The use of exit charts in iterative source-channel decoding

We consider the problem of quantizing, channel coding, and transmitting a continuous-valued correlated source over a noisy channel. This serial concatenation of the channel code and the source-redundancies calls for the use of the turbo principle for decoding; in our context this concept is known as iterative source-channel decoding. We determine the characteristic curves of the source decoder for use in the extrinsic information transfer charts (EXIT charts) and show how they vary with the quantizer bit mappings and with the amount of correlation in the source. Moreover, we discuss a method for the optimization of the quantizer bit mappings for use in iterative source-channel decoding.