Pilot Analysis on Soil Moisture Impact on Underground to Aboveground LoRaWAN Transmissions for IoUT Contexts

Data transmission from the underground can be a relevant task for a wide range of Internet of Things (IoT) applications (e.g., from Smart Agriculture to environmental monitoring) thus paving the way to the recent paradigm of the Internet of Underground Things (IoUT). In this context, Low Power Wide Area Network (LPWAN) technologies proved to be reliable solutions for underground to aboveground (UG2AG) data transmission: Long Range (LoRa) modulation and LoRa Wide Area Network (LoRaWAN) protocol in particular, demonstrated to be able to transmit from depths down to 1.5 m. Nevertheless, the quality of the transmission channel may significantly vary due to several factors: ranging from soil composition to presence of water. Specifically, soil moisture may have an attenuating effect on the transmitted signal. The aim of this paper is to preliminary analyze the impact of different Volumetric Water Contents (VWCs) in soil on the LoRa transmission channel. Radio parameters are collected by burying a LoRaWAN transmitter inside a plastic case filled up with sand. The underground attenuation is measured reproducing different VWCs by progressively adding different quantities of water: this methodology allows to re-create in laboratory well-defined VWCs unlike a real environment where the actual VWC is due to a plethora of different factors. Results achieved in this paper demonstrate the correlation among VWC and losses though showing the potential feasibility of LoRa links also in case of elevate VWC levels.