A simple ultrasonic Indoor/Outdoor detector for mobile devices

Context information is fundamental for mobile application. A system able to detect Indoor/Outdoor state switching can give useful information to upper-level applications permitting to improve their performance or reduce the computational load and consequently the lifetime of the smartphone. A localization application may exploit the Indoor/Outdoor information to smartly decide if using GPS (that performs well outdoors but poorly indoors) or other localization methods. In this paper we present an ultrasonic-signal-based Indoor/Outdoor detector for smartphones. The phone plays an ultrasonic ping by using its in-built speakers and records the echoes by using its microphone, therefore, no specific hardware is required to be added to the smartphone. The proposed detector shows good performance in terms of accuracy and latency.