  Wireless backhaul communication has been recently realized with large
antennas operating in the millimeter wave (mmWave) frequency band and
implementing highly directional beamforming. In this paper, we focus on the
alignment problem of narrow beams between fixed position network nodes in
mmWave backhaul systems that are subject to small displacements due to wind
flow or ground vibration. We consider nodes equipped with antenna arrays that
are capable of performing only analog processing and communicate through
wireless channels including a line-of-sight component. Aiming at minimizing the
time needed to achieve beam alignment, we present an efficient method that
capitalizes on the exchange of position information between the nodes to design
their beamforming and combining vectors. Some numerical results on the outage
probability with the proposed beam alignment method offer useful preliminary
insights on the impact of some system and operation parameters.
