Further Approaches

Approximate the terrain profile in large with simple geometrical objects, use ray optical methods or use empirical models for improved accuracy.

There are further approaches to the prediction of the field strength in large areas based on topographical databases.

Replacement Obstacles Technique

Simple geometrical objects represent the terrain profile. An approximation of the terrain profile is obtained by replacing the terrain obstacles by absorbing cylinders, wedges or knife edges depending on the elevation curve considered. This leads to a so-called “replacement obstacles” technique. Hence the propagation is described as multiple diffraction phenomena where reflections are neglected.

Figure 1. Replacement of the terrain profile by obstacles.

Ray-Optical Methods (Ray Tracing) Using GTD/UTD

For these objects, expressions exist to compute the UTD diffraction coefficients. For efficient computations, algorithms for the multiple diffractions calculation are derived. Forward scattering processes can be considered heuristically.

Empirical Models Considering the Shape of the Individual Obstacles

Based on measurement data and the dominant path above the path loss can be calculated taking the obstacles into consideration. An additional consideration of morphological data is possible by empirical correction factors depending on land usage. Models based on the replacement of the terrain profile by obstacles are available in ProMan.