  We investigate the benefits of integrating unmanned aerial vehicles (UAVs)
with reconfigurable intelligent surface (RIS) elements to passively relay
information sampled by Internet of Things devices (IoTDs) to the base station
(BS). In order to maintain the freshness of relayed information, an
optimization problem with the objective of minimizing the expected sum
Age-of-Information (AoI) is formulated to optimize the altitude of the UAV, the
communication schedule, and phases-shift of RIS elements. In the absence of
prior knowledge of the activation pattern of the IoTDs, proximal policy
optimization algorithm is developed to solve this mixed-integer non-convex
optimization problem. Numerical results show that our proposed algorithm
outperforms all others in terms of AoI.
