Path Classes
Characterize the ray types based on the expected path loss.
There are different types of rays (direct, reflected, diffracted) especially when we consider the combination of reflections and multiple diffractions. The path loss occurring along these rays depends on the number and the kind of interactions. Therefore the different ray types can be arranged in classes according to the expected path loss. When making the prediction, the type of rays that should be considered during the prediction is defined using these so-called path classes.
| Path Class | Description |
|---|---|
| 1 | Direct path |
| 2 | Single reflection |
| 3 | Double reflection |
| 4 | Single diffraction |
| 5 | Triple reflection |
| 6 | One reflection + one diffraction |
| 7 | Double diffraction |
| 8 | Two reflections + one diffraction |
| 9 | Four reflections |
| 10 | Five reflections |
| 11 | Six reflections |
Inside a specific class, a similar interaction loss for the different rays can be assumed and with increasing order of the path class the interaction loss to be expected increases. For the prediction, a maximum and a minimum number of path classes can be defined.
The maximum number defines the maximum path class which is computed. The minimum number defines the abort condition: The computation for an individual pixel is canceled if at least one ray is found that is in the minimum class or higher. That means that if the minimum number is chosen too small, the prediction could be too pessimistic since additional rays with an important contribution to the received power are neglected. In standard ray-tracing the number of path classes considered in the prediction process has a strong influence on the computation time. However with intelligent ray-tracing the computation time remains nearly constant and is independent of the selected path classes.
Acceleration
ProMan offers the possibility to accelerate the prediction by canceling the search for rays as soon as the accumulated prediction value reaches the free space loss. The consequent prediction error is small because the received power is rarely above the received power in the free space case. This might be only the case very near to the transmitter in a LOS situation with additional wave guiding effects.