Low Frequency Indoor Radiolocation

This thesis concerns the application of electromagnetic wave propagation to the problem of indoor radiolocation. Determining the location of people and objects relative to their environment is crucial for asset tracking, security, and human-computer interface (HCI) applications. These applications may be as simple as tracking the location of a valuable shipping carton or detecting the theft of a laptop computer, or as complex as helping someone to find his or her way around an unfamiliar building. Currently available technologies, such as GPS or differential GPS, can provide the position information to solve these problems as long as the people or objects to be tracked are outdoors, where the microwave radio signals from the 24 orbiting GPS satellites may be received, but there is an unmet demand for a similar system that works indoors, where the physics of microwave radio propagation results in greatly attenuated signals and correspondingly poor GPS reception. This thesis suggests a novel means of solving these problems involving the precise measurement of signals whose wavelengths are comparable to the size of a building. It is shown that this “mid-field” frequency regime can provide useful propagation characteristics with very little fixed infrastructure. Using a wavelength of 150m, over 4000 amplitude and differential carrier phase measurements were taken in the Wiesner Building. Least-squares power law fits to that data over paths of up to 30m yield meter-class position estimates at 1KHz acquisition rates. The contributions of this thesis include detailed indoor propagation measurements, as well as candidate empirical and theoretical models for that data. Additionally, new types of high precision measurement instrumentation and high efficiency RF power amplifiers have been created to enable these measurements. Thesis Supervisor: Neil A. Gershenfeld Title: Associate Professor of Media Arts and Sciences