Parallel decoding of turbo codes using soft output T-algorithms

Turbo codes need to be used with reasonably long blocks of data which invariably lead to considerable decoding delay. In fact, for a data block of size N, the decoding delay is O(N). Recently it was shown that if the hardware complexity of W processors was acceptable, then the decoding delay could be reduced to O(N/W) without much performance degradation, by decoding the turbo code in a parallel fashion. In this paper we have shown that the decoding delay could be further reduced if the component decoders use parallel versions of soft output T-algorithms instead of parallel versions of the MAP algorithm. Unlike the MAP algorithm which could be used with parallel and pipelined structures to reduce the decoding delay to the same extent, the soft output T-algorithms must be used with a parallel structure in order to reduce the decoding delay. This reduction in decoding delay is obtained without any appreciable degradation in performance.