A Study on Network-initiated Handover for Radio Resource Management in 802.16 Two-tiered Networks

In the Macro-Femto two-tiered wireless networks, due to the large amounts and random distributed of Femtocells, the interference among users is quite large, which could lead to users'' communication quality drop or even service terminated. In our previous work, an operation in IEEE 802.16m called low-duty operation mode (LDM) is applied to implement interference mitigation for the two-tiered network. By assigning “interlaced” LDM patterns to neighboring Femtocells, the interference among users could be largely reduced.

However, because of the resource adjustment on Femtocells according to their assigned LDM patterns, some of the Femtocells might not satisfy all of its subordinate users due to their less assigned resource. Thus, in this thesis, we proposed a network-initiated handover scheme which initiates some of the users in the two-tiered network to handoff to neighboring cells in order to satisfy all the users'' requirements. The problem is first formulated as an optimization problem, and our goal is to minimize the overall handoff user number in the two-tiered network while at the same time satisfying all users'' requirements. Thereafter, two methods, Best Candidate and Average Candidate, which consider every user''s serving and candidate base stations'' situations are proposed in order to approximate the performance of optimal solution while at the same time reducing the complexity of finding solutions. From the results in this thesis, we find out that in Macro-Femto two-tiered wireless network, by applying the network-initiated handover scheme, base stations could create a better communication quality without sacrificing some users'' performance, which leads to an overall increase of system service quality.