SOVA (Soft Output Viterbi Algorithm)类算法因其译码时延远低于MAP类算法已成为Turbo码的实用译码算法，为了进一步减小译码延迟，提高译码速度，该文在简单分析基-4Max-Log-MAP算法的基础上，提出了一种新的基-4SOVA算法，并进行了完整的数学推导。该算法的关键是提出了一种新的可信度更新方法，可实现编码网格图中两步状态转移合并后的可信度的更新。仿真结果表明，新算法的误码率性能非常接近基-4Max- Log-MAP算法，当自适应引入外信息系数后，逼近基-4MAP。而且新算法具有译码延迟小、存储资源占用少等优点，达到了与计算复杂度的良好折中。
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.