A statistical model for UHF radiowave signals within externally illuminated multi-storey buildings

Abstract

This thesis describes research undertaken as an initial investigation in the development of a statistical model for UHF radiowave signals within externally illuminated multi-storey buildings located in the urban centres of New Zealand cities. Experiments performed in Auckland at 851 MHz and 927 MHz to obtain a data base for model investigation are described. Measurements were made within a representative range of buildings encompassing the major constructural characteristics of buildings found in Auckland. The resulting propagation data was used to develop a model for predicting the median signal strength and a statistical model for the variability of the signal about this median. The statistical model for the signal variability was divided into two parts, a model for the statistics of the signal within small areas, and a model for the probability distribution of the signal level on an entire floor. Clarke's statistical scattering model is found to be a good model for the probability distribution, autocorrelation coefficient, and power spectrum of the signal within small areas up to about 20 wavelengths square, including areas having a line-of-sight path to the base station antenna through the building's windows. Various distributions are considered as possible models of the signal on an entire floor and it is shown that the Suzuki distribution which consists of a Rayleigh distribution with a lognormally distributed mean is the most reliable model. A free space based model is proposed for predicting the median of the lognormal part of the Suzuki distribution for path lengths less than 1 km for both the situation where there is a line-of-sight path from a building's floor to the base station antenna and the situation where this path is obstructed by intervening obstacles. The model residuals for both situations are approximately normally distributed and their variability is shown to have significant impact on the overall variability of the signal. Recommendations are made for the further development of the proposed model and areas requiring further investigation are identified.