Terahertz Meets Untrusted UAV-Relaying: Minimum Secrecy Energy
Efficiency Maximization via Trajectory and Communication Co-design
Abstract
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 a destination. We assume
that the UAV-mounted relay may act, besides providing relaying services,
as a potential eavesdropper called the untrusted UAV-relay (UUR). To
safeguard end-to-end communications, we present a secure two-phase
transmission strategy with cooperative jamming. Then, we devise an
optimization framework in terms of a new measure − secrecy energy
efficiency (SEE), defined as the ratio of achievable average secrecy
rate to average system power consumption, which enables us to obtain the
best possible security level while taking UUR’s inherent flight power
limitation into account. For the sake of quality of service fairness
amongst all the UEs, we aim to maximize the minimum SEE (MSEE)
performance via the joint design of key system parameters, including
UUR’s trajectory and velocity, communication scheduling, and network
power allocation. Since the formulated problem is a mixed-integer
nonconvex optimization and computationally intractable, we decouple it
into four subproblems and propose alternative algorithms to solve it
efficiently via greedy/sequential block successive convex approximation
and non-linear fractional programming techniques. Numerical results
demonstrate significant MSEE performance improvement of our designs
compared to other known benchmarks.