Estimating and Analyzing Long-Term Multi-GNSS Inter-System Bias Based on Uncombined PPP

Area of Science:

• Geodesy and Geomatics
• Satellite Navigation Systems
• Signal Processing

Background:

• Precise positioning using multiple Global Navigation Satellite Systems (multi-GNSS) is advancing.
• Inter-System Bias (ISB) arises from differences in satellite reference clocks and receiver hardware delays.
• ISB is a critical factor affecting the accuracy of multi-GNSS precise point positioning (PPP).

Purpose of the Study:

• To analyze the characteristics of multi-GNSS Inter-System Bias (ISB).
• To estimate and evaluate ISB parameters using a recommended processing model.
• To assess the impact of ISB on precise point positioning accuracy.

Main Methods:

• Developed a full-rank uncombined precise point positioning (PPP) model for GLONASS, BDS, and Galileo, using GPS as the reference.
• Adopted a recommended ISB parameter processing model.
• Analyzed 28 days of data from Multi-GNSS Experiment (MGEX) stations to estimate ISB parameters.

Main Results:

• Multi-GNSS PPP positional bias root mean square (rms) reached 4.6 mm (East), 3.4 mm (North), and 8.5 mm (Up).
• Intra-day ISB time series showed stability (standard deviation < 0.6 ns), with Galileo-GPS ISB being most stable (0.37 ns).
• Single-day ISB solutions exhibited instability (up to 60 ns jumps) but consistent variations across stations, influenced by satellite reference clocks and receiver types.

Conclusions:

• The ISB parameter solutions are reliable and accurate, ensuring precise positioning.
• Galileo-GPS inter-system bias demonstrates high stability, potentially due to signal quality.
• ISB variations are system-dependent and linked to receiver types, highlighting the need for careful modeling.