t) and w(t) denote the complex low pass representations of the channel input and output, respectively, then [2] (2.50) where Pn is the strength of the nth weight, and gn(t) is the complex Gaussian process weighting the nth replica. The Doppler spectrum of the nth path or the power spectrum of gn(t) controls the fading rate due to the nth path. Therefore, to define this channel model we can specify only the Doppler spectra of the tap weights {Pn(v); n = 1,...,N}, the tap delays {t n=1, ,N}, and the tap weight strengths {pn(v); 1,...,N}. Interpreting the process gn(t) as the superposition of unresolved multi-path components arriving from different angles and in the vicinity of the delay interval, we have: (2.51) where W is the bandwidth of the transmitted signal. Generally, each ray has a different Doppler shift corresponding to a different value of the cosine of the angle between the ray direction and the velocity vector. Which means that we can assume: first, very large number of receive-rays arrive uniformly distributed in azimuth at the MS and at zero elevation for each delay interval for outdoor channels7. At the BS in general the received rays arrive in a limited range in azimuth. Second, for indoor channels8 a very large number of receive-rays arrive uniformly distributed in elevation and azimuth for each delay interval at the BS. The first assumption matches the ones made in by Clarke [18] and Jakes [19] in narrow band channel modelling. Thus the same Doppler spectrum will result, i.e. Pn(v) (2.52) 7 Also, the antenna pattern is assumed to be uniform in the azimuthal direction. Assuming the antenna is either a short or half-wave vertical dipole. The UMTS Network and Radio Access Technology where V is the velocity of the mobile and a is the wavelength at the carrier frequency. The term CLASSIC is used to identify this Doppler spectrum [2]. The second assumption results in a Doppler spectrum that is nearly flat, and the choice of a flat spectrum has been made, i.e. P,(u)=P(u) (2.53) Hence, this Doppler spectr