Low Complexity Radix-4 Butterfly Design for the Viterbi Decoder

This study presents a new radix-4 butterfly design for Viterbi decoders. The branch symmetry of the radix-4 butterfly is exploited to design a low- complexity radix-4 butterfly module to simplify the implementation of the Viterbi decoder. By exploiting the branch symmetry, only a half of branch metrics need to be computed, while other metrics can be derived from the computed branches. Therefore, the branch metric computation of the radix-4 butterfly can be reduced by a factor of 2. Considering the convolutional code in the DAB system as an example, experimental results indicate that the proposed radix-4 butterfly design can reduce the number of FPGA slices of the radix-4 butterfly module by 24% over the conventional design.