SBAS enhancement using an independent monitor station in a local area

Different approaches have been developed to monitor the integrity of the Global Positioning System (GPS). The individual approaches rely on conservative error bounds and faces great challenges in meeting stringent integrity requirements set by the International Civil Aviation Organization (ICAO). These approaches, in fact, do not compete with one another but complement one another. We propose the vertical integration of the Satellite-Based Augmentation System (SBAS) and a local monitor station in this study. When the SBAS data deviate from the local monitor, users are informed to revert to the error bounds that are directly determined from SBAS data. Otherwise, the validation criterion that the error of the SBAS corrected solution is within a threshold is exploited to tighten the SBAS error bounds. The algorithm to integrate the SBAS with the independent monitor station is described, and its performance is evaluated based on simulations and real observations. The test results show that the vertical protection level (VPL) is reduced on average from 17.60 to 11.27 m, i.e., a 30.3% reduction in VPL while the integrity is guaranteed.