Synchronization recovery and state model reduction for soft decoding of variable length codes
<|reference_start|>Synchronization recovery and state model reduction for soft decoding of variable length codes: 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.<|reference_end|>
@article{malinowski2006synchronization,
    title={Synchronization recovery and state model reduction for soft decoding of
  variable length codes},
    author={Simon Malinowski (IRISA / INRIA Rennes), Herv'e J'egou (IRISA /
  INRIA Rennes, INRIA Rh^one-Alpes / GRAVIR-IMAG), Christine Guillemot (IRISA
  / INRIA Rennes)},
    journal={IEEE transactions on information theory (2006)},
    year={2006},
    archivePrefix={arXiv},
    eprint={cs/0612059},
    primaryClass={cs.NI cs.IT math.IT}
}