An Error Overbounding Method in Positioning Domain for Dual-Frequency Multi-Constellation GBAS

Compared with traditional single-frequency Ground Based Augmentation Systems (GBAS), Dual-Frequency Multi-Constellation (DFMC) GBAS has better navigation performance. This technology meets the accuracy and integrity requirements of CAT III, which is an important development direction for the future GBAS. Error overbounding is a key technique in the integrity monitoring process for conservatively handling error distributions and calculating protection levels. The integration of dual-frequency signals in DFMC GBAS leads to protection levels calculated by traditional pseudorange domain error overbounding methods being generally too conservative. In some cases, protection levels may even exceed the alarm limits, which makes it hard to meet the integrity requirements specified by CAT III. Additionally, error overbounding method in the pseudorange domain inevitably involves convolution calculations when projecting the pseudorange error distributions into the positioning domain. Computational load on the airborne platform is also a concern that needs to be considered. This paper proposes a positioning domain error overbounding algorithm suitable for DFMC GBAS. This algorithm directly projects the pseudorange residuals of GBAS into the positioning domain, thus avoiding convolution calculations on the error distribution during the projection process. In the positioning domain, the algorithm eliminates the impact of geometry on errors and conducts modeling, thus reducing the protection level. Compared with traditional overbounding methods, the algorithm reduces the protection level by 47.5%-64.8% in the ground vehicle test and 34.0%-53.7% in the unmanned aerial vehicle (UAV) filght test. The algorithm proposed in this paper provides a more suitable error overbounding method for DFMC GBAS system, which has the potential to meet the higher integrity requirements.