Interference mechanisms which affect frequency reuse on short line-of-sight millimetric links

At microwave frequencies, clear-air refraction (at small time percentages) and troposcatter (at large time percentages) are generally assumed to be the dominant propagation mechanisms for the coordination of line-of-sight systems; this is due to the long paths (>30 km) and large separations between adjacent paths (typically hundreds of kilometres). For shorter path separations over land, terrain diffraction must also be considered. The authors discuss the importance of the various interference mechanisms. In particular non-great circle mechanisms (such as building scatter) are shown to be important. These mechanisms are not adequately covered by current prediction methods. The models are discussed. An experimental programme of building, terrain and rain scatter measurements at 38 GHz has been planned to test the models