AoI Minimization in Broadcast Channels with Channel State Information

In this paper, we consider a status updating system where updates are generated at a constant rate at K sources and sent to the corresponding recipients through a broadcast channel. We assume that perfect channel state information (CSI) is available at the transmitter before each transmission, and the additive noise is negligible at the receivers. Under various assumptions on the number of antennas at the transmitter and the size of updates, our object is to design precoding and transmission scheduling schemes for the minimization of the summed time-average Age of Information (AoI) at the recipients. We show that when the transmitter has a single antenna, precoding is unnecessary, and the optimal policy is to update each recipient in a greedy round-robin fashion. When the transmitter has multiple antennas, updating with round-robin precoding is age-optimal.