Experimental and simulation studies of underground wireless sensor networks

This paper summarizes the experimental and simulation results in our studies of buried wireless sensor networks (B-WSN). The goal is to choose the suitable Industrial Scientific Medical Band (ISM) frequency which can be applied in the underground environment and then to investigate the underground communication ability of wireless modules based on the chosen frequency. As a key factor in point to point radio communication in WSN, the RF path loss in soil was evaluated and the results show that the attenuation significantly increases with high operating frequency. The penetration depth versus dielectric constant with various operation frequencies was also studied in this research. The simulation result shows that the penetration depth decreases with high moisture content and high operation frequency. Simulations indicate that the operation frequency in Sub-GHz range can acquire higher penetration depth and lower path loss compared to other high operation frequencies such as 2.4 GHz. The experimental results indicate that RSSI is significantly negatively related to the depth of filled soil. The results indicate that the maximal above ground horizontal transmission distance is 1.5m when the node was buried 1.3m underground.