Iterative source-channel decoder using symbol-level extrinsic information

An iterative source-channel decoding scheme which exploits the source residual redundancies on symbol-basis is proposed. We first derive a modified BCJR algorithm based on the sectionalized code trellis for symbol decoding of the convolutional codes. This is used in conjunction with a softbit source decoder that computes the interpolative a posteriori probabilities of quantizer indexes. Simulation results indicate that our proposed scheme can achieve significant improvement over the conventional bit-level schemes.