Method and apparatus for communicating digital information such as compressed video using treillis coded QAM

A method for decoding digital television signals containing compressed video information and transmitted using quadrature amplitude modulation, comprising the steps of:

• receiving a carrier containing said digital television signals;
• demodulating the received carrier to recover an interleaved modulation function containing said compressed video information;
• deinterleaving the recovered modulation function;
• decoding the deinterleaved modulation function in an inner trellis decoding algorithm of a concatenated decoder to recover interleaved Reed-Solomon symbols representative of the compressed video information;
• deinterleaving the recovered Reed-Solomon symbols for input to an outer Reed-Solomon decoding algorithm of said concatenated decoder, said Reed-Solomon decoding algorithm recovering variable length coded coefficients from the deinterleaved Reed-Solomon symbols;
• decoding said recovered variable length coded coefficients to recover transform coefficients representative of said compressed video information;
• inverse transforming the transform coefficients to recover video data in a pulse code modulated (PCM) or differential pulse code modulated (DPCM) format;
• processing recovered DPCM data using motion compensation to recover PCM video data represented by the recovered DPCM data;
• and
• formatting the recovered PCM video data for output to a digital television receiver,
• wherein said modulation function comprises an N-bit QAM modulation function in which a two-bit codeword identifies one of a plurality of QAM constellation subsets and the remaining N-2 bit portion represents a signal point within said one subset, said method further comprising the steps of:
• pruning the recovered modulation function to provide a set of metrics corresponding to said subsets and to provide a plurality of N-2 bit subgroups representing a plurality of conditional determinations of the signal point identified by the N-2bit portion;
• using said metrics in said trellis decoding algorithm to decode a rate 1/2 binary convolutional code to recover a first bit;
• encoding the recovered first bit using a rate 1/2 binary convolutional encoding algorithm to recreate said two-bit codeword;
• selecting one of said plurality of N-2 bit subgroups in response to said recreated two-bit codeword;
• and
• combining the selected subgroup with the recovered first bit to provide a Reed-Solomon symbol.

Apparatus for communicating digital television signals comprising:

• means for processing blocks of pulse code modulated (PCM) video data using motion estimation and compensation to provide corresponding differential pulse code modulated (DPCM) data;
• means for comparing said PCM video data to the corresponding DPCM data provided by said processing means and for selecting one of PCM video data or DPCM data for transmission based on a predetermined criterion;
• means for compressing the selected data using the discrete cosine transform to provide blocks of transform coefficients;
• means for quantizing said blocks of transform coefficients to improve the coding efficiency thereof;
• means coupled to an output of said quantizing means for variable length coding said transform coefficients;
• a concatenated coder including a Reed-Solomon outer coder and a trellis inner coder for coding said variable length coded transform coefficients to provide coded signals for transmission;
• and
• means for transmitting said coded signals as quadrature amplitude modulation (QAM) symbols from an N-point QAM constellation pattern having four subsets, each subset being identified by a different two-bit codeword and including N/4 symbol points of said N-point QAM constellation pattern;
• wherein said trellis inner coder encodes symbol from said Reed-Solomon outer coder by processing a first bit of said symbol with a rate 1/2 binary convolutional encoding algorithm to provide the two-bit codeword assigned to the subset in which said symbol resides in said constellation pattern;
• said two-bit codeword is mapped with remaining bits of said symbol to provide a modulation function, said remaining bits correlating said symbol with one of the N/4 symbol points included in the subset defined by said two-bit codeword;
• and
• said transmitting means modulate said modulation function onto a carrier, said apparatus further comprising:
• means for receiving said carrier at a receiver;
• means for demodulating said received carrier to recover said modulation function;
• means for pruning the modulation function to provide a set of metrics corresponding to said subsets and to provide a plurality of bytes representing different conditional determinations of a signal point identified by the remaining bits;
• trellis decoder means coupled to receive said metrics for use in decoding a rate 1/2 binary convolutional code to recover said first bit;
• means for encoding the recovered first bit using a rate 1/2 binary convolutional encoding algorithm to recreate said two-bit codeword;
• means for selecting one of said conditional determination bytes in response to said recreated two-bit codeword;
• and
• means for combining said selected byte with the recovered first bit to provide a decoded output.

Apparatus for decoding digital television signals containing compressed video information and transmitted using quadrature amplitude modulation (QAM), comprising:

• means for receiving said digital television signals;
• a QAM demodulator for demodulating a carrier containing said digital television signals to recover an interleaved modulation function containing said compressed video information;
• a first deinterleaver for deinterleaving the recovered modulation function;
• a concatenated decoder for decoding the deinterleaved modulation function using an inner trellis decoder to recover interleaved Reed-Solomon symbols representative of the compressed video information;
• a second deinterleaver for deinterleaving the recovered Reed-Solomon symbols for input to an outer Reed-Solomon decoder of said concatenated decoder, said Reed-Solomon decoder recovering variable length coded coefficients form the deinterleaved Reed-Solomon symbols;
• means for decoding said recovered variable length coded coefficients to recover transform coefficients representative of said compressed video information;
• means for inverse transforming the recovered transform coefficients to recover video data in a pulse code modulated (PCM) or differential pulse code modulated (DPCM) format;
• means for processing recovered DPCM data using motion compensation to recover PCM video data represented by the recovered DPCM data;
• and
• means for formatting recovered PCM video data for output to a digital television receiver;
• wherein said modulation function comprises an N-bit QAM modulation function in which a two-bit codeword identifies one of a plurality of QAM constellation subsets and the remaining N-2 bit portion represents a signal point within said one subset, said apparatus further comprising:
• means for pruning the recovered modulation function to provide a set of metrics corresponding to said QAM constellation subsets and to provide a plurality of N-2 bit subgroups representing a plurality of conditional determinations of the signal point identified by the N-2 bit portion;
• said concatenated decoder being coupled to receive said set of metrics for use in said trellis decoder to decode a rate 1/2 binary convolutional code to recover a first bit;
• means for encoding the recovered first bit using a rate 1/2 binary convolutional encoding algorithm to recreate said two-bit codeword;
• means for selecting one of said plurality of N-2 bit subgroups in response to said recreated two-bit codeword;
• and
• means for combining the selected subgroup with the recovered first bit to provide a Reed-Solomon symbol.

Apparatus for decoding transmitted digital signals to recover information therefrom, comprising:

• means for receiving a carrier containing said transmitted digital signals;
• a demodulator coupled to said receiving means for demodulating the received to recover a modulation function;
• a concatenated decoder comprising an inner trellis decoder and an outer Reed-Solomon decoder for decoding the modulation function, said inner trellis decoder recovering Reed-Solomon symbols representative of said information and said outer Reed-Solomon decoder recovering variable length codes from the Reed-Solomon symbols;
• and
• means for decoding said recovered variable length codes to recover said information;
• wherein:
• said modulation function is an N-bit modulation function in which a two-bit codeword identifies one of a plurality of constellation subsets and the remaining N-2 bit portion represents a signal point within said one subset;
• and
• said concatenated decoder comprises:
• means for pruning the recovered modulation function to provide a set of metrics corresponding to said constellation subsets and to provide a plurality of N-2 bit subgroups representing a plurality of conditional determinations of the signal point identified by the N-2 bit portion, said inner trellis decoder using said st of metrics to decode a rate 1/2 binary convolutional code to recover a first bit;
• means for encoding the recovered first bit using a rate 1/2 binary convolutional encoding algorithm to recreate said two-bit codeword;
• means for selecting one of said plurality of N-2 bit subgroups in response to said recreated two-bit codeword;
• and
• means for combining the selected subgroup with the recovered first bit to provide a Reed-Solomon symbol.