2.1. Radio Propagation Model 9Figure 2.1 This figure shows the hierarchy between analytical radio propagationmodels of different complexities on the left side. On the right side, the other majorapproach, the empirical propagation model, has been highlighted.Absorption: The rate of power loss at a media intersection, as some of the energyof the signal is transformed into other energy forms as for example heat.Reflection: The change of direction of a signal at an interface between two differ-ent media. The angle of the incoming direction equals the angle of the outgoingdirection with respect to the surface normal(see figure 2.2). Only a part ofthe signal is reflected, the remaining part of the signal follows the rules of thenext effect.Refraction: The change of direction at a media intersection for the unreflectedpart of the incoming signal. The unreflected part of the signal enters the newoptical medium, and depending of the frequency of the underlying wave ofthe signal and the refractive index of the medium, the direction of the signalchanges.Diffraction: If the underlying wavelengths of the simulated signals are in themagnitude of the physical obstacles, the diffraction effect leads to a change ofdirections in the form of bending around the corners of these objects.Interference: The phenomenon, that the overlapping waves lead to new waveforms. These superimpositions can either increase or decrease power of thesignal.Scattering: Small obstacles in the size of particles and rough surfaces induce anoisy reflection of the signal.Polarization: The orientation of the underlying waves for the radio signal influ-ences the absorption rate at different material types.A simulation of the radio propagation, obeying to a selection of these effects, can beobtained by raytracing algorithms. A requirement for such a raytracer simulationis the knowledge of the material parameters controlling the absorption rate and thechange of direction due to reflection, refraction and diffraction. The combinationof these material parameters controls the rate of signal strength decrease at mediaintersections and the amount of multipath effects due to reflection and diffraction.