Analysis of the perceptual impact of high frequency audio pulses in smartphone-based positioning systems

The ability to locate objects and people indoors remains a substantial challenge and effective centimeter-level smartphone-based indoor positioning, is still an open problem. Conventional smartphones have recently been used for centimeter-level indoor positioning by performing acoustic Time-of-Flight (ToF) ranging. Due to limitations in the smartphone hardware, i.e. available bandwidth typically below 24 kHz, these systems use signals with both audio and ultrasonic spectral content in the ranging process. By using signals with lower frequencies (in the audio band) it is possible to measure longer distances, thus circumventing the high attenuation that ultrasounds suffer. But a system using audible signals would be quite annoying for humans. In this paper we propose a methodology to design non-invasive audio pulses, i.e. pulses with reduced perceptual impact on humans. Additionally, we have evaluated the proposed non-invasive pulses with naïve subjects in a soundproof room for different sound pressure levels.