【2025】Aligning the Galileo code biases on the pilot and mixed signal channels to improve precise point positioning.
时间：2025-06-06
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Galileo satellites modulate pseudorandom code series for both the pilot (Q) and mixed (X) channels, which however undergo separate demodulation processes by different GNSS receivers (e.g., Septentrio receivers accept the pilot channel only whereas Javad the mixed channel only). It is usually assumed that the Galileo code biases on both channels are close to each other, and then all Galileo stations can be safely used to estimate satellite clock offsets and code/phase biases, regardless of their demodulation channels. In this study, we aligned the code biases on the pilot and mixed channels by estimating intra-frequency differential code biases (DCB), and examined whether this alignment could improve the performance of precise point positioning (PPP). We performed a series of satellite clock offset estimations, phase bias estimations and PPP assessments for Galileo using data from 230 stations from days 300 to 365 in 2023. Our analysis uncovered that the ignored DCBs could introduce systematic biases of up to 0.1 m in satellite clock offsets and up to 0.49 cycles in satellite phase biases. Using the aligned code bias products, the unified satellite clock offsets and phase biases across pilot and mixed channels can be estimated. The differences of pilot and mixed satellite clock offsets were reduced to within 0.03 m, while the UPD differences were reduced to an average of 0.02 cycles. With these modified precise products, the static PPP-AR wide-lane ambiguity fixing rates increased from 79.28% to 96.81%, and the maximum code residuals decreased from up to 7.5 to 2.3 cm. The convergence time of the kinematic PPP-AR decreased by an average of 23%. Therefore, aligning the Galileo code biases on the pilot and mixed channel signals to generate unified precision products can improve the performance of PPP-AR.
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