Terahertz Meets Untrusted UAV-Relaying: Minimum Secrecy Energy Efficiency Maximization via Trajectory and Communication Co-Design

Unmanned aerial vehicles (UAVs) and Terahertz (THz) technology are envisioned to play paramount roles in next-generation wireless communications. In this paper, we present a novel secure UAV-assisted mobile relaying system operating at THz bands for data acquisition from multiple ground user equipments (UEs) towards destination. We assume that the UAV-mounted relay may act, besides providing services, as potential eavesdropper called untrusted UAV-relay (UUR). To safeguard end-to-end communications, two-phase transmission strategy with cooperative jamming. Then, devise an optimization framework terms of new measure $-$ secrecy energy efficiency (SEE), defined ratio achievable average rate power consumption, which enables us obtain best possible security level while taking UUR’s inherent flight limitation into account. For sake quality service fairness amongst all UEs, aim maximize minimum SEE (MSEE) performance via joint design key parameters, including trajectory velocity, communication scheduling, network allocation. Since formulated problem is mixed-integer nonconvex computationally intractable, decouple it four subproblems propose alternative algorithms solve efficiently greedy/sequential block successive convex approximation non-linear fractional programming techniques. Numerical results demonstrate significant MSEE improvement our designs compared other known benchmarks.