Quantifying Performance Losses in Source-Channel Coding

In this paper, we identify and quantify loss factors causing sub-optimal performance in joint source-channel coding. We show that both the loss due to non-Gaussian distributed channel symbols and the loss due to non-Gaussian quantization error equals the relative entropy between the actual distribution and the optimal Gaussian distribution, given an average power constraint and an mean-squared error (mse) distortion measure, respectively. Furthermore, losses occur whenever each channel symbol has an information bit rate lower than the channel capacity, and due to the presence of inter-channel correlation, source coder redundancy (intra-channel correlation), suboptimal receiver structures, and decoding errors. We quantify the loss associated with some of these factors and provide an example of communication scheme, showing that calculations and simulations agree.