AOA-based Ultrasonic 3-D Location for Ubiquitous Computing

This thesis addresses the problem of simplifying indoor ultrasonic location systems through the disposal of the radio synchronization subsystem. The location approach proposed herein is completely based on angle-of arrival (AOA) estimation of ultrasonic frequency-hopping spread spectrum (FHSS) signals transmitted by fixed beacons with known positions. The proposed system is privacy-oriented, that is the device to be located only receives and does not transmit signals. In the proposed location system, the beacons transmit their IDs using ultrasonic signals. The receiver acquires these IDs and determines its room-level position by table lookup. Following beacon identification, the receiver exploits a priori knowledge of the hopping patterns associated with the beacons and a sensor array to determine the AOA of the signal from each beacon. Next, the AOA information is used to determine the receiver’s 3-D location using location algorithms proposed herein. In addition to location, these algorithms yield the receiver orientation. AOA estimation is achieved by exploiting the phase of the cross-power spectra of the received signals. Special attention is paid to the phase-difference ambiguity problem. Novel disambiguation methods are proposed that facilitate AOA estimation in the ultrasonic case. The proposed location system was tested experimentally in a prototype. The results confirm the effectiveness of the approach. Accuracy of about 30 cm for location, 5degrees for the x-axis orientation, 10 degrees for the y-axis orientation and 15 degrees for the z-axis orientation, at an 11 Hz update rate, was obtained. The experiments also reveal practical limitations leading to recommendations for future work. The contributions of this thesis include novel methods for phase-difference ambiguity resolution exploiting either spatial diversity or frequency diversity. These methods lead to novel AOA estimation techniques for the widely-spaced sensor case. Other contributions are novel algorithms for receiver’s location and orientation estimation using only AOA information. Also, a novel system for binary data transmission using ultrasonic signals, and a novel method for FHSS acquisition and synchronization, are proposed.