How durable and stable is File Sharing on the Move in Cellular-assisted D2D Communications?

File sharing is one of the most promising Proximity Service (ProSe) using device-to-device (D2D) communication technology. As the prospective D2D-enabled file sharing rely on mobile peer discovery and connection in physical proximity, the challenges come from the highly dynamic environment as a consequence of the unpredictable user mobility and the temporal-spatial locality of content popularity. A challenging yet open question is how users could move to fetch target files durably and stably. In this paper, we characterize mobile file sharing in temporal and spatial domains by how long time the service can be active (referred as service lifetime tau(L)), how far a mobile user can move away while keeping ongoing service (referred as service distance parallel to D-L parallel to), and how fast the ongoing service would be recovered once interruption caused by handover (classified into bundled handover and split handover in this paper) (referred as recover delay sigma(HO)). Answers to these questions offer a straightforward interpretation of the potentials of D2D communications for file sharing on the move. Both theoretical and simulation results suggest that D2D file sharing is more benefit for popular content among group moving users with longer service lifetime and distance and less delay caused by mobile user handover and peer discovery.