Global navigation satellite systems (GNSS) are widely used for navigation and time distribution1,2,3, features that are indispensable for critical infrastructure such as mobile communication networks, as well as emerging technologies such as automated driving and sustainable energy grids3,4. Although GNSS can provide centimetre-level precision, GNSS receivers are prone to many-metre errors owing to multipath propagation and an obstructed view of the sky, which occur particularly in urban areas where accurate positioning is most needed1,5,6. Moreover, the vulnerabilities of GNSS, combined with the lack of a back-up system, pose a severe risk to GNSS-dependent technologies7. Here we demonstrate a terrestrial positioning system that is independent of GNSS and offers superior performance through a constellation of radio transmitters, connected and time-synchronized at the subnanosecond level through a fibre-optic Ethernet network8. Using optical and wireless transmission schemes similar to those encountered in mobile communication networks, and exploiting spectrally efficient virtual wideband signals, the detrimental effects of multipath propagation are mitigated9, thus enabling robust decimetre-level positioning and subnanosecond timing in a multipath-prone outdoor environment. This work provides a glimpse of a future in which telecommunication networks provide not only connectivity but also GNSS-independent timing and positioning services with unprecedented accuracy and reliability.
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The datasets that support this paper are available at https://doi.org/10.34894/GFDJI1.
The code to process the datasets that support this paper is available under the MIT-0 License at https://doi.org/10.34894/GFDJI1.
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This research is funded through the Dutch Research Council (NWO) under grants 12346 and 13970, with additional support from KPN, VSL, OPNT and Fugro. We acknowledge support from L. Boonstra, T. Theijn and R. Smets on the optical infrastructure, from L. Colussi and F. van Osselen on obtaining the 3.96-GHz experimental license, and R. Tamboer and T. Jonathan on realizing the testbed at TGV.
J.C.J.K. is co-founder and shareholder of OPNT bv. The other authors declare no competing interests.
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Extended data figures and tables
Locations of data centres at Delft University of Technology (TU D) and schematic representation of the fibre-optic connections are shown. The reference atomic clocks that are used to realize UTC(VSL) and synchronize the WR network are located at VSL. Map data copyright OpenStreetMap (https://www.openstreetmap.org/copyright), obtained under Open Database License 1.0.
The Rx antenna and two 360° prisms are mounted onto the roof of a car. In the background part of the TGV test site is visible (viewing direction is south east). The various Tx-i antennas are indicated, as well as the two total stations. Tx-2 is hidden from the view by tree branches.
a, Ground-truth trajectories of two different runs, one with the Rx USRP operated in synchronous mode (blue), and one with the Rx USRP in asynchronous mode (yellow). b, TD position errors and 95% ellipses for the synchronous and asynchronous runs shown in a, following the same colour coding. The black cross indicates the GT solution and its uncertainty. c, Same as in b, but for CP ambiguity-float solutions. Note the different scale of the graph. d, Same as in b, but for CP ambiguity-fixed solutions. During the early stages of the run in synchronous mode (blue), an incorrect integer correction was applied, leading to small islands of biased position errors.
Horizontal positioning precision, (σEast2 + σNorth2)1/2, with σEast and σNorth the position standard deviations as determined from a nonlinear least-squares optimization that assumes ranging errors with a standard deviation of σr = 6 cm for all transmitters. Values above 50 cm are clipped and replaced by white areas. Shown also are OFDM-TD position solutions for the run with the asynchronous receiver of Extended Data Fig. 3 (blue curves), and the corresponding ground-truth path (red curves). a, Precision and position solutions for the full TNPS constellation. b, Precision and position solutions for the TNPS constellation with Tx-1 and Tx-3 removed. c, Precision and position solutions for the TNPS constellation with Tx-1, Tx-2, and Tx-5 removed. d, Precision and position solutions for the TNPS constellation with Tx-6 removed.
Modified Allan deviation measured between WR-GM and WR-SL at VSL (Fig. 1b) after a round trip through 8.2 km of installed optical fibre.
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Koelemeij, J.C.J., Dun, H., Diouf, C.E.V. et al. A hybrid optical–wireless network for decimetre-level terrestrial positioning. Nature 611, 473–478 (2022). https://doi.org/10.1038/s41586-022-05315-7