A Butterfly Structure for Rate 2/n Convolutional Codes

In this paper, we propose a butterfly structure for the Viterbi decoder which works for convolutional codes of rate 2/n. The butterfly structure provides an efficient way to find the inherent symmetry in trellis branches. By exploiting the symmetry, only a part of branch metric computation is required in the implementation of the Viterbi decoder. The applicability of the butterfly structure is validated through an example of best known code. By using the butterfly structure, the branch metric computation of the best known code can be reduced by a factor of 4