Real-time precise point positioning (RT-PPP) relies on the real-time service as satellite orbit and clock corrections for users to achieve decimeter or centimeter-level positioning. Although the real-time service is nearly always with high accuracy, it will inevitably have abnormal values or accuracy degradation. The faults from satellite orbit and clock corrections must be detected to provide a reliable positioning performance. In this contribution, a state-domain based integrity monitoring method of satellite orbit and clock corrections for RT-PPP is proposed. The prediction models for satellite orbit and clock correction parameters are constructed by analyzing the daily variation statistical characteristics of correction parameters in the state domain. After compensation for non-ideal error distribution by overbounding, the detection statistics and minimum detection errors are established based on the corrected precision satellite orbit and clock comprehensive errors, which aims to monitor the quality of satellite corrections. The experiment is used to test the false alarm and missed detection performance of the proposed method. The results confirm that the abnormal satellite orbit and clock corrections can be detected accurately with given missed detection rate 1×10 ^-3 , and false alarm rate 1×10 ^-5 . Moreover, using the proposed monitoring method, the RT-PPP results after excluding abnormal satellite orbit and clock corrections can be improved by an average of 6.51%, 13.94% and 8.14% in the east, north and up directions, respectively.

Anomalous ionospheric gradient is a critical risk to be monitored by ground-based augmentation systems (GBASs) utilized for safety-of-life navigation applications. A dual-frequency carrier phase-based ionospheric gradient monitoring method is proposed under the mixed Gaussian distribution. The minimum detection error of the proposed method can be greatly reduced by allowing acceptable ambiguity resolution failure modes, given the required averaging length. The real BeiDou navigation satellite system data were utilized to test the proposed method. The experimental results showed that the minimum detection error (MDE) of the proposed dual-frequency ionospheric gradient monitoring method can be reduced by at least 30% in comparison with the maximum acceptable anomalous ionospheric gradient of category III GBAS. This study demonstrated that the proposed method can be used to protect against the ionospheric gradient for a ground-based augmentation system.

Based on the statistical stability of the inter-system bias (ISB), we propose a tightly coupled Differential Global Navigation Satellite System (DGNSS) positioning method by using ionosphere-free combination for the long baseline applications. The proposed method is compatible with the traditional Radio Beacon (RBN) base station implementation. The tightly coupled DGNSS positioning method is utilized at the long baseline rover by eliminating the effect of ionosphere delay with ionosphere-free (IF) based differential ISB calibration. The improved positioning model strength can be obtained with the proposed method when compared with the traditional loosely coupled method, particularly under the satellite-deprived environment. GNSS datasets of different baselines were collected to test the proposed method. The results of the ISB stability show that the ISB has long-term stability and needs to be calibrated when the receiver is rebooted. The positioning results show that when compared with the IF-based loosely coupled method, the IF-based tightly coupled DGNSS method based on ISB calibration can obtain better positioning performance of accuracy and continuity within 240 km baselines.