Χαρακτηρισμός και μοντελοποίηση ραδιοδιαύλου για ασύρματα δίκτυα ultra wideband (UWB)
Σπηλιωτόπουλος, Χρήστος Γ.
SubjectWireless communication systems ; Broadband communication systems ; Ultra-wideband devices ; Radio -- Receivers and reception ; Signal processing
This doctoral thesis deals with the experimental characterization of the radio channel of ultra wideband (UWB) wireless communication systems. Aiming at this objective an UWB measurement campaign was designed and carried out in a Hercules C-130 military cargo airplane. The environment encompasses several metallic surfaces resulting in a large number of multipath components. The experimental data were initially used for the characterization of UWB radio channel and then for the selection of the appropriate transmission-reception techniques. Parameter estimation algorithms were implemented and applied to measured data for the estimation of path-loss factor representing the distance dependence of the channel path-loss as well as for the estimation of path-loss factor representing the frequency dependence of the channel path-loss. The estimation was carried out for various frequency centers and bandwidths. A path-gain calculation model based on the concept of reparability of distance and frequency variables is proposed and comparison to measurements is given. Furthermore, time dispersion parameter estimation algorithms were implemented and applied to measured data for the estimation of maximum excess delay, mean excess delay and root mean square (r.m.s.) delay spread as well as for the estimation of the number of multipath components and the percentage of the energy these components carry. The dependence of multipath components on transmitter-receiver antennas separation is investigated. A power law is then employed to model the relation between the number of multipath components and the r.m.s delay spread. The temporal correlation between adjacent path amplitudes is calculated. Finally, a modified Saleh-Valenzuela model is invoked to describe the clustering of multipaths, where a different power decay factor is used for the rays of the first cluster as opposed to subsequent clusters. Moreover, the Weibull distribution models the small scale channel fading with a lognormally distributed shape parameter. The average values of this parameter imply severe fading conditions. Finally, simulation results of the proposed statistical model are compared to measured data demonstrating reasonable agreement.