On SOVA for nonbinary codes

For binary codes, Fossorier et al. (see ibid., vol.2, p.137-9, 1998) have shown that the soft-output Viterbi algorithm (SOVA) becomes equivalent to the max-log-maximum a posteriori (MAP) algorithm after a modification. In this letter, we generalize such modified SOVA to nonbinary cases, motivated by the fact that the performance gap between the original SOVA and the max-log-MAP algorithm broadens in these cases, The equivalence between the two algorithms is proved in a more compact form. The modified SOVA requires only add-compare-select operations and is well suited for high-speed parallel implementation.