Patent ID: 6680986
Filing Date: 2004-01-20
Classification: H03M,H04B,H04L

Abstract:
A method for decoding an encoded input signal comprising a plurality of channel symbols, wherein a Viterbi survivor exchange algorithm having S trellis/decoding states is used to continuously decode the input signal via a plurality of decoding cycles, each decoding cycle c comprising a total number T of individual trellis/decoding steps t, the method comprising the steps of:(a) setting the decoding cycle c=0; (b) processing the channel symbols for trellis/decoding steps t=cD+1 to (c+1)D using the Viterbi survivor exchange algorithm to compute and store branch metrics Bt, path metrics &Ggr;t based on the branch metrics Bt and previous path metrics &Ggr;tâˆ’1, and survivor paths Et based on the path metrics &Ggr;t and previous survivor paths Etâˆ’1, and to exchange the path metrics &Ggr;t and the survivor paths Et, wherein the survivor paths Et are stored in S registers each comprising D bits where D is a whole number less than T; (c) storing the path metrics &Ggr;t as tentative path metrics &Ggr;(c+1)D at the end of the trellis/decoding step t=(c+1)D; (d) processing the received channel symbols for trellis/decoding steps t=((c+1)D)+1 to cD+T using the Viterbi survivor exchange algorithm to compute and update the path metrics &Ggr;t and to exchange, but not update, the survivor paths Et stored in the S registers; (e) selecting one of the survivor paths Et stored in the S registers as an estimate for D received information bits of the encoded input signal at the trellis/decoding step t=cD+T; (f) setting the decoding cycle c=c+1, the trellis decoding step t=cD+1, and the path metrics &Ggr;t to be equal to the tentative path metrics &Ggr;(c+1)D; and (g) repeating steps (b) through (f) to continuously decode the encoded input signal.