  In this paper, we consider an unmanned aerial vehicle (UAV) based wireless
network using non-orthogonal multiple access (NOMA) transmission in
millimeter-wave frequencies to deliver broadband data in a spectrally efficient
fashion at hotspot scenarios. The necessity for the NOMA transmitter to gather
information on user channel quality becomes a major drawback in practical
deployments. We therefore consider various limited feedback schemes for NOMA
transmission, to relieve the complexity of tracking and feeding back the full
channel state information (CSI) of the users. In particular, through
beamforming we allow NOMA to exploit the space domain, and hence the user angle
emerges as a promising (yet novel) limited feedback scheme. We show that as the
user region for NOMA transmission gets wider, the users become more distinctive
at the transmitter side with respect to their angles, making user angle
feedback a better alternative than distance feedback in such scenarios. We
rigorously derive and analyze the outage sum rate performance for NOMA
transmission considering various user ordering strategies involving full CSI,
angle, and distance feedback schemes. Our analytical results for NOMA outage
sum rates using those feedback schemes match closely with simulations, and
provide useful insights on properly choosing a limited feedback scheme for
different deployment geometries and operating configurations.
