Research On Fast Cross-zone’s Handoff Algorithms Based On WLAN

WLAN is the product of the combination of Computer Network and WirelessCommunication technology, which has the advantages of mobile support, fast buildand low cost. It has gained rapid development and wide application since the1900s.However，the coverage of a WLAN is usually only50-100m and the smallcoverage can only support users with low mobility. Handoff occurs when a mobilestation moves from the current access point coverage to another access point coverage.The traditional handoff scheme always results in a large latency, which can’t meet therequirement of some real-time services. Therefore, how to reduce the handoff latencyis one of the most important focuses in WLAN.The802.11standard defines that a handoff procedure can be divided into3processform logical view. There are scan process, reauthentication process and reassociationprocess. A great number of experiments showed that the latency of scan account foralmost90%of the total latency. Therefore, reducing the probe delay in the scanprocess would improve the MAC layer handofff greatly.In this thesis, the IEEE802.11MAC layer handoff process is analyzed. Severalfast handoff algorithms are introduced including their strengths and weaknesses.Moreover, a fast handoff scheme are proposed based on the HaND algorithm, the newalgorithm reduces the wireless frame type used in the scan process, improves thetransmission reliability of the scan results and reduces the probe delay at the same time.Experiments showed that the new algorithm can reduce the handoff latency in MAClayer effectively.