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Thesis Defense - Yee

Ordering and Combinatorial Effects of Wireless Optimizations in Beam Forming 802.11 WLANs
Computer Science PhD Candidate

Optimizing the aggregate throughput of 802.11 WLANs is an important challenge due to its increasing popularity and shared, finite spectrum. The common practice in optimization design is to address a problem domain, such as channel assignment or transmit power control, and test it across various environments, topologies and traffic rates. This approach, however, provides only a limited context for network administrators, who must decide not only the best combination, but also the best ordering of these independently derived and tested solutions.

This work presents a characterization of the combinatorial and ordering effects of algorithms from five optimization domains, including: channel assignment, association control, transmit power control, bit-rate adaptation and beam form selection. A centralized, measurement-driven system is proposed, implemented, and tested in a simulator and a field deployment to administer these optimization configurations in an outdoor 802.11b WLAN featuring multiple, beam forming access points. Aggregate throughput results are processed by a decision tree to classify optimization configurations into top and bottom tiers using pairwise ordering and algorithm selection attributes. The results demonstrate that: (1) the relative ranking of an algorithm from an optimization domain is dependent upon the combination and ordering in which it is applied and (2) the ordering of a set of algorithms is as significant to final performance as the combination selected. This not only provides a series of optimization design guidelines, but also implies that the design of optimization algorithms must be considered over a broad set of combinations and orderings to fully determine their real world efficacy.

Committee: Douglas Sicker, Associate Professor (Chair)
Dirk Grunwald, Professor
Timothy Brown, Department of Electrical and Computer Engineering
Shivakant Mishra, Associate Professor
Romit Choudhury, Duke University
Department of Computer Science
University of Colorado Boulder
Boulder, CO 80309-0430 USA
May 5, 2012 (14:20)