  This paper considers a multi-user downlink scheduling problem with access to
the channel state information at the transmitter (CSIT) to minimize the
Age-of-Information (AoI) in a non-stationary environment. The non-stationary
environment is modelled using a novel adversarial framework. In this setting,
we propose a greedy scheduling policy, called MA-CSIT, that takes into account
the current channel state information. We establish a finite upper bound on the
competitive ratio achieved by the MA-CSIT policy for a small number of users
and show that the proposed policy has a better performance guarantee than a
recently proposed greedy scheduler that operates without CSIT. In particular,
we show that access to the additional channel state information improves the
competitive ratio from 8 to 2 in the two-user case and from 18 to 8/3 in the
three-user case. Finally, we carry out extensive numerical simulations to
quantify the advantage of knowing CSIT in order to minimize the
Age-of-Information for an arbitrary number of users.
