GPS/Galileo/BDS三系统全频率PPP-AR性能分析

Performance analysis of GPS/Galileo/BDS three systems and all-frequency PPP-AR

相位偏差的精确估计是实现精密单点定位(precise point positioning,PPP)非差模糊度固定(ambiguity resolution,AR)的重要前提,但当前国际GNSS服务(International GNSS Service,IGS)分析中心(analysis center,AC)提供的相位偏差产品频率组合有限,使PPP-AR用户也只能使用相应频率的观测值,浪费了多频率的GNSS观测值.为了实现基于任意GNSS频率选择和观测值组合灵活实现PPP-AR(即全频率PPP-AR),我们针对全球均匀分布的100多个IGS测站1周的静态观测数据,估算全频率可观测相位偏差(observable specific signal bias,OSB),并使用开源PRIDE PPP-AR软件,进行静态PPP实验.结果表明:伪距和相位OSB产品的平均标准差分别是0.25 ns和0.34 ns,满足PPP模糊度固定的需求.Galileo、北斗三号(BeiDou-3 Navigation Satellite System,BDS-3)频率自由组合时的平均模糊度固定率分别为(98.25%、96.74%)、(90.31%、91.64%),而北斗二号(BeiDou-2 Navigation Satellite System,BDS-2)的平均模糊度固定率为81.27%、86.02%.定位精度和基准频率相比,E1/E6、G1/G5组合在三个方向上定位精度下降接近15%的.C2/C5组合在东(east,E)、北(north,N)方向上表现较好,但在天顶(up,U)方向上定位精度下降22.8%.GPS/Galileo/北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)三个系统中其余参与测试的各频率组合包括C2/C7、C1/C5、C1/C6、C1/C7、E1/E7、E1/E8均呈现出较稳定的定位精度,各个频率组合的定位精度在E、N、U方向上的变化范围分别为5%、5%、15%,与基准频率相比没有较大的偏差,因而全频率PPP-AR已具备相当程度的可靠性.全频率PPP-AR充分利用了多频率的GNSS观测值,相比使用基础频率的观测值实用价值更高;此外,全频率PPP-AR可以根据用户需求进行任意GNSS频率的选择和观测组合,从而更好地满足各种应用的需要.

The accurate estimation of phase biases is an essential prerequisite for achieving precise point positioning ambiguity resolution(PPP-AR).However,the phase bias products provided by the current International GNSS Service(IGS)analysis centers(ACs)are limited in terms of frequency combinations,which restricts PPP-AR users to using observations from corresponding frequencies only.This results in the underutilization of multi-frequency GNSS observations.In order to realize flexible PPP-AR based on arbitrary GNSS frequency selection and observation combinations(referred to as all-frequency PPP-AR),we conducted an analysis using static observation data from over 100 globally distributed IGS stations for a week.We estimated the observable phase biases(OSBs)for all available frequencies and conducted static precise point positioning experiments using the open-source PRIDE PPP-AR software.The results indicate that the average standard deviations of pseudo-range and phase OSB products are 0.25 ns and 0.34 ns,respectively,satisfying the requirements for PPP ambiguity fixing.The average ambiguity fixing rates for Galileo and BDS-3 frequency combinations are 98.25%and 96.74%,and 90.31%and 91.64%,respectively.For BDS-2,the average ambiguity fixing rates are 81.27%and 86.02%.Compared to the reference frequencies,the positioning accuracy decreases by nearly 15%in all three directions for E1/E6 and G1/G5 combinations.The C2/C5 combination performs well in the east(E)and north(N)directions but exhibits a 22.8%decrease in accuracy in the up(U)direction.In the testing of the GPS,Galileo,and BeiDou Navigation Satellite System(BDS),the remaining frequency combinations,including C2/C7,C1/C5,C1/C6,C1/C7,E1/E7,and E1/E8,all exhibited stable positioning accuracy.The positioning accuracy of each frequency combination varied by 5%in the E,5%in the N,and 15%in the U direction,with no significant deviation compared to the reference frequency.Therefore,full-frequency PPP-AR has achieved a considerable degree of reliability.Full-frequency PPP-AR takes full advantage of the multi-frequency GNSS observations,offering higher practical value compared to using observations from the base frequency alone.Furthermore,fullfrequency PPP-AR allows users to select and combine GNSS frequencies according to their specific requirements,thereby better satisfying the needs of various applications.