Research And Implementation Of Fast Handoff Scheme In Sharing WiFi System

Since the 1990s, the WLAN(Wireless Local Networks)with wireless communicationtechnology and computer network coverage ,wiring flexibility, fast transmisson speed and many other advantages has been rapidly developed and applied. In the WLAN standards, the IEEE 802.11 series standards have actually become the common standards of close distance wireless communication technology because of its simple spcefications, gond compaibiliy and many manufacturers'support.Althoug WLAN can provide sufficient bandwidth formpbile applications,because the wireless access point transmission power and the scope of its service coverage are limited the usere are increasingly unsatisfied with surfing the Internet in the fixed AP( Access Point)service area, which, makes thc MN(Mobile Node) need for frequent switching between different APs in the proess of moving. And IEEE 802. 11 "first break after link idea greatly limits the MN switching performance , resulting the handoff latency which seriously affectes yhe communication quality of service and real-time application userexperience.Therefore,how to reduce the handoff latency of MAC(Media Access Control) layer and improve the roaming switching performance of MN in the network have become a key technolngy to solved urgently in IEEE 802.11 mobile switching management research .In view of the above problems, this paper makes the following three points :(1) First of all, theoretically 1 analyze the traditional IEEE 802.11 wireless network MAC layer handoff mechanism and the latecy of each stage,and the conclusion that thescanning phase is an important gactor caused by handoff latency, and then take some improvemrnts to the stage of the alogorithm .(2)Based an charnnel priority and masking mechanism ,the paper designs a new channel selection and scanning algorithm ,that is, reducte the channel scan namber algorithm.On this basis, the improved selective neighbor graph caching algorithm was used to upload the AP-related information scanned and accessed by the MN to the server using the neighbor map principle. The server optimizes the sorting of the neighbor AP according to the signal strength indication, the user load and the historical access data received, and then caches the AP list information to the local, waiting for the MN to switch .(3) Finally, in the built-in shared WiFi system ,the network protocol analysis software WireShark was used to analyze the horizontal handoff performance of the MN between the APs.The experimental results show that compared with the traditional full-channel scanning algorithm, the improved handoff algorithm in this environment can effectively reduce the overall handoff latency, and finally meet the quality of service requirements of real-time business .