Tightly Coupled BDS/INS Integration With Track Constraint to Enhance Train Localization and Integrity

In railway transportation, accurate train localization and effective integrity monitoring are crucial for train control and safety. The integration of Chinese BeiDou Navigation Satellite System (BDS) and inertial navigation system (INS) is promising for train localization as it does not rely on trackside infrastructure; however, various factors such as BDS signal blockage and interruption may potentially degrade the positioning performance. As the motion of the train is constrained by the railway track, the motion constraint, such as nonholonomic constraint (NHC), is expected to enhance train localization and integrity performance in obstructed environments. This article proposes motion constraint-assisted BDS/INS tightly coupled integration to enhance train localization accuracy and integrity. We construct the tightly coupled BDS/INS/NHC integration model based on the extended Kalman filter (EKF), and accurate detection of multiple faults from satellites is realized by calculating the test statistic based on filtering innovation. To evaluate the performance of the proposed method, we calculate the test statistics of multiple faulty satellites and the protection level (PL) of the proposed system in case of satellite signal outage occurs. Experimental results show that the system integrity performance is improved significantly when NHC is applied. The proposed method achieves a 100% accuracy rate in multiple satellite fault detection (FD) and the integrity performance of the NHC-assisted BDS/INS integration for train localization can be maintained for about 20 s when the alert limit (AL) is 20 m.