A Model For Mobile Radio Fading Due to Building Reflections: Theoretical and Experimental Fading Waveform Power Spectra

Fluctuations in received signal amplitude occur during mobile communications because of the motion of the mobile station through the spatial standing-wave pattern resulting from the interaction of direct and reflected signals. A model is presented which permits a theoretical calculation of the power spectrum of these fluctuations and satisfactorily predicts the features of spectra computed from experimental fading data except for an observed rise at low frequencies. The model is based on the geometry of the reflections from nearby randomly placed vertical plane reflectors. Vertical polarization is assumed. Both the standing-wave pattern and the Doppler shift view of fading are used to obtain nearly identical results. The detailed shape and in particular the sharp cutoff frequency of the spectrum are shown to depend crucially on the angle a between the direction of vehicle motion and the direction to the fixed station. Detailed comparisons are made of theoretical spectra with experimental spectra representing a range of the angle a. The collection, digitization, calibration, plotting, and digital processing to obtain power spectra of actual recorded fading waveforms are described.