SSR改正数更新频率及中断时间间隔对实时PPP的影响分析

实验模拟服务器端不同更新频率的SSR改正数对实时精密单点定位的影响,以及客户端改正数中断时长对实时精密单点定位的影响。结果表明,服务器端SSR改正数的播发频率控制在30s以内可获得cm级定位精度;客户端的SSR改正数中断在150s之内可获得cm级定位精度,改正数中断200s可获得20cm的定位精度,改正数中断300s可获得亚m级定位精度。

基于RT-PPP的低轨卫星实时高精度时间同步方法

实现低轨导航增强的关键前提是实现低轨星座的整网时间同步,本文针对低轨导航增强系统,提出了一种基于实时精密单点定位(RT-PPP)的低轨卫星高精度时间同步方法,以解决低轨星座实时高精度时间同步的问题.本文分析了在处理过程中存在的各类误差,介绍了低轨卫星采用状态空间(SSR)改正信息通过精密单点定位(PPP)实现实时高精度时间同步方法的处理流程,将此方法应用于气象、电离层与气候星座观测系统(COSMIC)卫星实测数据的处理,并将该方法与采用广播星历伪距的方法以及事后精密星历的方法进行了比较分析.结果表明:采用SSR改正信息PPP的方式对2颗COSMIC卫星进行GPS双频观测值的解算,得到的轨道误差的标准差在分米级,钟差误差标准差分别在2.4 ns和2.3 ns左右,可以达到纳秒级.通过对不同方法解算的结果进行比较可以看出,采用SSR改正信息PPP的方法明显优于采用广播星历伪距方法的解算精度,且与事后精密星历PPP的方法解算精度相当.

数据时效性对多系统实时PPP的影响分析

针对服务器端和客户端的数据时效性问题,该文系统地分析了服务器端状态空间表示(SSR)改正数更新时间间隔和客户端观测值数据及SSR改正数中断对实时精密单点定位(PPP)的影响。实验结果表明:服务器端播发SSR改正数的时间间隔在30s以内,GPS+GLONASS+BDS、GPS+GLONASS和GPS实时PPP定位可获得厘米级定位精度,同时SSR改正数的播发时间间隔对GPS+GLONASS+BDS、GPS+GLONASS和GPS实时PPP定位影响无明显差异;客户端SSR改正数中断时长在150s以内,GPS+GLONASS+BDS、GPS+GLONASS和GPS实时PPP定位可获得厘米级定位精度,改正数中断360s可获得亚米级定位精度,单系统较多系统受SSR改正数中断的影响较大;观测值连续中断16min时,实时PPP需要重新收敛。

Comprehensive assessment of real-time precise products from IGS analysis centers

Real-Time Precise Point Positioning(RT-PPP)has been one of the research hotspots in GNSS(Global Navigation Satellite System)community for decades.Real-time precise products of satellite orbits and clocks are the prerequisite for RT-PPP.Thus,it is of great importance to investigate the current multi-GNSS real-time precise products in State Space Representation(SSR)from diferent analysis centers.In this article,SSR products from 10 analysis centers are comprehensively evaluated by comparing them with the fnal products and performing the kinematic PPP.The results show that analysis centers CNES(Centre National D’Etudes Spatiales)and WHU(GNSS Research Center of Wuhan University)provide the most complete products with the best quality.Concerning the accuracy of real-time products for the GNSSs,the accuracies of orbit and clock products are better than 5 cm and 0.15 ns,respectively,for Global Positioning System(GPS),followed by Galileo navigation satellite system(Galileo),BeiDou-3 Navigation Satellite System(BDS-3),GLObal NAvigation Satellite System(GLONASS),and BeiDou-2 Navigation Satellite System(BDS-2).Meanwhile,the results of the RT-PPP with quad-system show that the positioning accuracies are 1.76,1.12 and 2.68 cm in east,north,and up directions,respectively,and the convergence time to 0.1,0.1,0.2 m for corresponding directions is 15.35 min.

Models and performance of SBAS and PPP of BDS

Satellite Based Augmentation System(SBAS)is one of the services provided by the BeiDou Navigation Satellite System(BDS).It broadcasts four types of diferential corrections to improve user application performance.These corrections include the State Space Representation(SSR)based satellite orbit/clock corrections and ionospheric grid corrections,and the Observation Space Representation(OSR)based partition comprehensive corrections.The algorithms generating these SBAS corrections are not introduced in previous researches,and the user SBAS positioning performance with the contribution of BDS-3 has not been evaluated.In this paper,we present the BDS SBAS algorithms for these diferential corrections in detail.Four types of Precise Point Positioning(PPP)function models for BDS Dual-Frequency(DF)and Single-Frequency(SF)users using the OSR and SSR parameters are also proposed.One week of data in 2020 is collected at 20 reference stations including the observations of both BeiDou-2 Navigation Satellite System(BDS-2)and BeiDou-3 Navigation Satellite System(BDS-3)satellites,and the PPP under various scenarios are performed using all the datasets and the BDS SBAS broadcast corrections.The results show that the performance of BDS-2/BDS-3 combination is superior to that of BDS-2 only constellation.The positioning errors in Root Mean Square(RMS)for the static DF PPP are better than 8 cm/15 cm in horizontal/vertical directions,while for the static SF PPP are 11 cm/24 cm.In the scenarios of simulated kinematic PPP,three Dimension(3D)positioning errors can reach 0.5 m in less than 10 min for the DF PPP and 30 min for the SF PPP,and the RMSs of the DF and SF PPP are better than 17 cm/21 cm and 20 cm/32 cm in horizontal/vertical directions.In a real-time single-and dual-frequency kinematic positioning test,the positioning errors of all three components can reach 0.5 m within 30 min,and the positioning accuracy after solution convergence in the N,E and U directions is better than 0.3 m.

QZSS L6E增强服务改正数支持的PPP性能评估

准天顶卫星系统目前利用QZS-2~QZS-43颗卫星播发L6E信号,为东亚和大洋洲地区用户提供实时的增强服务。该文分析了L6E信号结构及轨道和钟差的计算模型,研究了目前L6E信号的覆盖范围和可用性,评估了L6E改正数恢复的卫星轨道和钟差及其用于动态PPP的精度水平。结果表明:我国用户在使用15°截止高度角时L6E信号仍有100%的可用性;L6E改正数恢复的GPS和GLONASS卫星轨道的3D RMS平均值分别为5.3和13.9 cm,卫星钟差的STD平均值分别为0.14和0.22 ns,利用GPS卫星的轨道和钟差进行的动态PPP可以获得水平优于10 cm、高程优于15 cm的精度,在加入GLONASS卫星后,东方向和高程方向定位误差和收敛时间均有明显改善。

广域实时亚米级单点定位算法

针对传统的单点定位方法无法满足应用需求日益提高的实时定位精度问题,提出一种新的广域实时亚米级单点定位算法。基于单频接收机提供的卫星原始观测值,通过网络获得由国际GPS服务(international GPS service,IGS)播发的GNSS卫星精密轨道和钟差以及格网电离层改正数据,在终端嵌入式软件或APP软件程序中,通过载波平滑伪距的定位模型进行定位解算得到用户精确位置。大量试验结果统计分析表明:该算法在全天候任意时段内均可实现平面方向优于0.8 m、高程方向优于2 m的静态定位精度,以单频接收机的硬件成本,快速收敛实现了实时亚米级定位精度,能够满足大量应用场景对连续稳定可靠的高精度实时定位要求。提出的广域实时亚米级单点定位技术,能够在无需大量建设地基增强基准站的情况下,提供广域范围内大部分应用场景下的实时亚米级高精度位置服务。