Remodelling of Lee’s Knife Diffraction Loss Model as a Function of Line of Site Percentage Clearance

Swinton C Nwokonko

doi:10.11648/j.ijtam.20170304.12

Abstract

In this paper, remodeling of Lee’s piecewise knife diffraction loss model is presented. The original Lee’s piecewise knife diffraction loss model is expressed as a function of Fresnel-Kirchoff diffraction parameter. The computation of the Fresnel-Kirchoff diffraction parameter requires detailed terrain and link parameters. However, for quick link planning the Fresnel-Kirchoff diffraction parameter can be computed from the knowledge of the line of site percentage clearance alone. Moreover, in line of site link design, the required or acceptable obstruction clearance is specified in terms of line of site percentage clearance. Consequently, in this paper, the Lee’s model is remodeled into new piecewise functions that are entirely functions of line of site percentage clearance. The new version of Lee’s model is validated with the results of knife edge diffraction loss obtained from the original Lee’s piecewise knife diffraction loss model. With the new model it is easier to determine the diffraction loss that will be caused by any obstruction at a given line of site percentage clearance.

Highlights

Diffraction is the bending of a wave around the edges of an opening or an obstacle [1]
Fresnel zones are used by propagation theory to calculate diffraction loss caused by obstruction located between the transmitter and receiver [8], [9]
The Fresnel zone in this case defines the cylindrical ellipsoidal path occupied by the signal as it propagates from the transmitter to the receiver

Summary

Introduction

Diffraction is the bending of a wave around the edges of an opening or an obstacle [1]. Where more than one obstacles are involved, the obstacles are treated as multiple knife edge In both cases, Fresnel zones are used by propagation theory to calculate diffraction loss caused by obstruction located between the transmitter and receiver [8], [9]. Determination of single knife edge diffraction loss requires the computation of obstruction clearance height, radius of the Fresnel zone and the diffraction loss. In most literatures studied, Lee’s piecewise function approximation of the graphical diffraction loss model is mostly used in knife edge diffraction loss computation. Due to the simplicity of using the line of site percentage clearance, in this paper the piecewise functions in the Lee’s model are express in terms of LOS percentage clearance of Fresnel zone 1. The new version of Lee’s model is compared with the diffraction loss computed from the original Lee’s model

Theoretical Background

Results and Discussion using

Conclusion