Repeatability test method of GNSS for safe train localisation in real and simulated environments (2016)

Safe train localization is the key element to provide reliable Position, Velocity and Timing (PVT) information for Automatic Train Operation (ATO), and will enable future applications such as moving block, real-time safety margin estimation for adjacent trains, and many more. The safety-assured train localization under many repeated tests along the test railway line providing acceptable performance level will allow Global Navigation Satellite Systems (GNSS) as part of the localization unit to be adopted into the elements of ATO system to perform localization function. But under real railway operation environmental conditions, the accuracy performance shows strong variations; but using the simulated GNSS signals in the laboratory will have more consistent and repeatable test sequence for GNSS receiver testing. The GNSS receiver for the application of ATO is based on the performance requirements for the localization function in predefined environmental conditions, both simulation and real world test procedures including standard test definitions will enable the possibility to examine the repeatability of GNSS performance in acknowledged railway operation environment. Based on this, the test results will give the repeatability facts of the tested GNSS receiver, then the repeatability performance criteria can be set for later railway application in different environments. But for the performance evaluation of the repeatability property as part of the GNSS performance testing concept, accuracy can be seen as the foundation of all the other performance properties. Accuracy in both along-track and cross-track direction of the train should be evaluated under dynamic movement using bidirectional error models. The dynamic train localization accuracy is among one of the key tests for the GNSS receiver for safe applications in railway applications. This paper firstly describes the repeatability performance as part of the GNSS receiver quality for safe train localization in definition and also the relation among the major performance properties of a GNSS receiver under dynamic measurements. Secondly, the test scenario and the data collection strategy on an existent railway line is settled for both real world and simulated data analysis. Then the collected data is evaluated using the proposed dynamic accuracy evaluation method with the consideration of measurement uncertainty caused by the movement of the measurement object. Thirdly, the accuracy evaluation is based on the GNSS receiver as the system under test (SUT) and the mobile reference measurement system (MRMS) developed based on mature solutions and further developed platform in our research lab. The same datasets for real world accuracy evaluation are loaded into the Spirent GSS8000 for the repeatability performance evaluation. The test procedure is restricted to follow the standard test requirements in both railway and navigation societies. Finally, with the test results following the defined procedure and evaluation method in this paper, the repeatability performance criteria can be clearly shown for the level of safety application in railway train operation.