 a and B are found by The rapid variations of the received signal over distances minimising the mean square error against measurements. of the order of a few wavelengths, or short periods of The double fading has been described earlier by time, due to the multipath channel behaviour, i.e. the [EFLR97] as cascaded Rayleigh fading, and it was shown changes in the magnitude and phase of arriving waves, is that the probability density for the power, S, is given by referred to as small-scale or short-term fading. Globally, p(s) = 2K0(2Vs) (4.7.11) the received signal magnitude is described by the su- perimposition of the distance-dependent path-loss value, where Ko is the modified Bessel function of the second long- and short-term fading effects. kind and zero order. The Cumulative Distribution Short-term fading results from the path length differ- Function (CDF) is then given by ence between waves arriving from different paths, i.e. from scatterers located within the propagation environment. Prob(s'<s)=1-2VsK1(2Vs) = (4.7.12) These differences lead to significant phase differences. In the narrowband case, all rays arrive essentially at with K1 representing the modified Bessel function of the the same time when compared to the system resolution; second kind and first order. hence, the short-term variations of the magnitude of the The advantage of this distribution is the insight it gives received signal can be represented by the sum of an LoS into the origin of the long-term fading, while its Propagation modelling and channel characterisation CHAPTER 4.7 disadvantage is the lack of a simple analytical function for the channel gains can have desired temporal, spatial and the PDF of the received power except in special cases, spectral correlation generated by time-correlation shap- e.g. the double product of Rayleigh fading paths. ing filtering and space-frequency correlation trans- This new model can be made similar in shape to the formation. The proposed short-term fading simulator Suzuki distribution, but it has a di