Better User Clustering Scheme in Distributed NOMA Systems

Abstract

Non-orthogonal multiple access (NOMA) is one of the promising techniques for 5G due to its good spectral efficiency for two-user cluster, with a distinctive channel gain difference. Generally before forming two-user clusters, NOMA divides users into groups (strong and weak channel gain groups). However, when the number of users in one group is larger than the others, the admission of single users into two-user clusters can cause a drop in performance of the NOMA system due to the strong interference. Therefore, these single users deploy the old orthogonal multiple access (OMA). This hybrid technique is known as the conventional NOMA (C-NOMA). In this paper, we examine in detail the admission conditions of additional users in two-user NOMA clusters in order to form three-user NOMA clusters and promote the massive connectivity. Then, we propose a new dynamic clustering scheme called DC-NOMA based on the channel gain difference to form clusters of more than two users. The simulation results show that, our proposed scheme can achieve a slightly better performance in terms of radio capacity and individual cluster throughput, compared to other NOMA schemes such as Conventional-NOMA (C-NOMA) and Random clustering. Specifically, DC-NOMA helps to promote massive connectivity as it allows more users to be inserted into NOMA clusters without degrading system performance.