Patent ID: 7620877

Claim:
A trellis decoder for decoding symbols of a received signal, said symbol comprising a sequence defined by transitions between states of a trellis, the trellis decoder comprising: means for performing a forward recursion through said trellis to determine a first set of probabilities (α(X t )) each defining a probability of a said trellis state (X t ) responsive to one or more current or earlier received signal values (y 1:t ); means for providing a second set of (β(X t )) probabilities each defining a probability of one or more received signal values (y t+1:T ) given an earlier said trellis state (X t ); means to decode said received signal to determine probabilities (p(b t |y 1:T )) for symbols of a corresponding transmitted sequence of symbols from said first and second sets of probabilities; and wherein said decoder further comprises: means to select states for determining said first set of probabilities responsive to one or more received signal values later than a said trellis state defining a probability in said first set.