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. While the transmitter is able to utilize the CSI information to precode the updates, our object is to design optimal precoding schemes to minimize the summed average age of information (AoI) at the recipients. Under various assumptions on the size of each update and the number of antennas at the transmitter and the receivers, this paper identifies the corresponding age-optimal precoding and transmission scheduling strategies. Specifically, for the case where each user has one receiving antenna, a round-robin based updating scheme is shown to be optimal. For the two-user case where the number of antennas at each receiver is greater than the size of updates, a framed alternating updating scheme is proven to be optimal.
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