ERASURE-FREE SEQUENTIAL-DECODING OF TRELLIS CODES

An erasure-free sequential decoding algorithm for trellis codes, calle d the buffer looking algorithm (BLA), is introduced. Several versions of the algorithm can be obtained by choosing certain parameters and se lecting a resynchronization scheme. These can be categorized as block decoding or continuous decoding, depending on the resynchronization sc heme. Block decoding is guaranteed to resynchronize at the beginning o f each block, but suffers some rate loss when the block length is rela tively short. The performance of a typical block decoding scheme is an alyzed, and we show that significant coding gains over Viterbi decodin g can be achieved with much less computational effort. A resynchroniza tion scheme is proposed for continuous sequential decoding. It is show n by analysis and simulation that continuous sequential decoding using this scheme has a high probability of resynchronizing successfully. T his new resynchronization scheme solves the rate loss problem resultin g from block decoding. The channel cutoff rate, demodulator quantizati on, and the tail's influence on performance are also discussed. Althou gh this paper considers only the decoding of trellis codes, the algori thm can also be applied to the decoding of convolutional codes.