CE-451 Spring 10-lec9 - CE-451 SPRING 2010MOBILE...

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Unformatted text preview: CE-451 SPRING 2010MOBILE COMMUNICATIONSLecture 9Mobile Radio Propagation: Large-Scale Path Loss InstituteofSpaceTechnology1FRESNEL SCREENS2InstituteofSpaceTechnologyThe excess path length () is the difference between the direct path and the diffracted path, given by for fig 4.10b:The corresponding phase difference is:Fresnel Kirchoff diffraction parameter v is given by:3InstituteofSpaceTechnology( 29212122ddddh+=( 2921212222ddddh+==( 29( 292121212122ddddddddhv+=+=FRESNEL DIFFRACTION GEOMETRY4InstituteofSpaceTechnologyFigure 4.12 Illustration of Fresnel zones for different knife-edge diffraction scenarios.KNIFE-EDGE DIFFRACTION MODELTreat single obstruction as a diffracting knife-edge.Consider a receiver in the shadowed region (called diffraction zone), RField strength at this point is a vector sum of fields due to all of the secondary Huygens sources5InstituteofSpaceTechnology6InstituteofSpaceTechnologyKNIFE-EDGE DIFFRACTION LOSS7InstituteofSpaceTechnologyMULTIPLE KNIFE-EDGE DIFFRACTION8InstituteofSpaceTechnologySCATTERINGInstituteofSpaceTechnology9When radio wave impinges on a rough surface, the reflected energy is spread out (diffused) in all directions due to scatteringSurface is smooth if its min to max protuberance h is less than hc,Surface is considered rough if protuberance is greater than hcWhere hc (critical height of surface protuberance for a given incident angle i) is given by:10InstituteofSpaceTechnologyichsin8=RADAR CROSS SECTION MODELKnowledge of physical location of large distant objects inducing scattering is used to predict signal strengthsRadar Cross Section (RCS) of a scattering object is...
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CE-451 Spring 10-lec9 - CE-451 SPRING 2010MOBILE...

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