Joint Optimization of IRS Phases, UAV Altitude, and AF Power Factor for Secrecy Rate Enhancement in 5G IoT Networks

This paper studies secrecy rate enhancement in 5G Internet-of-Things (IoT) networks by jointly optimizing intelligent reflecting surface (IRS) phase shifts, unmanned aerial vehicle (UAV) altitude, and amplify-and-forward (AF) power splitting factor. Two schemes are considered: a ground IRSassisted system and a UAV-mounted IRS with AF relaying. We derive a closed-form approximation for the optimal UAV altitude and propose a low-complexity coordinate ascent algorithm to maximize secrecy rate. A comprehensive complexity comparison is provided between coordinate ascent, semidefinite relaxation (SDR), genetic algorithm (GA), and particle swarm optimization (PSO). Simulation results demonstrate that the proposed approach significantly outperforms baseline methods and compares favorably with recent 2024-2025 literature.