ARIS-Assisted Energy-Efficient and Secure IoT Communications With AoI Guarantee

The integration of aerial reconfigurable intelligent surfaces (ARISs) into IoT networks offers transformative potential for enhancing secure and energy-efficient communication in the presence of blockages and eavesdropping threats. This paper proposes to integrate ARIS into Internet of Things (IoT) networks to simultaneously improve communication reliability, enforce information freshness, and defend against eavesdropping. We formulate a joint optimization problem to minimize the average total transmit energy of IoT devices through the coordinated design of unmanned aerial vehicle (UAV) trajectory, transmit power allocation, ARIS phase shifts, and device scheduling, subject to rigorous constraints on age of information (AoI), UAV energy budget, and secrecy rate guarantees. The optimization problem is formulated as a dynamic programming problem. To address the complexity of long-term dynamic optimization, we employ Lyapunov optimization to decompose it into a per-slot deterministic optimization problem, which can be solved without requiring future state information. However, the per-slot problem is a mixed-integer non-convex optimization problem, making it inherently challenging to solve optimally. To address this, we propose an efficient algorithm that effectively balances the tradeoff between minimizing average total energy consumption and stabilizing average total queue backlogs. Simulation results demonstrate that our algorithm reduces average transmit energy by 46% compared to the round-robin comparison scheme while strictly adhering to information freshness and UAV energy constraints.