Spectral properties of modulated signal in the doppler domain in urban radio channels with fading

We examine propagation of frequency modulated (FM ) radio signals in the urban environments for different elevations of base station (BS) and mobile subscriber (MS) antennas, below and above the rooftops, based on the stochastic multi-parametric approach. We concentrate our attention on the spectral properties of signal power variations in the frequency domain and describe them based on the Doppler-spread spectrum of bandpass signal power. In the framework of the stochastic approach, the total signal power, the correlation function, the Ricean K-parameter of fading, and the scale of correlation of different spectral components of the modulated signal are analyzed. A practical aspect of relationship between the correlation scale of any two components of the FM signal and the coherent bandwidth of the urban channel with fading is examined via prism of special experiment. New effects of buildings' density and the elevation of BS antenna on above characteristics of the FM signal are examined numerically. It is found that, depending on various scenarios occurring in the urban scene, the buildings' density and the elevation of BS antenna can significantly distort the modulated signal within radio link with fading.