Performance of a fixed delay decoding scheme for tail biting convolutional codes

A fixed delay decoding scheme for tail biting convolutional codes is described and its performance is investigated. Unlike other proposed algorithms that have iterative structures, the scheme requires a fixed number of computations and is suitable for practical DSP implementations. An analytic bound on the error probability is derived to indicate the decoding complexity and performance trade-off, and to provide criteria to determine the decoding parameters. It is shown that for the rate 1/4 tail biting convolutional code used in IS-54/IS-136 digital cellular standard, the bit error rate of the decoding scheme has negligible degradation from the maximum likelihood performance while the decoding complexity is less than twice the complexity of a single Viterbi algorithm trial.