TABLE OF CONTENTS Radio signals transmitted from a mobile-radio base station are not only subject to the same significant propagation-path losses that are encountered in other types of atmospheric propagations, but are also subject to the path-loss effects of terrestrial propagation. Terrestrial losses are greatly affected by the general topography of the terrain. The low mobile-antenna height, usually very close to ground level, contributes to this additional propagation-path loss. In general, the texture and roughness of the terrain tend to dissipate propagated energy, reducing the received signal strength at the mobile unit and also at the base station. Losses of this type, combined with free-space losses, collectively make up the propagation-path loss.
Mobile-radio signals are also affected by various types of scattering and multipath phenomena-which can cause severe signal fading-attributable to the mobile-radio communications medium. Mobile-radio signal fading compounds the effects of long-term fading and short-term fading, which can be separated statistically and are described in Chap. 3. Long-term fading is typically caused by relatively small-scale variations in topography along the propagation path. Short-term fading is typically caused by the reflectivity of various types of signal scatterers, both stationary and moving. Fading of this kind is referred to as "multi-path" fading.
Propagation between a mobile unit and a base station is most susceptible to the effects of multipath fading phenomena, because all communication is essentially at ground level. The effects of multipath phenomena are not significant in air-to-ground and satellite-to-earth-station communications, because the angle of propagation precludes ...
