A space-based augmentation system (SBAS) provides real-time GNSS correction signals via geostationary satellites for near-ground GNSS users. To use the SBAS correction for low Earth orbit (LEO) satellites, the correction, especially the ionosphere correction, must be adjusted for the LEO altitude. We apply modified SBAS data to LEO satellite onboard navigator to improve the positioning accuracy of a LEO satellite for possible real-time use. The onboard navigator requires high positioning reliability, and code pseudoranges, rather than phase pseudoranges, are used for the primary measurements. The Galileo NeQuick G model is used to determine the real-time conversion factor of the SBAS ionosphere correction for a LEO satellite. The GPS L1 data from GRACE satellite are combined with the SBAS data from the ground receiver. The onboard navigator combines the precise satellite dynamic model with an extended Kalman filter to improve positioning accuracy and stability. The kinematic positioning method, which uses the weighted least square method without the dynamic model, is also performed for comparison. The SBAS correction reduces the positioning error in both the kinematic positioning and the dynamic positioning. The positioning error reduction of the GPS and WAAS case over the GPS-only case is 25.2% for the kinematic method and 30.6% for the dynamic method. In the case of the dynamic method with the SBAS corrections, the positioning error remains smaller than that of the GPS-only dynamic method even after the satellite has left the SBAS service area.

中文翻译：

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基于 GPS-SBAS 的近地轨道卫星定轨

天基增强系统 (SBAS) 通过对地静止卫星为近地 GNSS 用户提供实时 GNSS 校正信号。要对低地球轨道 (LEO) 卫星使用 SBAS 校正，必须针对 LEO 高度调整校正，尤其是电离层校正。我们将修改后的SBAS数据应用于LEO卫星机载导航仪，以提高LEO卫星的定位精度，以实现实时使用。星载导航仪对定位可靠性要求较高，主要测量采用码伪距而非相位伪距。Galileo NeQuick G 模型用于确定 LEO 卫星 SBAS 电离层校正的实时转换因子。来自 GRACE 卫星的 GPS L1 数据与来自地面接收器的 SBAS 数据相结合。星载导航仪将精确的卫星动态模型与扩展卡尔曼滤波器相结合，提高定位精度和稳定性。还采用了没有动态模型的加权最小二乘法的运动学定位方法来进行比较。SBAS校正减少了运动定位和动态定位中的定位误差。与仅使用 GPS 的情况相比，GPS 和 WAAS 情况下的定位误差减少量为：运动学方法减少了 25.2%，动态方法减少了 30.6%。在带有 SBAS 校正的动态方法的情况下，即使在卫星离开 SBAS 服务区后，定位误差仍比仅使用 GPS 的动态方法小。