L1 SFMC SBAS Message for Service Expansion of Multi-Constellation GNSS Support

Currently operating satellite-based augmentation systems (SBASs) provide an augmentation service that improves global positioning system (GPS) performance at 250 bps via the L1 signal. Despite their efficiency, existing SBASs cannot support other global navigation satellite systems (GNSSs) owing to their narrow bandwidth, which prevents us from taking advantage of multi-constellation GNSS positioning. This paper proposes the concept of single-frequency multi-constellation (SFMC) SBAS, which enables the L1 legacy SBAS to support up to four or five constellations with minimal changes to existing standards and systems. Since upgrading existing SBAS avionics and changing international standards are not trivial tasks, we propose the SFMC SBAS messages that offer backward compatibility with legacy SBAS users. The transmission of fast corrections along with long-term corrections in message type (MT) 25 allows us to reserve the bandwidth for providing multi-constellation messages by removing MT 2 to 5, while modified MT 6 does not let the service compromise the timely alert requirements. Performance evaluations using the actual broadcast SBAS messages and observation data from GNSS reference stations show that the proposed SFMC SBAS reduces the maximum error of the legacy SBAS by 25% to 40% and enables Wide-Area Augmentation System (WAAS) to meet high integrity trucking user requirements anywhere in the continental United States (CONUS). Thus, SFMC SBAS is expected to not only improve the navigation performance of existing SBASs practically and effectively but also contribute to the improvements of accuracy and integrity performance. Specifically, we suggest the SFMC SBAS messages that are designed to be compatible with both L1 legacy and upgraded SBAS equipment, allowing for a smooth transition to the new technology.