Performance and convergence analysis of joint source-channel turbo schemes with variable length codes

Recently, we proposed a joint source-channel (JSC) turbo (de)coder combining a variable length code (VLC) and a turbo code, and applied it to image transfer (Jaspar, X. and Vandendorpe, L., SCC Conf., p.279-86, 2004; ICC Conf., p.2606-10, 2004). Simulation results showed that this scheme gave better performance and lower decoding complexity than previous ones. The paper assesses the performance of such a scheme at all signal-to-noise ratios on the channel. Analytical tools are provided for the understanding and optimization of a wide variety of similar schemes currently explored in the literature. More precisely, the bit, symbol and frame distance spectra are developed for VLCs and for VLCs turbo-concatenated with an error correcting code (ECC), in order to get bounds on the corresponding error rates. Also EXIT charts are extended to three dimensions in order to analyze the turbo-convergence of the scheme.