Analysis of Cross-Polarization Discrimination Statistics for Millimetric Waves Propagating Through Rain

Abstract

This thesis reports on the results of a general investigation into the depolarization statistics of a microwave signal after propagation through a rain medium, and their application to the design of a microwave communication system. Prediction of the long-term statistics for rain depolarization is presented for both spatially uniform and non-uniform rain and for any type of linear polarization (horizontal, vertical and at 45° inclination to the horizontal). Assuming a log-normal form for the rainrate statistics an approximate Gaussian model is deduced for the final crosspolarization isolation (XPI) or discrimination (XPD) distribution in decibels. The parameters of this normal distribution are related to the parameters of the radio link and the rainrate distributions.Applications of this conclusion to the estimation of radio outage time due to co-channel interference are also presented for various crosspolarization levels.A theoretical formula is then derived for the joint statistics of cross-polarization discrimination (XPD) or isolation (XPI) and rain attenuation for a microwave link. This formula is then applied to the prediction of the distribution of XPD conditional on the co-polar rain attenuation, and also to the prediction of the distribution of XPD during a rain fade. Application is also made to the estimation of outage time of a dual-polarization communication system. Theoretical results are compared with experimental data from the Eastern USA and Southern England, and the agreement is found to be good. ACKNOWLEDGEMENTS