Degree Distribution Design for LDPC Codes: A Derivative Matching Approach

A deterministic method to design degree distributions for low-density parity-check codes over the binary erasure channel is proposed. This method consists of matching the first and high-order derivatives of the extrinsic information transfer (EXIT) function of the variable node set to the corresponding derivatives of the inverse EXIT function of the check node set, in order to reduce the gap between the two curves in the EXIT chart. A sufficient condition for a check-concentrated distribution to achieve derivative matching up to some order is first obtained, and then a deterministic design algorithm, enabled by the Fourier-Budan theorem, is developed exploiting this sufficient condition. A comparison with other deterministic design techniques is also provided, revealing the potential of the proposed algorithm.