  With the rapid growth of real-time Internet of Things (IoT) applications, the
need for fresh information has surged. Age of Information (AoI) is a
tailor-made metric to characterize the information freshness perceived by the
devices. In this paper, we investigate the problem of scheduling updates to
minimize AoI in broadcast network. In this case, a central controller, e.g. a
base station, collects status updates from different sources and schedules them
to corresponding clients. Different from previous work, we consider both
stochastic status updates and unreliable links. The problem is first modeled as
an infinite horizon average constrained cost Markov decision problem (CMDP).
With Lagrangian relaxation, an approximation of Whittle's index is derived and
a scheduling policy is designed based on the approximate index. The results in
previous work can be view as degenerate cases of the approximation index policy
either with reliable links or periodic arrival constraints. Simulation results
demonstrate the near-optimal performance of the proposed policy.
