Network Control Overhead of Mobility Support in Millimeter-Wave Urban Cellular Networks

Abstract

Millimeter-wave (mm-wave) bands promise multi-Gbps rates for future cellular networks by utilizing high-gain beamforming antenna arrays. However, the directional mm-wave transmissions are prone to blockage, making seamless network coverage and mobility support very challenging. In this paper, we investigate the network control overhead requirements for mobility support in mm-wave urban cellular networks, using ray-tracing and realistic vehicular and pedestrian mobility models in Frankfurt and Seoul. We show that pedestrian mobility entails less network control overhead compared to vehicular, and that the latter is strongly dependent on the city layout, i.e. frequency of street intersections and traffic lights. This highlights the importance of realistically modeling the user (UE) trajectory in designing mobility support mechanisms. Our results also show that the rate of tracking events - i.e. adjusting the antenna alignment to maintain connectivity on the same \mboxline-of-sight (LOS) or \mboxnon-LOS link - is significantly higher than the rate of re-steering to a secondary link on the serving base station (BS), or handovers to another BS. This is due to the coverage being chiefly limited by building blockages, making it typically most attractive to provide mobility support via antenna realignment of the serving LOS link, emphasizing that UE tracking will be critical in mm-wave urban cellular network.