  This paper addresses the problem of Age-of-Information (AoI) in UAV-assisted
networks. Our objective is to minimize the expected AoI across devices by
optimizing UAVs' stopping locations and device selection probabilities. To
tackle this problem, we first derive a closed-form expression of the expected
AoI that involves the probabilities of selection of devices. Then, we formulate
the problem as a non-convex minimization subject to quality of service
constraints. Since the problem is challenging to solve, we propose an Ensemble
Deep Neural Network (EDNN) based approach which takes advantage of the dual
formulation of the studied problem. Specifically, the Deep Neural Networks
(DNNs) in the ensemble are trained in an unsupervised manner using the
Lagrangian function of the studied problem. Our experiments show that the
proposed EDNN method outperforms traditional DNNs in reducing the expected AoI,
achieving a remarkable reduction of $29.5\%$.
