Wi-Fi fine time measurement–Principles, applications, and future trends: A survey

IEEE 802.11–2016 proposed the Wi-Fi Fine Time Measurement (FTM) protocol, aiming at providing meter or sub-meter level ranging function between smart terminals and Wi-Fi access points (APs). Compared with other indoor positioning technologies for instance, Bluetooth, acoustic, visible light, Ultra-wideband, etc., Wi-Fi has been characterized by low cost, no deployment, and potentially high positioning precision, especially with the enhancement of FTM, which enables Wi-Fi to be a competitive technology for Internet of Things, indoor location-based services (iLBSs), smart city, and many other fields. In this article, we first present a comprehensive survey that focuses on the Wi-Fi FTM technology, which contains the working principle, measurement for positioning, and methods comparison. We highlight the current FTM-related localization methods especially learning and multi-source fusion-based approaches. Then, we review the real-world applications and existing commercial solutions, revealing the possible directions for the industrialization of Wi-Fi FTM localization. Finally, this paper analyzes existing open issues of Wi-Fi FTM positioning (e.g., capability, scalability, multipath, NLOS, device heterogeneity, and privacy) and discusses the potential development trends.