  Management of narrow directional beams is critical for mm-wave communication
systems. Translational or rotational motion of the user can cause misalignment
of transmit and receive beams with the base station losing track of the mobile.
Reacquiring the user can take about one second in 5G NewRadio systems and
significantly impair performance of applications, besides being energy
intensive. It is therefore important to manage beams to continually maintain
high received signal strength and prevent outages. It is also important to be
able to recover from sudden but transient blockage caused by a handor face
interposed in the Line-of-Sight (LoS) path. This work presents a beam
management protocol called BeamSurfer that is targeted to the use case of users
walking indoors near a base station. It is designed to be minimalistic,
employing only in-band information, and not requiring knowledge such as
location or orientation of the mobile device or any additional sensors.
Evaluations under pedestrian mobility show that96%of the time it employs beams
that are within3dB of what an omniscient Oracle would have chosen as the pair
of optimal transmit-receive LoS beams. It also recovers from transient LoS
blockage by continuing to maintain control packet communication over a
pre-selected reflected path that preserves time-synchronization with the base
station, which allows it to rapidly recover to the LoS link as soon as it is
unblocked
