[CUWiN] SPECIAL COMMUNICATIONS SEMINAR: "Wireless networking:
impact of the physical layer"
sascha at ucimc.org
Fri Mar 3 02:27:18 CST 2006
Title: "Wireless networking: impact of the physical layer"
Speaker: Rohit Negi, Carnegie Mellon University
Date: March 9, 2006
Time: 4-5 pm
Place: 141 CSL
We consider several illustrative situations to show that the details of the
physical layer have a strong impact on the optimal protocols for a wireless
network, and thus on the capacity of the network. These examples will also serve
to highlight some of my current research.
The first example considers a wireless ad hoc network, with a
'Ultrawideband-like' physical layer. Specifically, the assumption is that each
link has low spectral efficiency, with finite power and infinite bandwidth,
which is typical of UWB, or sensor networks. We show that, contrary to the
intuition in [GuptaKumar00], the capacity of such a network increases with node
density, on the order of n(α-1)/2, where n is the node density and α is the
distance-loss exponent. This also results in a different set of optimal protocols.
The second example considers the problem of joint optimization of an ad hoc
network, with network level metrics. We show that the problem decomposes neatly
into 'layers' of networking, where we are able to quantify the concept of
'network layering'. We solve the problem by designing optimal algorithms. An
application of the algorithms to a UWB ad hoc network verifies the dramatic
information theoretic result shown in the first example.
Finally, if time permits, I will show a third example in which we have designed
a 'queued channel code' for operation over a time-varying wireless channel. A
queued channel code is an information theoretic channel code, which incorporates
ideas from network queuing theory. We show that this code achieves better
performance than either pure coding or pure queuing. This is along the lines of
our previous work, where we defined an 'effective capacity' notion for a
time-varying wireless channel.
Rohit Negi received the B.Tech. degree in Electrical Engineering from the Indian
Institute of Technology, Bombay, India in 1995. He received the M.S. and Ph.D.
degrees from Stanford University, CA, USA, in 1996 and 2000 respectively, both
in Electrical Engineering. He has received IIT Bombay's prestigious President of
India Gold medal in 1995.
Since September 2000, he has been with the Electrical and Computer Engineering
department at Carnegie Mellon University, Pittsburgh, PA, USA, where he is
currently an Associate Professor. His research interests include communications
systems, information theory, and networking with a cross-layer viewpoint.
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