Reliable Communications over Rapidly Time-Varying Channels
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Editorial Reliable Communications over Rapidly Time-Varying Channels Geert Leus,1 Georgios Giannakis,2 Jean-Paul Linnartz,3 Xiaoli Ma,4 Ananthram Swami,5 and ˘ 6 Cihan Tepedelenlioglu 1 Faculty
of Electrical Engineering, Mathematics, and Computer Science, Delft University of Technology, Mekelweg 4, 2628CD Delft, The Netherlands 2 Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, USA 3 Philips Research, 5656 AA Eindhoven, The Netherlands 4 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA 5 Army Research Lab., 2800 Powder Mill Road, Adelphi, MD 20783-1197, USA 6 Department of Electrical Engineering, Arizona State University, Tempe, AZ 85287, USA Received 17 September 2006; Accepted 17 September 2006 Copyright © 2006 Geert Leus et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Wireless communications have become an important part of everyday life. Think for instance about mobile telephone applications, wireless local area networks (WLANs), and wireless ad hoc networks. Most of these systems have been designed assuming that the channel can be regarded as constant over a block of data. Nonetheless market studies predict a rapid growth of high data rate mobile applications such as TV broadcast and video streaming and multiperson wireless gaming. In such mobile applications, Doppler shifts introduce temporal channel variations, which become more pronounced as the carrier frequency increases, and basically violate the time-invariance assumption. Further, with high mobility, terrain changes induce rapid changes in the channel response. As a result, many existing wireless systems can only provide low data rates at high mobility (e.g., UMTS) or even break down completely at high speeds (e.g., DVB-T and IEEE802.16). This special issue therefore focuses on communications over rapidly time-varying channels, which cannot be viewed as time-invariant over a frame. It is intended to gather new and insightful results in this challenging research area that is gaining increasing attention due to its importance in future wireless applications. Different models have recently been proposed to track time-varying channels, such as the basis expansion model (BEM) and the Gauss-Markov model (GMM). Such channel models can be used to efficiently estimate the unknown time-varying propagation channel. In the first two papers,
the authors rely on the complex exponential BEM to develop training-based and semiblind channel estimators. Tugnait et al.exploit superimposed pilots in the first paper, whereas Barhumi et al. exploit time-multiplexed pilots in the second paper. In the third paper by Misra et al., the GMM is considered, and optimal time-multiplexed training is discussed. Channel models like the BEM or the GMM are mainly aimed at modeling the short-term fading. Long-term fad
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