Acoustic local positioning system using an iOS device

This work benefits from the capability of the iPhone's or iPad's microphone to acquire high-frequency sound for accurate acoustic code identification. Although the maximum theoretical value for the frequency response of the built-in iOS device microphone is 20 kHz, emissions with frequencies close to 22 kHz have been experimentally detected. The frequencies used in this work are in the range from 18 to 22 kHz, which are high enough to be inaudible for almost every people but low enough to be generated by standard sound hardware. The aim of this work is to develop an inexpensive indoor positioning system where the user gets its location by using an iOS device's microphone. For this purpose a third-generation iPad is used for high-frequency sound data acquisition and neither external acquisition system nor ultrasonic microphone are required. The capability of iOS devices to acquire acoustic signals in the vicinity of 20 kHz has been successfully demonstrated. This fact allows the use of this kind of device for acoustic code detection and accurate positioning by means of multilateration.