Exploiting Multi-GNSS Measurements to Improve Precise Point Positioning (PPP) Performance Under Scintillation Conditions

Precise Point Positioning (PPP) is a high-accuracy Global Navigation Satellite System (GNSS) positioning technique which enables global centimeter-level accuracy, after an initial convergence period, for single-receiver GNSS users. Ionospheric scintillation can cause large positioning errors and is characterized by rapid amplitude and phase fluctuations of the received GNSS signals. This contribution exploits the improved geometry, increased model redundancy and improved modernized signals available in a multi-GNSS PPP model to mitigate ionospheric scintillation effects.

The occurrence of moderate ionospheric scintillation was identified on 17-March-2019 from 00:00 to 03:00 UTC by analyzing the amplitude scintillation index S4 recorded by a low-latitude ionospheric scintillation monitoring receiver (ISMR) in São Paulo, Brazil. A GNSS receiver situated within 100-meters of the ISMR was selected to analyse a 24-hr RINEX file containing GPS (G), GLONASS (R) and Galileo (E) measurements. Kinematic coordinates were estimated for G, G/R, G/E, and G/R/E measurements using an extended Kalman filter and compared to the static G solution to quantify errors.

The multi-GNSS G/R/E rounded mean number of usable satellites was equal to 20, more than double the number of satellites in the G solution. The local tangent plane up component root-mean-square error (RMSE) during the entire 24-hour period for the G, G/R, G/E, and G/R/E solutions were 2.579, 0.139, 0.118, and 0.083 meters, respectively. The absolute maximum up error for the G solution exceeded 10 meters at multiple epochs while the G/E and G/R/E solutions did not exceed 3 meters at any epoch and the G/R solution exceeded 7 meters at one epoch.

The increased degrees of freedom for the G/R/E solution enabled more redundancy and better outlier detection to remove scintillation-affected measurements from the filter. The high-power Galileo AltBOC modulated E5 signal which is designed to improve receiver tracking loop performance may have contributed to lower maximum errors in the G/E solution compared to the G/R solution.

In this study, the combined G/R/E PPP solution benefited from the increased number of satellites to achieve centimeter-level local up coordinate accuracy during a low-latitude ionospheric scintillation event.