Propagation analysis of signal fading for basic exchange radios

Although empirical multipath fading models are available for microwave links above 2 GHz, these models are not directly applicable to basic exchange radio (BEXR) links because of the substantial differences in frequency, antenna beamwidth, and radio path clearance. A method for obtaining a scaling factor which accounts for the differences between BEXR and microwave links is presented. First, the terrain scattering is studied using a rough surface model, and the atmospheric refraction is studied using a ray tracing approach. Then, the received signal powers of a microwave link and two BEXR links on the same path under the same propagation condition are calculated. The signal characteristics are investigated and used to simulate the fading distributions for all three links. From the simulation results, a scaling factor is derived and used to modify the existing microwave multipath fading models for BEXR application. The predictions of the modified model agree well with measured BEXR data. This study shows that the probability distribution of signal fading on BEXR links is a strong function of antenna height and beamwidth