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

Simon Malinowski 1 Hervé Jégou 2 Christine Guillemot 1
1 TEMICS - Digital image processing, modeling and communication
IRISA - Institut de Recherche en Informatique et Systèmes Aléatoires, Inria Rennes – Bretagne Atlantique
2 LEAR - Learning and recognition in vision
Inria Grenoble - Rhône-Alpes, LJK - Laboratoire Jean Kuntzmann, Grenoble INP - Institut polytechnique de Grenoble - Grenoble Institute of Technology
Abstract : Variable length codes exhibit de-synchronization 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 obtained by running a length-constrained Viterbi decoder on aggregated state models approaches the one obtained with the bit/symbol trellis, with a significantly reduced complexity. It is then shown that the complexity can be further decreased by projecting the state model on two state models of reduced size.
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Contributor : Hervé Jégou <>
Submitted on : Tuesday, December 12, 2006 - 11:56:47 PM
Last modification on : Wednesday, February 10, 2021 - 3:34:23 AM
Long-term archiving on: : Monday, September 20, 2010 - 6:03:00 PM


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Simon Malinowski, Hervé Jégou, Christine Guillemot. Synchronization recovery and state model reduction for soft decoding of variable length codes. IEEE Transactions on Information Theory, Institute of Electrical and Electronics Engineers, 2007, 53 (1), pp.368 - 377. ⟨10.1109/TIT.2006.887512⟩. ⟨inria-00119600v2⟩



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