| Many measurements show that cellular mobile radio signals are scattered by objects in the vicinity of a mobile, as well as by tall buildings at some distance from the direct radio path. While it is known that scattering takes place, the objects and wave mechanisms responsible for the scattering are not known. The motivation of this dissertation is to understand scatterings produced by various common objects, such as vehicles, lampposts, and building facades. The scattering objects give rise to a number of possible paths by which the radio signals generated from a mobile can reach at the base station antenna and cause amplitude variation, delay spread and angle of arrival spread of the received signals.; We have analytically modeled various scatterers and run computer simulations to find their contributions and interferences on the path gain of the received signal. We have found that the presence of objects such as vehicles and lampposts are significant only when they are very close to the mobile, therefore, they cannot account for the measured delay spread and angle of arrival spread. However, diffuse scattering from building facades, modeled as a Lambertian surface, give rise to significant scattered power.; Unfortunately the assumption of Lambertian surface, applicable to rough surface, does not apply to scattering by a building facade because windows and other architectural features have a more nearly periodic structure. However, the exact structure of individual building is not usually known, so that each building may be considered to be one realization of a random process. Using the vectorial Kirchhoff-Huygens integral equation, the scattering pattern is found for each individual building realization. Monte Carlo techniques are then used to create a single statistical model that is used for scattering from all buildings.; In addition to local scattering visible to the mobile, additional scattering can take place at tall buildings and other structures located above the average rooftop level. A simulation model of residential environment has been set up to evaluate the effect of this scattering, namely fading pattern, the cross correlation coefficient and the distribution in angle and time of arrival of the received rays. |
