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.
=========================================================================
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.
