Wind-Blown Foliage and Human-Induced Fading in Ground-Surface Narrowband Communications at 400 MHz

Abstract

As small-scale fading is a spatial phenomenon, the movement of objects in the environment around static sensor nodes can induce significant fades. However, there have not been many works characterizing small-scale fading due to environmental factors for ground-surface wireless communications. We first measure the temporal fading characteristics experienced by antennas located just 1.5 cm above the surface of the ground due to wind-blown foliage or human movement in the environment for a narrowband channel in the 400-MHz frequency band. We then compare the extracted data to existing distributions and show that fading due to wind-blown foliage can be modeled as a Nakagami-m distribution, with wind speed and excess path-loss-dependent m shape factors. The alpha-mu distribution best characterizes the small-scale fading of a single human pedestrian, which is shown to have a repeatable pattern and can be up to 40 dB below the no-fading mean, whereas the Rician distribution, with an excess path-loss-dependent K-factor, can be used to characterize fading from multiple human pedestrians. We also report the second-order statistics of the average fade duration and the level crossing rate for fading caused by wind-blown foliage and multiple human pedestrians. Finally, we discuss the significance of the results on wireless sensor network protocol design and applications.