Method and apparatus for communicating digital data using trellis coded QAM

A method for communicating digital data using QAM transmission comprising the steps of:

• dividing an N-bit QAM constellation pattern into four subsets, each subset including N/4 symbol points of said constellation pattern;
• assigning a different two-bit codeword to each of said four subsets;
• encoding a symbol to be transmitted 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;
• mapping said two-bit codeword with the remaining bits of said symbol to provide a modulation function, wherein said remaining bits correlate said symbol with one of the N/4 symbol points included in the subset defined by said codeword;
• modulating a carrier with said modulation function for transmission on a communication channel;
• receiving said carrier at a receiver;
• demodulating the received carrier at said receiver to recover said modulation function;
• pruning the recovered 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;
• using said metrics in an algorithm for decoding a rate 1/2 binary convolutional code to recover said first bit;
• encoding the recovered first bit using a rate 1/2 binary convolutional encoding algorithm to recreate said codeword;
• selecting one of said plurality of bytes representing different conditional determinations in response to said recreated codeword;
• and
• combining said selected byte with the recovered first bit to provide a decoded output.

Apparatus for encoding digital data for QAM transmission comprising:

• means for parsing a symbol to be transmitted into a first bit and at least one remaining bits;
• means for encoding said first bit with a rate 1/2 binary convolutional encoding algorithm to provide a two-bit codeword that defines one of four subsets of symbol points in an N-bit QAM constellation pattern, each subset including N/4 symbol points of said constellation pattern;
• means for mapping said codeword with said remaining bit(s) to provide a modulation function, wherein said codeword forms the least significant bits of said modulation function and defines the columns of a matrix of coordinates of said constellation pattern, and said remaining bit(s) correlate said symbol with one of the N/4 symbol points included in the subset defined by said codeword and determine the size of said constellation pattern;
• and
• means for modulating a carrier with said modulation function for transmission on a communication channel.

Apparatus for decoding QAM symbol data comprising:

• means for demodulating a received carrier to recover 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;
• means for 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-2) bit portion;
• decoder means for using said metrics in an algorithm for decoding 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 codeword;
• means for selecting one of said plurality of (N-2) bit subgroups in response to said recreated codeword;
• and
• means for combining the selected subgroup with the recovered first bit to provide a decoded output.

Apparatus for encoding digital information bits for QAM transmission comprising:

• an outer encoder for encoding said information bits using an error correcting encoding algorithm to provide a symbol for transmission;
• means for parsing said symbol into a first bit and at least one remaining bit(s);
• an inner encoder for encoding said first bit with a rate 1/2 binary convolutional encoding algorithm to provide a two-bit codeword that defines one of four subsets of symbol points in an N-bit QAM constellation pattern, each subset including N/4 symbol points of said constellation pattern;
• means for mapping said codeword with said remaining bit(s) to provide a modulation function, wherein said remaining bit(s) correlate said symbol with one of the N/4 symbol points included in the subset defined by said codeword;
• and
• means for modulating a carrier with said modulation function for transmission on a communication channel.

A method for communicating digital information bits using QAM transmission comprising the steps of:

• dividing an N-bit QAM constellation pattern into four subsets, each subset including N/4 symbol points of said constellation pattern;
• assigning a different two-bit codeword to each of said four subsets;
• encoding said information bits using an error correcting outer encoding algorithm to provide a symbol for transmission;
• encoding a first bit of said symbol using an inner 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;
• mapping said two-bit codeword with the remaining bit(s) of said symbol to provide a modulation function, wherein said remaining bit(s) correlate said symbol with one of the N/4 symbol points included in the subset defined by said codeword;
• and
• modulating a carrier with said modulation function for transmission on a communication channel.