Design of Protograph-Based LDPC Codes for Two-User Gaussian Multiple Access Channel

In this letter, we study the performance of protograph-based low-density parity-check (LDPC) codes for two-user Gaussian multiple access channel (GMAC). Considering the characteristic of a joint protograph of two users, we first derive a joint protograph-based extrinsic information transfer (JP-EXIT) chart to analyze the iterative user decoding behavior of two-user GMAC. Guided by the JP-EXIT, we further propose a new design scheme and construct protograph base matrices of different code rates for two users, respectively. Both theoretical analyses and simulation results show that the proposed protograph-based LDPC codes of low decoding threshold outperform the conventional irregular LDPC codes for both equal-power and unequal-power GMAC with different code rates.