| Summary: | 碩士 === 國立交通大學 === 資訊管理研究所 === 85 === The performance of the handoff algorithm is the primary concern
for supporting mobile devices with roaming capability in
wireless communications. The IEEE 802.11 standard for wireless
local area networks(LANs) recommends carrier sense multiple
access with collision avoidance(CSMA/CA) as the medium access
control(MAC) protocol. The contention-based CSMA/CA access
mechanism is sensitive to the traffic load whereas the
assignment-based access mechanism used by wireless telephone
networks is not. Heavy traffic load in wireless LANs causes
significant degradation of network performance. Thus
conventional handoff algorithms employed in wireless telephone
networks are not applicable to wireless LANs. In this thesis,
after examining existing handoff algorithms for wireless
communications, we propose a handoff algorithm for wireless
LANs. This algorithm considers traffic load as an important
factor for initiating handoff. In normal traffic load, signal
strength measurements from various access points are used the
same as conventional handoff algorithms. However, in heavy
traffic load, absolute threshold and hysteresis margin of
channel traffic are taken into account. A simulation model is
developed to study the performance of the proposed algorithm.
The relationship between QoS parameters and handoff initiation
criteria is analyzed. Moreover, simulation results show how
handoff initiation criteria might be set in accordance with the
quality of services requested by users.
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