Patent ID: 6356586
Filing Date: 2002-03-12
Classification: H04L

Abstract:
An apparatus for use in decoding a sequence of received symbols, comprising:a decoder operative to compute branch metrics associated with transitions between states of a multi-stage trellis representation of a state machine, wherein for a given stage t of the trellis, the branch metrics are computed for at least two states s using a different input value yt(s) for each state, the input values corresponding to decision feedback equalization values computed for each of a plurality of different survivor paths; wherein the decoder includes a decision feedback computation unit which computes an extended survivor path for each of the states of the given stage t of the trellis; wherein the extended survivor path for a given one of the survivor paths is based on the last Nb decoded symbols in that survivor path, where Nb is the number of taps in a feedback filter used in decision feedback equalization; and wherein the survivor path at state s of decoding stage t is denoted by (xt(s, i), 1&lE;i&lE;t), where xt(s, i) is a decoded symbol on a branch of the trellis between stage iâˆ’1 and stage i, and wherein the extended survivor path for state s is computed by the decision feedback computation unit as: yt&af;(s)=&Sum;i=0Nf-1&it;wi&it;r&af;(t+i)-&Sum;j=1Nb&it;bj&it;xt&af;(s,t-j),where r(t) is an output of a feed-forward filter applied to an input of the decision feedback computation unit at stage t, Nf is a number of feed-forward taps in the feed-forward filter, and the feed-forward and feedback taps are w=(w1, . . . , wNf) and b=(b1, . . . , bNb), respectively, and the extended survivor path value yt(s) for a given state is used in computation of the branch metrics for that state.