Advances in soft-output decoding

This paper tries to give a unified presentation of soft-output decoding algorithms. It is intended to be tutorial on one hand, but on the other hand it covers some recent advances as well. The presentation includes the list-output Viterbi algorithm (LOVA), the soft (symbol)-output Viterbi algorithm (SOVA), the optimal symbol-by-symbol detector (OSSD, “symbol-by-symbol MAP”), the optimal subblock-by-subblock detector (OBBD, “vector MAP”), and finally a SOVA based on likelihood post-processing. The relation between these algorithms is derived in a structured manner. The average mutual information for i.i.d. input bits is chosen as a measure for the quality of the reliability outputs