GLONASS FDMA data for RTK positioning: a five-system analysis
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ORIGINAL ARTICLE
GLONASS FDMA data for RTK positioning: a five‑system analysis Andreas Brack1 · Benjamin Männel1 · Harald Schuh1,2 Received: 9 July 2020 / Accepted: 7 October 2020 © The Author(s) 2020
Abstract The use of the GLONASS legacy signals for real-time kinematic positioning is considered. Due to the FDMA multiplexing scheme, the conventional CDMA observation model has to be modified to restore the integer estimability of the ambiguities. This modification has a strong impact on positioning capabilities. In particular, the ambiguity resolution performance of this model is clearly weaker than for CDMA systems, so that fast and reliable full ambiguity resolution is usually not feasible for standalone GLONASS, and adding GLONASS data in a multi-GNSS approach can reduce the ambiguity resolution performance of the combined model. Partial ambiguity resolution was demonstrated to be a suitable tool to overcome this weakness (Teunissen in GPS Solut 23(4):100, 2019). We provide an exhaustive formal analysis of the positioning precision and ambiguity resolution capabilities for short, medium, and long baselines in a multi-GNSS environment with GPS, Galileo, BeiDou, QZSS, and GLONASS. Simulations are used to show that with a difference test-based partial ambiguity resolution method, adding GLONASS data improves the positioning performance in all considered cases. Real data from different baselines are used to verify these findings. When using all five available systems, instantaneous centimeter-level positioning is possible on an 88.5 km baseline with the ionosphere weighted model, and on average, only 3.27 epochs are required for a long baseline with the ionosphere float model, thereby enabling near instantaneous solutions. Keywords RTK · GLONASS FDMA · Integer ambiguity resolution · Partial fixing · Difference test · Best integer equivariant estimation · Multi-GNSS
Introduction With the exception of the Russian GLONASS, all current satellite navigation systems such as GPS, Galileo, BeiDou, and QZSS make use of the code division multiple access (CDMA) scheme to separate the signals from different satellites at the user receiver. Since with CDMA the carrierphase measurements from all satellites share common wavelengths, the resulting double-difference (DD) ambiguities are directly estimable as integers. The GLONASS legacy signals are based on frequency division multiple access (FDMA), where different satellites transmit on slightly different carrier frequencies. Differencing the carrier phases between two satellites, therefore, * Andreas Brack brack@gfz‑potsdam.de 1
Department of Geodesy, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
Chair of Satellite Geodesy, Technische Universität Berlin, Str. des 17. Juni 135, 10623 Berlin, Germany
2
involves measurements with different wavelengths, so that the conventional DD ambiguities are no longer integer estimable. In Teunissen (2019), a new FDMA model was introduced, in which a new set of integer ambiguity parameters is d
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