iction of indoor coverage by an outdoor BS is shown. It is evident that the field penetrates the car mainly through the windows, therefore providing a rela- tively good coverage in the passenger compartment. (Pmin Diffuse scattering studies Segment Conventional ray models only account for rays that un- Centre of a tile dergo specular reflections or diffractions, but neglect Centre of a segment diffuse scattering phenomena which can have a signifi- Receiving point cant impact on propagation. As intended here, diffuse scattering refers to the signals scattered in other than the specular direction as a result of deviations (surface or Figure 4.7-13 Tiles and segments of a wall. volume irregularities) in a building wall from a uniform flat layer. The modelling of diffuse scattering from (possible rays) are determined and stored in a file. The building walls is quite a difficult problem, since building visibility relations between all tiles and segments in the wall irregularities cannot always be modelled as Gaussian database are computed in this preprocessing phase, be- surface roughness, as assumed in most theoretical stud- cause they are independent of the terminal locations. For ies. Moreover, objects next to (instead of on to) building this purpose all elements are represented by their cen- walls such as street signs, traffic lights, advertising tres, which leads to the discretisation of the problem of boards, trees, etc. can all contribute to non-GO scatter- path finding, Figure 4.7-13. Based on this preprocessing ing in the urban environment. A growing interest has the path finding can be done similar to the ray launching been focused recently on the possibility to develop some algorithm by recursively processing all visible elements sort of ray theorisation (or characterisation) of diffuse and checking if the specific conditions for reflection and scattering phenomena. In [Bert02] an interesting study diffraction are fulfilled. The ray search is stopped if a re- using an electromagnetic method to determine the