Symbol-by-Symbol MAP Decoding of Variable Length Codes

Rainer Bauer and Joachim Hagenauer Institute for Communications Engineering (LNT) Munich University of Technology (TUM) e-mail: Rainer.Bauer@ei.tum.de, Hagenauer@ei.tum.de WWW: http://www.LNT.ei.tum.de Abstra t | In this paper we introduce a new approach in the decoding of variable length codes. Based on the tree structure of these codes a trellis representation is derived which allows the application of the BCJR algorithm. This algorithm provides us with the a posteriori probabilities of the transmitted source symbols. Therefore we do not only use soft information from an outer decoding stage but also produce a per symbol soft output that can be used in a successive decoding stage. We also propose a scheme where the soft output can be used in an iterative decoding structure.