An intuitive justification and a simplified implementation of the MAP decoder for convolutional codes

An intuitive shortcut to understanding the maximum a posteriori (MAP) decoder is presented based on an approximation. This is shown to correspond to a dual-maxima computation combined with forward and backward recursions of Viterbi algorithm computations. The logarithmic version of the MAP algorithm...

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Bibliographic Details
Published inIEEE journal on selected areas in communications Vol. 16; no. 2; pp. 260 - 264
Main Author Viterbi, A.J.
Format Journal Article
LanguageEnglish
Published IEEE 01.02.1998
Subjects
Approximation algorithms
Bit error rate
Block codes
Concatenated codes
Convolutional codes
Costs
Interleaved codes
Iterative decoding
Viterbi algorithm
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ISSN0733-8716
DOI10.1109/49.661114

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Summary:An intuitive shortcut to understanding the maximum a posteriori (MAP) decoder is presented based on an approximation. This is shown to correspond to a dual-maxima computation combined with forward and backward recursions of Viterbi algorithm computations. The logarithmic version of the MAP algorithm can similarly be reduced to the same form by applying the same approximation. Conversely, if a correction term is added to the approximation, the exact MAP algorithm is recovered. It is also shown how the MAP decoder memory can be drastically reduced at the cost of a modest increase in processing speed.
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ISSN:0733-8716
DOI:10.1109/49.661114