Abstract: Unequal error protection is provided for an HDTV signal by separately coding each one of the classes of information in the HDTV signal by using a conventional coded modulation scheme and then time-division-multiplexing the various coded outputs for transmission. In particular, each class of information is separately coded by a 4-dimensional 8-state trellis code and a uniformly-spaced (QAM) signal constellation.

Abstract: Primary and secondary data are communicated from a transmitter to a receiver in a communication system. The value of an individual primary data word is communicated by transmitting an individual one of first plurality of channel symbols associated with that value while the value of a combined data word comprising an individual primary data word and an individual secondary data word is communicated by transmitting an individual one of second plurality of channel symbols associated with that value. In the receiver, both the primary and secondary data word values are recovered from the channel symbols thus transmitted. The approach of alternating two sets of channel symbols for transmission depending on the data word size can further apply to data communications at various fallback speeds.

Abstract: The theoretical coding gain associated with an error correction technique can be realized in a digital communications system employing this error correction by providing the equalization in the transmitter instead of the receiver. In a first embodiment, an automatic equalizer in the receiver of a digital communications system is adjusted using a training sequence. The equalizer coefficients for optimum adjustment are then transmitted back to the transmitter and supplied to an equalizer therein. After the training period is over, this transmitter equalizer, now having optimum coefficients, is activated and the receiver equalizer is disabled. In a second embodiment, the use of a training sequence can be eliminated and the receiver equalizer can be adjusted in response to actual data using "blind" equalization. The generated coefficients, as in the first embodiment, are then transmitted back to the transmitter.