Combining iterative SOVA and Log-MAP algorithms for turbo decoding

This paper considers combining the iterative soft output Viterbi algorithm (SOVA) and the logarithm maximum a posteriori (Log-MAP) algorithm for decoding turbo codes. We examine the differences between the two algorithms and discuss the suitability of combining both algorithms. In the proposed hybrid decoding scheme, frames are first applied with SOVA iterations with error detection for iteration termination. After a fixed maximum number of SOVA iterations, the erroneous frames are continued with Log-MAP iterations. In order to reduce the number of necessary Log-MAP iterations, the extrinsic soft output from the last SOVA iteration are selectively fed to the first Log-MAP iteration as initial a priori input. The benefit of this hybrid decoding scheme is that both the original low complexity by SOVA and the high performance by Log-MAP are well maintained.