Combining FEC and optimal soft-input source decoding for the reliable transmission of correlated variable-length encoded signals

We utilize both the implicit residual source correlation and the explicit redundancy from a forward error correction (FEC) scheme for the error protection of packetized variable-length encoded source indices. The implicit source correlation is exploited in a novel symbol-based soft-input a-posteriori probability (APP) decoder, which leads to an optimal decoding process in combination with a mean-squares or maximum a-posteriori probability estimation of the reconstructed source signal. When, additionally, the variable-length encoded source data is protected by channel codes, an iterative source-channel decoder can be obtained in the same way as for serially concatenated codes, where the outer constituent decoder is replaced by the proposed APP source decoder. Simulation results show that, by additionally considering the correlations between the variable-length encoded source indices, the error-correction performance can be highly increased.