Revisiting the Max-Log-Map Algorithm With SOVA Update Rules: New Simplifications for High-Radix SISO Decoders

Abstract

This paper proposes a new soft-input soft-output decoding algorithm particularly suited for low-complexity high-radix turbo decoding, called local soft-output Viterbi algorithm (local SOVA). The local SOVA uses the forward and backward state metric recursions just as the conventional Max-Log-MAP algorithm does, and produces soft outputs using the SOVA update rules. The proposed local SOVA exhibits a lower computational complexity than the Max-Log-MAP algorithm when employed for high-radix decoding in order to increase throughput, while having the same error correction performance even when used in a turbo decoding process. Furthermore, with some simplifications, it offers various trade-offs between error correction performance and computational complexity. For instance, employing the local SOVA algorithm for radix-8 decoding of the LTE turbo code reduces the complexity by 33% without any performance degradation and by 36% with a slight penalty of only 0.05 dB. Moreover, the local SOVA algorithm opens the door for the practical implementation of turbo decoders for radix 16 and higher.