Analytical derivation of EXIT charts for simple block codes and for LDPC codes using information combining

The extrinsic information transfer (EXIT) chart describes the input-output behavior of a decoder by means of the mapping from a-priori information and channel information to extrinsic information. In this paper, we consider single parity check and repetition codes over binary-input symmetric memoryless channels. Using the concept of information combining, we derive bounds on the extrinsic information for these codes, which depend only on the a-priori information and on the channel information, but not on the channel models. The bounds are applied to the EXIT charts of these codes and to the EXIT charts of low-density parity-check codes.