GNSS导航电文空间信号测距误差分析

空间信号测距误差(Signal-In-Space Range Error,SISRE)描述卫星广播星历误差和钟差参数误差在用户平均星站方向的投影,是影响用户定位授时精度的关键因素.本文以事后精密轨道和钟差参数为基准,分别评估Galileo,GPS和BDS-3卫星的广播星历轨道用户测距误差(User Range Error,URE)、钟差参数误差、SISRE的大小和特征.结果表明,Galileo,GPS,BDS-3的SISRE分别为0.14,0.49,0.35 m.三者的广播星历轨道URE分别为0.14,0.27,0.09 m.三者的钟差参数误差分别为0.14,0.41,0.35 m.Galileo广播星历径向轨道误差和钟差参数误差之间具有很强的相关性.两者相互抵消,可有效降低Galileo卫星的SISRE.不同类型GPS卫星的钟差参数误差和SISRE有明显区别.随着GPS卫星的更新换代,其钟差参数误差和SISRE会逐步降低.BDS-3卫星具备与GPS和Galileo卫星显著不同的特征:(1)BDS-3卫星广播星历轨道径向误差和钟差参数误差的相关性较小,自洽性较差;(2)BDS-3卫星广播星历轨道URE较小,而钟差参数误差较大.其中,BDS-3卫星的广播星历轨道URE小于Galileo和GPS,但是其钟差参数误差对SISRE的贡献显著大于Galileo和GPS.通过比对上述卫星的SISRE大小及特征,指出提高钟差参数精度是提高BDS-3卫星空间信号精度的关键.

Analysis of signal-in-space ranging error of GNSS navigation message

The signal-in-space ranging error(SISRE)is a major factor that affects the accuracy of positioning and timing.It describes the projection of the satellite-broadcast ephemeris error and clock difference error in the average direction from satellites to stations.In this study,the size and characteristics of the broadcast ephemeris user range error(URE),clock difference error,and SISRE are evaluated with respect to GPS,Galileo,and BDS-3.The results indicate that the SISREs of Galileo,GPS,and BDS-3 are 0.14,0.49,and 0.35 m,respectively,the broadcast ephemeris UREs of Galileo,GPS,and BDS-3 are 0.14,0.27,and 0.09 m,respectively,and the clock difference errors of Galileo,GPS,and BDS-3 are 0.14,0.41,and 0.35 m,respectively.In case of Galileo,the radial orbit error and the clock difference error exhibit strong correlation.Both these errors cancel each other,and the SISRE associated with Galileo can be effectively reduced.Further,obvious differences can be observed with respect to the clock difference error and SISRE in case of different types of GPS satellites.The clock difference error and SISRE of GPS will gradually decrease with the upgradation of satellites.The SISRE of BDS-3 exhibits different characteristics when compared with those exhibited by the SISREs of GPS and Galileo.First,the radial error of BDS-3 is less correlated with the clock difference error,which exhibits poor self-consistency.Second,the BDS-3 satellite-broadcast ephemeris URE is small,whereas the clock difference error is large.Furthermore,the broadcast ephemeris URE associated with BDS-3 is lower than those associated with Galileo and GPS.However,the contribution of the clock difference error associated with BDS-3 to SISRE is considerably greater than those of the clock difference errors associated with GPS and Galileo to SISRE.In this study,the sizes and characteristics of the SISRE of BDS-3,Galileo,and GPS are compared,indicating that signal-in-space accuracy of BDS3 can be improved by reducing the clock difference error.