Application of u-blox SPARTN Corrections in RTKLib

The ongoing development and modernization of global navigation satellite systems (GNSS) have significantly enhanced location-based services in positioning, navigation, and timing (PNT) applications. Today’s applications increasingly demand decimeter- and centimeter-level accuracy, especially in safety-critical scenarios where both high availability and integrity are essential. Traditional methods such as Real-Time Kinematic (RTK) and Precise Point Positioning (PPP) have been instrumental in achieving high-accuracy GNSS solutions. However, RTK is limited by the need for proximity to a base station, while PPP suffers from longer convergence times. The PPP-RTK approach mitigates these challenges by providing State Space Representations (SSRs) to enhance accuracy and reduce convergence times. This study focuses into the integration of u-blox's Secure Position Augmentation for Real-Time Navigation (SPARTN) corrections into the open-source RTKLib Precise Point Positioning (PPP) software. SPARTN is an open standard multi-GNSS correction format that promotes integrity and safety while allowing for low-bandwidth, unidirectional data streams. Experimental assessment with static and kinematic GNSS data revealed that SPARTN performs similar to CNES ultra-rapid products in terms of horizontal accuracy and convergence times in PPP, saving up to 50% bandwidth. Static data analysis found that performance differed amongst IGS stations, with SPARTN demonstrating slightly larger variability in positioning error than CNES. Kinematic experiments revealed SPARTN's vulnerability to satellite availability, affecting solution convergence and continuity. While both SPARTN and CNES showed centimeter-level carrier-phase residuals, SPARTN had occasional pseudorange residual biases. Overall, the integration of SPARTN into RTKLib shows promise for improving PPP, particularly in scenarios where bandwidth limits and fast convergence are critical. However, during testing, performance differences appeared to be related to the availability of satellite data rather than the SPARTN protocol itself. Further testing under varying satellite conditions will help better understand its performance characteristics and ensure its consistent operation, alongside proven correction products such as CNES.