Real-time single-frequency pseudorange positioning in China based on regional satellite clock and ionospheric models

Improving performance of single-point positioning (SPP) with single-frequency pseudorange measurement is important for users equipped with mass-market or low-cost receivers. Considering a regional single-frequency SPP service is available, it is not necessary to realize precise orbit determination for single-frequency SPP. Instead, the ionospheric modeling is of utmost importance. Based on BDS/GPS broadcast ephemeris, we establish a regional satellite clock model (CLK) and two regional ionospheric models in China using 155 reference stations and investigate their efficiency in improving the performance of BDS/GPS SPP with additional 499 reference stations. Two ionospheric models are established based on different total electron content (TEC) observables; one is the low-order spherical harmonic function model (SHF) with vertical TEC observables and the other is the satellite-based ionospheric model (SIM) with slant TEC observables. It is demonstrated that the SIM model performs better than SHF model as it avoids the error due to the ionospheric mapping function. Overall, the positioning results with CLK + SIM perform the best for BDS-only, GPS-only, and BDS/GPS SPP. Compared to the positioning results with the broadcast ephemeris and the Klobuchar model, the SPP positioning accuracy with the CLK + SIM model improves by about 50% on average. By using the improved model CLK + SIM, the BDS/GPS SPP positioning accuracy is better than 1.5 m and 2.0 m at the 95% confidence level in the horizontal and vertical directions, respectively. Also, by comparing the SPP performance with IGS final products, including the GeoForschungsZentrum precise orbits and clock products and Center for Orbit Determination in Europe final GIMs, the proposed model in this study performs better than that with the IGS final products in terms of positioning accuracy and model complexity.