Acoustic positioning with wireless radio devices

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Fehér Gábor
Department of Broadband Infocommunications and Electromagnetic Theory

In this BSc thesis building blocks of an indoor localization system is presented. The system is based on the time of arrival measurement of a traveling acoustic signal. The system hopefully will be used in museums, exhibitions, and - by the requirement - it should be able to manage at least 100 visitors.

First, commonly used indoor positioning methods including their physical and technological parameters will be presented, and a few existing indoor positioning systems will be introduced as examples.

After this, the exactly specification of the system is shown taking in consideration the cheapness, low power consumption and the simplicity. The system will work with three transmitters placed on the ceiling of the target room. They transmit a combination of radio and audio signal. The mobile station receives both the radio and the audio signal, then computes the distance from each transmitter stations using the delay time between the reception of the two types of signals. The most important part of the task was the design of the active filter of the receiver section, which is should be able to detect the sound waves from 10 m of distance. During the measurements and tests, it became apparent that the necessary level gain - due to the risk of self oscillation - is not available with a conventional multi-stage amplifier. The solution is the isolation of the power supply on each stages. Because of this, the test circuit is worked reliably 30-40cm distance, instead of 10 m. The separate power supply for each stages - and thus the higher amplification – will be realized in a future version.

At the end of the thesis I discuss the design and operation of distance measurement software, and finally I close the thesis with the evaluation of the results and the future tasks (higher signal gain access, etc.).


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