Reduced-complexity trellises for the joint source-channel decoding of variable-length encoded data

摘要

Many trellis-based soft decoding techniques have been proposed for data encoded using variable-length codes (VLC).udHowever, for actual VLC tables, these trellises are too complex to allow real-time soft decoding. This paper presents theudprinciple of an algorithm for grouping VLC codewords into classes, which allows significant reductions of the complexityudof the resulting trellises and of the soft decoding techniques. The adapation of decoding algorithms such as SOVA orudBCJR to the reduced-complexity trellises is detailed. Illustrations are provided on the VLC table used for texture encodingudin H.263+. The performance of a decoding technique for the localization of block frontiers in a bitstream generated byudan H.263+ coder is also presented.