Study On Handover Method For Mobile WiMAX Network

The elaboration of IEEE 802.16e specification for mobile broadband wireless access has driven the convergence of multimedia service and mobile wireless technology, but has also arise discussions on issues surrounding mobile BWA technology, among which stands out the handover problem. With the increasing number of mobile subscribers and myriad type of high-speed multimedia applications, the system capacity of WiMAX system is under challenge. How to design an appropriate handover method which helps users to promptly and smartly switch between WiMAX cells has become an interesting subject.Regarding this problem, this thesis proposes a novel WiMAX handover method based on capacity estimation and neighbor advertisement. The method is suitable and has evident enhancement for a network with multiple WiMAX cell coverage with large number of mobile subscribers and heavy data traffic.This thesis presented the WiMAX standards and current handover methods including the handover algorithms, strategy, control mode and techniques in the first place. Among those handover methods, this thesis further studies the 802.16g fast handover technique for mobile WiMAX network, analyses the performance of this technique, verifies with a network simulation and reaches to a conclusion that the fast handover technique could decrease the packet loss due to handover, yet it fails to effectively solve the continuous packet loss due to network congestions.By summarizing the problems and difficulties on applying the current handover methods to WiMAX network, this thesis proposes a novel handover method based on capacity. Innovations of the proposed method include: the method bases itself on WiMAX cell capacity estimation and neighbor advertisement technology, uses effective idle capacity as a trigger metric in order to achieve traffic load balance; in the system model, we proposes a theoretical calculation method which accurately estimates the effective capacity of WiMAX cell inline with the OFDM PHY specifications in the 802.16 standard; the proposed method also originally introduces a global handover probability factor which effectively controls the"handover synchronization effect"problem during cell handover.An important part of the work load during our study is to construct the simulation environment for WiMAX handovers. Since the NS-2 simulation software does not provide native support for WiMAX network and WiMAX handovers, we have studied the structure of NS-2 and NIST mobility package and modified many source codes within different classes to construct the simulation environment under NS-2 with WiMAX handover support and realized the proposed method. The simulation result shows that the proposed handover method could effectively solve network congestions and enhance system throughput in a fast and obvious manner.