Outdoor networks transmit singals which maybe received indoor. When relatively low frequencies are used, for instance in broadcast, the diffraction is most of the times considered as predominant compared to the absorption and the fact that the receiver is indoor is taken into account through an increase of the reception threshold (cf.Chester 97 Agreement for the coordination and planning of DVB-T).

On the other hand, for purely indoor networks, the standard approach is to neglect the diffraction and to focus on the absorption due to the materials crossed by the signal (cf. IMT-2000/ITU-1225).

With the emergence of the new proximity networks (WiFi, WiMax, DECT....), using outdoor base station with indoor subscribers at relatively high frequencies, the border between absorption and diffrection becomes much fuzzier, and there is a need to use mixed models, as illustrated on the figure below. For proximity networks, the model of buildings absorption is based in ICS Telecom on three hypothesis :

• Each building is homogeneous, i.e. made of only one material
• The absorption attenuation, expressed in dB, is proportional to the length of the path crossed by the signal inside the building
• The coefficient of proportionality, also called absorption coefficient, is a characteristic of each material (concrete, glass, brick…)

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