Link Quality Characterization and Deployment Optimization of Wireless Underground Sensor Networks for Precision Agriculture

Wireless Underground Sensor Networks (WUSNs) are extensively utilized in agricultural information monitoring due to their flexibility in deployment and adaptability to environmental conditions. However, the higher attenuation of radio waves in soil and the complexity of underground to aboveground (UG2AG) channels cause more variability in the signal coverage range of monitoring nodes compared to surface networks. It is meaningful to quantify signal attenuation through channel assessment and reveal the impact of different variables on the channel. In this study, a channel assessment device operating at 470MHz was developed based on the LoRaWAN standard protocol, and a series of UG2AG channel assessments were conducted in farmland. Several key metrics, including Received Signal Strength Indication, Signal-to-Noise Ratio, and Packet Delivery Ratio, were parsed as quantitative indicators of channel quality. Communication parameters including transmit power, antenna configuration, and spreading factor were considered. Furthermore, the effects of environmental variables on channel quality, such as end node burial depths, gateway installation heights, precipitation and burial methods, were analyzed. The experiments were conducted under two scenarios: one scenario with the crop layer and another without the crop layer. Comparison of results in both scenarios highlights the crop layer's impact on channels for agricultural monitoring, which should be considered when deploying WUSNs in farmland. The simulation results show that the optimized deployment scheme has achieved advantages, clearly demonstrating the necessity of conducting channel assessment before deploying WUSNs.