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Joint ScaleLag Diversity in Mobile Wideband Communications
, 2005
"... We consider the effect of mobility on a wideband direct sequence spread spectrum (DSSS) communication system, and study a scalelag Rake receiver capable of leveraging the diversity that results from mobility. A wideband signal has a large bandwidthtocenter frequency ratio, such that the typical n ..."
Abstract

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We consider the effect of mobility on a wideband direct sequence spread spectrum (DSSS) communication system, and study a scalelag Rake receiver capable of leveraging the diversity that results from mobility. A wideband signal has a large bandwidthtocenter frequency ratio, such that the typical narrowband Doppler spread assumptions do not apply to mobile channels. Instead, we assume a more general temporal scaling phenomenon, i.e., a dilation of the transmitted signal’s time support. Based on a uniform ring of scatterers model, we determine that the wideband scattering function, which quantifies the average scale spreading, has a “bathtubshaped” scale profile. We investigate, through frametheoretic tools, the translation and dilationspacing parameters of a scalelag Rake basis, and compare the performances of a scalelag Rake and a Dopplerlag Rake, each capable of leveraging the diversity that results from mobility. When the translation spacing of the Rake functions is equal to the minimum resolvable lag, there is no significant performance difference between the receivers. For wider spacings, the receiver is more reliant on dilation diversity; hence, the scalelag Rake receiver performs relatively better. Such analysis applies, for example, to ultrawideband (UWB) radio frequency channels and underwater wideband acoustic channels. We study the correlation structure of the scalelag Rake fingers and show that the normalized scale spread parameter relates directly to the timevariability of the ii channel. We discover that much of the channel energy is concentrated in few eigenmodes and hence propose principal components combining for a reducedcomplexity solution. Finally, we perform physical experiments in the airacoustic channel to demonstrate the applicability of the wideband channel model.
1 Joint ScaleLag Diversity in Mobile UltraWideband Systems
"... Abstract — In this paper, we consider the effect of mobility on an ultrawideband (UWB) direct sequence spread spectrum communication system. Based on a uniform ring of scatterers model, we determine that the wideband scattering function has a “bathtubshaped ” scale spectrum. We compare the the per ..."
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Abstract — In this paper, we consider the effect of mobility on an ultrawideband (UWB) direct sequence spread spectrum communication system. Based on a uniform ring of scatterers model, we determine that the wideband scattering function has a “bathtubshaped ” scale spectrum. We compare the the performances of a scalelag Rake and a frequencylag Rake, each capable of leveraging the diversity that results from mobility. The scalelag Rake receiver, whose scale and lagshifted basis functions are matched to the dilationdelay dynamics of the wideband channel, exploits greater diversity. Finally, we suggest a lowcomplexity implementation of the scalelag Rake receiver. I.