Worldwide SBAS Broadcast Between 2018 and 2023: A Comparative Study
Alessandra Calabrese, David Tacero Puerto, Pedro Muñoz Lacedón, Alejandro Fernández Guerrero, Gloria Calzada Viniegra, Javier Arenas Rodríguez, José Gabriel Pericacho Bustos, Julián Barrios Lerma, GMV
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Satellite-Based Augmentation Systems (SBAS) provide safe civil aviation navigation services for En-route through LPV-200 precision approach operations. Current operational L1 SBASs improve user accuracy and integrity over specific regions by monitoring the GPS satellites in conjunction with ionosphere effects on GNSS signal propagation.
SBAS L1 systems have already been commissioned and operated in the United States (WAAS), the European Union (EGNOS), India (GAGAN) and Japan (MSAS). Additionally, SBAS deployments are currently underway in other regions, including Australia and New Zealand (SouthPAN), China (BDSBAS), Korea (KASS), Russia (SDCM), Algeria (ASAL) and Africa (NSAS/ASECNA). Also, during 2022 the United Kingdom SBAS Testbed (UK-SBAS) started broadcasting its signal. Between 2017 and 2023, more than twenty SBAS L1 GEO PRN signals have been broadcast belonging to ten different SBAS systems.
The development and establishment of the SBAS systems are currently at a turning point. This transition is motivated by several elements, which can be summarized in three main points. The first one is the deployment of the traditional L1 SBAS services in new regional areas. The extension of the L1 SBAS coverage involves, on many occasions, the deployment of new infrastructures, the adaptation of the civil navigation procedures, and the tackling of new challenges, such as the monitoring of the ionosphere in areas not previously covered in the context of Safety of Life navigation.
The second point is that SBASs are being upgraded to consider Dual-Frequency and Multi-Constellation (DFMC) services, since DFMC standards already count with a mature technical baseline through EUROCAE/RTCA and ICAO documentation.
The third point is that SBASs are intensively exploring synergies with other GNSS-based services like ARAIM or PPP. Additionally, studies are ongoing on how SBAS services can extend their positive impact from the civil-aviation sector (SBAS primary target) towards a wider range of different communities, including maritime, road, rail, mining, and others.
The main aim of this paper is to analyze the status of all the SBAS systems currently broadcasting a signal in space, including WAAS, EGNOS, GAGAN, MSAS, SouthPAN, BDSBAS, SDCM, UKSBAS, ASAL and NSAL, during the last seven years. The SBAS augmentation messages are obtained from available open FTPs (mainly supported by CNES, and EMS) and processed with GMV’s SREA to obtain a statistical characterization of their satellite and ionosphere information error. The paper provides several metrics, including satellite orbit and clock error, user range error histograms and time-series, or operational systems UDRE bound ratios. The tool is also able to review the ionospheric performances, with indicators such as the GIVD corrections availability, accuracy, and the operational systems GIVE bound ratio over the long-time historical data available.
GMV’s SREA can also provide long-term performance statistics for other GNSS satellites navigation information, such as the original GNSS ephemeris and clock data, post-processing reference sets like the NGA or IGS products. In this sense, the SBAS analysis can be complemented by reviewing the original error of GNSS navigation data. This analysis contextualizes the benefit of the SBAS services for general purpose multi-modal users from the point of view of the accuracy.
The analysis considers both quantitative and qualitative elements. It is important to remark that each SBAS works under independent constraints, covers separate ionosphere regions, uses alternative MT27/MT28 approaches, and has targeted different service level commitments (from LPV-200 SoL certification to non-SoL demonstration services). While this comparison does not intend to benchmark the performance of one system with another, the exercise can show how every service responds to the augmentation information need, at which level the SBAS corrections accuracy can support other services, and how civil aviation integrity requirements drive the confidence interval of the integrity information.
In conclusion, this paper will give an updated analysis of the accuracy and integrity of some of the SBAS systems worldwide and the evolution of their performances during the last few years.
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