Multi-Antenna Gaussian Broadcast Channels

Mr. Sriram Vishwanath

Stanford University, California

Monday, April 7th, 10:30 AM, ENS 637

Abstract

Wireless systems continue to strive for ever higher data rates. This goal is particularly challenging for systems that are power, bandwidth, and complexity limited. However, another domain can be exploited to significantly improve system performance the use of multiple transmit and receive antennas. The study of the fundamental limits of these multiple antenna (also called multiple input multiple output) systems is essential for understanding and exploiting the enormous potential of these systems.

In this talk we present new results on the multi-antenna downlink system, also called the MIMO broadcast system. The downlink is a one-to-many communication system, where one transmitter (a base-station, an access-point) transmits different data to many receivers (cellular phones, laptops etc.), and the channels between the transmitter and receivers are given by matrices. Since matrices have no absolute ordering, i.e. no receiver is clearly better or worse than the others, analysis of the multi-antenna downlink is a difficult problem.

We present a "duality" connection between the multi-antenna downlink and the multi-antenna uplink, a many-to-one system. This duality builds a mathematical connection between the two systems, and highlights the synergy between them. We then exploit this duality connection to characterize the maximum sum of rates (sum capacity) of the system. We also obtain results on the entire capacity region of the downlink. Specifically, we characterize the capacity region when the input to the system is constrained to be Gaussian. Lastly, we obtain asymptotic results such as growth rate and limiting distribution of capacity with the number of transmit antennas.

Biography

Sriram Vishwanath received his B.Tech. in Electrical Engineering from the Indian Institute of Technology (IIT) Madras in 1998, and an M.S. in Electrical Engineering from the California Institute of Technology, Pasadena in 1999. He is currently working towards his Ph.D. in Electrical Engineering at Stanford University. His research interests include information theory, coding theory and wireless systems. His industry experience includes work at the National Semiconductor Corporation (NSC) in the summer of 2000 and at the Lucent Bell labs during the summer of 2002.

Mr. Vishwanath is a recipient of the Stanford graduate fellowship and the Stanford graduate community service award.

A list of Wireless Networking and Communications Seminars is available at from the ECE department Web pages under "Seminars". The Web address for the Wireless Networking and Communications Seminars is http://signal.ece.utexas.edu/seminars