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G. Retscher, A. Kealy, V. Gikas, H. Hofer, A. Ettlinger, F. Obex:
"Cooperative Localization in Indoor Environments Using Constrained Differential Wi-Fi and UWB Measurements";
Talk: 10th International Symposium on Mobile Mapping Technology, Kairo, Ägypten (invited); 2017-05-06 - 2017-05-08; in: "International Symposium on Mobile Mapping Technology", (2017), Paper ID 49, 2 pages.

To locate a group of mobile smartphone users within a neighbourhood Cooperative Positioning (CP) can be applied whereby the user localization is performed using its own measurements plus any additional information coming from neighbouring users in the form of inter-nodal ranges or other means. In this study, Wi-Fi and UWB are employed to form a networked solution. Two new differential Wi-Fi positioning approaches based either on the Differential GPS (DGPS) or Very Long Baseline Interferometry (VLBI) operational principle are developed for (tri)lateration. By the use of reference station observations the received signal strength (RSS) measurements of the access points is corrected to reduce short- and long-time variations of the RSS at the user side. Static and kinematic tests using six users carrying different smartphones were conducted in an indoor lab in the practical evaluation. Five Raspberry Pi´s served as reference stations and access points together with another three additional Wi-Fi routers. One user enabled the hotspot function on his mobile device so that the other users could measure the RSS to derive inter-nodal ranges for the cooperative positioning solution. Additional five UWB units were carried by the users serving as either a reference for the derivation of the inter-nodal ranges or in order to be integrated into the overall positioning solution. Ground truth for these experiments was measured using a robotic total station. It is proven that both DWi-Fi approaches outperform conventional RSS lateration and the integration with UWB further strengthens the CP solution.

Cooperative positioning, Indoor positioning, Wi-Fi, RSS measurements, Differential technique, Reference stations