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Series in Communication Theory
Edited by Helmut Bölcskei
Diversity-Multiplexing Tradeoff in Selective-Fading Channels.
1st edition 2009. XX, 146 pages; € 64,00. ISBN 3-86628-251-6
Recent years have seen the proliferation of new wireless data applications that have fueled the demand for communication systems capable of delivering very high quality-of-service (QoS) in terms of data rate and reliability. At the same time, due to the surge in the number of wireless devices, the spectrum available for communication has become scarcer, and the level of interference has increased significantly. The design of systems satisfying stringent QoS requirements is therefore a particularly challenging task that requires an accurate understanding of the ultimate performance of communication over wireless channels. In fading channels, the diversity-multiplexing (DM) tradeoff framework proposed by Zheng and Tse (2003) has proved to be very helpful in understanding performance in terms of how rate and reliability interplay in the high SNR regime. The analysis conducted in this thesis adopts this framework and uses the notions of diversity and multiplexing to capture, respectively, the reliability and data rate of the system.
In many situations of practical relevance, the wireless channel exhibits time and frequency selectivity arising from temporal variations in the environment and multipath propagation. A direct characterization of the DM tradeoff in this class of channels, referred to as selective-fading channels, is in general difficult because the corresponding mutual information is a sum of correlated random variables. This thesis presents a technique that bypasses this difficulty and establishes the optimal DM tradeoff of selective-fading channels in both the point-to-point case and the multiple-access (MA) case. The essence of our approach is to study the "Jensen channel" that is associated with the original channel and that has the same behavior in the regime of high SNR relevant to the DM tradeoff framework.
In the point-to-point case, we obtain a code design criterion that guarantees optimal performance, and we develop a systematic procedure to construct optimal codes. Our investigation of selective-fading MA channels yields an interesting conceptual relation between the DM tradeoff framework and the notion of dominant error event, which was first introduced in AWGN channels by Gallager (1985). Studying the dominant error event as a function of the users' rates reveals the existence of operational regimes in which multiuser interference has only a negligible impact on error performance. As in the point-to-point case, we obtain a set of code design criteria that guarantees optimal performance to all users. We finally examine a code construction which satisfies our criteria for the two-user flat-fading channel.
About the Author
Pedro E. Coronel received the M.Sc. degree from EPF Lausanne, Switzerland, in 2002. He was an exchange student at KTH Stockholm, Sweden, in 1999 and studied at the Eur´ecom Institute, Sophia-Antipolis, France, in 2001. In 2002, Mr. Coronelwas an intern with the IBM Zurich Research Laboratory, Switzerland, where he worked on a wireless local area network (WLAN) prototype. He returned to IBM Research as a pre-doctoral fellow in 2003, pursuing a doctorate at ETH Zurich in parallel. In 2006, he joined the Communication Technology Laboratory at ETH Zurich as research assistant. Mr. Coronel received the Dr. sc. degree from ETH Zurich in 2008.
Keywords: diversity-multiplexing tradeoff, performance limits of communication, Jensen channel, wireless communication, selective-fading channels, point-to-point channels, multiple-access channels, code design criteria, code construction
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