Precise Real-Time Multi-GNSS PPP
Engineering--Marine and Ocean
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AbstractGlobal Navigation Satellite System (GNSS) technology has undergone enormous developments over the last three decades. The majority of PNT (Positioning, Navigation and Timing) applications are now based on GNSS. This increasing dependence on GNSS technology is acknowledged by several nations, some of which are even developing their own regional or global systems. Several techniques exist to increase accuracy, reliability and availability of GNSSs. Real-time PPP (Precise Point Positioning) is the preferred GNSS positioning technology for most offshore applications that require higher performance than standalone GNSS provides. PPP is possible in any location worldwide without the need of local infrastructure. This makes PPP very advantageous when at sea far away from land. PPP uses precise orbits and precise clocks and can be provided globally with a network of fewer reference stations than any other comparable GNSS augmentation technology. PPP has over the last few years become the industry standard for offshore vessels operating with Dynamic Positioning (DP) systems. Further improvements of PPP technology are still desirable with respect to availability, reliability, accuracy and convergence time even for offshore applications. The research presented herein addresses improvements in these areas from three different angles, namely integration of different GNSSs, multi-frequency observations and PPP-RTK methods. The first innovative part of this research is the interchangeable integration of GPS-Galileo and GPS-BeiDou in PPP. It improves availability and accuracy in situations when few satellites are in view. New ionosphere-free widelane combinations for Galileo, GPS, BeiDou and GLONASS have been developed. These can improve PPP initial position accuracy by a factor two or more, i.e. from the 1.6 m to 0.8 m level. An ionosphere estimation technique for UPDs (Uncalibrated Phase Delays) especially tailored for multi-frequency observations is developed with applications smoothing and merging. Findings show how multi-frequency observations can increase PPP-RTK performance in offshore environments. Furthermore, improved precise clocks using UPDs increase position accuracy of both float PPP and PPP-RTK. Finally ten recommendations are given. The combination of these, the completion of the new GNSSs Galileo and BeiDou and the scheduled improvements of the existing GPS and GLONASS are expected to make instant high-accuracy PPP-RTK possible.
CitationMelgård, T. E. (2015). Precise Real-Time Multi-GNSS PPP (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/27398
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