Direct Connection on the Move: Characterization of User Mobility in Cellular-Assisted D2D Systems

Next-generation device-to-device (D2D) communication technology, in which a cellular network assists proximal users at all stages of their interaction, is rapidly developing. Previous research has thoroughly characterized D2D performance aspects from discovery to connection establishment, security, and service continuity; however, prospective D2D-enabled applications and services envision highly opportunistic device contacts as a consequence of unpredictable human user mobility. Therefore, mobility's impact on D2D communication requires careful investigation to understand the practical operational efficiency of future cellular-assisted D2D systems. This article offers a first-hand tutorial on various implications of D2D mobility across different user movement patterns and mobility-related parameters and proposes an assessment methodology for D2D-enabled systems. The rigorous system-level evaluation conducted for this study delivers important conclusions on the effects of user mobility in emerging D2D-centric systems.