erm effects depend on the MT position, which in network basis, tenths of wavelengths being usually considered level simulations are usually close to each other, a better [Pars92]. This type of long-term variation is commonly approximation to reality should be obtained if shadowing justified by the changes in the visibility or obstruction of effects are not modelled independently for each MT. multipath components due to MT or scattering environ- Taking into account that long-term fading effects are ment changes (movement). This phenomenon is related modelled by the addition of a Gaussian distributed to the denotation of shadow fading, which is sometimes random variable, this does not completely model the used when referring to long-term fading. shadowing process. An additional aspect should be con- This distribution is a well accepted model for mod- sidered: shadowing is a slowly variant characteristic of elling narrowband fading, being frequently used for the radio channel. This variation rate indicates the exis- system simulation and analytical calculation purposes. tence in the time domain of a non-zero shadowing au- Nevertheless, a different long-term fading behaviour can tocorrelation. As mobility is included, time correlation is be found in specific environments, e.g. tunnels [Corr01]. intimately related to the space one. In fact physical ex- Wideband channel modelling is usually based on the planation of shadowing is primarily associated to position channel impulse response of the propagation channel. [Lee85]. Spatial correlation can be modelled as [ETSI97] Contrary to the narrowband case, in which the channel re- sponse is described by one single component, in the wide- band one, it is described by different components (paths) R(Ar) = 2 dcorr (4.7.7) arriving at different delays, being related to distinct propa- gation paths. Thus, from the long-term point of view, it is where Ar is the space shift and dcorr the decorrelation common to model each path as a narrowband channel, i.e. distance, for which typic