  Massive multiple-input multiple-output (MIMO) is a promising technology
aiming at achieving high spectral efficiency by deploying a large number of
base station (BS) antennas using coherent combining. Channel aging due to user
mobility is a significant degrading factor of such systems. In addition, cost
efficiency of massive MIMO is a prerecuisite for their deployment, that leads
to low cost antenna elements inducing high phase noise. Since phase is
time-dependent, it contributes to channel aging. For this reason, we present a
novel joint channel-phase noise model, that enables us to study the downlink of
massive MIMO with maximum ratio transmission (MRT) precoder under these
conditions by means of the deterministic equivalent of the achievable sum-rate.
Among the noteworthy outcomes is that the degradation due to user mobility
dominates over the effect of phase noise. Nevertheless, we demonstrate that the
joint effects of phase noise and user mobility do not degrade the power scaling
law $1/\sqrt{M}$ ($M$ is the number of BS antennas), as has been established in
massive MIMO systems with imperfect channel state information.
