red with measurements. The upper simulation minutes (complete map) to 300 minutes (simplified frequency is limited due to the limited Random-Access map) virtually without degradation in DS and AS pre- Memory (RAM) resources of the computer, because the diction. On the contrary, wideband results obtained with calculating area has to be divided in cuboids that are much the guessed map are unacceptable. smaller than the wavelength. With about 4 giga byte (GB) of RAM and a calculation area of about 10 m X 5 m X 3 m, 4.7.3.3 Electromagnetic models it is possible to simulate frequencies up to about 500 MHz. In order to determine the so-called 'room at- Electromagnetic methods are aimed at directly solving tenuation', a transmitter was located inside a room and Maxwell's equations in some sort of discretised way (see the pathloss to the adjacent rooms was simulated or Section 4.7.2). Depending on the adopted form of measured. Maxwell's equations and on the kind of discretisation of In Figure 4.7-9 room attenuation with vertical polar- the domain, various methods can be identified such as isation for different kinds of rooms is reported. It is Finite Element Method (FEM), FDTD, MoM and others. evident that the simulations are in good agreement with Electromagnetic methods are not commonly used for field the measurements. Moreover, room attenuations for prediction at radio frequencies, the main reason being the different polarisation are obtained: results show that, due small wavelength with respect to the dimensional scale of to the orientation of slots inside walls, room attenuation the environment in this kind of problem. In fact, since the and the field pattern strongly depend on polarisation. space discretisation step must be a fraction of the wave- length, the overall grid dimension would be huge, and 4.7.3.4 Ray models consequently memory occupation and computation may become unbearable. Moreover the overall level of accuracy Ray models are based on GO theory and its extensions to both available in input databases 