Distribution of Arrival Rays in a Small Time Interval in Ultra Wideband Channels

The characteristics of multipath arrivals have been studied in an indoor environment by using 3-D ray- tracing model. The number of multipath components for different receiving locations was confirmed to follow a Rayleigh distribution under the condition that all multipath components carrying power below a -10dB threshold with respect to the peak power path are neglected. The number of arrival paths in a small time interval (used to define a time bin in a rake receiver) is found to follow an exponential distribution and the corresponding parameters are given for different time bin sizes. It is pointed out that when the bin size (equivalent to the time resolution of the receiver) is greater than 2 ns, the probability of more than one path arriving in a particular bin is greater than 50%. It reveals that the robustness of UWB signals in a multipath channel needs to be reconsidered when the size of the bin is greater than 1 ns.