Characterization of indoor time reversal UWB communication systems: Spatial, temporal and frequency properties

In this paper, an indoor UWB communications system that applies time reversal (TR) for transmitting the desired signal is proposed. First we define equivalent channel model of TR-UWB, which is the convolution of channel impulse response and its complex conjugate time-reversed version. Then spatial, temporal and frequency characteristics of equivalent channel are analyzed and the analytical or semi-analytical results are validated by comparing measurements with simulation. (Semi) analytical expression of equivalent channel transfer function, TR UWB power delay profile (PDP), focusing gain, spatial correlation and power azimuth spectrum (PAS) is performed. Also probability density function (PDF) of TR-UWB amplitude and path-gain is derived. Analysis and simulation results of different distributions, such as uniform, Laplacian and Gaussian for PAS, are considered and presented. It is shown that uniform and truncated Laplacian distributions are appropriate fits to the measurement results for power azimuth spectrum of TR-UWB. It is seen that for distances greater than λ/2 from the authorized receiver, received signal decreases 10 dB, where λ is the wavelength of the central frequency. Finally, PDF of TR-UWB path-gain is described. Measurement results show that for small time windows, the densities of the path-gain are highly non-Gaussian. But for starting time of 10Tw or more, and window size of 2Tw or more the densities are nearly Gaussian, where Tw is the transmitted pulse duration. Copyright © 2010 John Wiley & Sons, Ltd. Extensions of TR techniques to radio electromagnetic propagation for ultra wideband communications were investigated. The main features of the current paper are: Analysis of Time Reversal UWB power delay profile is presented and a closed form is derived for focusing gain. It is shown that uniform and truncated Laplacian distributions are appropriate fits to the measurement results for PAS of TR-UWB. Closed form of spatial correlation and channel transfer function of TR-UWB are presented. PDF of TR-UWB amplitude and path gain is derived.

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