Modified soft output viterbi algorithm for truncated trellis

In concatenated codes, the performance of the outer decoder can be improved with a soft output from the inner decoder. Soft output Viterbi algorithm (SOVA) is one such technique when the inner decoder is Viterbi based. However, when the trellis does not terminate to a single final state, the outer decoder performance does not improve substantially. In this work, we propose two methods to restore the performance. Simulation results illustrating the performance of the proposed algorithms are presented.