A Time Sharing Based Approach to Accommodate Similar Gain Users in NOMA for 5G Networks

Abstract

This paper investigates a time sharing (TS) based user pairing strategy to accommodate similar gain users in non-orthogonal multiple access (NOMA) systems, termed as TS- NOMA. A scenario is considered in which the distribution of users in a cellular area is non-uniform, such that the number of cell center users is less than cell edge users. In this case, if two user conventional NOMA (C-NOMA) pairing between cell center and cell edge users is applied, then some cell edge users remain unpaired as they are more in number. These unpaired users can be served using conventional multiple access (OMA) schemes. To accommodate these unpaired users and to efficiently utilize their spectrum, the TS-NOMA user pairing pairs a cell center user with two or more clustered (closely located) cell edge users in a TS fashion. Ergodic sum capacity of TS-NOMA is analytically derived, which is later validated through simulations. It is shown through simulations that the performance of TS-NOMA in terms of ergodic sum capacity is better than C-NOMA and OMA.