Pivot single-difference ambiguity resolution for multi-GNSS positioning with non-overlapping frequencies

Ambiguity resolution in real-time kinematic (RTK) positioning is increasingly dependent on the combination of multi-GNSS observations, especially in challenging signal environments such as urban canyon areas. By applying a priori calibration to the receiver-dependent differential inter-system bias (DISB), a DISB-fixed multi-GNSS combination method with overlapping frequencies is widely used to strengthen the positioning model. However, as for non-overlapping frequencies, the differential inter-frequency bias (DIFB), which correlates with ambiguities, needs to be further corrected in case of the DISB-fixed multi-GNSS combination method. Since the DIFB is related to a pivot single-difference (SD) ambiguity, the DIFB is generally reduced by means of a SD ambiguity resolution. Owing to the code multipath and the code–carrier inconsistency, the traditional carrier-minus-code combination method will result in a large SD ambiguity bias and affect the DIFB correction. Thus, a SD ambiguity resolution method based on the integer least squares ambiguity estimator is proposed to deal with the issue. A kinematic experiment is conducted in urban areas, which is based on single-frequency observations from GPS L1 and BDS B1. The result shows that the proposed method can improve the performance of ambiguity resolution and positioning continuity when compared with the traditional multi-GNSS RTK methods.