[CUWiN] SPECIAL COMMUNICATIONS SEMINAR: "Wireless networking: impact of the physical layer"

Sascha Meinrath 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.

Sascha Meinrath
Policy Analyst    *  Project Coordinator  *  President
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