  The coupling between cell-free massive multiple-input multiple-output (MIMO)
systems operating at millimeter-wave (mmWave) carrier frequencies and user
mobility is considered in this paper. First of all, a mmWave channel is
introduced taking into account the user mobility and the impact of the channel
aging. Then, three beamforming techniques are proposed in the considered
scenario, along with a dynamic user association technique (handover): starting
from a user-centric association between each mobile device and a cluster of
access points (APs), a rule for updating the APs cluster is formulated and
analyzed. Numerical results reveal that the proposed beamforming and user
association techniques are effective in the considered scenario.
