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. Hence, this paper presents a novel secure UAV-assisted mobile relaying system operating at THz bands for data acquisition from multiple ground user equipments towards a destination. We assume that the UAV-mounted relay may act, besides providing relaying services, as a potential adversary called the untrusted UAV relay. To safeguard end-to-end communications, we present a secure two-phase transmission strategy with cooperative jamming. Then, we formulate an optimization problem 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 UAV's inherent flight power limitation into account. This optimization problem leads to a joint design of key system parameters, including UAV's trajectory and velocity, communication scheduling, and power allocations. Since the formulated problem is a mixed-integer nonconvex optimization and computationally intractable, we propose alternative algorithms to solve it efficiently via greedy/sequential block coordinated descent, successive convex approximation, and non-linear fractional programming techniques. Numerical results demonstrate significant SEE performance improvement of our designs when compared to other known benchmarks.

Aerial Intelligent Reflecting Surface Enabled Terahertz Covert Communications in Beyond-5G Internet of Things

“…Terahertz (THz) communication is celebrated to be one of the emerging technologies for B5G wireless communications thanks to the abundance of unexplored available spectrum (0.1 − 10THz) and the potentiality of fulfilling remarkable wireless capacity enhancement [15]- [18]. Recently, THz transmissions have been investigated for UAV communication applications [19], [20]. THz signals can pave the way for sharper directionality and may guarantee improved secure and reliable transmissions compared to traditional low radio frequency (RF) counterparts.…”

“…Further, due to UAV's limited on-board battery resource, we assume that UIRS and UCJ fly at the fixed altitudes H r and H j for a finite period T , where the altitudes are properly chosen to avoid possible collision with environmental obstacles. This fixedaltitude operation can avoid mechanical energy consumption caused by UAVs' rise and fall [11], [20].…”

“…We consider network power consumption is dominated by the mechanical power consumption of the energy-limited rotary-wing UIRS and UCJ in terms of propulsion for aerial operation, which can be mathematically expressed as [20]…”

“…Since our work examines transmissions over THz frequencies, the THz channel gain for direct links from UCJ to UE k in time slot n can be denoted, similar in [19], [20], [47], as carrier frequency. Furthermore, κ(f c , µ) represents the overall molecular absorption coefficient of THz channels as a function of f c and the volume of the mixing ratio of water vapor µ, describing the relative absorbing area of the molecules in the wireless medium per unit volume.…”

“…Note that improving received signal energy at Bob via improving the channel gain ( 48) leads to mAEE improvement according to (20) and (32). Thus, by properly aligning the phases of different paths, we can improve the channel quality by setting…”