# Hybrid Predictions

Ray-optical propagation models consider a maximum number of reflections and diffractions. Use a hybrid approach combining empirical prediction with ray-optical prediction.

Due to the limited number of considered reflections and diffractions, not all prediction points may be reached with the ray-optical algorithms (especially far away from the transmitter). This remaining part of the pixels can be computed with empirical models, based on the direct ray between transmitter and receiver. For urban scenarios, the COST-Walfisch-Ikegami model is implemented.

A transition function between the empirical prediction and the ray-optical prediction leads to a smooth transition between the two models. An example of the transition function between the two models is shown in Figure 1.

Depending on the difference between the ray-optical and the empirical prediction, a weighted sum of both predictions is computed. The functions for the weight factor are either ${\mathrm{sin}}^{2}\left(x\right)$ or ${\mathrm{cos}}^{2}\left(x\right)$ . Therefore the sum of both functions is always equal to 1 for all possible values of x.

Investigations have shown that the hybrid prediction reduces the overall prediction error.