a stable average value after minimising the effect of random variable over a number of 3D RTruns in a simple small signal variations. This contrasted with the tradi- indoor environment. The standard deviation of the tional approach used in outdoor environments of aver- random variable can be varied to study different degrees aging larger blocks of (10% X 10%) or (20% X 20%). The of wall displacement. The uniform distribution is se- average field level obtained from the wall imperfection lected to calculate the local mean field strength by av- model seems to have reached its final value after 50 to eraging out all phases with equal weighting. A similar 100 runs, therefore with a reduction of 87.5% in the methodology can be used to study imperfections of wall number of computer runs. material properties by adding a random variable with an In [FuMa03] a full-3D RT tool is used to perform arbitrary distribution (uniform or Gaussian) to the a wideband characterisation at 2 GHz in a typical urban electromagnetic wall property values to account for un- macrocellular scenario, Figure 4.7-21. The model con- certainties in these values. This proposed approach in siders multiple reflections, multiple diffractions and estimating the average local value of the signal strength combinations of both. Here the maximum reflection has the advantage of decreasing the number of computer order is set to six and the maximum diffraction order to runs compared to the approach of averaging blocks of two. The simulation environment is a 719 X 539 m points with high resolution (x/4) grids. The wall imper- section of the city of Karlsruhe and 'BS' marks the place fection model was tested for several environments. For of the BS (transmitter), which is located on a 12.5 m example, the model is applied to estimate the signal level high building on a pole 13 m above the roof. The receiver Table 4.7-3 Comparison of the average local field value around the receiver obtained from the wall imperfection model and the spatial sampling approach for dif