Metro Train Autonomous Positioning Using Zero-Velocity Update Based on Train Motion Characteristics

Safe and stable operation of metro requires accurate kinematic measurement and positioning of the train. Traditional metro navigation and positioning methods are realized with the help of odometer or beacons such as RFID and WIFI, which means external information is necessary. However, accurate, reliable and fast metro applications call for an innovative method that can obtain high-precision, continuous metro attitude and track without being interfered by the outside world. Compared with other navigation technology, inertial navigation system (INS) is the sole navigation system that can realize independent navigation. However, INS generally has large noise and drift accumulated with time, especially MEMS inertial measurement unit (MIMU) with low cost and small volume. In this article, we proposed a novel method of autonomous positioning suitable for metro applications only using MIMU. The selection of zero-velocity-detection variables and the determination of criterion value are realized according to the motion characteristics of train. Then, the selection of variables is proved scientific according to the generalized likelihood ratio test (GLRT). When zero-velocity state is detected, the horizontal attitude of zero-velocity interval is corrected through coarse alignment method. In addition, a dead reckoning method based on kinematic constraint of train is adopted. In order to verify the advantages of the proposed method, tests of attitude and positioning precision are performed. The field experiment results show that our method could achieve high-precision attitude keeping with less computation. The test results are presented in terms of detection versus false-alarm rate. It can be seen from our results that the new detector outperformed the traditional detectors. Furthermore, the relative positioning error is less than 11.6%.