Connectivity analysis of underground sensors in wireless underground sensor networks

Wireless underground sensor networks consist of sensors that are buried under the ground and communicate through soil medium. Due to channel characteristics, the connectivity analysis of wireless underground sensor networks is more complicated than that in the traditional over-the-air wireless sensor networks. This paper focuses on analyzing the connectivity of underground sensors in wireless underground sensor networks in terms of the probability of node isolation and path probability which captures the effects of the environment parameters such as soil moisture and soil composition, and system parameters such as sensor node density and propagation techniques. Throughout this paper, both qualitative and quantitative comparisons between electromagnetic wave system and ordinary magnetic induction system for underground communications are provided. More specifically, we derive the exact closed-form mathematical expressions for the probability of node isolation of these two communication systems and validate the correctness of analytical models through simulations. We also provide the simulation-based path connectivity of these two communication systems. The results obtained in this paper provide useful guidelines on the design of reliable wireless underground sensor networks.