Prototype of Satellite-Based Augmentation System and Evaluation of the Ionospheric Correction Algorithms

The SBAS, satellite-based augmentation system, is basically the wide-area differential GPS (WADGPS) effective for numerous users within continental service area. For a practical investigation of wide-area augmentation technique, the authors have implemented the prototype system of the SBAS. This prototype generates the complete SBAS messages capable of wide-area differential correction and providing integrity based on the dual frequency observation dataset. The system has been successfully implemented and tested with the SBAS user receiver simulator. It has achieved positioning accuracy of 0.3 to 0.6 meter in horizontal and 0.4 to 0.8 meter in vertical, respectively, over mainland of Japan during nominal ionospheric conditions with 6 monitor stations located similar to the MSAS. The historical severe ionospheric activities might disturb and degrade the positioning performance to 2 meters and 3 meters for horizontal and vertical, respectively. In all cases, both horizontal and vertical protection levels have never been exceeded by the associate position errors regardless of ionospheric activities. This kind of prototype system is not only a proof of feasibility of the actual system but also a practical tool to evaluate and compare algorithms inside the MCS. The authors evaluated the current and improved ionospheric correction algorithms in a practical manner using the prototype in offline mode. The proposed algorithm of adaptive switching between the planar and zeroth order fit reduced protection levels down to one third relative to the current baseline so will contribute to improve the availability of the SBAS.