Synchronization recovery and state model reduction for soft decoding of variable length codes

Abstract-- Variable length codes (VLCs) exhibit desynchronization problems when transmitted over noisy channels. Trellis decoding techniques based on Maximum A Posteriori (MAP) estimators are often used to minimize the error rate on the estimated sequence. If the number of symbols and/or bits transmitted are known by the decoder, termination constraints can be incorporated in the decoding process. All the paths in the trellis which do not lead to a valid sequence length are suppressed. This paper presents an analytic method to assess the expected error resilience of a VLC when trellis decoding with a sequence length constraint is used. The approach is based on the computation, for a given code, of the amount of information brought by the constraint. It is then shown that this quantity as well as the probability that the VLC decoder does not re-synchronize in a strict sense, are not significantly altered by appropriate trellis states aggregation. This proves that the performance obtaine...

• Type: Journal
• Year: 2006
• Where: CORR
• Authors: Simon Malinowski, Herve Jegou, Christine Guillemot
• Keywords: CORR 2006, Education, Exhibit Desynchronization Problems, Sequence Length, State Models