  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 noise-free broadcast channel. We assume that perfect
channel state information (CSI) is available at the transmitter before each
transmission, and 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 \emph{age of information} (AoI) at the recipients.
Under various assumptions on the size of each update $B$, the number of
transmit antennas $M$, and the number of receive antennas $N$ at each user,
this paper identifies the corresponding age-optimal precoding and transmission
scheduling strategies. Specifically, for the case when $N=1$, a round-robin
based updating scheme is shown to be optimal. For the two-user systems with
$N>B$ or $M\notin[N:2N]$, framed updating schemes are proven to be optimal. For
other cases in the two-user systems, a framed alternating updating scheme is
proven to be $2$-optimal.
