Ultrasonic LPS adaptation for smartphones

In this paper we present a privacy-oriented Ultrasonic Local Positioning System (U-LPS) allowing users with portable devices, such as smartphones or tablets, to accurately determine their position in indoor environments. Indoor U-LPSs have been widely used to provide location information with centimeter or even sub-centimeter level accuracy at high rates. However, most of these systems demand specific hardware in the reception stage that cannot be used with current smartphones. Hence, the user cannot benefit from the versatility of services that these kind of devices offer. This work presents the design of an external device which translates the high frequency ultrasonic information emitted by a CDMA-based U-LPS, into a low frequency band understandable for the mobile phone by means of an analog multiplier. The output of the multiplier is connected to the smartphone or tablet using the Jack input connector as if it was a microphone. Then, the mobile device processes the low band frequency signals and estimates its position.