Research On Mobility Managements For Future Heterogeneous Integrated Networks

With the development of wireless access technology and the evolvement of network architecture, the convergence and interworking of various networks is seen as the target of network evolution. In such heterogeneous integrated deployment scenario, mobility management is one of the most critical func-tions that ensures the seamless and stable use of broadband services. There-fore, this thesis focuses on mobility managements in Heterogeneous Integrated Networks. The main research contents of this thesis are summarized as follows:Based on stochastic geometry, we make theoretical analysis on cross-tier handover in Heterogeneous Integrated Networks. The cross-tier handover is de-fined as the handover occurred from a macro cell tier to a small cell tier, or vice versa. In Heterogeneous Networks, the cross-tier handover shows the worst performance in terms of handover failure rate. Therefore, we first propose a practical model to study the small cell coverage area. Two methods are used to derive the closed-form expressions of small cell boundary, namely a Tay-lor series approach and a linear approximation approach. Using the proposed method, we then derive analytical expression for cross-tier handover rate and sojourn time inside a small cell. These parameters play a key role in mobility performance evaluation. According to the analysis, we show that the small cell coverage area can be well represented by a biased circle, and the expected value of small cell size is inversely proportional to the square root of the BS density in the macro cell tier. Another important observation is that the handover rate and sojourn time change linearly with the reciprocal of small cell radius. These analytical results could provide fundamental supports for improving mobility management in Heterogeneous Integrated Networks.Existing cell discovery mechanism is tailored for homogeneous networks (macro only), User Equipment (UE) can’t energy-efficiently detect the small cells on a dedicated carrier or maximally exploit the offloading opportunities provided by such heterogeneous deployments. Therefore, we propose a Predic-tive Connection time based Inter-frequency Measurement (PCIM) solution to cope with the problems. With the aid of the positioning results, the small cell connection time is derived, both user velocity and moving direction are taken into account. Using3rd Generation Partnership Project (3GPP) LTE-A Het-erogeneous Network (HetNet) mobility evaluation methodology, the proposed PCIM scheme is compared with some currently standardized techniques. Sim-ulation results provide insights on the small cell discovery schemes in terms of energy efficiency and small cell usage efficiency, and demonstrate the benefits of the proposed PCIM scheme over the other alternatives.