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Ultra-wideband (UWB) technology has developed rapidly over the past several years. This technology is especially attractive in high-data-rate and short-range wireless communications. These applications make UWB technology suitable for indoor mobile communication applications, such as wireless personal-area networks (WPAN). This interest has motivated the study of the propagation of the UWB signals in indoor environments as an important task for the implementation of WPANs. In the last decades, significant effort has been focused on the characterization of the indoor channel for narrowband systems. Statistical (Motley & Keenan, 1990; Saleh & Valenzuela, 1987; Seidel & Rappaport, 1992; Tornevik et al., 1993) and deterministic (Lauer et al., 1984; Saez de Adana et al., 2000; Tarng et al., 1997; Whitman et al., 1995) models have been used most frequently in these studies. The statistical models are based on the obtention of closed formulas to characterize the propagation channel. These formulas are derived from the data obtained from measurement campaigns in different environments. Alternatively, the deterministic models are based mostly on the use of ray-tracing techniques (Saez de Adana et al., 2000; Tarng et al., 1997; Whitman et al., 1995) to predict the multipath phenomena and the Uniform Theory of Diffraction (UTD) technique (Kouyoumjian & Pathak, 1974) to calculate the received power or the propagation losses. However, the features of the UWB systems (with bandwidth in the range of GHz) render the conventional narrowband propagation models, both statistical and deterministic, inapplicable. These models are based primarily on frequency-domain analysis, while UWB requires a time-domain analysis due to its wide bandwidth. Therefore, special models must be used to predict the signal propagation in UWB systems. Although the number of statistical models developed for UWB systems is not as extensive as that for narrowband systems, some recent examples can be found in the literature (Cassioli et al., 2001, 2002, Dabin et al., 2006; Molisch et al., 2006). These models have been obtained, as in the case of narrowband systems, by obtaining closed expressions that fit the behavior of the received signal measured in several locations in a measurement campaign. Regarding the deterministic models, frequency-domain UTD can be applied, performing an analysis at several frequencies and obtaining the time response using an Inverse Fourier Transform. However, this procedure is computationally inefficient in comparison to direct analysis in the time domain. Instead, the Time-Domain Uniform Theory of Diffraction (TDUTD) was developed to obtain a solution in the time domain for the reflection and the

Propagation Models for the Characterization of the Indoor UWB Channel