The Hybrid GNSS/WCT Multi-coach Multi-constellation Train Positioning and Integrity System

Yuheng Zheng, Michael Hutchinson, David Lowe, Saioa Arrizabalaga, Jon Goya, Leticia Zamora-Cadenas, Javier Valera, Jose Sanchez

Abstract: GNSS have already been successfully used in safetycritical aviation and maritime applications. However, GNSS suffers from Line-Of Sight (LOS) problems. This causes a problem for railway use in tunnels, covered stations, cuttings etc. When the trains travel in these areas, the reception of NLOS (non-LOS) signals and lack of LOS signals not only affects GNSS availability, but also positioning accuracy and integrity. Therefore, the use of GNSS alone cannot reach the ETCS (European Train Control System) level 3 requirements for train location. To compensate the GNSS deficiencies, the Smart Train Positioning System (STPS) has been developed in the European Commission EATS (ETCS Advanced Testing and STPS) project. The STPS is based on two steps: firstly, the GNSS positioning is integrated with the WCT (Wireless Communications Technology) positioning on every coach of the train; secondly, a hybrid algorithm is developed to derive the “Front” and “Rear” position of the train by combining all hybrid GNSS/WCT train coach solutions. The KFMI (Kalman Filter Measurement Innovation) is an algorithm developed for multi-constellation GNSS positioning and integrity. KFMI includes an innovation Fault Detection and Exclusion (FDE) technique and a comprehensive integrity algorithm, to provide continuously accurate positioning and high integrity performance. Another characteristic of the STPS system is the ability to use WCT to locate the train. The WCT uses both GSM-R (Global System for Mobile Communications – Railway) and UMTS (Universal Mobile Telecommunication System) technologies. GSM-R and UMTS are mobile communications systems that can also be utilised to provide coarse positioning in any location served by the networks involved, often including those areas in which GNSS is unavailable. The novel WCT algorithm is developed especially including the calibration from the GNSS solution to improve the positioning accuracy. For the Train Integrity and Train Standstill Monitoring applications, the STPS core function brings together the outputs from the STPS Hybrid GNSS/WCT from the train’s constituent coaches and processes these to obtain consolidated or value-added front and rear end train positions. Therefore, if one of the GNSS/WCT train coach solutions is poor or unavailable, the front and rear end train position can still benefit from other coaches. Additionally, in case of the train integrity being broken, the availability of the front and rear end train positions could provide the vital information for the rescue. From the test results, we can see that the GNSS KFMI algorithm has better availability, accuracy and integrity when extra constellations are added. The hybridization with WCT then provides 100% availability. Integrity can also be provided by the hybrid GNSS/WCT algorithm in urban areas and tunnels. Therefore, the STPS approach has the potential to provide the EVC (European Vital Computer) kernel with train positioning and integrity information to allow migration from ETCS level 2 to level 3. Besides that, STPS could also be used in ETCS Level 2 to provide train positioning.
Published in: Proceedings of the 2016 International Technical Meeting of The Institute of Navigation
January 25 - 28, 2016
Hyatt Regency Monterey
Monterey, California
Pages: 293 - 304
Cite this article: Zheng, Yuheng, Hutchinson, Michael, Lowe, David, Arrizabalaga, Saioa, Goya, Jon, Zamora-Cadenas, Leticia, Valera, Javier, Sanchez, Jose, "The Hybrid GNSS/WCT Multi-coach Multi-constellation Train Positioning and Integrity System," Proceedings of the 2016 International Technical Meeting of The Institute of Navigation, Monterey, California, January 2016, pp. 293-304.
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