Secrecy Analysis and Optimization of UAV-Assisted IoT Networks With RF-EH and Imperfect Hardware

This article introduces uncrewed aerial vehicles (UAVs) assisted communication system for energy-constrained Internet of Things (IoT) devices. Herein, a power beacon transmits radio frequency (RF) signals to enable energy harvesting at the IoT devices (IoDs). The source IoD utilizes harvested energy to transmit information to the destination IoD through multiple UAV relays. Among multiple UAV relays, a selected UAV applies a decode-and-forward operation to relay the information to the destination. An eavesdropper near the destination IoD poses a threat to information secrecy. Consequently, the selected UAV injects artificial noise to degrade the accessibility of the eavesdropper's link. For this setup, we employ a composite fading channel model by combining log-normal distribution for shadowing effects and Nakagami-m distribution for small-scale fading to evaluate system performance. Specifically, the compact expressions for secrecy outage probability and effective secrecy throughput (EST) are derived using the Gauss-Hermite quadrature method. Moreover, we conduct a tradeoff analysis between reliability and security by factoring in outage and intercept probabilities. Lastly, we formulate an EST maximization problem by optimizing the system parameters and UAV's locations under the outage and secrecy constraints. We propose a particle swarm optimization and continuous genetic algorithm-based hybrid algorithm for solving the nonlinear optimization problem. The numerical findings demonstrate that the proposed algorithm outperforms the baseline algorithms regarding the achieved EST.