Optimizing Information Freshness in RIS-Assisted Non-Orthogonal Multiple Access-Based IoT Networks

This letter investigates the benefits of integrating reconfigurable intelligent surface (RIS) on minimizing the average sum age of information in uplink NOMA-based IoT networks. A problem is formulated to optimize the RIS configuration, the transmit power of IoT devices (IoTDs) and their clustering policy. The formulated problem is a mixed-integer non-convex one, and in order to solve it, we obtain first the RIS configuration by resorting to difference-of-convex and successive convex approximation. Afterwards, the joint power allocation and clustering problem is solved using the concept of bi-level optimization and is decomposed into an outer IoTDs clustering problem and an inner power allocation problem. Optimal closed-form expressions are derived for the inner problem and one-to-one matching is employed to solve the outer one. Numerical results demonstrate the performance superiority of our scheme.