2-D Localization System for Mobile IoT Devices Using a Single Wi-Fi Access Point With a Passive Frequency-Scanned Antenna

Abstract

A novel 2-D indoor location system for Internet of Things devices employing a single Wi-Fi access point (AP) is presented. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\{x, y\}$ </tex-math></inline-formula> position is estimated with a combination of Direction-of-Arrival (DoA) and Time-of-Flight (ToF) algorithms. The azimuthal DoA is estimated using a modified MUSIC technique, which requires the acquisition of the received signal strength indicator (RSSI) using different Wi-Fi frequency channels in the 2.4-GHz band, together with a dual-port frequency-scanning antenna (FSA). This allows a wide Field of View (FoV) of 180° for the DoA. To estimate the ranging distance, an algorithm based on the 802.11mc fine time measurement (FTM) protocol is employed to consider the effects of the channel hopping. Therefore, the proposed system does not rely on channel state information (CSI) or complex IQ information, which is not available in commercial Wi-Fi APs. The proposed system has been fully implemented with a commercial Wi-Fi AP and tested in a practical scenario, proving a root-mean-square error (RMSE) when estimating the localization of mobile devices of only 1.43 m, in a wide area of 12 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times12$ </tex-math></inline-formula> m.