The high-level view of the proposed ARAIM Evolution for Rail is depicted in the following figure.
The train will be equipped with an On-Board Unit (OBU) including the following elements:
- A GNSS receiver compatible with ARAIM and SBAS.
- An odometer.
The navigation data and observations from the GNSS satellites (GPS + Galileo constellations, with the possibility to include up to 4 constellations) will be processed by the on-board user equipment, as well as the SBAS messages disseminated by EGNOS. The GNSS measurements will be hybridised with the odometer output.
With this high-level design of the ARAIM Evolution for Rail, the following strengths will be exploited:
- Combination of SBAS with ARAIM which will improve accuracy at user level and could allow to decrease of
and
due to the enhanced monitoring of system-level events.
- Hybridization with an Odometer. To provide additional resilience upon local effects and continuity and availability of the positioning solution.
- Allocation of integrity budget to the Along Track dimension which would enable the exploitation of the unique characteristics of most applications within the Rail sector, where movement is performed in a one-dimensional space.
- Multipath model for Urban Environment as worst-case scenario.
- Sequential ARAIM approach to better meet the required rail service levels under harsh conditions.
