An Efficient CVA-Based Decoding Algorithm for Tail-Biting Codes

Tail-biting convolutional codes (TBCC) provide an efficient method to eliminate the rate loss caused by the known-tail encoding. To simplify the decoder design, circular Viterbi algorithm (CVA) has been proposed by recording and repeating the received block of (soft) symbols beyond the block boundary and continuing Viterbi decoding. However, CVA does not converge in the presence of circular trap. A checking rule is proposed for detecting the circular trap in existing CVA. Based on this rule, an efficient CVA-based decoding algorithm is obtained for tail-biting codes, which exhibits near-optimal performance for both short and long tail-biting codes. This new scheme provides faster convergence speed than the conventional CVA without increasing in complexity and storage space.