导航电文星历参数对卫星轨道精度的影响

卫星导航定位的关键是获知导航卫星的精确位置,其轨道精度与导航电文中广播星历参数密切相关。分析了由广播星历参数计算的卫星广播轨道与精密星历确定的真实轨道之间的误差,并将其投影到卫星切向、径向和法向进行仿真研究。比较了民用导航电文（CNAV）和旧民用导航电文（NAV）的星历参数的差异,利用精密星历拟和出对应的广播星历参数,研究其星历参数的变化对卫星轨道精度的影响。分析了GPS不同频点播发的导航电文中星历参数在数据帧内的结构。研究结果表明：GPS卫星广播轨道误差一周内在2到4m内变化,而其在切向、径向和法向的投影值呈现周期性余弦变化,其演变周期与GPS轨道周期近似相等,而选取改进后的17个广播轨道参数表示的星历数据于15个星历参数对比,其轨道拟和误差值改善2～3cm.

The Orbit Accuracy of SV Impacted by Ephemerides in Navigation Message

The key point of satellite positioning is acquiring SV position,which closely related to ephemerides in navigation message.The orbit error existing in the precise position of SV determined by exact ephemerides and broadcasting orbit calculated by the parameters in navigation message is analyzed,and its projections to three orthogonal directions: the along track direction,the across track direction and radial direction are discussed.The difference between CNAV and NAV is compared,and its impaction on SV orbit accuracy fitted by IGS precise ephemerides is researched.The structure of ephemerides in data message broadcasted in different frequency is presented.The results show that the broadcasting orbit error of SV will change from 2 m to 4 m in a GPS week,the projection of error in three directions have the cosine wave shape,with the same period as orbit cycle,and the orbit fitting error of improved ephemerides parameters is meliorated by two to 3 cm comparing with the fifteen parameters.