Joint Uplink and Downlink NOMA for UAV Relaying Network With Multi-Pair Users

Unmanned aerial vehicle (UAV) communications have emerged as a promising solution for future full coverage networks. To further meet the massive connection demands in beyond-fifth-generation (B5G) systems, in this paper, we propose to employ non-orthogonal multiple access (NOMA) in both uplink and downlink relaying hops in an amplify-and-forward (AF) based UAV relaying network with multiple source-destination (SD) user pairs. Specifically, taking NOMA design in both hops into a joint consideration in relaying networks is investigated for the first time and presents a new challenge for the joint optimization problem in terms of the deployment of the UAV relay, the two-hop NOMA user grouping, and the transmit power control for both the source users and the UAV. To maximize the system sum rate, we propose an efficient joint uplink and downlink NOMA-based relay (JUDNR) scheme to decompose the problem into three sub-problems and adopt the alternating optimization (AO) method to iteratively obtain a promising solution. In detail, we provide a joint NOMA groups design of both the uplink and downlink and propose a novel recursive two-hop NOMA grouping (RTNG) algorithm to efficiently group users. Simulation results demonstrate that our proposed JUDNR scheme outperforms various baselines in terms of sum rate.