Research on a method of real-time combination of precise GPS clock corrections

The acquisition of real-time satellite orbit and clock corrections is necessary for real-time PPP. There are nine International GNSS Service (IGS) analysis centers (ACs) that provide real-time satellite orbit and clock products. Given the influence of network transmission, observation data and solution methods, a single AC product suffers from outages and outliers. A combination of real-time data streams is an effective method of improving these problems. We focus on a combination method with regard to anomalous data in a single AC solution. Processing techniques such as parameter separation, weight estimation and exception handling are proposed. Experimental results indicate that, after the process, the frequency of unavailability and anomaly in the combined (simply COMB later) clock correction obtained using the above-mentioned method decreases relative to that of a single AC and IGS01 and IGS02 products. IGS01 is a single-epoch combined product provided by European Space Agency (ESA). IGS02 is a Kalman filter combined product provided by the Federal Agency for Cartography and Geodesy (BKG). In a 7-day experimental period, the performance of real-time products is also examined regarding availability and accuracy. The availability of COMB is as high as 99.9 %, which is superior to that of single AC and IGS01 and IGS02 products. The accuracy of COMB is 0.15 ns in standard deviation, which is at the same level as the Centre National d'Etudes Spatiales (CNES) product, but higher by 40, 17, 29, 42 and 32 % than that of the German Aerospace Center (DLR), ESA, GeoForschungsZentrum (GFZ), IGS01 and IGS02 products. The 3D positioning accuracy applying COMB product is 9.1 cm in root mean square (RMS), which is higher by 41, 44, 5, 43, 43 and 42 % than applying CNES, DLR, ESA, GFZ, IGS01 and IGS02 products, respectively. The results demonstrate that the real-time COMB clock correction obtained by the method proposed is more stable and reliable than single AC and IGS01 and IGS02 products.