Implementation of indoor positioning algorithms using Android smartphones

This paper proposes a software android application to compute the absolute position of smartphones or tablets in an indoor Ultrasonic Local Positioning System (U-LPS) based on hyperbolic trilateration. U-LPS can enhance mobile devices indoor positioning allowing sub-meter accuracy results by a suitable encoding of the ultrasonic transmissions. An external hardware device based on an ultrasonic microphone and an acquisition system can digitize the signals coming from the U-LPS and send them to the mobile device. Once in the device, by means of correlation techniques, time difference of arrival (TDOA) can be computed to obtain the device position and offer a wide variety of Location Based Services (LBS) to the user (building navigation, augmented reality...). Nevertheless, the correlation and positioning algorithms imply a high computational load. An Android application is presented to positioning mobile devices. It can be configured in real-time for different encoding schemes and allows to manage the reception of data coming from an external acquisition module and perform the low level (demodulation, correlation and peak detection) and high level (TDOA computation and hyperbolic trilateration) tasks. The proposed algorithms have been validated in an indoor U-LPS.