  In this work we investigate ultra-reliable low-latency massive multiple-input
multiple-output (MIMO) communication links in vehicular scenarios, where
coherence between uplink and downlink cannot be assumed. In such scenarios the
channel state information obtained in the uplink will be outdated for the
following downlink phase. To compensate for this channel aging we will utilize
orthogonal precoding with two-dimensional precoding sequences in the
time-frequency domain within an orthogonal frequency division multiplexing
system. The channel hardening effect of massive MIMO transmission decreases,
due to channel aging, with increasing frame duration and increasing velocity,
while the channel hardening effect of orthogonal precoding (OP) increases with
increasing time- and frequency-selectivity of the wireless communication
channel. By combining massive MIMO and OP we can show by numeric link level
simulation that the performance with outdated channel state information in
terms of bit-error rate versus signal-to-noise ratio can be improved by two
orders of magnitude.
