The principle behind the facets component

Synapse uses facets to evaluate the contribution of multipath while the electro-magnetic connection takes place across an irregular terrain. It allows you to predict the signal strength received by the mobile taking into account the reflections produced on mountain slopes. This improves the precision in relation to classic components that only take into consideration the propagation phenomena in the vertical cross-section of the terrain between the transmitter and the receiver. The inclusion of reflection is very complex and depends on numerous factors. It is suitable then to make simplified hypotheses so that the component is usable by the operator of radio mobile networks.

•The first simplification is the inclusion of paths that encompass only the reflection on a mountain. It can be assumed that this hypothesis introduces a slight error because the received paths by multiple reflections on the topography are strongly mitigated and not significant at the receiver.

•The second simplification is that only the zones on mountain slopes that are in "height" visibility of both the transmitter and receiver are considered. Note that there is visibility when the different obstacles do not protrude from the axis of the Fresnel ellipsoid.

•The third hypothesis is that the determination of the reflected paths is only performed if the direct transmitter-receiver path is obstructed by the terrain.

•The fourth hypothesis is to limit the extent of the search area for possible reflectors by fixing a maximum delay for the consideration of the echoes. The measurement campaigns of impulse responses have allowed validation to a value of 50 μs. Because of the calculation time, the value is, by default, fixed to 25 μs, which corresponds to a maximum distance C.∆tmax = 300 x 25 = 7500 m (where C equals the speed of light).

•Finally, the fifth hypothesis is the understanding that there is a reflection, or diffusion, (as opposed to a discrete reflection on plane surface) given the large irregularities of mountainous slopes in relation to wavelengths. The received signal is uniformly diffused in the half-space above the slope of the mountain, and the diffused power is inconsistent. Nevertheless, by analogy with the radar equation, it is assumed that all the contributions of the diffused power could be added together by the receiver. This hypothesis has been verified on the terrain and explains why large quantities of energy nonetheless reach the mobile even though there are rarely discrete reflections in the direction of the mobile.

The modelling and function of the facets component

Activating the facets component is only effective if the propagation context is hilly enough. The search of reflection zones is performed using the facets index parameter. The files generated with the aid of an algorithm based on the Delaunay triangulation method are defined in this parameter. These files contain the information about the modeling of the relief (reflection facets, visibility in relation to the reflection facets, etc.).

Once the user has obtained the reflection zones, the facets component calculates the loss of the reflected paths to determine the total strength received by the receiver.

The profile loss is calculated and is added to the facets component loss to form the total loss of Synapse.