A new transfer chart similar to an EXIT chart is proposed to analyze and design iterative decoding schemes. The chart uses a measure related to mean squared error (MSE) instead of mutual information. With this new measure, we prove a relationship between the rate of any block code and the area under an appropriate transfer chart, when the log likelihood ratio (LLR)'s are assumed to be Gaussian. This extends Ashikhmin et al's result on the area property to the case when the LLRs are Gaussian such as what is typically used in EXIT charts. This provides a theoretical justification for designing codes by matching transfer charts for Gaussian LLRs. The new measure is robust and can be computed without knowledge of the transmitted bits and, hence, can be done fully at the receiver.
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