On variable length codes for iterative source/channel decoding

We focus on a trellis-based decoding technique for variable length codes (VLCs) which does not require any additional side information besides the number of bits in the coded sequence. A bit-level soft-in/soft-out decoder based on this trellis is used as an outer component decoder in an iterative decoding scheme for a serially concatenated source/channel coding system. In contrast to previous approaches using this kind of trellis we do not consider the received sequence as a concatenation of variable length codewords, but as one long code word of a (weak) binary channel code which can be soft-in/soft-out decoded. By evaluating the distance properties of selected variable length codes we show that some codes are more suitable for trellis-based decoding than others. Finally we present simulation results which show the performance of the iterative decoding approach