  This paper presents an inertial sensor aided technique for beam alignment and
tracking in massive multiple-input multiple-output (MIMO) vehicle-to-vehicle
(V2V) communications based on millimeter waves (mmWave). Since directional
communications in vehicular scenarios are severely hindered by beam pointing
issues, a beam alignment procedure has to be periodically carried out to
guarantee the communication reliability. When dealing with massive MIMO links,
the beam sweeping approach is known to be time consuming and often unfeasible
due to latency constraints. To speed up the process, we propose a method that
exploits a-priori information on array dynamics provided by an inertial sensor
on transceivers to assist the beam alignment procedure. The proposed inertial
sensor aided technique allows a continuous tracking of the beam while
transmitting, avoiding frequent realignment phases. Numerical results based on
real measurements of on-transceiver accelerometers demonstrate a significant
gain in terms of V2V communication throughput with respect to conventional beam
alignment protocols.
