Integrity Monitoring Using ARAIM in Bridging DFMC SBAS Outages for Road Transport

Abstract

The new generation of the satellite-based augmentation system (SBAS) has been initiated in Australia and New Zealand since 2017 and is anticipated to be a fully operational system by 2023. In addition to the traditional L1 service, the new SBAS also supports the dual-frequency multi-constellation (DFMC) service and the precise point positioning (PPP) service for GPS and Galileo dual-frequency users. Making use of the DFMC SBAS service, horizontal positioning accuracy at sub-meter to meter level can be realized in real-time depending on the measurement environment, which should benefit users of the intelligent transport system (ITS) in road transport. The integrity monitoring is essential for the ITS users to guarantee the reliability of the positioning service. During possible outage of the SBAS messages, the integrity monitoring of the DFMC SBAS positioning becomes difficult due to the missing corrections integrity information that should be updated regularly. Even when relieving these strict time-out windows for land-based applications, the increase of the horizontal protection levels (HPLs) with time is shown to be dramatic. In this contribution, a modified version of the advanced receiver autonomous integrity monitoring (ARAIM) algorithm is used during such SBAS outages. The HPLs are computed based on the ARAIM algorithm with different integrity parameters assumed to investigate their impact on the HPL. Under the expectation that higher precision of the satellite clocks and orbit corrections can be achieved for the new generations of the GPS and Galileo satellites in the future, the HPLs computed with the proposed modified ARAIM algorithm are shown to be close to the level of those based on the DFMC SBAS. In such a case, the ARAIM is expected to be a useful alternative approach for bridging the integrity monitoring of the non-safety-of-life ITS applications during the SBAS outages.