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Modeling propagation channels for future pico-cellular indoor THz communication systems requires the knowledge of the reflective properties of building materials. The reflectivity of smooth, optically thick materials can be modeled with Fresnel equations. In case of materials with a rough surface, diffuse scattering reduces the power reflected in the specular direction. Kirchhoff scattering theory can be employed to derive modified Fresnel equations which account for these losses by introducing a Rayleigh roughness factor calculated from the measured surface height distribution of the sample under observation. Using the resulting, analytically derived reflection coefficient based on material parameter and surface measurements in propagation models enables the simulation of arbitrary configurations. We present a set of calculated and measured reflection coefficients for a selection of common indoor building materials which are in good agreement, thus verifying our modeling approach. Furthermore, we illustrate by ray-tracing simulations the effect of wall and ceiling roughness on propagation in future indoor scenarios. Both, absolute power levels and propagation patterns are shown to be strongly influenced by scattering. In some cases, reflected transmissions with longer propagation paths can be more efficient than the shorter ones in terms of incurred losses.
Date of Publication: Nov. 2007