Investigating new approaches for narrowband but nevertheless high-precision wireless locating in multipath environments by means of iterative recursive non-linear state estimation techniques based on aperture synthesis and phase difference analysis in antenna array constellations
Final Report Abstract
In this project, fundamental research was conducted on high-precision indoor localization based on the evaluation of relative spatial phase measurements. The research was divided into two main parts. In the first part, foundational investigations were carried out to determine the achievable accuracy of Phase Difference of Arrival (PDOA)-based positioning. These findings informed the development of the Iterative Holographic Extended Kalman Filter (IHEKF), which demonstrated record-level positioning accuracy in the millimeter range within an experimental setup. The initial step involved comparing the measurement sensitivity of PDOA-based indoor positioning with that of Time of Arrival (TOA)-based systems. While TOA sensitivity depends solely on the bandwidth used, PDOA sensitivity increases with larger receiver aperture size, higher transmission frequencies, and shorter measurement distances. This direct comparison enabled the definition of an equivalent bandwidth, which can be used to assess the relative performance of TOA and PDOA systems. The results showed that, given the typically short distances in indoor environments and the continuously increasing transmission frequencies in modern communication systems (especially in 5G and 6G), relative phase evaluation can offer significant advantages. In addition to sensitivity, robustness against multipath propagation is critical for achieving high localization accuracy. UWB systems address this by leveraging large bandwidths to separate line-of-sight (LOS) signals from multipath components. In contrast, PDOA systems with large apertures can spatially distinguish between waves arriving from different directions. However, in precise PDOA-based systems with large receiver apertures and nearby beacons, the assumption of plane waves becomes invalid, as spherical wavefronts are received instead. This results in different wavefront shapes for LOS and multipath components, meaning that efficient evaluation of the spatially distributed phases inherently enhances robustness against multipath propagation. In the second part of the project, to optimally exploit the favorable conditions of PDOA-based indoor localization with large receiver apertures, the IHEKF algorithm was developed. This algorithm directly evaluates the phase differences across spatially distributed measurements, avoiding the plane wave assumption typically made in angle-of-arrival estimations. The IHEKF applies an incremental update strategy: it first evaluates phase differences between neighboring antenna pairs and then progressively incorporates pairs with increasing spacing. This approach allows for the simultaneous resolution of phase ambiguities in closely spaced antenna pairs and utilization of the high measurement sensitivity from more widely spaced antennas. To validate the research outcomes, a narrowband 24 GHz indoor localization system was implemented. This system achieved record-level results for PDOA-based localization, demonstrating millimeterrange accuracy. The developed system matches the best performance of UWB-based systems while avoiding their typically high implementation costs.
Publications
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Exchanging Bandwidth With Aperture Size in Wireless Indoor Localization - Or Why 5G/6G Systems With Antenna Arrays Can Outperform UWB Solutions. IEEE Open Journal of Vehicular Technology, 2, 207-217.
Sippel, Erik; Geiss, Johanna; Bruckner, Stefan; Groschel, Patrick; Hehn, Markus & Vossiek, Martin
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Holographic 3D Indoor Localization, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2022
SIPPEL, ERIK
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Phase Difference Based Precise Indoor Tracking of Common Mobile Devices Using an Iterative Holographic Extended Kalman Filter. IEEE Open Journal of Vehicular Technology, 3, 55-67.
Bruckner, Stefan; Sippel, Erik; Lipka, Melanie; Geiss, Johanna & Vossiek, Martin
