Full-Duplex Non-Orthogonal Multiple Access Systems

Abstract

Full-duplex communications and non-orthogonal multiple access (NOMA) each can deliver high spectral efficiency for modern wireless systems. In this chapter, we investigate the joint performance of full-duplex and NOMA when applied in multiple antenna systems, systems based on the antenna selection and relaying systems based on the cognitive radio principle. First, we explore the current research progress reported in the recent literature. Next, we consider downlink NOMA operation in which a central transmitter communicates with a pair of near and far located users with the help of a multi-antenna equipped full-duplex relay. In particular, optimum and suboptimal beamforming schemes are proposed to counter the self-interference effect and inter-user interference at the strong user. Next, we study the problem of selecting best transmit/receive antennas in full-duplex NOMA systems. To this end, a multi-antenna equipped access point and a full-duplex relay setup is considered in which a base station serves a user located nearby while at the same time, a relay is used to assist communication between the access point and a far user. Finally, we investigate the integration of full-duplex and NOMA in cognitive relay systems and pose an optimization problem to maximize the near/far user information rate region. The presented results clearly demonstrate that full-duplex operation at terminals with NOMA is capable of ushering in performance gains for the systems studied. We also identify several future research directions that are useful in designing future full-duplex enabled NOMA systems.