# An antenna-independent approach to the capacity of a wireless system

Abstract (Summary)

KISHORE, PINAK. An Antenna-Independent Approach to the Capacity of a Wireless
System. (Under the direction of Professor Brian L. Hughes.)
Information theory (IT) promises a huge increase in capacity for systems equipped
with multiple antennas at both the transmitter and receiver (called Multiple-Input
Multiple-Output or MIMO) in a rich multipath scattering environment relative to
single antenna systems (called Single-Input Single-Output or SISO). Since the first
results on capacities for MIMO systems were published by Telatar [2] and Foschini
et al. [3], there has been an extensive research effort to develop techniques and
algorithms to realize the gains promised by MIMO systems. Most of these studies
have focussed on particular antenna systems such as uniform linear arrays and have
derived channel capacities using a statistical signal-space approach under ideal fading
conditions. The number and locations of the antennas in such systems, however
constrains the information that is extracted from the underlying electromagnetic field
thereby giving antenna-dependent capacity results. To overcome these constrains
imposed by particular antenna systems and to find the true capacity of systems
limited only by their volume, we need to look at continuous-time systems in an
antenna-independent way. In this thesis, we look at one such system which consists
of a spherical volume at the transmitter having some arbitrary current distribution
and radiating an electric field around it. The receiver consists of a spherical shell
located in the far-field of the transmitter capturing all the signals radiated by it. We
then use electromagnetic theory to derive the input-output equation for this system
and use an orthonormal series expansion to reduce it to the form of a MIMO channel.
We then calculate the capacity and the spatial degrees of freedom for such a system
and look at how they vary with the size of the transmitting volume and the available
transmitter power. We show that the spatial degrees of freedom grow linearly with
the effective aperture of the spherical volume and the capacity grows even faster.
We also investigate the increase in spatial degrees of freedom and capacity that can
be achieved by using three-dimensional (tri-polarized) current distributions at the
transmitter instead of one-dimensional (uni-polarized) current distributions. We show
that capacity gains of 3 times can be achieved for a sufficiently large transmitter.
Lastly, we look at a more realistic complete transmit-receive system with an identical
spherical volume at the receiver and an ideal fully-scattered channel connecting the
transmitter to the receiver. We model the channel as a Rayleigh fading channel and
compare the results on capacity and spatial degrees of freedom with previous results.
An Antenna-Independent Approach to the Capacity of a Wireless System
by
Pinak Kishore
A thesis submitted to the Graduate Faculty of
North Carolina State University
in partial fulfillment of the
requirements for the Degree of
Master of Science
Department of Electrical and Computer Engineering
Raleigh
August 12, 2005
Bibliographical Information:

Advisor:

School:North Carolina State University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:north carolina state university

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