  Millimeter-wave transceivers use large antenna arrays to form narrow
high-directional beams and overcome severe attenuation. Narrow beams require
large signaling overhead to be aligned if no prior information about beam
directions is available. Moreover, beams drift with time due to user mobility
and may need to be realigned. Beam tracking is commonly used to keep the beams
tightly coupled and eliminate the overhead associated with realignment. Hence,
with periodic measurements, beams are adjusted before they lose alignment. We
propose a model where the receiver adjusts beam direction "continuously" over
each physical-layer sample according to a carefully calculated estimate of the
continuous variation of the beams. In our approach, the change of direction is
updated using the rate variation prediction of beam angles via three different
solutions. Our approach incurs no additional overhead in pilots, yet, the
performance of beam tracking is improved significantly. Numerical results
reveal an SNR enhancement associated with reducing the MSE of the beam
directions. In addition, our approach reduces the pilot overhead by 60% and up
to 87% while achieving a similar total tracking duration as the
state-of-the-art.
