A Comprehensive Survey on Non-Orthogonal Multiple Access (NOMA) for 5G Networks

The rapid development of 5G wireless communication networks, driven by the increasing demands of mobile internet and the Internet of Things (IoT), necessitates innovative solutions to meet stringent performance requirements. Non-Orthogonal Multiple Access (NOMA) has emerged as a promising technology to address these challenges by enabling efficient use of spectral resources through the sharing of resource blocks by multiple users. This survey comprehensively analyses various user pairing and power allocation strategies in NOMA, highlighting their effects on system capacity, spectral efficiency, and user fairness. Additionally, the integration of NOMA with advanced 5G technologies such as MIMO, cognitive radio, and cooperative communication is explored, addressing key challenges and potential solutions. The survey identifies significant research gaps, including the need for scalable user pairing algorithms, advanced power allocation methods, effective interference management, and robust security mechanisms. This review aims to provide insights into optimizing NOMA performance and guiding future research to enhance 5G networks.