  MIMO communication may provide high spectral efficiency through the
deployment of a very large number of antenna elements at the base stations. The
gains from massive MIMO communication come from the use of multi-user MIMO on
the uplink and downlink, but with a large excess of antennas at the base
station compared to the number of served users. Initial work on massive MIMO
did not fully address several practical issues associated with its deployment.
This paper considers the impact of channel aging on the performance of massive
MIMO systems. The effects of channel variation are characterized as a function
of different system parameters assuming a simple model for the channel time
variations at the transmitter. Channel prediction is proposed to overcome
channel aging effects. The analytical results on aging show how capacity is
lost due to time variation in the channel. Numerical results in a multicell
network show that massive MIMO works even with some channel variation and that
channel prediction could partially overcome channel aging effects.
