Apollonius Circles Based Outbound Handover in Macro-Small Wireless Cellular Networks

Mobility management and handover, in the presence of the macro-small wireless cellular networks, are of the critical challenging issues, owing to the large- scale small cells deploying and frequent mobility of user equipment (UE). Existing literatures include variously studied the inbound handover, namely the UE's movement from a macrocell to a small cell. The outbound handover (OHO), which refers to the UE's movement from a small cell to a macrocell, is also of importance. In this paper, instead of the concentric circles based handover regions, we propose a novel model for the OHO regions by utilizing the principle of the circle of Apollonius. Based on the mathematical analysis for the boundaries of OHO regions, we derive the closed-form expression to characterize the relationship between the OHO hysteresis margin and UE's mobility in terms of the velocity and the moving direction. Then, we develop the UE's movement based regulatory algorithm to adaptively adjust hysteresis for achieving the proper OHO. Simulation results show the effectiveness of the proposed OHO model. The proposed hysteresis adjusting algorithm outperforms the existing schemes in terms of the decrease for radio link failure and pingpong effect during OHO process.