October 15, 2010
EE Conference Room
Hosted by: Columbia University Joint CS/EE Networking Seminar Series
Speaker: Dr Vijay G. Subramanian (Hamilton Institute NUIM, Ireland)
Given the wide-spread deployment of 802.11-based WLANs and proposals of mesh networks constructed using these WLANS, there is considerable interest in extending established concepts of fair resource allocation in wired networks to wireless networks. To do this, wired model assumptions must be adapted to be relevant for wireless networks as, for example, in wireless networks losses due to environmental conditions may occur even in the absence of queueing congestion. Thus fundamental questions of the existence and uniqueness of fair rate allocations must be reconsidered. In this talk we treat wireless networks characterized by lossy channels, spatial channel reuse, multiple routes and frequencies. First we consider an omniscient view and establish the existence and uniqueness of utility fair and max-min fair solutions and that, as loss rates decrease, fair allocations converge to the loss-less ones. Through examples we illustrate distinctive features of fair solutions that arise when non-congestion based losses occur. In the second part of the talk we consider the implications of the 802.11 Distributed Coordination Function. We establish the log-convexity of the rate region in 802.11 WLANs. This generalises previous results for Aloha networks and has immediate implications for optimisation based approaches to the analysis and design of 802.11 wireless networks. We then build upon the log-convexity result and, for the first time, characterise max-min fair rate allocations for a large class of 802.11 wireless mesh networks. We conclude with some recent work on directly using maximal convex subsets of the rate-region to characterise utility fairness that cannot be achieved through the log-convexity approach.
Vijay G. Subramanian received the B.Tech. degree from the Department of Electrical Engineering, Indian Institute of Technology, Madras, India, in 1993, the M.S. degree in Electronic Communication Engineering from the Indian Institute of Science, Bangalore, India, in 1995, and the Ph.D. degree in Electrical Engineering from the University of Illinois at Urbana-Champaign, Urbana, in 1999. From 1999 to 2006, he was with the Networks Business, Motorola, Arlington Heights, IL. Since May 2006, he has been a Research Fellow at the Hamilton Institute, NUIM, Ireland. His research interests include information theory, communications, communication networks, wireless networks, queueing theory, applied probability and stochastic processes, and theoretical immunology.
More information about Subramanian is available at: http://www.hamilton.ie/vsubramanian/