Ionospheric-Constrained PPP using Triple-GNSS Constellations

The technique of Precise Point Positioning (PPP) has wide-spread application in positioning, navigation, and timing (PNT) due to its improved accuracy and low cost. However, the technique continues to suffer from long convergence period in order to attain Real-Time Kinematic (RTK) comparable performance. The fusion of multi-GNSS constellations remains today’s most probable remedy to the long convergence time with improved positioning accuracy, availability, redundancy, and integrity. Besides, the Ionosphere and Hardware Delay (IHD) derived from Global Ionosphere Maps (GIM) generated by the International GNSS service (IGS) have proved significant in accelerating single-frequency PPP convergence time. Previous literature has a deficiency in triple constellation PPP incorporating both ionosphere constrained single frequency PPP and dual-frequency PPP. In this paper, GPS+GLONASS+Galileo GNSS constellations are evaluated in kinematic mode over nine (9) Multi-GNSS Experiment (MGEX) stations. Twenty-four (24) hour observations for the first week of February, 2017 are processed in four PPP scenarios (GPS-only, GLONASS-only, GPS+GLONASS, and triple-constellation of GPS+GLONASS+Galileo) at a 7º elevation angle cut-off. To validate the findings, standard single-frequency PPP and dual-frequency PPP are analyzed. The results indicate that the application of GIM in ionosphere-constrained PPP improves the overall convergence time and standard deviation with respect to standard single-frequency PPP. Furthermore, better convergence time is obtained in dual-frequency PPP without virtual observations. Moreover, augmenting GPS with GLONASS and Galileo, triple constellation, improves in relation to GPS-only PPP in standard single-frequency PPP, standard dual-frequency PPP, and in ionosphere-constrained PPP. Thus, this study fills the gap in literature by unveiling the threshold of performance for the ionosphere-constrained PPP using triple-GNSS constellations.