Use a visibility tree and building database for fast prediction.

Figure 1 illustrates the visibility relations computed in the preprocessing in the shape of a “visibility tree”. Only the relations in the first layer of the tree must be computed in the prediction which can be done very fast - all other visibility relations are determined during the preprocessing stage and can be read from file. The stored visibility relations (except the first layer) can be used for all predictions with the same database.

Figure 1. Determination of ray paths by searching in a tree structure.
Figure 2 shows a field strength prediction of the building database. This prediction indicates the typical behavior of ray-optical modeling including wave guiding along the corridor. The difference between measurement and prediction for a part of the building leads to good values for the mean error (1.9 dB) and the standard deviation (2.8 dB).

Figure 2. Field strength prediction with IRT (transmit power 0.1 W at 1800 MHz).

For the prediction shown in Figure 2, a resolution of 1 m for the discretization of the building database was selected. However, it is possible to increase the resolution to some extent without reducing accuracy.