Monday March 9, 2009
8:20 - 10:00AM

Computational Aspects and Algorithms for Dynamic Spectrum Allocation

Dr. Vahid Tarokh
Harvard University
United States

 

 

 



Abstract

In many emerging wireless networks (such as ad hoc networks, cognitive radios, etc.), no central frequency allocation authority is available. This makes distributed frequency allocation an important but mostly unchartered territory in wireless networking. However, it is well-known that optimal dynamic frequency assignment is a computationally hard problem.

We will first discuss emerging applications for dynamic frequency allocation and then discuss the underlying computational issues. We then discuss some of the existing proposed solutions to dynamic frequency allocation in different contexts, such as methods based on graph coloring and iterative water filling. These approaches either excessively simplify the interference models, or are not fully decentralized, or require too much information exchange between autonomous entities, or suffer from all these shortcomings. Additionally, they are all too complex to implement.

Subsequently, for a specific class of networks, we disclose a simple, fully distributed, greedy asynchronous interference avoidance algorithm (GADIA) that requires neither any information exchange between autonomous devices, nor even any knowledge of the existence of other autonomous entities. The GADIA algorithm achieves performance close to that of a centralized optimal algorithm for this class of networks, and achieves about 90% of the Shannon capacities corresponding to the optimum/near-optimum centralized frequency band assignments. Additionally, it can be used in conjunction with any realistic wireless radio channel model such as those commonly employed in wireless standards.

We prove the convergence of the GADIA algorithm to a sub-optimal solution, and develop performance bounds showing that this sub-optimal solution is near-optimal under various practical node activity models. In particular, using stochastic analysis, we introduce a framework to analyze the performance of the GADIA in the presence of time-varying activity rates of clusters. This framework opens the possibilities of both open loop and closed loop stochastic control to improve the performance of distributed frequency allocation. Extension of Gadia to more general networks and addressing the underlying computational problems remain an open problem.

This is a joint work with Behtash Babadi.

Speaker's Bio
Dr. Vahid Tarokh worked at AT&T Labs-Research and AT&T wireless services until August 2000, where he was the head of the Department of Wireless Communications and Signal Processing. In September 2000, he joined Department of Electrical Engineering and Computer Sciences (EECS) at MIT as an associate professor. In June 2002, he joined Harvard University as a Gordon McKay Professor of Electrical Engineering . Since July 2005, he is a Hammond Vinton Hayes Senior Fellow of Electrical Engineering at Harvard University, and a Perkins professor. His research is mainly focused in the areas of Signal processing, Communications (wireline and wireless) and Networking. He has received a number of awards and holds 2 honorary degrees.

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Wednesday March 11, 2009
8:20 - 10:00AM

Astronomy in Hawaii: Exploring Our Universe with the Largest Telescopes in the World

Dr. Rolf-Peter Kudritzki
Director of the University of Hawaii's Institute for Astronomy

United States

 

 

 



Abstract

Astronomy, like no other science, has revolutionized our thinking about the world and our human existence. With every new generation of technology, more and more powerful telescopes have contributed to extending our knowledge of the universe. Today, the largest and most powerful telescopes in the world are located in Hawaii on the summit of Mauna Kea (14,000 feet). The many spectacular and fundamental discoveries made with these new facilities are the subject of this presentation. We will discuss the detection of new worlds such as planets orbiting around other stars, proto-planetary disks forming new planetary systems, the black hole in the center of our galaxy, dark matter and dark energy and the accelerated expansion of the universe, and the detection of galaxies 13 billion light years away from us. We will also discuss the scientific potential and scope of the coming next generation telescopes, which will take us even further in this breathtaking endeavor to understand the cosmos we live in.

Speaker's Bio
Dr. Rolf-Peter Kudritzki has been the Director of the University of Hawaii's Institute for Astronomy since October of 2000. Dr. Kudritzki was formerly a Professor of Astronomy and Director of the Institut für Astronomie und Astrophysik at the University of Munich. Since the summer of 1999, he has been Dean of the Faculty of Physics at the University of Munich. He has also been a director of the Max-Planck-Institut für Astrophysik. Dr. Kudritzki's research activities and international collaborations have led to his participation and membership in a wide range of international committees. For many years he has been a member and chair of the advisory Visiting Committee for the Hubble Space Telescope Science Institute, located at the Johns Hopkins University. In addition, he was chair of the European Southern Observatory Advisory Committee, and is a member of the Board of Directors of the Association of Universities for Research and Astronomy (AURA). AURA manages U.S. national observatories located in Arizona, New Mexico and Chile; the two international Gemini observatories, which are located in Chile and Hawaii; and the Hubble Space Telescope Science Institute. He is also the chair of the National Science Working group for the Next Generation Giant Segmented Mirror Telescope. In addition to his administrative responsibilities, Dr. Kudritzki has continued to pursue a career as an active researcher. His recent research has been in the area of the investigation of the physics of stars and galaxies, and in particular their evolution. For the past ten years, he has been involved in the development of new telescopes and telescope instrumentation. He has published more than 200 publications in refereed journals and has been invited frequently to give presentations at international science conferences. He has supervised more than 30 Ph.D. students, many of whom now are professors themselves. From January 2003 to December 2004, Dr, Kudritzki has held the title of Interim Vice Chancellor for Research and Graduate Education at the University of Hawaii. Dr. Kudritzki holds a diploma in Physics and a Ph.D. in Astronomy from the Technische Universität, Berlin.



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