Joint scale-lag diversity in mobile ultra-wideband systems

Abstract

Abstract-In this paper, we consider the effect of mobility on an ultra-wideband (UWB) direct sequence spread spectrum communication system. Based on a uniform ring of scatterers model, we determine that the wideband scattering function has a "bathtub-shaped" scale spectrum. We compare the the performances of a scale-lag Rake and a frequency-lag Rake, each capable of leveraging the diversity that results from mobility. The scale-lag Rake receiver, whose scale-and lag-shifted basis functions are matched to the dilation-delay dynamics of the wideband channel, exploits greater diversity. Finally, we suggest a low-complexity implementation of the scale-lag Rake receiver.

On the efficiency of time-varying channel models

“…For y (t) t / (t, T)X(t -T)dT7, (1) ease of presentation, we consider in this work exclusively that the signal is an audio signal so that we may ignore relativistic time-frequency domain, effects. This simplifies the derivation of the Doppler effect, although the resulting channel for electromagnetic waves has a y(t) = S(O, T)X(t -T)ej27OtdTdO, (2) similar, but not identical, form. The results presented here can be extended to apply to wireless signals in a straightforward and time-scale domain, manner.…”

“…time-frequency characterization represents the channel output Im,m jj L(a, b)sinc -in ao) abo J as a series of weighted discrete delayed and frequency shifted (9) versions of the input signal, and the time-scale characterization In the above models, W, T, ao, bo are related to channel and represents the channel output as a series of weighted discrete signal characteristics [1][2][3][4]. Each of these three models and delayed and dilated versions of the input signal.…”

“…Each of these three models and delayed and dilated versions of the input signal. Given that their discrete expansions have been studied, in some cases, for practical receivers must model the channel using a limited nearly 50 years [1][2][3][4][5][6][7][8][9]. In each case, the channel is captured by number of channel coefficients, we examine how accurately a set of coefficients (hn, Sm,n, and Lm,n).…”

Canonical time-frequency, time-scale, and frequency-scale representations of time-varying channels

“…which is equivalent to (5) for positive time supported input signals and positive time horizon receivers, as we show in Appendix C. The canonical channel model derived from ( 10) is ( 11) Each of the three doubly spread canonical channel models discussed above motivates the development of a different two-dimensional rake receiver. A delay-dilation rake receiver based on the canonical time-scale channel characterization [9,11,10] leverages the diversity in wideband signaling environments in the same way that the delay-Doppler rake leverages the diversity in narrowband signaling environments [5].…”

Scale-Lag Diversity Reception in Mobile Wideband Channels

“…it can be shown [11] that for large , the autocorrelation (11) Fig. 4 displays the eigenvalues 6 of the basis-coefficient autocorrelation matrix for various values of normalized scale spread.…”