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TITLE: Multi-Antenna Gaussian Broadcast Channels
SPEAKER: Sriram Vishwanath
Department of Electrical and Computer Engineering
University of Texas at Austin
DATE: 2:00 - 3:00 P.M., Wednesday November 19, 2003
LOCATION: Sigma, 1 L (PA)
HOST: Vinay Deolalikar
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.
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