  This paper investigates the benefits of integrating reconfigurable
intelligent surface (RIS) on minimizing the average sum age of information
(AoI) in uplink non-orthogonal multiple access-based Internet-of-Things (IoT)
networks. In this setup, an optimization problem is formulated to optimize the
RIS configuration, the transmit power per IoT device and the clustering policy
of IoT devices. The formulated problem is a mixed-integer non-convex one, and
in order to solve it we obtain first the RIS configuration by adopting a
semi-definite relaxation (SDR) approach. Afterwards, the joint power allocation
and user-clustering problem is solved using the concept of bi-level
optimization and is decomposed into an outer user clustering problem and an
inner power allocation problem. Optimal closed-form expressions are derived for
the inner problem and the Hungarian method is employed to solve the outer one.
Numerical results demonstrate the performance superiority of our approach.
