  This paper investigates the achievable sum-rate of massive multiple-input
multiple-output (MIMO) systems in the presence of channel aging. For the
uplink, by assuming that the base station (BS) deploys maximum ratio combining
(MRC) or zero-forcing (ZF) receivers, we present tight closed-form lower bounds
on the achievable sum-rate for both receivers with aged channel state
information (CSI). In addition, the benefit of implementing channel prediction
methods on the sum-rate is examined, and closed-form sum rate lower bounds are
derived. Moreover, the impact of channel aging and channel prediction on the
power scaling law is characterized. Extension to the downlink scenario and
multi-cell scenario are also considered. It is found that, for a system
with/without channel prediction, the transmit power of each user can be scaled
down at most by $1/\sqrt{M}$ (where $M$ is the number of BS antennas), which
indicates that aged CSI does not degrade the power scaling law, and channel
prediction does not enhance the power scaling law; instead, these phenomena
affect the achievable sum-rate by degrading or enhancing the effective signal
to interference and noise ratio, respectively.
