A hybrid uplink-downlink secure transmission scheme for UAV-aided coordinated multi-point networks

Recognized as a pivotal facet in Beyond Fifth-Generation (B5G) and the upcoming Sixth-Generation (6G) wireless networks, Unmanned Aerial Vehicle (UAV) communications pose challenges due to limited capabilities when serving as mobile base stations, leading to suboptimal service for edge users. To address this, the collaborative formation of Coordinated Multi-Point (CoMP) networks proves instrumental in alleviating the issue of the poor Quality of Service (QoS) at edge users in the network periphery. This paper introduces a groundbreaking solution, the Hybrid Uplink-Downlink Non-Orthogonal Multiple Access (HUD-NOMA) scheme for UAV-aided CoMP networks. Leveraging network coding and NOMA technology, our proposed HUD-NOMA effectively enhances transmission rates for edge users, notwithstanding a minor reduction in signal reception reliability for strong signals. Importantly, the system's overall sum rate is elevated. The proposed HUD-NOMA demonstrates resilience against eavesdroppers by effectively managing intended interferences without the need for additional artificial noise injection. The study employs a stochastic geometry approach to derive the Secrecy Outage Probability (SOP) for the transmissions in the CoMP network, revealing superior performance in transmission rates and lower SOP compared to existing methods through numerical verification. Furthermore, guided by the theoretical SOP derivation, this paper proposes a power allocation strategy to further reduce the system's SOP.