On June 27, 2025, the Wuhan Combination Center (WCC) of the International GNSS Service (IGS), led and established by Professor Jianghui Geng, officially released its combined product. Compared with the IGS combined product from individual Analysis Centers (ACs), the WCC product not only meets users' PPP-AR requirements but also provides continuous satellite availability. Currently, the WCC product includes both Final and Rapid series. Its timeliness is comparable to that of IGS ACC product, while the positioning accuracy meets or exceeds the IGS ACC standard.

WCC is jointly established by the State Key Lab of Precision Geodesy, CAS, and the Satellite Navigation and Positioning Technology Research Center of Wuhan University. Dr Qiang Wen and Mr Yahao Zhang is responsible for the daily clock/bias combination and quality evaluation tasks at the Wuhan Combination Center.

Fig 1 RMSE of GPS clock/bias compared to combination in week 2368

WCC began generating combined product on March 9, 2025 (GPS Week 2357).Its Final product combines multi-GNSS (GPS/Galileo/GLONASS) orbits, clock , and bias products from 6 ACs (Analysis Centers), incorporating midnight discontinuity alignment correction.Figure 1 shows the clock/bias RMSE and outlier rate of each AC with respect to the combined integer clock over one week. Each grid represents a satellite on a particular day.Blank grids indicate unavailable products, while a slash inside a grid denotes an outlier excluded from the combination. The line chart below displays the daily outlier rate of satellite clocks for each AC, with gray blocks indicating that the corresponding satellite clocks were given zero weight in the combination. The statistics at the bottom provide the overall RMSE of AC-specific clock/bias products for this week.Modified Allan Deviation (MDEV) can characterize the frequency stability and noise characteristics of integer clock biases over a one-week period. Figure 2 presents the MDEV values of several representative satellites from each AC and WCC product. A smaller MDEV indicates better stability of the clock products.The Rapid product combines multi-GNSS (GPS/Galileo/ GLONASS) orbits, clock , and bias products from 8 ACs.The combination performance of the products and the PPP-AR positioning test results are displayed on the IGS WCC webpage (https://igs.org/wg/wcc), with weekly updates.

Fig 2 Mdev in week 2368

The combined product guarantees wide-lane ambiguity fix rates exceeding 98% and narrow-lane ambiguity fix rates above 93%.when using the discontinuity-aligned product, positioning deviations are constrained to within 3 mm (East), 3 mm (North), and 6 mm (Up). The final combined products ensure daily boundary discontinuities within 10 ps. Static PPP/PPP-AR processing was performed using PRIDE PPP-AR software for GPS/GLONASS/Galileo data with a 300s sampling rate from 10 globally distributed stations. Figure 3 shows the ambiguity fixing rates and positioning accuracy for individual constellation solutions. The IGS daily solutions were adopted as reference truth values, where "WCC" denotes the combined product.This product is available at FTPS servers: ftps://bdspride.com. Note: The Final product is updated weekly with a 1-2 week latency, while the Rapid product is updated daily with a 2-3 day latency.

The Wuhan Combination Center will stay at the forefront of technological advancement by continuously enhancing its capabilities in precise satellite product combination. We are committed to achieving new heights in both product accuracy and stability, thereby making even greater contributions to the advancement of GNSS positioning technologies.

Fig 3 PPP(-AR)results in week 2368