Energy Efficiency Techniques in Non-orthogonal Multiple Access (NOMA) in 5G Network: An Overview and Outlook

Abstract

This review paper critically examines energy efficiency schemes in Non-Orthogonal Multiple Access (NOMA) systems, focusing on critical topics such as the integration of NOMA with cutting-edge technologies like Multi-Input Multi-Output (MIMO), beamforming, Mobile Edge Computing (MEC), and Reconfigurable Intelligent Surface (RIS), and discusses the challenges in radio resource allocation and environmental sustainability. The review aims to summarise the current state-of-the-art techniques, evaluate their performance, and identify future research directions to enhance energy efficiency in NOMA systems. This paper addresses several key findings: power allocation methods can enhance energy efficiency by up to 30% in specific scenarios; relay-assisted and hybrid NOMA schemes can boost data rates by 20–25%; and energy harvesting shows potential for improving energy efficiency, reducing power consumption by up to 15% in certain cases. These challenges include system complexity, which can increase the computational overhead by 40% when optimising resource allocation, and user fairness, where trade-offs in power allocation can reduce the data rate up to 10% for edge users in certain scenarios, ultimately affecting overall energy efficiency.