Bidirectional sequential decoding for convolutional codes

Abstract

Sequential decoding is a very powerful decoding technique for convolutional codes. The main drawback of sequential decoding is the variability of the computational effort. Efficient bidirectional sequential decoding (BSD) algorithms are presented. With the bidirectional decoding algorithms, the tree code is searched simultaneously from the root and end nodes of the tree. It is shown that the distribution of the number of computations per decoded block of the bidirectional algorithms is still Pareto. However, the advantage of these bidirectional sequential decoding algorithms appears as an increase in the Pareto exponent, and hence in the computational variability. With the bidirectional algorithms, the Pareto exponent is twice that of the unidirectional sequential decoding (USD) algorithm. >