Effects of nearby objects on fading and coupling in Line-Of-Sight environments

Frequency-agile wideband radios may be susceptible to non-linear effects from strong electromagnetic signals coupled from co-site or nearby emitters. Also, such signals can impact spectrum sensing capability of Dynamic Spectrum Access (DSA) systems. Therefore, it is important to understand the characteristics of the coupling channel between nearby systems due to Line-of-Sight (LOS) propagation and reflections from nearby objects, such as buildings in the urban environment or hills in the rural environment. The presence of nearby objects can cause significant variations in the strength of the coupling leading to enhancement or fading of the coupled signal. Significant fading or variation in coupling may inadvertently cause DSA radios or other systems that have spectrum sensing capability to make erroneous decision on the selection of the operating frequency. In this paper we define a channel model for coupling among nearby systems. Our analysis considers two-ray and six-ray propagation models to define the nearby LOS coupling channel. We investigate the variation of the coupling as a function of frequency and the arrangement of the surrounding obstructions. We aggregate this data to provide a comprehensive channel model that can be used by radio designers and system integrators to help analyze the electromagnetic environment caused by nearby emitters.