Optimizing duration of energy harvesting for downlink NOMA full-duplex over Nakagami-m fading channel

In this paper, we propose and analyze a downlink non-orthogonal multiple access (NOMA) relay system with full-duplex transmission model and decode-and-forward (DF) scheme. We assume that the source and the destination nodes have fixed power, whereas relay nodes have constrained energies and should harvest radio frequency (RF) energy from the source for operation power. The outage performance of this system is analyzed over the Nakagami-m fading channel, full-duplex transmission protocol and imperfect channel state information (CSI), and then the duration of energy harvesting in every block time, αT, is optimized to achieve the maximal throughput. Furthermore, the closed-form of outage probabilities and the fraction α are derived and evaluated in several scenarios. Moreover, the optimal power allocation coefficients that achieve the minimal outage probability while keeping the fairness in outage performance of end users are discussed. The analytical results are verified by Monte Carlo simulations.