Complexity-reduced iterative source-channel decoding by conditional quantization

Iterative source-channel decoding (ISCD) exploits the residual redundancy of source codec parameters by using the Turbo principle. However, ISCD might require more computational complexity than available. The main reason is that the utilized soft decision source decoder (SDSD) can be computationally quite expensive. In this paper we propose a joint source-channel coding approach which reduces the computational complexity of the SDSD by slightly modifying the quantizer such that the complexity of the source decoder is reduced. The complexity of the SDSD is further reduced by transforming the SDSD equations into the logarithmic domain. We give analytical expressions for the expected quality loss by the modified quantizer, simulation results showing the overall ISCD system performance, as well as complexity figures.