Empirical Study of Near Ground Propagation in Forest Terrain for Internet-of-Things type Device-to-Device Communication

This paper presents continuous wave power measurements conducted in forest terrain with a focus on path-loss in a Device-to-Device (D2D) communication scenario. The measurements have been conducted at 917.5 MHz with measurement ranges extending to more than 2.5 kilometers using a purpose developed measurement system with a dynamic range of 180 dB. The impact of different antenna heights has been investigated by placing antennas at 1.5, 2.5 and 3.5 meters elevation over the terrain. The measurements showed that the antenna elevation in the given scenario did not have a significant impact on the received power. The measurements also showed that the dominant path of propagation is through the foliage for the first approximately 1000 meters where foliage excess loss is dominant in this region. After approximately 1000 meters the measured received power tend to follow the fourth-power law indicating that the excess loss due to foliage has to be limited. The measurement results have been compared to models proposed in the literature based on empirical data, as well as models proposed by ITU and COST. The comparison showed that only two models predicted the limit in foliage excess loss in the measurement data observed. By applying these excess loss models in combination with path-loss models it was possible to model the measured total path-loss with an RMS error of less than 10 dB. This was achieved by either applying a model proposed by Tewari or a combination between the two-ray path-loss model and the ITU-R P.2108 clutter loss model.