Tightly Coupling Integration of GNSS Observables and Wi-Fi RTT Ranges

Miquel Garcia-Fernandez, Malgorzata Siutkowska, Alex Lopez-Cruces, Eduardo Paredes Brito, Aleix Tejada Giménez, Xavier Banque-Casanovas

Abstract:	As it is known, Wi-Fi is being widely used nowadays for indoor navigation by means of using Received Signal Strength (RSS) in what is known as “Fingerprinting”. However, with the rollout of the 802.11mc-2016 standard, users of Wi-Fi technology can have also access to the Fine Time Measurement (FTM), also known as Round Travel Time (RTT), which is a measurement of the range between the access point and the user equipment. This Time-of-Arrival (ToA) measure is much less susceptible to the environment than RSS and, provided that the user has access to the position of the access points, absolute navigation could be achieved. This opens the possibility of having meter level navigation indoors. Moreover, the range nature of the RTT observable makes it possible to adopt a tightly coupling strategy with other range-based navigation systems such as GNSS in order to achieve a seamless indoor-outdoor navigation solution or improve the position estimates in areas where GNSS is challenged (e.g., high multipath levels in urban canyons). In general, the quality of the Wi-Fi RTT ranges is fairly good in terms of measurement noise, with ranges of ca. 20 cm, which theoretically allows positioning with meter-level accuracy. However, despite being Wi-Fi RTT a “bistatic” technology (the range is obtained by measuring the time that the signal goes and comes) and thus not being affected by biases due to clock synchronization as GNSS does, it does present some significant hardware biases. Fortunately, enough, these biases are fairly constant and channel dependent, which makes it possible to build a database of access point position and biases, as a function of the BSSID (MAC) address. This database can be then sent to the user in order to perform the navigation session. This work provides with an overview of the RTT technology in terms of measurement quality and the level of quality for indoor positioning (Wi-Fi only) as well as hybrid positioning with GNSS.
Published in:	Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022) September 19 - 23, 2022 Hyatt Regency Denver Denver, Colorado
Pages:	1074 - 1084
Cite this article:	Garcia-Fernandez, Miquel, Siutkowska, Malgorzata, Lopez-Cruces, Alex, Brito, Eduardo Paredes, Giménez, Aleix Tejada, Banque-Casanovas, Xavier, "Tightly Coupling Integration of GNSS Observables and Wi-Fi RTT Ranges," Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022), Denver, Colorado, September 2022, pp. 1074-1084. https://doi.org/10.33012/2022.18416
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