  Due to severe signal attenuation at millimeter-wave (mmWave) frequencies
large antenna arrays are required at both base station and user equipment to
achieve necessary beamfoming gain and compensate for the signal power loss. The
initial access and beamforming algorithms are typically designed assuming
sparsity of mmWave channels, resulting from a very few significant multipath
clusters, and considering fixed locations of terminals and scatterers. Channel
tracking algorithms have been proposed to account for channel variations due to
user mobility. Existing works did not consider mobility of the scatterers,
which adds new challenges and opportunities into a channel tracking problem. In
this work, we consider a more realistic assumption of mobile scatterers and
their impact on channel tracking algorithms. We propose a novel channel
tracking algorithm that takes into account the dynamics of cluster evolution,
and adaptively tracks channel parameters with the objective to reduce training
overhead. We also propose a simple implementation of aperiodic tracking to
accommodate tracking to different channel variations. We analyze the
performance of the proposed tracking algorithm under highly dynamic channels,
and compare it to existing channel tracking algorithms with respect to tracking
accuracy, achievable rate, and required training overhead, when aperiodic and
periodic trackings are used.
