Rca Inc.

Sarnoff Corporation

Liston Abbott

Krishnamurthy Jonnalagadda

Robert E Flory

Edward Coley Fox

Guy Ward Beakley

Error correction in a data transmission system transmitting data as a sequence of data packets, each data packet containing a number of data bytes, employs parity bytes generated for each data byte in each data packet (e.g., row parity bytes) in conjunction with parity bytes for certain data bytes in predetermined data byte positions over a number of data packets (column data bytes). In a transmission arrangement, row parity bytes are generated and transmitted in a principal data channel along with the data packets, and column parity bytes are generated and transmitted in an ancillary data channel. In a receiver arrangement, row parity bytes are decoded in a principal data channel along with the data packets, and column parity bytes are decoded in an ancillary data channel and are employed to correct the data bytes in the principal data channel. A transmission system includes a transmission arrangement and a receiver arrangement communicating via a transmission medium.

Forward error correction for video signals

A method and apparatus for recovering an information carrier which has been transmitted as a sub-carrier in the lower VSB spectral region of a television signal. The invention utilizes a spectral inversion method to shift the data carrier frequency from the normal VSB spectral region to a spectral region normally associated with video information in a standard television signal. The data carrier is then recovered using a standard video demodulator and provided to a data utilization circuit, such as a QPSK demodulator.

Recovering data from a vestigial sideband of a standard television signal

A method and apparatus for reducing video crosstalk in a data carrier located within a lower vestigial sideband (VSB) of a standard television signal. Specifically, an apparatus according to the invention comprises a single bandpass filter for conditioning a VSB television signal, and a frequency interleaver for spectrally adding the data carrier to the lower VSB of the standard VSB video signal. The filter removes removing video components from the lower VSB of a standard VSB video signal, including frequencies greater than the highest frequency nominally associated with the lower VSB of the standard television signal, illustratively 250 Khz above the nominal VSB bandedge. The filter also boosts frequencies in a spectral boost region within a passband for boosting region. The boosted frequencies comprise image frequencies associated with the non-VSB spectrum attenuated by the filter. The compensation is required to ensure that the above image frequencies are not over-attenuated by a standard television receiver Nyquist filter.

Reducing video crosstalk in a data carrier located within a vestigial

A decoder for reconstructing a standard composite video signal with standard synchronizing pulses from a video signal V with only gray sync encoding E.sub.GS, of a repetition rate f.sub.GS, and comprising a first generator for generating a signal E.sub.VCO having a controllable frequency f.sub.VCO which, in the absence of frequency control, is slightly different from f.sub.GS, a second generator responsive to E.sub.VCO to form a composite blanking signal E.sub.B having a repetition rate equal to f.sub.VCO so that E.sub.B will slew with respect to E.sub.GS until E.sub.B and E.sub.GS become synchronized and a summer for summing E.sub.B and V to produce a reconstructed standard composite video signal when E.sub.B and E.sub.GS become synchronized. There is further provided a phase lock circuit for phase locking E.sub.VCO with the standard synchronizing pulses of said reconstructed video signal to maintain E.sub.B and E.sub.GS in a synchronized relationship.

TV Privacy system using gray sync

When two color television signals are transmitted over a common non-linear path, such as a transponder in a communications satellite, the two color subcarriers at slightly different frequencies cross modulate each other and produce disturbances on the screens of color monitors and receivers. The color cross talk can be cancelled by delaying alternate lines between horizontal synchronizing pulses of solely one of the television video signals by half the period of the color subcarrier at the transmitting terminal, and delaying intermediate lines between horizontal synchronizing pulses of solely the same television video signal by half the period of the subcarrier at the receiving terminal. Color synchronizing disturbances in television receivers receptive to the same one of the video signals are avoided by cancelling the color subcarrier frequency components on the horizontal synchronizing pulses of the video signal at the receiving terminal.

Cancelling cross modulation in two color TV signals passed through

In a system in which alternate lines of one color television video signal normally are delayed half the period of the color subcarrier at a transmitting terminal to minimize the cross modulation of the color subcarrier with the color subcarrier of another video signal amplified in a common amplifier such as in a satellite transponder, an intermediate line delay unit at the receiving terminal is normally operative to delay intermediate lines of the one video signal half the period of the color subcarrier, and is automatically inhibited from delaying intermediate lines of the one video signal when the received alternate lines of said one video signal are for any reasons not delayed at the transmitting terminal.

System for transmitting two color TV signals

When two color television signals are transmitted over a common non-linear path, such as a transponder in a communications satellite, the two color subcarriers at slightly different frequencies intermodulate each other and produce a disturbing flickering of color on the screens of monitors and receivers. The crosstalk is made invisible in the present system by translating the flicker to fluctuations occurring at too high a frequency to be seen. At the transmitting terminal, alternate lines of one of the television video signals are delayed by half the period of the color subcarrier, and at the receiving terminal, intermediate lines of the same television video signal are delayed by half the period of the subcarrier. The fluctuations may be made invisible to signal-monitoring instruments by passing both the delayed and undelayed television video signals through chroma averaging circuits at the receiving terminal.

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East Windsor, NJ, United States of America

Liston Abbott