SST Viterbi Decoder Branch Metric Computation Based on MAP Estimation Method

Masato TAJIMA; Hideo SUZUKI; Kenzo KOBAYASHI

SST Viterbi Decoder Branch Metric Computation Based on MAP Estimation Method

Masato TAJIMA, Hideo SUZUKI, Kenzo KOBAYASHI

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This paper discusses branch metric computation in the main decoder placed in an SST (Scarce State Transition) Viterbi decoder. The basic assumptions that all the message sequences are equally likely and that the channel is memoryless do not hold for the main decoder in an SST Viterbi decoder, when an inverse encoder or a pseudo-inverse encoder is used as a pre-decoder. Therefore, in contrast to a conventional method, an MAP (Maximum A Posteriori probability) estimation method itself, which is the starting point of the maximum likelihood decoding, has been applied to branch metric computation. Then, it has been clarified that the conventional branch metric computed in a usual SST Viterbi decoder happens to be equal to the branch metric derived using the MAP estimation method only for systematic codes. For general non-systematic codes, in particular, it has been found that it is impossible to decompose a path metric into such branch metrics that follow the original code trellis structure, because the branch metric derived at time k is also dependent on future state transitions.

Publication: IEICE TRANSACTIONS on transactions Vol.E72-E No.5 pp.485-493

Publication Date: 1989/05/25

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Type of Manuscript: Special Section PAPER (Special Issue on Information Theory and Its Applications)

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Masato TAJIMA
Hideo SUZUKI
Kenzo KOBAYASHI

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Masato TAJIMA, Hideo SUZUKI, Kenzo KOBAYASHI, "SST Viterbi Decoder Branch Metric Computation Based on MAP Estimation Method" in IEICE TRANSACTIONS on transactions, vol. E72-E, no. 5, pp. 485-493, May 1989, doi: .
Abstract: This paper discusses branch metric computation in the main decoder placed in an SST (Scarce State Transition) Viterbi decoder. The basic assumptions that all the message sequences are equally likely and that the channel is memoryless do not hold for the main decoder in an SST Viterbi decoder, when an inverse encoder or a pseudo-inverse encoder is used as a pre-decoder. Therefore, in contrast to a conventional method, an MAP (Maximum A Posteriori probability) estimation method itself, which is the starting point of the maximum likelihood decoding, has been applied to branch metric computation. Then, it has been clarified that the conventional branch metric computed in a usual SST Viterbi decoder happens to be equal to the branch metric derived using the MAP estimation method only for systematic codes. For general non-systematic codes, in particular, it has been found that it is impossible to decompose a path metric into such branch metrics that follow the original code trellis structure, because the branch metric derived at time k is also dependent on future state transitions.
URL: https://global.ieice.org/en_transactions/transactions/10.1587/e72-e_5_485/_p

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@ARTICLE{e72-e_5_485,
author={Masato TAJIMA, Hideo SUZUKI, Kenzo KOBAYASHI, },
journal={IEICE TRANSACTIONS on transactions},
title={SST Viterbi Decoder Branch Metric Computation Based on MAP Estimation Method},
year={1989},
volume={E72-E},
number={5},
pages={485-493},
abstract={This paper discusses branch metric computation in the main decoder placed in an SST (Scarce State Transition) Viterbi decoder. The basic assumptions that all the message sequences are equally likely and that the channel is memoryless do not hold for the main decoder in an SST Viterbi decoder, when an inverse encoder or a pseudo-inverse encoder is used as a pre-decoder. Therefore, in contrast to a conventional method, an MAP (Maximum A Posteriori probability) estimation method itself, which is the starting point of the maximum likelihood decoding, has been applied to branch metric computation. Then, it has been clarified that the conventional branch metric computed in a usual SST Viterbi decoder happens to be equal to the branch metric derived using the MAP estimation method only for systematic codes. For general non-systematic codes, in particular, it has been found that it is impossible to decompose a path metric into such branch metrics that follow the original code trellis structure, because the branch metric derived at time k is also dependent on future state transitions.},
keywords={},
doi={},
ISSN={},
month={May},}

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TY - JOUR
TI - SST Viterbi Decoder Branch Metric Computation Based on MAP Estimation Method
T2 - IEICE TRANSACTIONS on transactions
SP - 485
EP - 493
AU - Masato TAJIMA
AU - Hideo SUZUKI
AU - Kenzo KOBAYASHI
PY - 1989
DO -
JO - IEICE TRANSACTIONS on transactions
SN -
VL - E72-E
IS - 5
JA - IEICE TRANSACTIONS on transactions
Y1 - May 1989
AB - This paper discusses branch metric computation in the main decoder placed in an SST (Scarce State Transition) Viterbi decoder. The basic assumptions that all the message sequences are equally likely and that the channel is memoryless do not hold for the main decoder in an SST Viterbi decoder, when an inverse encoder or a pseudo-inverse encoder is used as a pre-decoder. Therefore, in contrast to a conventional method, an MAP (Maximum A Posteriori probability) estimation method itself, which is the starting point of the maximum likelihood decoding, has been applied to branch metric computation. Then, it has been clarified that the conventional branch metric computed in a usual SST Viterbi decoder happens to be equal to the branch metric derived using the MAP estimation method only for systematic codes. For general non-systematic codes, in particular, it has been found that it is impossible to decompose a path metric into such branch metrics that follow the original code trellis structure, because the branch metric derived at time k is also dependent on future state transitions.
ER -