[Paper Review] Terahertz-supported Untrusted UAV-Relaying: Secrecy Energy Efficiency Maximization via Trajectory and Communication Co-design.

Milad Tatar Mamaghani, Yi Hong|arXiv (Cornell University)|Jul 21, 2021

UAV Applications and Optimization8 references4 citations

TL;DR

This paper proposes a secure UAV-relaying system in the terahertz band with an untrusted relay, using a two-phase transmission with cooperative jamming to maximize secrecy energy efficiency (SEE). By jointly optimizing trajectory, velocity, power allocation, and scheduling via advanced optimization techniques, the scheme achieves significant SEE gains over benchmarks under UAV power constraints.

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.

Motivation & Objective

• Address the security vulnerability in UAV-relaying systems where the UAV relay may act as an untrusted adversary.
• Design a two-phase transmission protocol with cooperative jamming to protect data from eavesdropping by the untrusted UAV relay.
• Maximize secrecy energy efficiency (SEE), defined as the ratio of average secrecy rate to system power consumption, under strict UAV flight power constraints.
• Jointly optimize UAV trajectory, velocity, communication scheduling, and power allocation to enhance both security and energy efficiency.
• Develop efficient algorithms to solve the computationally intractable mixed-integer nonconvex optimization problem arising from the SEE maximization framework.

Proposed method

• Propose a two-phase transmission strategy: first, the source transmits to the UAV relay; second, the UAV forwards data to the destination while transmitting artificial noise to confuse potential eavesdroppers.
• Introduce cooperative jamming from the source and the destination to degrade the eavesdropping channel capacity, enhancing secrecy.
• Formulate a secrecy energy efficiency (SEE) maximization problem as a mixed-integer nonconvex optimization, incorporating UAV mobility and power constraints.
• Apply successive convex approximation (SCA) to handle nonconvexity, and use non-linear fractional programming to transform the fractional SEE objective into a tractable form.
• Employ greedy/sequential block coordinated descent to iteratively optimize trajectory, velocity, power allocation, and scheduling variables.
• Integrate UAV mobility constraints (e.g., maximum speed, acceleration limits) and power consumption models into the optimization framework.

Experimental results

Research questions

• RQ1 How can secrecy be ensured in a THz-band UAV-relaying system when the UAV relay is untrusted and may eavesdrop on the communication?
• RQ2 What is the optimal joint design of UAV trajectory, velocity, power allocation, and communication scheduling to maximize secrecy energy efficiency under practical UAV power constraints?
• RQ3 How does the proposed two-phase transmission with cooperative jamming improve secrecy performance compared to conventional relaying without jamming?
• RQ4 What optimization techniques are effective in solving the mixed-integer nonconvex SEE maximization problem arising in this secure UAV-relaying setup?
• RQ5 What performance gains in SEE are achievable through the proposed co-design framework compared to existing benchmark schemes?

Key findings

• The proposed SEE-maximizing framework achieves significant performance gains over benchmark schemes, demonstrating the effectiveness of joint trajectory, power, and scheduling optimization.
• The use of cooperative jamming significantly enhances secrecy rate by degrading the eavesdropping channel, especially in the THz band with high path loss and directional transmission.
• The successive convex approximation and non-linear fractional programming techniques effectively handle the nonconvexity and fractional objective of the SEE problem, enabling convergence to high-quality solutions.
• Greedy/sequential block coordinated descent enables efficient optimization of the coupled trajectory, velocity, and power allocation variables, balancing computational complexity and performance.
• Numerical results confirm that the proposed design outperforms conventional schemes in SEE, particularly under stringent UAV power limitations.
• The system achieves a higher average secrecy rate per unit of system power consumption, validating the utility of SEE as a performance metric in energy-constrained UAV networks.