Joint Source-Channel Coding: a Practical Approach and an implementation Example

The basic building blocks of most state-of the art source coders are: a linear transformation; scalar quantization of the transform coefficients; probability modeling of the sequence of quantization indices; an entropy coding stage. The weakness of conventional separated source-channel coding approaches lies in the catastrophic behavior of the entropy coding stage. Hence, we replace this stage with linear coding, that maps directly the sequence of redundant quantizer output symbols into a channel codeword. We show that this approach does not entail any loss of optimality in the asymptotic regime of large block length. Furthermore, for practical block lengths and moderate complexity, our approach yields very significant improvements. We develop a full implementation example based on the JPEG2000 image coder and punctured turbo codes. The gain over a conventional separated scheme is demonstrated by extensive numerical experiments on test images.