Title: Information-Theoretic Prescriptions for Outdoor Wireless Communication
Speaker: Upamanyu Madhow, University of California, Santa Barbara
Date: Thursday, November 14, 2002, 4:30 pm
Location: DIMACS Center, Room 431 CoRE Bldg., Rutgers University, Busch Campus, Piscataway, NJ
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.
Seminar Sponsored by DIMACS Special Focus on Computational Information Theory and Coding.