ECE Seminar Series

Electrical and Computer Engineering Seminar

Title: Interference Alignment in MIMO Interference Channels: Feasibility and Transceiver Design
Speaker: Ignacio Santamaria
Affiliation: University of Cantabria, Spain
Day: Wednesday, September 9, 2015
Time: 11:00 am - 12:00 pm
Location: LSC 376-378

Abstract: Recently, it has been shown that to achieve the maximum degrees of freedom (DoF) of the K-user multiple-input multiple-output (MIMO) interference channel, the interference from other transmitters must be aligned at each receiver in a lower-dimensional subspace. This is the basic idea of the interference alignment (IA) technique, which has received a lot of attention since it was first proposed for the 2-user X network in 2008. In this talk, we will present some recent results obtained by our research group on this topic. In the first part of the talk, we will consider the feasibility of linear interference alignment (IA) for arbitrary MIMO networks, and propose a polynomial-time test for this problem, which amounts to checking the rank of a matrix. In the second part of the talk, we will consider the problem of how many different IA solutions exist for a given scenario. We show that when the number of polynomial equations matches the number of variables and the system is feasible, the number of IA solutions for a given scenario is finite and constant for any channel realization out of a zero-measure set. To systematically count (or accurately estimate) all IA solutions, besides being of theoretical interest on its own right, proves to be useful to further reveal the rich algebraic-geometric structure of IA problems. An integral formula, which generalizes previous IA feasibility results, gives the theoretical answer to this problem. For single-beam MIMO networks this formula admits a closed-form expression, which allows us to establish some connections between our results and well-known combinatorial problems in graph theory. Since even for moderate size systems the number of solutions is huge, in the last part of the talk we will analyze how many solutions should be explored to achieve a given portion of the maximum attainable sum-rate. As we will show, all these solutions can be systematically found by using homotopy-continuation algorithms.

Bio: Ignacio Santamaría received his Telecommunication Engineer Degree and his Ph.D. in electrical engineering from the Universidad Politécnica de Madrid (UPM), Spain, in 1991 and 1995, respectively. In 1992 he joined the Department of Communications Engineering, University of Cantabria, Spain, where he is currently Full Professor. He has co-authored more than 200 publications in refereed journals and international conference papers and holds 2 patents. His current research interests include signal processing algorithms and information-theoretic aspects of multi-user multi-antenna wireless communication systems, multivariate statistical techniques and machine learning theories. He has been involved in numerous national and international research projects on these topics. Dr. Santamaria was a Technical Co-Chair of the 2nd International ICST Conference on Mobile Lightweight Wireless Systems (MOBILIGHT 2010), Special Sessions Co-Chair of the 2011 European Signal Processing Conference (EUSIPCO 2011), General Co-Chair of the 2012 IEEE Workshop on Machine Learning for Signal Processing (MLSP 2012). He has been a member of the IEEE Machine Learning for Signal Processing Technical Committee (2009-2014). Currently, he serves as Associate Editor and Senior Area Editor of the IEEE Transactions on Signal Processing. He was a co-recipient of the 2008 EEEfCOM Innovation Award, as well as coauthor of a paper that received the 2012 IEEE Signal Processing Society Young Author Best Paper Award.