| Summary: | As one of the commonly used solutions for vehicular dynamic positioning, the stability of Global Navigation Satellite Systems (GNSS)/ Inertial Navigation System (INS) integrated positioning when applied in an urban environment is still struggling. Generally, carrier-phase ambiguity fixing requires continuous several epochs, the stability and continuity of integrated positioning are significantly reduced if the signal is frequently blocked. To reduce the impact of frequent signal blockage, an improved tightly-coupled algorithm is proposed in this paper. Firstly, a step-wise ambiguity processing method is introduced to form instantaneous fixed Wide-Lane (WL) observations for calibrating INS measurement. Secondly, by estimating the differential inter-system bias (DISB) parameter, the pivot satellite can be shared between different constellations, to increase the number of usable satellites under the limited observation conditions and improve the positioning performance. The proposed method is verified with vehicular experiments on semi-simulated and actual urban canyon scenarios. In the artificial GNSS outage experiment, in the situation of 4 satellites that can be observed in BeiDou Navigation Satellite System (BDS) and Global Positioning System (GPS), the positioning accuracy of the proposed algorithm can achieve 4.1cm horizontally and 15.2cm vertically. An improvement of 26.9% horizontally and 20.4% vertically is gained accordingly compared to the conventional method. In the actual urban environment experiment, in case of insufficient satellite and low signal-to-noise ratio (SNR), when the conventional method can no longer maintain a fixed solution of GNSS/INS integrated positioning, the proposed algorithm can still achieve an accuracy of 49.7cm horizontally and 67.0cm vertically.
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