by Mike Hutchinson, Principal Navigation Engineer, NSL

1. STEMS: System Suitability Study for Train Positioning using
GNSS in the European Rail Traffic Management System
Space for Innovation in Rail
19/03/2018, Vienna, Austria
Michael Hutchinson, NSL

2. • System Suitability Study for Train Positioning using GNSS in the
European Rail Traffic Management System
• STEMS is a study undertaken for the European Space Agency
• Led by NSL with subcontractors:
‒ Telespazio Vega UK: GNSS service provision expertise
‒ GMV: GNSS and SBAS expertise
‒ University of Pardubice: railway safety concepts
‒ TUV Rheinland UK: accredited safety independent safety assessor
STEMS introduction
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3. • Objective 1: Review and consolidate requirements and assumptions on virtual
balise detection in ERTMS using GNSS;
• Objective 2: Study the suitability of the current generation of SBAS for use in the
evolution of the European Traffic Management System (ERTMS) with virtual
balise detection using GNSS, confirming the feasibility of current SBAS system
allocations;
• Objective 3: Assess the suitability of SBAS for cross-acceptance by railway safety
authorities, to be performed by an accredited railway independent safety
assessor;
• Objective 4: Propose a methodology for building a suitable safety case for SBAS
for use by the railway community in the ERTMS virtual balise application.
STEMS objectives
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4. • Value for safe positioning concept
‒ Fault Detection of System Feared Events (stronger than RAIM)
‒ Assumptions on faults -> pseudoranges for satellites monitored by SBAS can be
assumed to be fault-free from Feared Events originating from satellites, GNSS
ground segment and ionosphere (to target level of integrity)
• Improved position accuracy
• Leverages existing investment in aviation
Added value of EGNOS to GNSS
positioning in ERTMS
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5. • Based on SBAS ‘as-is’ i.e. GPS L1 legacy services (EGNOS V2, V3.1)
• Provision of integrity in range domain
• GNSS Augmentation Distribution Function to retrieve SBAS messages
from Signal in Space and distribute to Onboard
• Considers Virtual Balise Detection in ERTMS as well as other potential
evolutions including developments to odometry
STEMS Baseline Assumptions
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