UAV-Assisted Cooperative Downlink NOMA with Virtual Full-Duplex Operation

In this paper, we investigate an unmanned aerial vehicle (UAV)-assisted downlink cellular network where there exist a single base station (BS), two mobile stations (MSs), and multiple UAV relay stations (RSs) between the BS and MSs. We assume that there exist no direct communication links from the BS to the MSs due to unexpected blockages from obstacles or disasters and the BS is assumed to exploit a non-orthogonal multiple access (NOMA) technique for support two MSs. We propose a novel spectrally-efficient successive relaying technique, also known as virtual full-duplex operation, which selects a single UAV-RS among randomly deployed UAVs to send a superimposed NOMA signal for two MSs. It is shown that the proposed cooperative NOMA technique with virtual full-duplex operation outperforms the conventional cooperative NOMA technique with half-duplex operation in terms of outage probability.