Precision and safety-critical Global Navigation Satellite System (GNSS) applications require high-fidelity monitoring of space weather conditions, particularly ionospheric disturbances. These systems are highly sensitive to sharp spatial gradients and rapid Total Electron Content (TEC) variations. To support both operational and scientific needs, this study proposes and evaluates two variants of the Gradient Ionosphere indeX (...

Mixed-integer (MI) estimation theory is fundamental to carrier-phase GNSS, where real-valued parameters are coupled with integer ambiguities. The class of integer-equivariant (IE) estimators is the largest class that properly respects this structure. Its unbiased minimum mean-squared-error member is the best integer equivariant (BIE) estimator, whose precision is never worse than that of the BLUE and whose performance is often...

Real-time precise point positioning (PPP) time transfer is a crucial technique for the time and frequency field. However, its performance remains limited by the relatively long convergence time resulting from unstable parameter estimation in the initial stage. In this contribution, predicted tropospheric products provided by the Global Forecast System (GFS) are employed to derive predicted Zenith Wet Delays (ZWDs) for each sta...

This study presents a simulation-based analysis to evaluate the impact of satellite clock stability, particularly that of emerging optical clocks, on global navigation satellite systems (GNSS) positioning performance. A controlled single-station precise point positioning-real time kinematic (PPP-RTK) framework is employed, with the provider and user receivers located over a short baseline to minimise spatially correlated error...

Global Navigation Satellite System (GNSS) signals are increasingly affected by man-made intentional interferences, such as jamming and spoofing, underscoring the need for reliable and extensively evaluated interference detection techniques in protected GNSS frequency bands. This paper presents a GNSS signal anomaly detection method based on a Chi-Square statistical test applied directly to raw digitized intermediate-frequency...