# Computation Settings

Note: Multipath propagation results are only available with:
• intelligent ray-tracing model
• standard ray-tracing model
Prediction Model
Different models can be selected depending on the type of transmitter. Special models, which are used for the prediction of leaky feeder cables only, can be selected at the bottom of the dialog depicted above. The settings of the models can be changed by using the Settings button.
Computation Mode of Signal Level
The deterministic mode uses Fresnel equations for the determination of the reflection and transmission loss and the GTD / UTD for the determination of the diffraction loss. This model has a slightly longer computation time and uses four physical material parameters (thickness, permittivity, permeability and conductivity). When using GTD / UTD and Fresnel coefficients arbitrary linear polarizations (between +90° and –90°) can be considered for the transmitters.

The empirical mode uses five empirical material parameters (minimum loss of incident ray, maximum loss of incident ray, loss of diffracted ray, reflection loss, transmission loss). For correction purposes or for the adaptation to measurements, an offset to those material parameters can be specified. Herewith the empirical model has the advantage that the needed material properties are easier to obtain than the physical parameters required for the deterministic model. Also the parameters of the empirical model can be calibrated with measurements more easily. It is therefore easier to achieve a high accuracy with the empirical model.

Besides the angles of the given propagation path, the diffraction loss also depends on the relationship between the wedge direction and the polarization direction. According to physics and verified by measurements there is an additional loss of about 5 dB if both directions are parallel (for example diffraction on vertical wedge for vertically polarized signal). While this effect is automatically considered if using the GTD / UTD model, an offset is available for the empirical diffraction model. This additional loss is added to the diffraction loss in case the wedge direction and the polarization direction are parallel. In case the wedge direction and the polarization direction are orthogonal no additional loss is considered. In between there is a linear scaling of this additional loss.
Note: The computation mode for the signal level along the propagation path applies for all propagation models.