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Abstract
The recent emergence of Internet of Underground Things (IOUT) in many areas including environment and infrastructure monitoring, border patrol, transportation, and precision agriculture, underscores the importance of wireless underground (UG) communications. Yet, existing solutions are limited by relatively short communication distances and low data rates that prohibit widespread adoption. Extending the communication ranges and increasing data rates in wireless UG communications faces unique challenges because of the interactions between soil and communication components: (1) antenna properties, such as resonance frequency and antenna bandwidth, depend on soil type and varies with changes in soil parameters (e.g., soil moisture). Therefore, an antenna designed for over-the-air communication is no longer matched to the transceiver when buried in soil, and the system bandwidth, which is limited by antenna bandwidth varies in time. (2) Delay spread of the UG channel, which determines its coherence bandwidth, is a time-variant function of the soil parameters. Accordingly, the channel bandwidth varies significantly with physical changes in the environment. (3) The soil-air interface results in fluctuations in both antenna performance and EM wave propagation, which should be considered in system design. Consequently, next generation wireless UG communication solutions should be tailored to deployment parameters such as soil composition and depth while being robust to variations in environmental parameters.
In this dissertation, the UG channel is characterized and environment-aware, cross-layer communication solutions are developed to achieve high data rate, long range communications. Moreover, applications to agriculture and smart lighting are illustrated. The impulse response of the wireless UG channel is captured and analyzed through extensive experiments. Based on this analysis, multi-carrier modulation and wireless underground channel diversity reception schemes have been developed. Furthermore, based on UG antenna analysis, soil moisture adaptive beamforming using underground antenna arrays is also designed. A wide variety of applications can potentially utilize UG communication solutions with diverse requirements. Among these, smart agriculture solutions that highlight long range and high data rate aspects of UG communications are considered to evaluate the developed solutions. The findings of this research are also evaluated using computational electromagnetics simulations.
