DIFFERENCE-METRIC VITERBI DECODING OF MULTILEVEL CLASS-IV PARTIAL-RESPONSE SIGNALS

The paper describes the decoding of unconstrained L-ary signals (L gre ater-than-or-equal-to 2) transmitted over a noisy partial-response cha nnel with transfer function 1 - D2. Signals received at even and odd s ampling times are independently decoded in a pipeline fashion. After s tating the known results for full-state maximum-likelihood sequence de coding, a 2-state decoding algorithm is introduced in which the differ ence between the metrics of the retained two most-likely states is ite ratively computed. An analysis of its error-event probability shows th at two types of error events are most likely, regular free-distance ev ents and induced free-distance events. The latter cause only a rather small degradation of error performance compared to full-state decoding . In addition, the symbol-error probability for modulo-L encoded user symbols and decoding with finite decoding delay is computed. The 2-sta te decoder can be realized for arbitrary values of L with low hardware complexity.