Abstract: In speech signal transmission system, residual redundancy is still left in the parameters after source encoding. The redundancy includes non-uniform distribution and time correlation of subsequent frame. Exploiting the redundancy on bit-level, the paper is proposed iterative algorithm based on soft-in/soft-out channel and parameter estimation, and applies the algorithm to GSM EFR system. The result shows this method reduces the BER and improves SNR of decoded speech.