Abstract: [Purposes] Aiming at the challenge of ambiguity resolution in tightly coupled GNSS and INS within complex urban environments,this paper proposes a quality control-based stepwise ambiguity fixing method. [Methods] This method classifies satellite data quality and partitions ambiguities into high-quality and low-quality subsets using the extended Kalman filter innovation sequence and IGG-Ⅲ robust estimation.A stepwise fixing strategy is adopted: the high-quality subset first undergoes decorrelation processing; after dual confirmation via the Bootstrapping success rate and fixed failure-rate ratio test,it serves as constraints to update the float solution of the low-quality subset,thereby achieving final fixation. [Findings] Experiments show that,compared with traditional methods,the proposed method improves the ambiguity fix success rate from 50.62% to 92.18%,with a valid fix rate of 91.58%.The RMS errors in the east,north,and up directions are reduced by 50.1%,48.7%,and 47.3%,respectively. [Conclusions] This method significantly enhances the ambiguity fix success rate and positioning accuracy in urban environments,providing an effective quality control solution for vehicle navigation.

Key words: tightly coupled GNSS/INS, quality control, ambiguity resolution, robust estimation