ABOUT | Seminar

Seminars 2010

Current seminar series coordinator: Daniel Cederman.

The quest for bridging Information-theoretic and Networking views of shared channels, like the Multi-Access Channel, has utilized many different approaches. In this talk we propose a simple framework to model a 2-user Multi-Access channel that incorporates features of Networking, like random arrivals, queueing, and stability, as well as properties of the physical layer like bit rates and multi-packet reception capability. We characterize the stable throughput region in terms of achievable rate values and explain the connections to the broader issues of rate control. We also consider a related problem of emptying a network in minimum time in terms of rate control.

Anthony Ephremides holds the Cynthia Kim Professorship of Information Technology at the Electrical and Computer Engineering Department of the University of Maryland in College Park where he holds a joint appointment at the Institute for Systems Research, of which he was among the founding members in 1986. He obtained his PhD in Electrical Engineering from Princeton University in 1971 and has been with the University of Maryland ever since. He has held various visiting positions at other Institutions (including MIT, UC Berkeley, ETH Zurich, INRIA, etc) and co-founded and co-directed a NASA-funded Center on Satellite and Hybrid Communication Networks in 1991. He has been the President of Pontos, Inc, since 1980 and has served as President of the IEEE Information Theory Society in 1987 and as a member of the IEEE Board of Directors in 1989 and 1990. He has been the General Chair and/or the Technical Program Chair of several technical conferences (including the IEEE Information Theory Symposium in1991 and 2000, the IEEE Conference on Decision and Control in 1986, the ACM Mobihoc in 2003, and the IEEE Infocom in 1999). He has served on the Editorial Board of numerous journals and was the Founding Director of the Fairchild Scholars and Doctoral Fellows Program, a University-Industry Partnership from 1981 to 1985. He has received the IEEE Donald E. Fink Prize Paper Award in 1991 and the first ACM Achievement Award for Contributions to Wireless Networking in 1996, as well as the 2000 Fred W. Ellersick MILCOM Best Paper Award, the IEEE Third Millennium Medal, the 2000 Outstanding Systems Engineering Faculty Award from the Institute for Systems Research, and the Kirwan Faculty Research and Scholarship Prize from the University of Maryland in 2001, and a few other official recognitions of his work. He also received the 2006 Aaron Wyner Award for Exceptional Service and Leadership to the IEEE Information Theory Society.

In mobile ad hoc networks (MANETs) mobile nodes do not have access to a fixed network infrastructure and they set up a communication network by themselves. MANETs require implementation of a wireless Medium Access Control (MAC) layer. Existing MAC algorithms that consider no mobility, solve the problem of eventually guaranteeing every node with a share of the communications bandwidth. In the context of MANETs, we ask: Is there an efficient MAC algorithm when mobility is considered?

MANETs are subject to transient faults, from which self-stabilizing systems can recover. The self-stabilization design criteria, and related concepts of self-*, liberate the application designer from dealing with low-level complications, and provide an important level of abstraction. Whereas stabilization criteria are important for the development of autonomous systems, adaptation is imperative for coping with a variable environment. Adapting to a variable environment requires dealing with a wide range of practical issues, such as relocation of mobile nodes and changes to the motion patterns.

This work proposes the design and proof of concept implementation of a MAC algorithm named Chameleon-MAC, which is based on a self-stabilizing algorithm by Leone et al., and uses self-* methods in order to further adapt its behavior according to the mobility characteristics of the environment. Moreover, we give an extensive treatment of the aspects and parameters that can bring the algorithm into the practical realm and we demonstrate documented behavior on real network studies (MICAz 2.4 GHz motes) as well as using simulation (TOSSIM), showing improved overhead and fault-recovery periods than existing algorithms. We expect that these advantages, besides the contribution in the algorithmic front of research, can enable quicker adoption by practitioners and faster deployment.

Almost all data found in the real world have a temporal component, or can be visualized with respect to time. Temporal data is prevalent in virtually all scientific domains, and permeates societal phenomena as well---examples include computer and network logs, chronological history, political poll data, stock market information, and climate measurements. One common property of this wide range of data is that the datasets tend to be large, not only in the length of the time period but also in the number of observed attributes. These problems are exacerbated by the fact that many temporal analysis tasks often involve multiple such time series.

Visualization has been suggested as a way to handle this problem, but understanding large-scale temporal datasets require both effective visual representations for viewing them as well as powerful interaction techniques for exploring them. In this talk, I will describe some of my recent and ongoing work on supporting both the visual and interactive aspects of these tasks. More specifically, I will present TraXplorer, a novel system supporting multi-focus interaction of time series data, as well as results from a study evaluating the graphical perception of viewing multiple time series simultaneously using different visual representations.

Navigation capabilities, enabled by GPS, have become an important part of our lives. Unfortunately, in GPS-challenged environments, such as indoors, in urban canyons, or under tree canopies, alternative navigation technologies need to be considered. These include inertial navigation, ultra-wide bandwidth (UWB), and Wi-Fi. Ideally, a mobile device should be able to fuse information from different sources and wireless technologies, as this can improve accuracy and coverage.

In this talk, I will describe recent efforts to leverage to position information from nearby devices to improve overall performance. This leads to so-called cooperative navigation, where mobile devices help one another navigate. The talk will comprise three components. First, I will cover the fundamental performance improvements that cooperation can yield. Secondly, I will show how to develop scalable distributed algorithms that can perform near optimal data fusion, based on the powerful framework of factor graphs. Through computer simulations, I will demonstrate that these algorithms can provide orders of magnitude performance improvements compared to non-cooperative positioning, even in large mobile, networks. Finally, to demonstrate the practical feasibility of cooperative navigation, I will describe the development of a small-scale UWB testbed on the MIT campus.

Henk Wymeersch is Assistant Professor with the Department of Signals and Systems at Chalmers University of Technology, Sweden. Prior to joining Chalmers, he was a Postdoctoral Associate with the Laboratory for Information and Decision Systems (LIDS) at the Massachusetts Institute of Technology (MIT). Henk Wymeersch obtained the Ph.D. degree in electrical engineering/applied sciences in 2005 from Ghent University, Belgium. He is author of the book .Iterative Receiver Design. (Cambridge University Press, August 2007). In 2009 he was part of a team that won the L3 Communication Award for .the practical demonstration of Bayesian UWB localization.. His research interests include algorithm design for wireless transmission, statistical inference, indoor navigation, and iterative processing.