Assessment of Static PPP Accuracy Over Observation Time Using Qinertia Cloud: GPS vs. GPS+GLONASS Integration

The Global Navigation Satellite Systems (GNSS) provides continuous, high-precision positioning and timing capabilities on a global scale through satellite-based observations. However, exclusive reliance on a single GNSS constellation imposes inherent limitations associated with satellite visibility and geometric strength, which may degrade positioning reliability, particularly under conditions of poor satellite geometry or partial signal obstruction. In this study, the performance of static Precise Point Positioning (PPP) is rigorously evaluated as a function of fixing time using the Qinertia Cloud free online processing service. Two processing strategies are examined: GPS-only and combined GPS+GLONASS. The analysis is conducted under ideal open-sky conditions to effectively eliminate multipath effects and isolate the influence of constellation configuration. Dual-frequency GNSS observations were acquired from ten spatially distributed stations across Libya, each consisting of continuous 24-hour datasets. Static PPP solutions were computed for fixing intervals ranging from 1 hour to 24 hours, with the fully converged 24-hour solution adopted as the reference benchmark for accuracy and stability assessment.
The results demonstrate that both configurations yield highly precise and reliable positioning solutions. Nevertheless, the integration of GLONASS observations with GPS systematically enhances solution robustness and positional stability across all fixing intervals. The improvement is particularly pronounced during short observation durations, especially within the first hour, where absolute errors in the East, North, Height, 2D, and 3D components are reduced by approximately 4, 2, 2, 4, and 4 cm, respectively, when adopting the GPS+GLONASS configuration. The superiority of the multi-constellation approach is most evident during the initial convergence phase, when PPP solutions are highly sensitive to satellite geometry and stochastic modeling. Although the improvement in mean absolute positioning accuracy diminishes for longer observation durations, the inclusion of GLONASS significantly mitigates the occurrence of outliers and reduces the dispersion of coordinate residuals. These findings confirm that even under near-ideal open-sky conditions, where multipath effects are negligible, multi-constellation integration contributes substantially to enhancing the robustness and reliability of static PPP solutions. In agreement with existing literature, the Qinertia Cloud platform demonstrates high-quality performance in static mode for both GPS-only and GPS+GLONASS configurations, with results comparable to those obtained from advanced PPP services such as CSRS-PPP. Overall, while long-term accuracy gains from GLONASS integration remain marginal, its contribution during early convergence stages is substantial, with one-hour dual-frequency PPP solutions (GPS+GLONASS) achieving accuracy levels comparable to 2–3 hours of GPS-only observations.