Iterative source/channel decoding based on a trellis representation for variable length codes

A new trellis representation for variable length codes (VLC) is proposed which allows soft-in/soft-out decoding of these codes. Applying the BCJR-algorithm on this trellis either symbol-level or bit-level reliability information for the variable length coded sequence can be obtained. By using this soft-in/soft-out VLC decoder for iterative (“turbo”) decoding of a serially concatenated scheme consisting of an outer variable length code and an inner convolutional code separated by an interleaver significant gains can be yielded compared to a instantaneously decoded variable length code of the same overall source and channel code rate