Improvements in SOVA-based decoding for turbo codes

In this paper, we propose two modifications to soft output Viterbi algorithm (SOVA) for turbo code decoding. One is to limit the reliability values to a small range to compensate for the defect brought by overestimating those values in the original SOVA. The other is to employ a new block interleaver to combat the tail effect of SOVA-based turbo code decoding. The simulation results show that the new SOVA with both modifications is able to obtain a similar result to that achieved by a maximum a posteriori (MAPI) algorithm with a random interleaver. In this paper, we also provide the results of the SOVA with the Battail's updating rule and compare them to those of the SOVA with the updating rule proposed by Hagenauer.