Synchronization recovery and state model reduction for soft decoding of variable length codes
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.
- Publication:
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arXiv e-prints
- Pub Date:
- December 2006
- DOI:
- 10.48550/arXiv.cs/0612059
- arXiv:
- arXiv:cs/0612059
- Bibcode:
- 2006cs.......12059M
- Keywords:
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- Computer Science - Networking and Internet Architecture;
- Computer Science - Information Theory
- E-Print:
- IEEE transactions on information theory (2006)