Wireless Signal Networks: A Proof of Concept for Subsurface Characterization and A System Design with Reconfigurable Radio
Abstract
Subsurface monitoring has been accomplished through traditional techniques including
direct soil sampling, probing and soundings, and using geophysical mapping tools.
Although these techniques have been successfully implemented to characterize the global
state of geo-media in an interested site, there are challenges associated with these techniques including difficulties in providing real-time data to track geo-hazards and deployment challenges specifically the requirement of wired connections in some conventional techniques. To address these challenges, wireless sensor networks have been used recently for subsurface monitoring. However, wireless sensor nodes in existing solutions only provide point measurements and are incapable of providing global measurement for characterization of subsurface medium.
The key contribution of this dissertation is to bridge the gap between real-time monitoring and global measurements by introducing a novel concept of Wireless Signal Networks (WSiNs) with a proof of concept for subsurface monitoring using actual wireless
sensor nodes (i.e., MICAz) and a system design with a reconfigurable radio platform.
Wireless signal networks use the real-time link quality signals among distributed wireless sensor nodes as the main indicator of an event in the physical domain. Our thesis is that "the variation of the link quality between wireless sensor nodes can be used as an effective global sensing mechanism which reflects characteristics of geo-media subjected to various geo-events". To prove this thesis, the dissertation proposes an accurate and simple radio propagation model for underground environments, and the model quantitatively explains that the changes of soil properties and conditions affect the link quality and strength of the radio waves within the region of the event. Then, the dissertation presents real-time global subsurface monitoring applications with wireless signal network concepts based on the proposed underground propagation model including experimental evaluations. Experiments demonstrated that calibrated wireless signal strength variations can be used as indicators to sense changes in the subsurface.
To extend underground communication distance, prolong network lifetime, and provide
adaptive topology construction, we propose a system design for wireless signal networks
with the reconfigurable radio platform. Based on the theoretical and empirical
analysis of the radio propagation model, the dissertation proposes practical solutions of
extending the underground communication distance and an evaluation platform for the
system design with reconfigurable radio (i.e., Universal Software Radio Peripheral). The
dissertation describes a novel topology control mechanism by introducing a new control
dimension, i.e., frequency control, with the reconfigurable radio that supports underground communication distance extension, network lifetime enhancement, and adaptive
topology construction in underground environments of high signal attenuation affected by
geo-events.