A rate-k/n heuristic soft-output Viterbi algorithm (SOVA) that is postdetector-compatible

A soft-output Viterbi algorithm (SOVA) that can be used on trellis-coded modulation (TCM), rate-k/n convolutional codes, and intersymbol interference (ISI) channels is proposed. The algorithm utilizes the postdetector architecture proposed by Berrou et al. (1993) to achieve low computational complexity. By starting with Battail's (1987) generalized revision algorithm and rereferencing the "relative values" to the surviving path to each state, substantial simplifications are made possible. By comparing the revision operations dictated by the simplified revision equation for a rate-1/n convolutional code to the operations mandated by the rate-1/n postdetector algorithm presented by Berrou et al., it is possible to deduce the additional modifications necessary to produce a rate-k/n postdetector algorithm. Computer simulations suggest that the derived rate-k/n algorithm produces reasonably good a posteriori input probability estimates for rate-k/n convolutional codes and trellis codes. The algorithm may also be used for soft-output Viterbi equalization (SOVE) provided that the channel impairments are not too severe.