Broadband acoustic local positioning system for mobile devices with multiple access interference cancellation

This paper presents an Acoustic Local Positioning System (ALPS) suitable for indoor localization of mobile devices, based on the transmission of high frequency Code Division Multiple Access (CDMA) audio signals from a fixed beacon network to a tablet computer. The system permits positioning of the device (and the user carrying it) within a few centimeters, which is accurate enough for most location-based applications. It also implements a CDMA scheme for localization, including compensation for the limited transmission frequency band of the sensors which causes Intersymbol Interference (ISI), as well as Multiple Access Interference (MAI) between the different beacons. Signal reception, processing and estimation of position all take place within the tablet, operating at real time and with an update rate of 2 Hz. Experimental results show that the MAI/ISI compensation algorithm increase both the system's robustness (availability ⩾90%) and accuracy (errors ⩽10 cm) under adverse circumstances such as near-far effect or noisy conditions.