Non-Orthogonal Multiple Access (NOMA) is a promising technology for 5G and beyond, offering significant bandwidth efficiency improvements over conventional orthogonal multiple access (OMA) techniques by allowing multiple users to share the same resource block. This paper provides a comprehensive overview of the state-of-the-art in power-domain multiplexing aided NOMA, focusing on theoretical principles, multiple antenna aided design, NOMA and cooperative transmission, resource control, coexistence with other 5G techniques, and comparisons with other NOMA variants. It highlights the advantages of power-domain NOMA over other existing techniques and summarizes challenges and potential solutions. The paper also offers design guidelines and identifies future research opportunities. NOMA has evolved from early wireless communication systems, with key developments in 2G, 3G, and 4G networks. The 5G networks face challenges in supporting large-scale heterogeneous data traffic, and NOMA is seen as a solution. The paper discusses the development of multiple access techniques, including code-domain and power-domain NOMA, and their applications in 5G networks. It also explores the integration of NOMA with other emerging 5G technologies such as massive MIMO, D2D, and machine-to-machine (M2M) communication. The paper identifies the main advantages of NOMA, including high bandwidth efficiency, fairness, ultra-high connectivity, compatibility, and flexibility. It also discusses the performance gain of NOMA over OMA from an information-theoretic perspective, showing that NOMA can outperform OMA in terms of throughput, sum rate, and energy efficiency. The paper also addresses the challenges of implementing NOMA, including the need for efficient algorithms for resource allocation and the impact of imperfect channel state information (CSI) on performance. The paper concludes that NOMA is a promising technology for 5G and beyond, with significant potential for improving the efficiency and capacity of wireless networks. It highlights the importance of further research in NOMA, particularly in the areas of resource allocation, interference management, and integration with other emerging 5G technologies. The paper also emphasizes the need for standardization and practical implementation of NOMA in real-world scenarios.Non-Orthogonal Multiple Access (NOMA) is a promising technology for 5G and beyond, offering significant bandwidth efficiency improvements over conventional orthogonal multiple access (OMA) techniques by allowing multiple users to share the same resource block. This paper provides a comprehensive overview of the state-of-the-art in power-domain multiplexing aided NOMA, focusing on theoretical principles, multiple antenna aided design, NOMA and cooperative transmission, resource control, coexistence with other 5G techniques, and comparisons with other NOMA variants. It highlights the advantages of power-domain NOMA over other existing techniques and summarizes challenges and potential solutions. The paper also offers design guidelines and identifies future research opportunities. NOMA has evolved from early wireless communication systems, with key developments in 2G, 3G, and 4G networks. The 5G networks face challenges in supporting large-scale heterogeneous data traffic, and NOMA is seen as a solution. The paper discusses the development of multiple access techniques, including code-domain and power-domain NOMA, and their applications in 5G networks. It also explores the integration of NOMA with other emerging 5G technologies such as massive MIMO, D2D, and machine-to-machine (M2M) communication. The paper identifies the main advantages of NOMA, including high bandwidth efficiency, fairness, ultra-high connectivity, compatibility, and flexibility. It also discusses the performance gain of NOMA over OMA from an information-theoretic perspective, showing that NOMA can outperform OMA in terms of throughput, sum rate, and energy efficiency. The paper also addresses the challenges of implementing NOMA, including the need for efficient algorithms for resource allocation and the impact of imperfect channel state information (CSI) on performance. The paper concludes that NOMA is a promising technology for 5G and beyond, with significant potential for improving the efficiency and capacity of wireless networks. It highlights the importance of further research in NOMA, particularly in the areas of resource allocation, interference management, and integration with other emerging 5G technologies. The paper also emphasizes the need for standardization and practical implementation of NOMA in real-world scenarios.