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

Unmanned aerial vehicle (UAV) relays are increasingly playing a significant role with their advantages of quick establishment for emergency communication, expansion of communication coverage, and increase of system capacity. As demand for massive simultaneous connections is ever-increasing, UAV relaying communication aided by non-orthogonal multiple access (NOMA) can more efficiently utilize spectrum resources to further improve capacity. To fully unlock the potential of NOMA in complex and practical relaying networks, we investigate a pioneering two-hope NOMA UAV relaying network with multi-pair separated users, where the uplink and downlink resources are jointly considered. For the purpose of enhancing the efficiency of our challenging UAV relaying, a developed joint uplink and downlink NOMA relay (JUDNR) scheme is proposed, which jointly optimizes UAV location, user grouping, and power control. Specifically, based on alternating-optimization (AO) method, we iteratively solve non-convex sub-problems by successive-convex-approximation (SCA) algorithm, a novel recursive reformulation grouping (RRG) algorithm based on fractional programming, and difference-of-convex (DC) algorithm, respectively. Simulation results demonstrate that our scheme can significantly enhance the system sum rate performance compared with reference strategies.