A Fast Viterbi Decoding in Optical Channels

Hiroyuki YASHIMA  Jouji SUZUKI  Iwao SASASE  Shinsaku MORI  

Publication
IEICE TRANSACTIONS on Communications   Vol.E75-B   No.1   pp.26-33
Publication Date: 1992/01/25
Online ISSN: 
DOI: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Optical Communication
Keyword: 
viterbi decoding,  optical channel,  

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Summary: 
A fast Viterbi decoding technique with path reduction in optical channels is presented. This decoding exploits the asymmetric characteristic of optical channels. In the decoding trellis, the branches with low or no possibility being correct path are eliminated based on the detected signal level. The number of Add-Compare-Select (ACS) operations which occupy the dominant part of Viterbi decoding is considerably reduced due to branch eliminations, and fast decoding is realized by decoding asynchronously to received sequence. The reduction of the number of ACS operations is derived for the codes with rate 1/2. It is shown that the number of ACS operations is considerably reduced compared with the conventional Viterbi decoding. The bit error probability of the proposed decoding is derived for noiseless photon counting channel. It is also shown that the decoding technique can be applied to the cases using avalanche photo diode (APD) based receiver with dark current noise at a cost of negligible degradation on the bit error probability.