Power Allocation and Successive Relay Selection in UAV-assisted Cooperative NOMA System

This paper investigates the performance of nonorthogonal multiple access (NOMA) successive relaying system consisting of one base station (BS), two users and multiple unmanned aerial vehicles (UAVs) as relays. In the successive relaying transmission scheme, one relay is in the transmission mode while simultaneously the others are operating in the reception mode sharing the same frequency band, which causes the inter-relay interference (IRI). Therefore, the power allocation and relay selection problem for maximizing the minimum rates of users is proposed in consideration of the IRI. By converting the quasi-concave problem into the feasible problem and then considering the equivalent convex problem, the optimization problem is solved. Simulation results verify the effectiveness of the proposed power allocation scheme in comparison to the scheme with fixed power transmission.