that of NTSC to further minimize such co-channel interference.

Abstract: A video signal comprising a successive series of frames is sub-band coded to derive a plurality of groups of coefficients for each frame. Each group of coefficients comprises a spectral representation of the video content of a respective portion of the frame, which portions are spatially decorrelated relative to the corresponding portions of the immediately preceding and immediately following frames to reduce block artifacts in the reproduced image.

Abstract: A video signal transmission system includes a dispersal filter having a variable dispersal characteristic for time dispersing a video signal. The filter is supplied with dispersal coefficients from a ROM for continually varying its dispersal characteristic over each line of the video signal. The low frequency content of the video signal is removed and the resultant high frequency video signal is applied to the dispersal filter. The variably dispersed video signal is combined with data, including a coded representation of the low frequency portion and transmitted. A receiver receives the dispersed signal, removes the data and applies the dispersed signal to an inverse dispersal filter that is supplied with dispersal coefficients from a ROM for providing a complementary (inverse) time dispersal function for recovering the high frequency video signal. The data is decoded and the low frequency portion reconstituted and combined with the high frequency video signal.

Abstract: A television signal transmission signal comprises a suppressed carrier, VSB signal having respective Nyquist slopes at the lower and upper edges of a 6 MHz television channel, the center frequency of the Nyquist slope at the lower edge of the channel being substantially coincident with the frequency of the suppressed carrier, and a pilot signal in quadrature relation with the suppressed carrier. The suppressed carrier is modulated by an N-level digitally encoded signal having a sample rate fs substantially equal to three times the NTSC color subcarrier frequency, with the frequency of the color subcarrier being less than the co-channel NTSC picture carrier by an amount equal to about fs/12. The received signal is demodulated by a synchronous detector in response to the received pilot signal and interfering NTSC beat components are attenuated by a linear filter having notches at fs/12, 5fs/12 and fs/2.

Abstract: A co-channel interference reduction system for digital high definition television includes a transmitter having a modulo 4 processing precode filter. A receiver includes a pair of selectable video processing modes. The first mode provides a comb filter for removing co-channel interference signals together with a modulo 4 interpreter for restoring the four level data signal despite the intersymbol interference signal introduced by the comb filter segment. In the alternate mode operable in the absence of co-channel interfering signals, a level slicer and postcoder are used to restore the precoded signal to the original four level data signal.

Abstract: A 787.5 line progressively scanned wideband video signal is sub-band coded for providing a plurality of (9.times.9) blocks of spectral coefficients, each representing a respective spatial portion of the video signal. Each block of coefficients is transmitted in truncated form and received by either a first receiver or a second receiver. The first receiver processes the received coefficients for deriving a (9.times.9) block of video pixels corresponding to each block of coefficients and produces a high resolution 787.5 line progressively scanned video image in response thereto. The second receiver processes the received coefficients for deriving a (6.times.6) block of video pixels corresponding to each block of coefficients and produces a lower resolution 525 line progressively scanned video image in response thereto.

Abstract: A television system includes a plurality of complementary transmitter and receiver stages for processing an HDTV signal to minimize co-channel interference to and from NTSC signals, thereby facilitating the use of so-called "taboo" channels for the transmission of HDTV signals. The HDTV signals are encoded for transmission in a format exhibit dominant periodicities equivalent to that of NTSC to further minimize such co-channel interference.

Abstract: A hybrid television signal of less transmission power or better signal to noise performance is made up by removing low frequency analog components from the video signal, digitizing them and sending them as data in non-active video portions of the transmitted signal. A two step hybridization process, with the first step removing the line averaged value of the video components of the video signal and the second step removing the remainder of the video components under 200 KHz, is described. Temporal filtering, signal pre-emphasis, compression, dispersal and double sideband suppressed carrier modulation about a centered carrier are disclosed for reducing peak signal amplitudes and for minimizing co-channel interference to and from NTSC signals. In an FM implementation, the benefits of the hybrid signal are realized as a reduction in bandwidth and consequent improved noise performance. The hybrid signal system is uniquely adapted to a high definition television signal in a limited frequency channel.

Abstract: A hybrid television signal of less transmission power or better signal to noise performance is made up by removing low frequency analog components from the video signal, digitizing them and sending them as data in non-active video portions of the transmitted signal. A two step hybridization process, with the first step removing the line averaged value of the video components of the video signal and the second step removing the remainder of the video components under 200 KHz, is described. Temporal filtering, signal pre-emphasis, compression, time dispersion and double sideband suppressed carrier modulation about a centered carrier are disclosed for reducing peak signal amplitudes and for minimizing co-channel interference to and from NTSC signals. Time dispersion is done horizontally, vertically or both to reduce the peak signal amplitudes. Time dispersion in conjunction with low frequency removal and temporal filtering is preferred.

Abstract: A high definition television system includes an encoder for encoding a video source signal having a horizontal bandwidth of about 28-30 MHz for transmission through a 6 MHz RF channel. The video source signal is provided in the form of a plurality of horizontal video lines occurring at a vertical rate equal to the NTSC field repetition rate and at a predetermined horizontal rate greater than the NTSC horizontal scanning rate. The video lines of the source signal are encoded for transmission at NTSC vertical and horizontal rates, with the lines representing the lower frequencies of the video source signal being transmitted at a higher temporal rate than the lines representing the higher frequencies. The transmitted lines are converted to a plurality of display lines by a receiver for display at a vertical rate equal to the NTSC field repetition rate and at a horizontal rate equal to the predetermined horizontal rate.

Abstract: A method of transmitting a video signal includes separating one or more parts of the video signal into a high frequency component and a low frequency component, encoding the low frequency component using an adaptive delta modulation process and transmitting the encoded low frequency components during non-active intervals of the high frequency component. In one embodiment, the high frequency component is encoded using an entropy code. A receiver is provided for reconstructing a video signal in response to the received encoded signals.

Abstract: A method of operating a pay per view (PPV) television system includes transmitting global data packets alternately encrypted with two different session keys. Subscriber terminals store three session keys, and automatically sequence through the session keys in an ateempt to decrypt the data packets. A program tag in the global data packet identifies a television program and a memory location in the subscriber authorization memory and may also include a tag identifying an upcoming program for which the subscriber may self-authorize his terminal by accessing the memory location identified by the PPV tag. The program tag is required to enable the subscriber terminal descrambling means to descramble the accompanying television program. Subscriber terminals are periodically polled by addressed data packets whereupon the contents of their authorization memories are sent to the cable heat-end for billing purposes. After successful polling, a new session key is downloaded to the subscriber in an addressed data packet.

Abstract: A reduced co-channel interference television transmission system includes a transmitter that transmits a video signal dispersed in one sense and a receiver having a selectively reversible dispersal filter for recovering the transmitted signal. The transmitted signal includes data concerning the sense or direction of the transmitter dispersal filter. The data is received by the receiver and used to automatically select the correct sense of the receiver dispersal filter. A SAW implementation of a reversible dispersal filter is shown.

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 transmission system for minimizing the visibility of ghost images develops a transmission signal having groups of video information alternately reversed at the group rate. The resultant signal corresponds to a signal generated by scanning an image in one direction for a predetermined time and scanning the image in the opposite direction for a predetermined time. The transmitted signal and any ghost signals received by a receiver result in a pair of ghost images, one on each side of the real image. The visibility of the ghost image is reduced by approximately one-half. In one version, video processing is reversed on a horizontal line basis. In the field version of the invention, video processing is reversed for each successive field and successive pairs of fields are averaged in the receiver to minimize flicker of the ghost images.

Abstract: A television encoding system passes a modulated video carrier through a pair of SAW filters for attenuating and reversing the phase of the carrier during horizontal intervals. Another pair of SAW filters impart intermediate amplitude and phase changes to the video carrier during transitions into and out of the horizontal intervals to minimize switching transients and frequency disturbances in the color and audio carriers.

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 TV scrambling system includes means for scrambling a TV signal by phase reversing the carrier at a horizontal rate. A sound masking circuit includes a phase locked loop which operates at five times the horizontal frequency. The program sound signal is used to frequency modulate the VCO in the phase locked loop and the output is added to the regular program sound for modulation onto an RF carrier to create an interfering sound signal. Detection of the program sound signal in an unauthorized receiver is accompanied by beating between the 5 H harmonic of the phase reversal frequency and the interfering sound signal, which masks the program sound.