FSI: A FTM Calibration Method Using Wi-Fi Physical Layer Information

Abstract

Fine Time Measurement (FTM) protocol is included by IEEE 802.11–2016 to address the challenging problem of the high accuracy of the existing system in Wi-Fi positioning. Although FTM promises meter-level ranging accuracy in line-of-sight (LOS) conditions, non-line-of-sight (NLOS) and multipath effects cause accuracy to decline sharply. In this paper, by diving into fine-grained PHY layer information of higher time resolution, we explore the relationship deeply between FTM error and multipath channel response. On this basis, we propose FSI, a method for calibrating FTM errors using PHY layer information, which can identify environmental characteristics automatically and estimate the length of signal propagation paths. Finally, we design an optimation method based on the mobility of users, to further improve positioning accuracy in actual environments. Experimental results show that FSI improves the ranging accuracy by 24.80% and positioning accuracy by 28.45%.