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Information-Theoretic Prescriptions for Outdoor Wireless Communication
Upamanyu Madhow
University of California, Santa Barbara:
Thursday November 14, 2002 4:30 pm, Rutgers University, CoRE 431:
Shannon capacity on the classical Additive White Gaussian Noise (AWGN)
channel can now be attained using iteratively decodable random-looking
codes, such as turbo codes and low density parity check codes. It is
the belief of many researchers that similar techniques are broadly
applicable to a much larger class of communication systems. This
observation motivates research in two closely related directions:
computing information-theoretic limits for channel models appearing in
practice, and devising turbo-like techniques for attaining such
limits. In this talk, we examine outdoor wireless communication
systems from this perspective, paying special attention to channel
variations in time (due to relative mobility between transmitter and
receiver), frequency (due to multipath propagation), and space (due to
the angular spread of multiple paths from transmitter to receiver).
Two special cases are discussed in detail. The first focuses on
narrowband, time-varying, frequency nonselective channels. Our
investigation of time-varying channels reveals that standard
constellations, used in conjunction with suitable ``noncoherent''
turbo-like frameworks, can be used to approach capacity when the
fading is relatively slow, but that new kinds of constellations and
design techniques must be devised for high-rate communication over
rapidly varying channels. The second class of systems considered is
that of wideband, time-invariant, frequency selective channels,
possibly with multiple antennas at the transmitter and/or receiver.
By abstracting the essential features from channel measurements and
models reported in the literature, we obtain a framework for
characterizing the outage rate in a simple fashion as a function of a
statistical description of the wideband ``space-time'' channel in
terms of a few key parameters.
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