PROBABILISTIC CONSTRUCTION OF LARGE CONSTRAINT LENGTH TRELLIS CODES FOR SEQUENTIAL-DECODING

Probabilistic algorithms are given for constructing good large constraint length trellis codes for use with sequential decoding that can achieve the channel cutoff rate bound at a bit error rate (BER) of 10(-5) - 10(-6), The algorithms are motivated by the random coding principle that an arbitrary selection of code symbols will produce a good code with high probability, One algorithm begins by choosing a relatively small set of codes randomly. The error performance of each of these codes is evaluated using sequential decoding and the code with the best performance among the chosen set is retained. Another algorithm treats the code Construction as a combinatorial optimization problem and uses simulated annealing to direct the code search. Trellis codes for 8 PSK and 16 QAM constellations,vith constraint lengths upsilon up to 20 are obtained. Simulation results with sequential decoding show that these codes reach the channel cutoff rate bound at a BER of 10(-5) - 10(-6) and achieve 5.0-6.35 dB real coding gains over uncoded systems with the same spectral efficiency and up to 2.0 dB real coding gains over 64 state trellis codes using Viterbi decoding.