The high integrity GNSS/ INS based train position locator
Aleš Filip, Jan Taufer, Hynek Mocek, Lubor Bazant, Maixner · WIT transactions on the built environment · 2004
Integration of a GNSS receiver with additional inertial sensors can significantly improve the performance and reliability of the train position locator (TPL). However, if the TPL is intended for safety related applications like signalling and train control, it should also be robust to sensor and system failures. This means that the locator must meet the high safety integrity design and have its own diagnostics capable of providing timely warnings to a user in the case of a failure. This paper deals with the high integrity architecture of the TPL. The architecture consists of the two fundamental subsystems: 1) the dual navigation system providing the state vector estimate by means of the two independent navigation loops and 2) autonomous safety integrity monitor (AIM) which continuously checks the safety integrity status of the locator. The state vector estimator is based on the indirect robust Kalman filter which continuously corrects the gyro-odometry positioning subsystem by means of the GNSS receiver. The employed microwave Doppler speedometer and the accelerometer provide necessary redundancy for the sensor data validation and integrity monitoring. The design of the AIM results from the already specified user safety requirements. The basic principle and states of the AIM are described in terms of the position error, protection level and horizontal alert limit. The failure recognition methodology by means of the hypotheses testing is outlined. The performance of the AIM is measured by means of the probabilities of missed detection and false alarm and other parameters.