Viterbi algorithms with list and soft symbol output: extensions and comparisons

Improvements in the performance of a concatenated coding system that uses the Viterbi algorithm (VA) (inner decoder) can be obtained when an indicator of the reliability of the VA decision is delivered to the outer stage of processing. Two different approaches are considered. (1) The VA is extended with a soft output (SOVA) unit that calculates reliability values for the decoded output information symbols. (2) The VA provides a list of the L best estimates of the transmitted data sequence, the list Viterbi decoding algorithm (LVA). We define a list output VA using the reliability information of the SOVA to generate a list-SOVA that has a lower complexity than the LVA for a long list size. We also introduce a low complexity SOVA that forms a short list output of the LVA calculated output symbol reliability values, the soft-LVA. A new implementation of the iterative serial version of the LVA is also presented