A Preliminary Study of UG2AG Link Quality in LoRa-based Wireless Underground Sensor Networks

A reliable communication channel between the underground sensor nodes and aboveground devices is vital and mostly desirable for data collection, relay and upload for the wireless underground sensor networks (WUSNs). In particular, the analysis of the underground-to-aboveground (UG2AG) link quality is crucial for the practical realization and deployment of WUSNs. Recently, LoRa, as one of the low-power wide-area networks (LPWANs) technologies, has attracted substantial attentions for its unique advantages such as the low power consumption and long-range capability. However, to the best of our knowledge, its performance has not yet been quantitatively analyzed for LoRa-based WUSNs. In this paper, a preliminary evaluation of the LoRa's capability of serving a UG2AG channel are presented at various burial depths in two challenging media, i.e., attenuative soils and water. We experimentally analyze the influence of various physical layer (PHY) parameters, e.g., spreading factor (SF), bandwidth (BW), and coding rate (CR) on the LoRa's propagation performance in the field. The results reveal that the reliable UG2AG communication link (without packet loss) can be established at an internode distance greater than 50m when the LoRa device is buried 0.4m deep, even in soils with relatively high volumetric water content (VWC). Our field results successfully verify the theoretical model for the UG2AG channel. These results may have a significant impact on the deployment of LoRa-based WUSNs with the potential applications in underground utilities monitoring.