Soft output viterbi algorithm method and decoder

Abstract

A method of decoding a block with a Soft Output Viterbi Algorithm (SOVA) using a trellis representation and a sliding window wherein each position of the sliding window has a path determination stage at one end of the sliding window and a symbol decision stage at another end of the sliding window is disclosed. The method comprises determining, for each path determination stage and for each node of the path determination stage, a surviving path (including a surviving path input symbol and a surviving decision stage node) and a concurrent path (including a concurrent path input symbol and a concurrent decision stage node) based on path metrics. A path metric disparity value is calculated and stored for each node. Based on decision criteria, a soft output value of the surviving decision stage node is determined as either of the path metric disparity value of the node of the path determination stage, a function of the path metric disparity value of the node of the path determination stage and the stored path metric disparity value of the concurrent decision stage node, and the stored path metric disparity value of the surviving decision stage node. Corresponding computer program product, decoder and communication apparatus are also disclosed.