Research On Fast Cross-zone's Handover Algorithms Based On MAC Layer In WLAN

Wireless local area network (WLAN) is the combination of computer network and wireless communication technology, which has been widely used at present. Because of the limitation of AP's power in WLAN lead to a restriction of the service coverage area, the mobile station (STA) need fast handover when crossing the zone from the current coverage cell to another cell. The problem about cross-zone handover is the key issue of the current application technology in WLAN, which not only is related to the reliability and security of network processing, but the continuous quality of voice and video's real-time multimedia application. It should be pointed out that handovers first have to occur on the MAC layer, on the other hand, most of the handovers are just on the MAC layer. Therefore, there are important theoretical significance and practical value for the research on the cross-zone handoff technology based on the MAC layer.Based on the relevant literatures at home and abroad, in this dissertation the work are finished as follows:1. The status of current researches in terms of domestic and foreign handover technology based on the MAC layer in WLAN are analyzed and summarized. It is the brief introduction and evaluation of the selective scan algorithm (including Neighbor Graph algorithm, WSN algorithm), advanced scan algorithm, the authentication stage algorithm (including FHR prediction algorithm, Orientation algorithm, Neighbor Graph authentication algorithm), reassociation stage algorithm (including prediction algorithm, Neighbor Graph reassociation algorithm) and so on. The complete handover process is included three stages: channel scan, authentication and reassociation. especially the delay time of scan stage is about 90%, but authentication and reassociation are short, and it is compared with the WLAN and GSM's handover problems.2. Those algorithms concerning the various stages in the handover process based on neighbor graph technology are in summary unified for the Neighbor Graph algorithm series (NGAS), and is proposed to the technology synthetic unity to NGAS.3. The Mobile Station Orientation algorithm based on NG (MSO) is proposed in this dissertation, which is a quasi-minimum time delay's algorithm. According to apply to various users in WLAN environment with different density, structure and layout, three mechanisms to achieve the program are proposed, including selelcting the target AP based on the distance among neighbor APs, selelcting the target AP based on the movement direction and selelcting the target AP based on QoS protection.These three mechanisms can be used by setting the priority order, which can be dealed with the current initial neighbor graphs and effectly streamlined the current neighbor graph's numbers to reduce the handover's time delay superiorly.4. According to the characteristics in the subway or light rail model about the wireless AP's scheme is linear, the STA's mobile trajectory is assurance, the adjacent AP along the track line with the same frequency wireless network structure, it is applied to the MSO algorithm in the subway or light rail project's cross-zone handovers, which is pointed out the algorithm can be reduced delays very well and achieved the mobile communication's application needs between the train and ground.5. Finally, the simulation experiment is made by using the OPNET's network simulation tools for various algorithms in the dissertation and the subway or light rail project's application, which is pointed out the new algorithm proposed in this dissertation compared with the existing algorithms is better to reduce handover delays.