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Home | Seminars and Symposia | Past seminars/symposia: Monday, May 6, 2002

DTC Seminar Series

Low-Complexity Rake Receivers in Wideband Wireless Channels


Moe Win
Wireless Systems Research Department
AT&T Labs — Research

Monday, May 6, 2002
10:00–11:00 am

402 Walter Library

Multipath fading has been considered traditionally as a major limitation for wireless transmissions in dense multipath channels. However, a wideband system can turn this alleged disadvantage to an advantage by utilizing a high degree of path diversity provided by the channel. Additionally, low-cost technology to process wideband signals is on the horizon, thus great interest in the use of wideband signals for wireless applications now exists. Consequently, wideband systems have recently received much attention from the scientific community, regulatory agencies (e.g., FCC, ITU), and funding agencies (e.g., DARPA, MURI, EC), as well as from the commercial and military sectors. The potential strength of these techniques lies in the use of wide transmission bandwidths, resulting in desirable capabilities including accurate position location and ranging. In this talk, we develop an analytical framework to quantify the effects of spreading bandwidth (BW) on wideband transmission systems operating in dense multipath environments. Our goal is to lay foundations and provide fundamental insights on how wideband reduced complexity Rake receivers can best take advantage of multipath and a theoretical basis for deciding how many "fingers" should be included in the receiver architecture, thus saving cost and power consumption for handheld wireless devices. The focus of the talk is to characterize the performance of reduced-complexity Rake receivers, which are based on either partial combining (called PRake) or selective combining (called SRake). The first is suboptimum and combines the first arriving multipath components, while the second combines the strongest multipath components. Closed form expressions for the mean and the variance of the combiner output signal-to-noise ratio (SNR) as well as analytical symbol error probability (SEP) expressions of the Rake receiver are derived in terms of the number of combined paths, the spreading BW, and the multipath spread of the channel. The proposed problem is made analytically tractable by transforming the physical Rake paths, which are correlated when ordered, into the domain of a "virtual Rake" receiver with independent virtual paths. This enables a simple derivation of the mean, variance, and the SEP for any given spreading BW and an arbitrary number of combined paths.


Dr. Win is a member of Eta Kappa Nu, Tau Beta Pi, Pi Mu Epsilon, Phi Theta Kappa, and Phi Kappa Phi. He was a University Undergraduate Fellow at Texas A&M University, where he received, among others awards, the Academic Excellence Award. At USC, he received several awards including the Outstanding Research Paper Award and the Phi Kappa Phi Student Recognition Award. He was the recipient of the IEEE Communications Society Best Student Paper Award at the Fourth Annual IEEE NetWorld+Interop '97 Conference. He has been involved actively in chairing and organizing sessions and has served as a member of the Technical Program Committee in a number of IEEE conferences. He currently serves as the Technical Program Chair for the IEEE Conference on Ultra Wideband Systems and Technologies (2002) and Technical Program Vice-Chair for IEEE International Conference on Communications (2002). He served as the Tutorial Chair for IEEE Semiannual International Vehicular Technology Conference (Fall-2001) and the Technical Program Chair for the IEEE Communication Theory Symposium of Globecom-2000. He is the current Editor for Equalization and Diversity for the IEEE Transactions on Communications and a Guest-Editor for the 2002 IEEE Journal on Selected Areas in Communications, Special Issue on Ultra Wide Band Radio in Multi-Access Wireless Communications.