Radiative energy transfer prediction of excess attenuation of microwave radio signals in a regularly planted orchard

Abstract

Mobile wireless service providers operate at microwave frequencies and they are very likely to continue or move up in frequency in the foreseeable future. The large growth in the use of microwave frequency bands for mobile wireless communication poses an increasing risk of vegetation forms attenuating and scattering the transmitted signal. This, in turn, leads to significant signal degradation, increased error rates and loss in the information content of the transmitted signal. Radio system planners need accurate engineering models, which can be used in the prediction of the effects of vegetation forms on radio signals propagating at frequencies above 1 GHz. Vegetation encountered in mobile radio applications, take the form of single trees, line of trees and a body of trees such as a wood or forest. Using a model based on the Radiative Energy Transfer (RET) theory, the vegetation medium can be characterized by four distinct parameters. These are: the absorption cross section per volume /spl sigma//sub A/, the scatter cross section per volume /spl sigma//sub s/, the ratio of the forward-scattered power to the total scattered power /spl alpha/, and the beamwidth of the forward scatter lobe /spl Delta//spl gamma//sub S/. This paper outlines the RET model and presents results of solutions, yielding the excess attenuation of the vegetation medium as a function of distance into the medium. The paper presents a reliable method for evaluating the four parameter (/spl sigma//sub A/, /spl sigma//sub S/, /spl alpha/, /spl Delta//spl gamma//sub S/) using measured results obtained in an orchard. The paper concludes by comparing the RET characterisation with measurements.