Design of Root Protograph LDPC Codes Simultaneously Achieving Full Diversity and High Coding Gain

Abstract: This paper presents a novel design framework for protograph-based LDPC codes that simultaneously achieves full diversity in block-fading channels (BFCs) and nearcapacity performance in additive white Gaussian noise channels (AWGNCs). By leveraging a Boolean approximation-based analysis--Diversity Evolution (DivE)--we derive structural constraints for generalized rootchecks that guarantee full diversity. Based on these constraints, we propose a protograph template tailored for two-block BFCs. Furthermore, we employ a genetic algorithm guided by density evolution to optimize the protograph edges within this template for superior AWGNC performance. The resulting codes effectively bridge the gap between diversityoriented and capacity-oriented designs, exhibiting robust performance across both channel environments.