Outage Performance of Multi-Antenna Mobile UAV-Assisted NOMA Relay Systems Over Nakagami-m Fading Channels

This paper investigates the outage performance of the communications between two pairs of source-destination in a non-orthogonal multiple access (NOMA) system where a multi-antenna mobile unmanned aerial vehicle (UAV) acts as the relay for these communications. We first characterize the signal-to-interference-plus-noise ratio (SINRs) of uplink and downlink, taking into account the influences of power allocation, successive interference cancellation (SIC) capability, and the number of antennas at the UAV. We then derive the exact closed-form expression of the outage probability (OP) of each source-destination communication pair. Monte-Carlo simulations are conducted to verify the correctness of our mathematical analysis. Numerical results show that the outage performance of the proposed NOMA-UAV relay system greatly depends on the line-of-sight (LoS) probability, the SIC capability, the velocity, and the number of antennas of the UAV. The best outage performance is obtained when the UAV is in the middle of the source and destination or when suitable power allocation coefficients are assigned to the uplink and downlink.