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-cod ed modulation (TCM), rate-kin convolutional codes, and intersymbol int erference (ISI) channels is proposed. The algorithm utilizes the postd etector architecture proposed by Berrou et nl, [6] to achieve low comp utational complexity. By starting with Battail's [4] generalized revis ion algorithm and rereferencing the ''relative values'' to the survivi ng path to each state, substantial simplifications are made possible. By comparing the revision operations dictated by the simplified revisi on equation for a rate-1/n convolutional code to the operations mandat ed by the rate-1/n postdetector algorithm presented by Berrou ef al,, it is possible to deduce the additional modifications necessary to pro duce a rate-k/n postdetector algorithm. Computer simulations suggest t hat the derived rate-k/n algorithm produces reasonably good a posterio ri input probability estimates for rate-k/n convolutional codes and tr ellis codes. The algorithm may also be used for soft-output Viterbi eq ualization (SOVE) provided that the channel impairments are not too se vere.