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PhD thesis

Title Ultrasonic Location System
Author Daniel Albuquerque
School Universidade de Aveiro
Address Campus Universitário Santiago, Aveiro, Portugal
Month July
Year 2013
Advisor Paulo J S G Ferreira, José M. N. Vieira, Carlos A C Bastos
Group (before 2015) Signal Processing Laboratory

This thesis presents a location system exclusively ultrasonic based, without using any other technology. This location system was designed to operate in environments where the use of other technologies are not possible or the use of them is limited, such as underwater applications or hospital environments. The proposed location system uses a fixed beacons network allowing the mobile stations to locate. Due to the necessity of data transmission and distance measurement it was developed an ultrasonic pulse robust to echoes that allows to perform both tasks with success. The location system allows that mobiles locate themselves only listening the information in ultrasonic pulse sent by the beacons, for that it is used an algorithm based on time difference of arrival. Therefore, the user privacy is guaranteed as well as the complete independence of the number of users. To simplify the network implementation it is only necessary to manually define the position of some of the beacons, called anchor beacons. These will allow the remaining autonomous beacons to locate themselves by an iterative location algorithm based on a local cost function minimization. For this system work properly beacons must synchronize their clocks and measuring the distance between them. Therefore, this thesis proposes a clock synchronization protocol which also allows measure the distance between the beacons by exchanging only three ultrasonic messages. Additionally, the location system permits that damaged beacons could be replaced without compromising the network operability reducing the maintenance complexity. Additionally, a simplified ultrasonic simulator for indoor environments was developed, which has proved to be very accurate and a valuable tool to simulate the location system behavior under controlled conditions.