  This paper discusses the feasibility of beam tracking against dynamics in
millimeter wave (mmWave) nodes placed on overhead messenger wires, including
wind-forced perturbations and disturbances caused by impulsive forces to wires.
Our main contribution is to answer whether or not historical positions and
velocities of a mmWave node is useful to track directional beams given the
complicated on-wire dynamics. To this end, we implement beam-tracking based on
deep reinforcement learning (DRL) to learn the complicated relationships
between the historical positions/velocities and appropriate beam steering
angles. Our numerical evaluations yielded the following key insights: Against
wind perturbations, an appropriate beam-tracking policy can be learned from the
historical positions and velocities of a node. Meanwhile, against impulsive
forces to the wire, the use of the position and velocity of the node is not
necessarily sufficient owing to the rapid displacement of the node. To solve
this, we propose to take advantage of the positional interaction on the wire by
leveraging the positions/velocities of several points on the wire as state
information in DRL. The results confirmed that this results in the avoidance of
beam misalignment, which would not be possible by using only the
position/velocity of the node.
