A Soft Output Viterbi Algorithm Demodulator for Pre-coded Binary CPM Signals

A method and processing system for determining a soft decision metric for each input symbol, including and/or performing the steps of: computing trellis branch metrics based on a received sample sequence; updating initial state metrics from time (n-1) with a Viterbi algorithm (VA); constraining M trellises differently at time n such that only state transitions caused by an input value associated with a particular trellis are allowed; executing the VA on the M constrained trellises for a finite number (N.sub.d) steps; and computing likelihood ratios by taking a difference of a maximum state metric at time (n+N.sub.d) for each trellis with a maximum state metric of a reference trellis.