Wolfgang Utschick - Distinguished Lecture - Tuesday June 29 - 12:00 - Sala de Seminarios D5

Interference Alignment in Single-Beam MIMO Networks: Algorithms and
Large System Analysis

Summary

To achieve the full multiplexing gain of MIMO interference networks at high SNRs, the interference from different transmitters must be aligned in lower-dimensional subspaces at the receivers. Recently a distributed max-SINR algorithm for precoder optimization has been proposed that achieves interference alignment for sufficiently high SNRs. We show that this algorithm can be interpreted as a variation of an algorithm that minimizes the sum Mean Squared Error (MSE). To maximize sum utility, where the utility depends on rate or SINR, a weighted sum MSE objective is used to compute the beams, where the weights are updated according to the sum utility objective. We specify a class of utility functions for which convergence of the sum utility to a local optimum is guaranteed with asynchronous updates of beams, receiver filters, and utility weights. In the second part we consider a network of K interfering transmitter receiver pairs, where each node has N antennas and at most one beam is transmitted per user. We investigate the asymptotic performance of different strategies, as characterized by the slope and y-axis intercept (or offset) of the high signal-to noise ratio (SNR) sum rate asymptote. It is known that a slope (or multiplexing gain) of 2N-1 is achievable with interference alignment. On the other hand, a strategy achieving a slope of only N might allow for a significantly higher offset. With the assumption that only a discrete number of strategies is able to achieve a slope of 2N-1 for a given channel realization, we approximate the average offset when the best out of a large number L of these solutions is selected, by means of extreme statistics. Furthermore, we derive a simple large system approximation for a successive beam allocation scheme achieving a slope of N. We show that both approximations provide good matches to numerically simulated results for moderate system dimensions and discuss how the approximated asymptotes behave for larger systems depending on the relationship between L and N. (Joint work with David Schmidt from TUM and Michael L. Honig from Northwestern University, Illinois, USA).

Bio

Wolfgang Utschick completed several industrial education programs before he received the diploma ('93) and doctoral degrees ('98) in electrical engineering, both with honors, from Technische Universität München (TUM). In this period, he held a scholarship of the Bavarian Ministry of Education for exceptional students. From '98 - '02, he co-directed the Signal Processing Group at the Institute of Circuit Theory and Signal Processing at TUM. From '00 to '02, he was consulting in 3 GPP standardization in the field of multi-element antenna systems. In 2000, he was a visiting researcher at ETH Zurich and in 2005, he was a guest professor at the University of Edinburgh. In 2002, Dr. Utschick was appointed Professor at TUM where he is head of the Fachgebiet Methoden der Signalverarbeitung (Associate Institute for Signal Processing). He gives courses on Signal Processing, MIMO Systems, Stochastic Processes, and Optimization Theory (Crosslayer Design, Resource Allocation) in the field of Wireless Communications. He holds some 10 patens in the field of multi-antenna signal processing and has authored and co-authored more than 200 technical articles in international journals and conference proceedings. Dr. Utschick is editor of the Springer book series "Foundations in Signal Processing, Communications and Networking". Dr. Utschick serves as a coordinator and spokesman of the new German wide DFG focus program "Communications over Interference limited Networks" (COIN) which is devoted to topics as cooperative communications, crosslayer design, ad-hoc wireless networks. He is a senior member of the VDE and of the IEEE where he serves as an associate editor for T-SP since '09. From '06 to '09, he was an associate editor for T-CAS1 and T-CAS 2. Dr. Utschick is recipient of the 2007 Award of the German Informationstechnische Gesellschaft (Award of the German Society for Information Technology).