A Novel Radix-4SOVA Algorithm

Soft Output Viterbi Algorithm (SOVA) is more practical than MAP in the algorithms for decoding Turbo codes, because of its shorter decoding delay. In order to decrease further the decoding delay and increase the decoding speed, based on the simple analysis of the radix-4Max-Log-MAP algorithm, a novel radix-4SOVA algorithm is proposed and a comprehensive mathematical explanation is given. The key of the algorithm is to propose a novel reliability update method which achieves the reliability update after combining two-step state transitions in trellis diagram. Simulation results show that the BER performance of the novel algorithm is very close to that of radix-4Max-Log-MAP, and approaches radix-4MAP when the extrinsic information coefficient is adaptively added. Moreover, it reduces greatly the decoding delay and memory unit and achieves a good trade-off with the computational complexity.