Performance analysis of real-time and post-mission kinematic precise point positioning in marine environments

This article focuses on the performance analysis of both real-time and post-mission kinematic precise point positioning(PPP)in challenging marine environments.For this purpose,a real dynamic experiment lasting 6 h was carried out on a lake dam in?orum City of Turkey.While the kinematic test was continuing,the real-time PPP coordinates were obtained for each measurement epoch with a commercial real-time PPP(RT-PPP)service,namely the Trimble Center Point RTX.Then the post-mission PPP(PM-PPP)coordinates were calculated by using Multi-GNSS data and the Multi-GNSS Experiment(MGEX)precise products.The kinematic RT-PPP and PM-PPP results showed that the PPP coordinates were consistent with the relative solution at centimetre and decimetre level in horizontal and height components,respectively.This study implies that PPP technique is a powerful tool for highly accurate positioning in both real-time and post-mission modes,even for dynamic applications in harsh environments.

Quality monitoring of real-time GNSS precise positioning service system

The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centimeter-level positioning with a stand-alone receiver in real-time.Although the products are available with high accuracy almost all the time,they may occasionally suffer from unexpected significant biases,which consequently degrades the positioning perfor-mance.Therefore,quality monitoring at the system-level has become more and more crucial for providing a reliable GNSS service.In this paper,we propose a method for the monitoring of realtime satellite orbit and clock products using a monitoring station network based on the Quality Control(QC)theory.The satellites with possible biases are first detected based on the outliers identified by Precise Point Positioning(PPP)in the monitoring station network.Then,the corresponding orbit and clock parameters with temporal constraints are introduced and esti-mated through the sequential Least Square(LS)estimator and the corresponding Instantaneous User Range Errors(IUREs)can be determined.A quality indicator is calculated based on the IUREs in the monitoring network and compared with a pre-defined threshold.The quality monitoring method is experimentally evaluated by monitoring the real-time orbit and clock products generated by GeoForschungsZentrum(GFZ),Potsdam.The results confirm that the problematic satellites can be detected accurately and effectively with missed detection rate 4×10^(-6) and false alarm rate 1:2×10^(-5).Considering the quality alarms,the PPP results in terms of RMS of positioning differences with respect to the International GNSS Service(IGS)weekly solution in the north,east and up directions can be improved by 12%,10%and 27%,respectively.

Efficient Harmonic Analysis Technique for Prediction of IGS Real-Time Satellite Clock Corrections

Real-time satellite orbit and clock corrections obtained from the broadcast ephemerides can be improved using IGS real-time service (RTS) products. Recent research showed that applying such corrections for broadcast ephemerides can significantly improve the RMS of the estimated coordinates. However, unintentional streaming interruption may happen for many reasons such as software or hardware failure. Streaming interruption, if happened, will cause sudden degradation of the obtained solution if only the broadcast ephemerides are used. A better solution can be obtained in real-time if the predicted part of the ultra-rapid products is used. In this paper, Harmonic analysis technique is used to predict the IGS RTS corrections using historical broadcasted data. It is shown that using the predicted clock corrections improves the RMS of the estimated coordinates by about 72%, 58%, and 72% in latitude, longitude, and height directions, respectively and reduces the 2D and 3D errors by about 80% compared with the predicted part of the IGS ultra-rapid clock corrections.

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.

Improved precise positioning with BDS-3 quad-frequency signals

The establishment of the BeiDou global navigation satellite system(BDS-3)has been completed,and the current constellation can independently provide positioning service globally.BDS-3 satellites provide quad-frequency signals,which can benefit the ambiguity resolution(AR)and high-precision positioning.This paper discusses the benefits of quad-frequency observations,including the precision gain of multi-frequency high-precision positioning and the sophisticated choice of extra-wide-lane(EWL)or wide-lane(WL)combinations for instantaneous EWL/WL AR.Additionally,the performance of EWL real-time kinematic(ERTK)positioning that only uses EWL/WL combinations is investigated.The results indicate that the horizontal positioning errors of ERTK positioning using ionosphere-free(IF)EWL observations are approximately 0.5 m for the baseline of 27 km and 1 m for the baseline of 300 km.Furthermore,the positioning errors are reduced to the centimetre level if the IF EWL observations are smoothed by narrow-lane observations for a short period.

GNSS smartphones positioning: advances, challenges, opportunities, and future perspectives

Starting from 2016,the raw Global Navigation Satellite System(GNSS)measurements can be extracted from the Android Nougat(or later)operating systems.Since then,GNSS smartphone positioning has been given much attention.A high number of related publications indicates the importance of the research in this field,as it has been doing in recent years.Due to the cost-effectiveness of the GNSS smartphones,they can be employed in a wide variety of applications such as cadastral surveys,mapping surveying applications,vehicle and pedestrian navigation and etc.However,there are still some challenges regarding the noisy smartphone GNSS observations,the environment effect and smartphone holding modes and the algorithm development part which restrict the users to achieve high-precision smartphone positioning.In this review paper,we overview the research works carried out in this field with a focus on the following aspects:first,to provide a review of fundamental work on raw smartphone observations and quality assessment of GNSS observations from major smart devices including Google Pixel 4,Google Pixel 5,Xiaomi Mi 8 and Samsung Ultra S20 in terms of their signal strengths and carrier-phase continuities,second,to describe the current state of smartphone positioning research field until most recently in 2021 and,last,to summarize major challenges and opportunities in this filed.Finally,the paper is concluded with some remarks as well as future research perspectives.

Real‑time service performances of BDS‑3 and Galileo constellations with a linear satellite clock correction models

In order to facilitate high-precision and real-time Precise Point Positioning(PPP),the International GNSS(Global Navigation Satellite System)Service(IGS),BDS-3(BeiDou-3 Navigation Satellite System),and Galileo navigation satellite system(Galileo)have provided real-time satellite clock correction,which is updated at a high-frequency.However,the frequent updates pose the challenges of increasing the computational burden and compromising the timeliness of these correction parameters.To address this issue,an improved Real-Time Service(RTS)method is developed using an extrapolation algorithm and a linear model.The results indicate that a 1 h arc length of the satellite clock correction series is optimal for fitting a linear model of the RTS.With this approach,the 1 h extrapolation results for BDS-3 and Galileo are superior to 0.09 ns.Moreover,when these model coefficients are transmitted and updated at the intervals of 1,2,5,and 10 min,the corresponding PPP can converge at the centimeter-level.It is evident that these improved RTS methods outperform the current approach with high-frequency interval transmission,as they effectively mitigate the challenges associated with maintaining the timeliness of correction parameters.

Multi-GNSS products and services at iGMAS Wuhan Innovation Application Center:strategy and evaluation

Over the past years the International Global Navigation Satellite System(GNSS)Monitoring and Assessment System(iGMAS)Wuhan Innovation Application Center(IAC)dedicated to exploring the potential of multi-GNSS signals and providing a set of products and services.This contribution summarizes the strategies,achievements,and innovations of multi-GNSS orbit/clock/bias determination in iGMAS Wuhan IAC.Both the precise products and Real-Time Services(RTS)are evaluated and discussed.The precise orbit and clock products have comparable accuracy with the precise products of the International GNSS Service(IGS)and iGMAS.The multi-frequency code and phase bias products for Global Positioning System(GPS),BeiDou Navigation Satellite System(BDS),Galileo navigation satellite system(Galileo),and GLObal NAvigation Satellite System(GLONASS)are provided to support multi-GNSS and multi-frequency Precise Point Positioning(PPP)Ambiguity Resolution(AR).Compared with dual-frequency PPP AR,the time to first fix of triple-frequency solution is improved by 30%.For RTS,the proposed orbit prediction strategy improves the three dimensional accuracy of predicted orbit by 1 cm.The multi-thread strategy and high-performance matrix library are employed to accelerate the real-time orbit and clock determination.The results with respect to the IGS precise products show the high accuracy of RTS orbits and clocks,4–9 cm and 0.1–0.2 ns,respectively.Using real-time satellite corrections,real-time PPP solutions achieve satisfactory performance with horizontal and vertical positioning errors within 2 and 4 cm,respectively,and convergence time of 16.97 min.