ty number of single-bounce reflectors, called scatterers. CHAPTER 4.7 Propagation modelling and channel characterisation Comparison with real measurements at 1.95 GHz and faster and more synthetic because their output can de- a bandwidth of 20 MHz yield good accuracy for the scribe an entire class of problems instead of a single one. single-bounce echoes in a half-open environment, just by Generally, statistical channel models are used in the link tuning the size of the scattering clusters, the number of level design phase while deterministic models are used in scattering coefficients and the Rician K-factor. the planning phase of mobile radio systems. However, RT methods can also be used to determine the per- despite the fact that the use of deterministic field predic- mittivity of building materials. Indeed, [JKVW05] uses tion may in principle lead to great advantages in terms of simple amplitude-only reflection measurements at dif- deployment cost reduction and service quality increase, the ferent incidence angles to fit the permittivity of flat walls. widespread adoption of deterministic models is still very It is even possible to introduce diffuse radiation into the limited due to the high cost and the low reliability of input reflection model, giving a more realistic behaviour of the databases and to the high complexity and computation scattered field, by introducing a scattering coefficient, time of the corresponding computer programs. For these which increases as expected from a small value (0.05) for reasons, most research within COST 273 addressed a nearly flat hangar wall, up to 0.4 for more irregular rural topics such as database handling [ScWi03], [CoLA03], building walls [EFVG05]. [DeFA04], sensitivity to database accuracy [NaCB04] and CPU time reduction [HoWW03], [CoLA03], [DeFA04], [WWWW04], [BCFF02]. In principle, deterministic 4.7.3 Deterministic propagation models such as RT allow a multidimensional character- modelling isation of propagation, i.e. may give information on the dis- tribution in 