Outage performance of full/half-duplex user relaying in NOMA systems

Abstract

This paper investigates the performance of cooperative non-orthogonal multiple access (NOMA) systems, where one near user works as a decode-and-forward (DF) full-duplex (FD) or half-duplex (HD) relaying to help far user. Two cooperative relay scenarios are considered insightfully. 1) The first scenario is that no direct link exists between the base station (BS) and the far user; and 2) The second scenario is that direct link exists between the BS and the far user. To characterize the performance of FD NOMA in two considered scenarios, new closed-form expressions for both exact and asymptotic outage probability as well as delay-limited throughput are derived for each NOMA user. Based on the analytical results derived, the diversity orders achieved by users are obtained. It is confirmed that the use of the direct link overcomes the zero diversity order of far NOMA user inherent to FD relaying. Simulation results demonstrate that the outage performance of FD NOMA is superior to HD NOMA at low SNR region rather than at high SNR region.