Method and apparatus for communicating digital data using trellis coded QAM
First Claim
1. A method for communicating digital data using QAM transmission comprising the steps of:
 dividing an Nbit QAM constellation pattern into four subsets, each subset including N/4 symbol points of said constellation pattern;
assigning a different twobit 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 twobit codeword assigned to the subset in which said symbol resides in said constellation pattern;
mapping said twobit codeword with the remaining bit(s) of said symbol to provide a modulation function, wherein said twobit 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) form the most significant bits of said modulation function, 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
modulating a carrier with said modulation function for transmission on a communication channel.
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Abstract
Coded modulation schemes based on codes for QPSK modulation are directly incorporated into QAM based modulation systems, forming trellis coded QAM for communicating information. Concatenated coding with QPSK based trellis coding and symbol error correcting coding is used. In an encoder, an Nbit QAM constellation pattern is divided into four subsets, each including N/4 symbol points of the constellation pattern. A twobit QPSK codeword is assigned to each of the four subsets. A symbol to be transmitted is first encoded using an outer error correcting encoding algorithm. Part of the symbol is then encoded with an inner code that comprises a rate 1/2 trellis encoding algorithm to provide a QPSK codeword, which is mapped with the remaining bits of the symbol to provide a modulation function. The remaining bits correlate the symbol with one of the symbol points included in the subset defined by the QPSK codeword. A receiver is provided to recover information from the modulation function.
120 Citations
19 Claims

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

dividing an Nbit QAM constellation pattern into four subsets, each subset including N/4 symbol points of said constellation pattern; assigning a different twobit 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 twobit codeword assigned to the subset in which said symbol resides in said constellation pattern; mapping said twobit codeword with the remaining bit(s) of said symbol to provide a modulation function, wherein said twobit 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) form the most significant bits of said modulation function, 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 modulating a carrier with said modulation function for transmission on a communication channel.  View Dependent Claims (2, 3)


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

dividing an Nbit QAM constellation pattern into four subsets, each subset including N/4 symbol points of said constellation pattern; assigning a different twobit 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 twobit codeword assigned to the subset in which said symbol resides in said constellation pattern; mapping said twobit 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.  View Dependent Claims (5, 6)


7. 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 twobit codeword that defines one of four subsets of symbol points in an Nbit 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.  View Dependent Claims (8, 9)


10. Apparatus for decoding QAM symbol data comprising:

means for demodulating a received carrier to recover an Nbit QAM modulation function in which a twobit codeword identifies one of a plurality of QAM constellation subsets and the remaining (N2) 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 (N2) bit subgroups representing a plurality of conditional determinations of the signal point identified by the (N2) 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 (N2) 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.  View Dependent Claims (11, 12, 13, 14, 15, 16, 17)


18. 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 twobit codeword that defines one of four subsets of symbol points in an Nbit 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.


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

dividing an Nbit QAM constellation pattern into four subsets, each subset including N/4 symbol points of said constellation pattern; assigning a different twobit 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 twobit codeword assigned to the subset in which said symbol resides in said constellation pattern; mapping said twobit 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.

1 Specification