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1.2 COMPUTER AND INFORMATION SCIENCE
In this paper we discuss how the innate ability of mobile phone speakers to produce ultrasound can be used for accurate indoor positioning. The frequencies in question are in a range between 20 and 22 KHz, which is high enough to be inaudible by humans but still low enough to be generated by today’s mobile phone sound hardware. Our tests indicate that it is possible to generate the given range of frequencies without significant distortions, provided the signal volume is not turned excessively high. In this paper we present and evaluate the accuracy of our asynchronous trilateration method (Lok8) for mobile positioning without requiring knowledge of the time the ultrasonic signal was sent. This approach shows that only the differences in time of arrival to multiple microphones (control points) placed throughout the indoor environment is sufficient. Consequently, any timing issues with client and server synchronization are avoided.
Filonenko, V., Cullen, C., Carswell, J.: Asynchronous Ultrasonic Trilateration for Indoor Positioning of Mobile Phones. Web & Wireless 2012; Naples, Italy, April 12-13, 2012. Springer LNCS Volume 7236.