GNSS广播星历轨道和钟差精度分析

为了对多个全球导航卫星系统（global navigation satellite system, GNSS）当前的广播星历精度进行一个全面的分析，对比了2014—2018年共5 a的GNSS广播星历与精密星历，并对全球定位系统（global positioning system, GPS）、格洛纳斯卫星导航系统（global navigation satellite system, GLONASS）、伽利略卫星导航系统（Galileo satellite navigation system, Galileo）、北斗卫星导航系统（BeiDou navigation satellite system, BDS）、准天顶卫星系统（quasi-zenith satellite system, QZSS）等5个系统的广播星历长期精度变化进行了分析。结果表明:5 a中GPS的广播星历轨道及钟差精度最稳定；GLONASS的广播星历轨道精度稳定性较好，但其钟差精度存在较大的离散度；Galileo得益于具备全面运行能力（full operational capability, FOC）卫星的大量发射及运行，其广播星历轨道、钟差精度大幅度变好，切向轨道、法向轨道与钟差精度已赶超GPS；BDS的广播星历轨道精度离散度较大，钟差精度出现不稳定现象；QZSS的广播星历轨道与钟差精度的稳定性与离散度相对最差。以2018年1 a的广播星历与精密星历为例分析了各个系统当前的广播星历精度，结果表明，当前GPS、GLONASS、Galileo、BDS、QZSS的考虑轨道误差与钟差误差贡献的空间信号测距误差（signal-in-space ranging error，SISRE）分别为0.806 m、2.704 m、0.320 m、1.457 m、1.645 m，表明Galileo广播星历整体精度最高，GPS次之，其次分别是BDS、QZSS和GLONASS。只考虑轨道误差贡献的SISRE分别为0.167 m、0.541 m、0.229 m、0.804 m、0.675 m，表明GPS广播星历轨道精度最高，其次分别是Galileo、GLONASS、QZSS和BDS。GPS卫星广播星历中新型号卫星的钟差精度总体要优于旧型号卫星。

Accuracy Analysis of GNSS Broadcast Ephemeris Orbit and Clock Offset

  Objectives  At present, the accuracy analysis of global navigation satellite system(GNSS) broadcast ephemeris mostly focuses on the accuracy analysis of single system or short time, there is left relatively certain limiations.  Methods  We present a comprehensive comparison and analysis of the current broadcast ephemeris accuracy for multiple global navigation satellite systems (GNSS). The analysis is performed by comparing GNSS broadcast ephemeris with corresponding precise ephemeris. The long-term accuracy change of the broadcast ephemeris of various systems is analyzed using the GNSS broadcast ephemeris with the corresponding precise ephemeris from 2014 to 2018.  Results  The experimental results show that the orbit and clock offset accuracy of the broadcast ephemeris from the global positioning system (GPS) is the most stable during five years. The broadcast ephemeris of global navigation satellite system (GLONASS) has better orbit accuracy stability, but its clock offset accuracy has a large dispersion. The Galileo satellite navigation system (Galileo) has benefited from the large number of launches and operations of satellites with full operational capability. The orbit and clock offset accuracy of its broadcast ephemeris have greatly improved. In particular, the accuracy of orbit in tangential and normal directions and clock offset accuracy has surpassed that of GPS. The orbit accuracy of the broadcast ephemeris of the BeiDou navigation satellite system (BDS) has a large dispersion, and its accuracy of the clock offset shows instability. The stability of orbit and the clock offset accuracy of the broadcast ephemeris from the quasi-zenith satellite system (QZSS) is the worst. The current accuracy of the broadcast ephemeris for five systems is compared and analyzed using the one-year (2018) GNSS broadcast ephemeris and the corresponding precise ephemeris.The signal-in-space ranging errors(SISRE) considering the contribution of satellite orbital error and clock offset error for GPS, GLONASS, Galileo, BDS, and QZSS are 0.806 m, 2.704 m, 0.320 m, 1.457 m, and 1.645 m, respectively. The SISRE considering only the contribution of orbital error for GPS, GLONASS, Galileo, BDS, and QZSS are 0.167 m, 0.541 m, 0.229 m, 0.804 m, and 0.675 m, respectively.  Conclusions  These indicate that the broadcast ephemeris of the Galileo has the highest overall accuracy, followed by GPS, BDS, QZSS and GLONASS. The GPS broadcast ephemeris has the highest orbit accuracy, followed by Galileo, GLONASS, QZSS and BDS. Moreover, we found that the clock offset accuracy of the new kind of satellite is generally better than that of old kind of satellite in GPS satellite broadcast ephemeris.