Interference Alignment and the Capacity of Wireless Networks

Prof. Syed Jafar
University of California Irvine

Tuesday December 9, 2008 at 1:00 - 2:00pm
Conference Room 54-134 EIV

Abstract
The talk will present new insights into the capacity of wireless networks with a finite number of interfering nodes. A widely held belief in network design, and also a formal conjecture, is that for an interference network with K users competing for the same spectrum, at high SNR (when both signal and interference powers are strong), it is capacity-optimal to divide the network degrees of freedom (bandwidth) among the users in a cakecutting fashion so that each user gets a fraction 1/K of the total spectrum. We disprove this conjecture and establish that even with K > 2 users competing for the same spectrum, each user is able to access a fraction 1/2 of the total spectrum free from interference - i.e. everyone gets half the cake. To prove this result we introduce a new scheme, called interference alignment, where signals are designed to cast overlapping shadows at the receivers where they are not desired while they remain distinct at the receivers where they are desired. Interference alignment is shown to be the capacity optimal scheme for a wide variety of wireless interference networks at high SNR and for certain classes of networks at any SNR. Examples are provided for different types of interference alignment schemes that exploit the relativity of alignment in space, time, frequency and code dimensions.

Biography
Syed Ali Jafar received the B. Tech. degree in Electrical Engineering from the Indian Institute of Technology (IIT) Delhi, India in 1997, the M.S. degree in Electrical Engineering from California Institute of Technology (Caltech), Pasadena USA in 1999, and the PhD degree in Electrical Engineering from Stanford University, Stanford, CA in 2003. His industry experience includes positions at Lucent Bell Labs, Qualcomm Inc. and Hughes Software Systems. He is currently an Assistant Professor in the Department of Electrical Engineering and Computer Science at the University of California Irvine, Irvine, CA USA. His research interests include multiuser information theory and wireless communications. Dr. Jafar received the NSF CAREER award in 2006 and the ONR Young Investigator Award in 2008. He received the UC Irvine Engineering Faculty of the Year Award in 2006 for excellence in teaching. He is a corecipient of the DARPA ITMANET Young Investigator Team Award. Dr. Jafar serves as Associate Editor for IEEE Transactions on Communications and for the IEEE Communications Letters.