  We consider transmission of system information in massive MIMO. This
information needs to be reliably delivered to inactive users in the cell
without any channel state information at the base station. Downlink
transmission entails the use of downlink pilots and a special type of precoding
that aims to reduce the dimension of the downlink channel and the pilot
overhead, which would otherwise scale with the number of base station antennas.
We consider a scenario in which the base station transmits over a small number
of coherence intervals, providing little time/frequency diversity. The system
information is transmitted with orthogonal space-time block codes to increase
reliability and performance is measured using outage rates. Several different
codes are compared, both for spatially correlated and uncorrelated channels and
for varying amount of time/frequency diversity. We show that a massive MIMO
base station can outperform a single-antenna base station in all considered
scenarios.
