Virtual cell-based mobility enhancement and performance evaluation in ultra-dense networks

Future mobility management is expected to provide high data rate, low delay, and dense deployment to offer seamless coverage. As a main issue for the future network, Ultra-Dense Networks (UDNs) leads to frequent measurement, intolerable handover failure (HOF) rate and ping-pong (PP) rate. Meanwhile, most existing works either focus on handover decision rules design or handover parameters adjustment without considering the redundant handover and signaling overhead causing by the dense deployment environment. To solve this problem, mobility enhancement based on Virtual Cell (VC) design with dense deployment is firstly proposed in our work to provide seamless coverage and improve handover performance, which is promising for future 5G networks. The relationship between key handover parameters and mobility performance in UDNs is illustrated to seek for the optimal configuration of Time-to-Trigger (TTT) and A3 Offset and achieve low HOF rate and PP rate. VC forming/reforming process is optimized in terms of user's moving direction and speed to satisfy its preference. And we evaluate the impact of VC size and angle threshold for prediction on handover performance to provide basis for specific VC forming/reforming by which most users will have an SINR value higher than a fixed threshold, thus maximizing the residence time in the serving cell. Simulation results show that the system HOF rate is minimizing by optimizing the configuration of handover parameters applying for UDNs. In addition, PP rate achieves a decrease of more than 50% for moderate-speed users based on VC with dense deployment compared with handover in LTE system.