Global, Instantaneous, Centimetre, Satellite-Based Positioning with Precise Point Positioning

Real-Time Kinematic (RTK) has been the reference technique when it comes to precise (centimetre-level) positioning for Global Navigation Satellite Systems (GNSSs). The fact that RTK performance depends heavily on the distance between the receiver and the base station has led to the technique being deployed only regionally, in areas where GNSS reference station infrastructure is present. Precise Point Positioning (PPP) is a global solution by design, though requiring tens of minutes to reach RTK levels of performance. In this research, attempts are made to improve PPP performance to reach RTK-type performance. Given that PPP is a measurement-dependent technique, this research starts with making use of signals from all four major GNSS constellations: GPS, GLONASS, Galileo, and BeiDou-2/3. These constellations are coupled with the use of up to four frequencies, as opposed to only two frequencies as is typical for PPP. Carrier-phase ambiguities are resolved to their integer values on all processed signals as well. A model is derived from first principles to process all these measurements and fix their ambiguities. Results show that incorporating four frequencies has great benefits in improving user positions and increasing the likelihood of correct fixing of ambiguities due to the correlation that exists between ambiguities from the same satellite. Results demonstrate that PPP can reach regional RTK levels of performance with only using global corrections, as instantaneous convergence to 2.5 cm error is achieved consistently, making of PPP a truly global precise positioning technique. With these results in mind, corrections from Galileo’s High Accuracy Service (HAS) are analyzed, where, for the first time on a global scale, corrections are being transmitted by a GNSS constellation. Thanks to early access to these signals, an in-depth analysis of the corrections and user performance is carried out. Good performance is found to be achieved with these limited test signals, showing that PPP can become the de facto global precise positioning technique.
In cases where PPP needs to be augmented, a proof-of-concept is proposed where a global PPP solution is augmented with ionospheric corrections generated from an NRTK network. The generated corrections are found to improve PPP solution by reducing convergence time.