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.

中文翻译：

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基于原图的二用户高斯多址信道LDPC码设计


在这封信中，我们研究了两用户高斯多址信道 (GMAC) 的基于原图的低密度奇偶校验 (LDPC) 码的性能。考虑到两个用户联合原图的特点，我们首先推导基于联合原图的外部信息传递（JP-EXIT）图来分析两个用户GMAC的迭代用户解码行为。在JP-EXIT的指导下，我们进一步提出了一种新的设计方案，并分别为两个用户构建了不同码率的原图基矩阵。理论分析和仿真结果表明，对于不同码率的等功率和不等功率GMAC，所提出的低解码阈值的基于原图的LDPC码优于传统的不规则LDPC码。