Fast 5G Beam Tracking at The User Equipment with Analog Beamformer

Fifth generation (5G) cellular networks can operate with millimeter waves (mmWave), which require appropriate beamforming at both the base station and the user equipment (UE). In this paper we consider an automotive scenario, where the UE is mounted on a car and is using a single radio-frequency (RF) chain and a configurable analog beamformer, so that the effective firing direction of the antenna (i.e., only one beamforming angle) can be set at any given time. As the UE moves, the beamforming angle should be tracked using the reference signals transmitted in downlink by the base station. While in a basic solution all possible beamforming angles are explored and a long time is needed, we propose here the adaptive-step tracking algorithm, a procedure that learns from past channel changes which angles to explore, yielding a short tracking time. Numerical results are provided for two scenarios, where the UE either rotates (thus making the angle tracking challenging) or moves along a straight line (with variations of the received power).