Multi-GNSS all-frequency SDB calibration and its impact on high-precision products and positioning

Signal distortion bias (SDB) is a systematic pseudorange bias associated with receiver types. Its presence reduces the consistency of GNSS clock and signal bias estimated from inhomogeneous networks, significantly decreasing the ambiguity resolution rate and negatively affecting positioning and timing performance. Current research does not provide a comprehensive understanding of the error characteristics of SDB, and traditional SDB calibration methods exhibit certain limitations.

This paper first identifies the correlation between SDB and factors such as receiver brand, model, as well as the dependencies on firmware versions, antennas, and radomes. In addition, we propose a geometry-free (GF)-aided multi-GNSS all-frequency SDB calibration method and strategy. The GF assistance addresses the ±0.5 cycle limitation associated with wide-lane (WL) ambiguity rounding, further improving the precision of SDB calibration. Based on this method and MGEX data, we calibrated and analyzed the SDB for all-frequency signals of GPS, Galileo, and BDS-3. Ultimately, we provide SDB corrections for all satellites per receiver group in SINEX BIAS format.

We further investigated the impact of SDB on satellite clocks, code biases, phase biases, and PPP-AR both theoretically and experimentally. Results show that SDB correction significantly enhance the consistency of satellite clock and bias estimates across networks, with BDS-3 improving by over 90% and wide-lane ambiguity fixing rates for different receivers increasing by up to 20% at most. Moreover, an analysis of one-month data from 132 MGEX stations with hourly reset indicates that SDB correction reduces the multi-GNSS kinematic PPP convergence times for Septentrio, Leica, Javad, and Trimble receivers by an average of 0.43, 2.74, 2.63, and 4.28 epochs, respectively, with corresponding PPP-AR convergence improvements of 1.9%, 8.5%, 14.7%, and 17.7%. The average convergence performance across stations with different receiver types improved by 2.4%, 12.1%, 31.3%, and 25.2%, with maximum improvements of up to 70.8%. These analyses fully demonstrate the necessity of SDB modeling and correction, and it is recommended that the IGS Analysis Center adopt it.