Efficient Pairing Distance for Better Radio Capacity in NOMA Systems

Among the radio access techniques promoted for 5G and beyond, Non-Orthogonal Multiple Access (NOMA) has received the most research attention due to its spectral efficiency. It is proven in several literatures that NOMA exploits the wide difference in distance between two-users NOMA pair to enhance the NOMA system radio capacity. But, when the distance selection policy is not appropriate, the user's high channel gain throughput is affected, and that of the system as well. This paper explore the appropriate coupling distance between the high channel condition user (User near to the base station) and low channel condition user (User far to the base station) to allow a large user number to participate in NOMA with two users and meet the demands of massive connectivity. First of all we provide a complete pairing coupling analysis. Hereafter, we propose a novel pairing approah named Efficient Pairing Distance NOMA (EPD-NOMA) based on the calculated non-maximum coupling distance of a far user. The numerical results showed that EPD-NOMA can achieve a considerable performance in terms of paired user number and overall throughput compared with some exiting approaches such as Maxinimum Distance of Far-NOMA (MDF-NOMA), Similar User Index NOMA (SIU-NOMA), Traditional-NOMA (T-NOMA) and Conventional Orthogonal Multiple Access (OMA).