Quantifying short-range surface-to-surface communications links

As wirelessly connected embedded systems become ubiquitous, previously undocumented propagation environments must be explored to support their design. This paper describes the results of a study of such an environment: short-range wireless propagation outdoors, near the ground. In the study, frequencies were considered within three industrial, scientific, and medical (ISM) bands: 902-928 MHz, 2400-2426 MHz, and 5725-5752 MHz. Experimental propagation loss was summarized based on measurements in eighteen environments, at varying heights, distances, and polarizations. Based on the data collected, the appropriateness of a simple design guideline, based on a two-ray propagation model, is discussed. Summaries of the path loss, fading, and the influences of antenna height, antenna separation, and surrounding clutter in highly variable environments are given. Additionally, limited numerical modeling of the impact of surface roughness is provided. Particular focus was given in the study to heights and distances appropriate for randomly deployed wireless sensor networks, such as autonomous unattended ground-sensor systems.