Interference Alignment and Degrees of Freedom of Wireless Networks

SPEAKER: Professor Syed Jafar, University of California, IrvineABSTRACT: The talk will present new insights into the capacity of fully connected wireless networks with finite number of nodes through capacity approximations that are accurate to within a bounded constant for all SNR. While the best known outerbound for the K user interference channel states that there cannot be more than K/2 degrees of freedom, it has been conjectured that in general the constant interference channel with any number of users has only one degree of freedom. In this talk, we show that K/2 degrees of freedom can be achieved by channel design, i.e. if the nodes are allowed to choose the best constant, finite and non-zero channel coefficient values. Even if channel coefficients cannot be controlled by the nodes but are selected by nature, i.e., randomly drawn from a continuous distribution, the total number of spatial degrees of freedom for the K user interference channel is almost surely K/2 per orthogonal time and frequency dimension. In other words we will show how to achieve K/2 interference free channels per time and frequency dimension in a K user interference network of single antenna nodes. Thus, only half the spatial degrees of freedom are lost due to distributed processing of transmitted and received signals on the interference channel. We will also characterize the benefits of cognitive message sharing among nodes from a degrees of freedom perspective.BIO: 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 Ph.D. degree in Electrical Engineering from Stanford University, Stanford, CA USA 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 and the UC Irvine Engineering Faculty of the Year award in 2006. Dr. Jafar serves as the Editor for Wireless Communication Theory and CDMA for the IEEE Transactions on Communications.Host: Giuseppe Caire, caire@usc.edu

Location: Hughes Aircraft Electrical Engineering Center (EEB) - 248

Audiences: Everyone Is Invited

Contact: Mayumi Thrasher