05.053GPPRadio transmission and receptionTS
Radio propagation in the mobile radio environment is described by highly dispersive multipath caused by reflection and scattering. The paths between base station and MS may be considered to consist of large reflectors and/or scatterers some distance to the MS, giving rise to a number of waves that arrive in the vicinity of the MS with random amplitudes and delays.
Close to the MS these paths are further randomized by local reflections or diffractions. Since the MS will be moving, the angle of arrival must also be taken into account, since it affects the doppler shift associated with a wave arriving from a particular direction. Echos of identical delays arise from reflectors located on an ellipse.
The multipath phenomenon may be described in the following way in terms of the time delays and the doppler shifts associated with each delay:
where the terms on the right‑hand side represent the delayed signals, their amplitudes and doppler spectra.
It has been shown that the criterion for wide sense stationarity is satisfied for distances of about 10 metres. Based on the wide sense stationary uncorrelated scattering (WSSUS) model, the average delay profiles and the doppler spectra are necessary to simulate the radio channel.
In order to allow practical simulation, the different propagation models will be presented here in the following terms:
1) a discrete number of taps, each determined by their time delay and their average power;
2) the Rayleigh distributed amplitude of each tap, varying according to a doppler spectrum S(f).