Communication Through Soil in Wireless Underground Sensor Networks – Theory and Practice

Abstract

Wireless Underground Sensor Networks (WUSNs) constitute one of the promising application areas of the recently developed wireless sensor networking techniques. WUSN is a specialized kind of WSN that mainly focuses on the use of sensors at the subsurface region of the soil, that is, the top few meters of the soil. For a long time, this region has been used to bury sensors, usually targeting irrigation and environment monitoring applications, although without wireless communication capability; WUSNs promise to fill this gap and to provide the infrastructure for novel applications. The main difference between WUSNs and the terrestrial WSNs is the communication medium. In fact, the differences between the propagation of electromagnetic (EM) waves in soil and in air are so significant that a complete characterization of the underground wireless channel was only available recently. This chapter presents advanced channel models that were developed to characterize the underground wireless channel considering the characteristics of the propagation of EM waves in soil and their relation with the frequency of these waves, the soil composition, and the soil moisture. Additional important aspects such as the burial depth, the reflection, the refraction, and multi path fading effects on the EM waves are also considered. The results from the field experiments in conjunction with the simulation results, both considering the path loss and the bit error rate, prove the feasibility of WUSNs. The chapter concludes with an outlook on potential research topics that are essential for the realization of WUSNs.