Validity of Geometrical Optics multiple reflections inside materials with far-receiver and rays infinity assumptions

Modelling multiple reflections inside materials, using ray-tracing technique and Geometrical Optics (GO), is very important when deterministic propagation modelling is used in indoor environments. Indeed, when an electromagnetic wave undergoes a transmission or a reflection, the thickness of the interacting material has to be taken into account to model the wave propagation in an accurate way. Most of the time, to model the multiple reflections due to the material thickness, it is assumed an infinity of rays and a receiver far from the interacting material, implying the use of simplified coefficients. This paper makes a study of the validity of these coefficients, comparing them with authors coefficients extracted from a method described in which finds the exact rays that undergo multiple reflections inside materials with no simplifying hypothesis.