Performance of Single-Epoch EWL/WL/NL Ambiguity-Fixed Precise Point Positioning with Regional Atmosphere Modelling

Precise point positioning (PPP) with ambiguity resolution (AR) can improve positioning accuracy and reliability. The narrow-lane (NL) AR solution can reach centimeter-level accuracy but there is a certain initialization time. In contrast, extra-wide-lane (EWL) or wide-lane (WL) ambiguity can be fixed instantaneously. However, due to the limited correction accuracy of the empirical atmospheric model, the positioning accuracy is only a few decimeters. In order to further improve the real-time performance of PPP while ensuring accuracy, we developed a multi-system multi-frequency uncombined PPP single-epoch EWL/WL/NL AR method with regional atmosphere modelling. In the proposed method, the precise atmosphere, including zenith wet-troposphere delay (ZWD) and the slant ionosphere, is extracted through multi-frequency stepwise AR, which then is both interpolated and broadcast to users. By adding regional atmosphere constraints, users can achieve single-epoch PPP AR with centimeter-level accuracy. To verify the algorithm, four sets of reference networks with different inter-station distances are used for experiments. With atmosphere constraints, the accuracy of the single-epoch WL solution can be improved from the decimeter level to a few centimeters, with an improvement of more than 90%, and the epoch fix rate can also be improved to varying degrees, especially for the dual-frequency case. Due to the enlarged noise of the EWL combination, its accuracy is at the decimeter level, while the accuracy of the WL/NL solution can reach several centimeters. However, reliable NL ambiguity-fixing tightly relies on atmosphere constraints with sufficiently high accuracy. When the modelling of the atmosphere correction is not accurate enough, the NL AR performance is degraded, although this situation can be improved to a certain extent through the multi-GNSS combination. In contrast, in this case, the WL ambiguity can be successfully fixed and can support the precise positioning with an accuracy of several centimeters.

Download Full-text

Single-Frequency Precise Point Positioning Using Multi-Constellation GNSS: GPS, GLONASS, Galileo and BeiDou

GEOMATICA ◽

10.5623/cig2016-203 ◽

2016 ◽

Vol 70 (2) ◽

pp. 113-122 ◽

Cited By ~ 1

Author(s):

Mahmoud Abd Rabbou ◽

Ahmed El-Rabbany

Keyword(s):

Urban Areas ◽

Precise Point Positioning ◽

Cost Effective ◽

Convergence Time ◽

Single Frequency ◽

Dual Frequency ◽

Positioning Accuracy ◽

Point Positioning ◽

Beidou Satellites ◽

Gnss Observations

Single-frequency precise point positioning (PPP) presents a cost-effective positioning technique for a large number of users. However, it possesses low positioning accuracy and convergence time compared with the dual-frequency PPP. Single-frequency PPP commonly employs GPS satellite systems that suffer from poor satellite geometry, especially in dense urban areas. We develop a new single-frequency PPP model that combines the observations of current GNSS constellations, including GPS, GLONASS, Galileo and Beidou. The MGEX IGS final precise products are utilized to account for the orbital and clock errors, while the IGS final global ionospheric maps (GIM) model is used to correct for the ionospheric delay. The GNSS inter-system biases are treated as additional unknowns in the estimation process. The con tri bution of the additional GNSS observations to single-frequency PPP is assessed through solution comparison with its traditional GPS-only counterpart. Various GNSS combinations are considered in the assessment, including GPS/GLONASS, GPS/Galileo, GPS/BeiDou and all-constellation GNSS. It is shown that the additional GNSS observations enhance the PPP solution accuracy and convergence time in comparison with the tra di tional GPS-only solution. Except for stations with a sufficient number of tracked BeiDou satellites, both Galileo and BeiDou have marginal effects on the positioning accuracy due to their limited number of satel lites. However, for stations with a sufficient number of visible BeiDou satellites, an average of 40% PPP accuracy improvement is obtained. The major contribution to the PPP accuracy enhancement is obtained from GLONASS satellite observations.

Download Full-text

Study on Multi-GNSS Precise Point Positioning Performance with Adverse Effects of Satellite Signals on Android Smartphone

Sensors ◽

10.3390/s20226447 ◽

2020 ◽

Vol 20 (22) ◽

pp. 6447

Author(s):

Hongyu Zhu ◽

Linyuan Xia ◽

Dongjin Wu ◽

Jingchao Xia ◽

Qianxia Li

Keyword(s):

Adverse Effects ◽

Precise Point Positioning ◽

Phase Error ◽

Three Dimensional ◽

Satellite System ◽

Dual Frequency ◽

Positioning Accuracy ◽

Noise Ratio ◽

Point Positioning ◽

Gnss Observations

The emergence of dual frequency global navigation satellite system (GNSS) chip actively promotes the progress of precise point positioning (PPP) technology in Android smartphones. However, some characteristics of GNSS signals on current smartphones still adversely affect the positioning accuracy of multi-GNSS PPP. In order to reduce the adverse effects on positioning, this paper takes Huawei Mate30 as the experimental object and presents the analysis of multi-GNSS observations from the aspects of carrier-to-noise ratio, cycle slip, gradual accumulation of phase error, and pseudorange residual. Accordingly, we establish a multi-GNSS PPP mathematical model that is more suitable for GNSS observations from a smartphone. The stochastic model is composed of GNSS step function variances depending on carrier-to-noise ratio, and the robust Kalman filter is applied to parameter estimation. The multi-GNSS experimental results show that the proposed PPP method can significantly reduce the effect of poor satellite signal quality on positioning accuracy. Compared with the conventional PPP model, the root mean square (RMS) of GPS/BeiDou (BDS)/GLONASS static PPP horizontal and vertical errors in the initial 10 min decreased by 23.71% and 62.06%, respectively, and the horizontal positioning accuracy reached 10 cm within 100 min. Meanwhile, the kinematic PPP maximum three-dimensional positioning error of GPS/BDS/GLONASS decreased from 16.543 to 10.317 m.

Download Full-text

Changes in the GNSS precise point positioning accuracy during a strong geomagnetic storm

E3S Web of Conferences ◽

10.1051/e3sconf/202019601001 ◽

2020 ◽

Vol 196 ◽

pp. 01001

Author(s):

Anna Yasyukevich ◽

Semen Syrovatskii ◽

Yury Yasyukevich

Keyword(s):

Geomagnetic Storm ◽

Precise Point Positioning ◽

Global Navigation Satellite Systems ◽

Maximum Effect ◽

Electron Content ◽

Dual Frequency ◽

Period Range ◽

Positioning Accuracy ◽

Total Electron ◽

Point Positioning

Based on the data from dual-frequency receivers of global navigation satellite systems (GNSS), we analyze the changes in GNSS positioning accuracy during the August 25-26, 2018 strong geomagnetic storm on a global scale. The storm is one of the strongest geomagnetic events of the solar cycle 24. To analyze the positioning quality, we calculated coordinates using the precise point positioning (PPP) method in the kinematic mode. We recorder a significant degradation in the PPP positioning accuracy during the main phase of the storm. The maximum effect is observed in the middle and high latitudes of the US-Atlantic longitude sector. The average PPP error during the storm is shown to exceed ~0.5 m, that is up to 5 times higher than the values typical on quiet days. Areas with increased PPP errors is revealed to correspond to the regions with significant increase in the intensity of total electron content variations of 10–20 min period range. This increase is presumably due to the auroral oval expansion toward middle latitudes.

Download Full-text

BDS-3/Galileo Time and Frequency Transfer with Quad-Frequency Precise Point Positioning

Remote Sensing ◽

10.3390/rs13142704 ◽

2021 ◽

Vol 13 (14) ◽

pp. 2704

Author(s):

Yulong Ge ◽

Xinyun Cao ◽

Fei Shen ◽

Xuhai Yang ◽

Shengli Wang

Keyword(s):

Mathematical Models ◽

Precise Point Positioning ◽

Tropospheric Delay ◽

Dual Frequency ◽

Time Transfer ◽

Positioning Accuracy ◽

Frequency Transfer ◽

Point Positioning ◽

Transfer Method ◽

Stability And Accuracy

In this work, quad-frequency precise point positioning (PPP) time and frequency transfer methods using Galileo E1/E5a/E5b/E5 and BDS-3 B1I/B3I/B1C/B2a observations were proposed with corresponding mathematical models. In addition, the traditional dual-frequency (BDS-3 B1I/B3I and Galileo E1/E5a) ionospheric-free (IF) model was also described and tested for comparison. To assess the proposed method for time transfer, datasets selected from timing labs were utilized and tested. Moreover, the number of Galileo or BDS-3 satellites, pseudorange residuals, positioning accuracy and tropospheric delay at receiver end were all analyzed. The results showed that the proposed quad-frequency BDS-3 or Galileo PPP models could be used to time transfer, due to stability and accuracy identical to that of dual-frequency IF model. Furthermore, the quad-frequency models can provide potential for enhancing the reliability and redundancy compared to the dual-frequency time transfer method.

Download Full-text

Improving the Performance of Galileo Uncombined Precise Point Positioning Ambiguity Resolution Using Triple-Frequency Observations

Remote Sensing ◽

10.3390/rs11030341 ◽

2019 ◽

Vol 11 (3) ◽

pp. 341 ◽

Cited By ~ 8

Author(s):

Gen Liu ◽

Xiaohong Zhang ◽

Pan Li

Keyword(s):

Ambiguity Resolution ◽

Precise Point Positioning ◽

Simulated Data ◽

Satellite System ◽

Dual Frequency ◽

Positioning Accuracy ◽

Processing Mode ◽

Beidou Navigation Satellite System ◽

Triple Frequency ◽

Point Positioning

Compared with the traditional ionospheric-free linear combination precise point positioning (PPP) model, the un-differenced and uncombined (UDUC) PPP model using original observations can keep all the information of the observations and be easily extended to any number of frequencies. However, the current studies about the multi-frequency UDUC-PPP ambiguity resolution (AR) were mainly based on the triple-frequency BeiDou navigation satellite system (BDS) observations or simulated data. Limited by many factors, for example the accuracy of BDS precise orbit and clock products, the advantages of triple-frequency signals to UDUC-PPP AR were not fully exploited. As Galileo constellations have been upgraded by increasing the number of 19 useable satellites, it makes using Galileo satellites to further study the triple-frequency UDUC-PPP ambiguity resolution (AR) possible. In this contribution, we proposed the method of multi-frequency step-by-step ambiguity resolution based on the UDUC-PPP model and gave the reason why the performance of PPP AR can be improved using triple-frequency observations. We used triple-frequency Galileo observations on day of year (DOY) 201, 2018 provided by 166 Multi-GNSS Experiment (MGEX) stations to estimate original uncalibrated phase delays (UPD) on each frequency and to conduct both dual- and triple-frequency UDUC-PPP AR. The performance of UDUC-PPP AR based on post-processing mode was assessed in terms of the time-to-first-fix (TTFF) as well as positioning accuracy with 2-hour observations. It was found that triple-frequency observations were helpful to reduce TTFF and improve the positioning accuracy. The current statistic results showed that triple-frequency PPP-AR reduced the averaged TTFF by 19.6 % and also improved the positioning accuracy by 40.9, 31.2 and 23.6 % in the east, north and up directions respectively, compared with dual-frequency PPP-AR. With an increasing number of Galileo satellites, it is expected that the robustness and accuracy of the triple-frequency UCUD-PPP AR can be improved further.

Download Full-text

Precise Point Positioning Using World’s First Dual-Frequency GPS/GALILEO Smartphone

Sensors ◽

10.3390/s19112593 ◽

2019 ◽

Vol 19 (11) ◽

pp. 2593 ◽

Cited By ~ 14

Author(s):

Abdelsatar Elmezayen ◽

Ahmed El-Rabbany

Keyword(s):

Real Time ◽

Precise Point Positioning ◽

Low Cost ◽

Time Windows ◽

Reference Station ◽

Dual Frequency ◽

Post Processing ◽

Short Baseline ◽

Positioning Accuracy ◽

Point Positioning

The release of the world’s first dual-frequency GPS/Galileo smartphone, Xiaomi mi 8, in 2018 provides an opportunity for high-precision positioning using ultra low-cost sensors. In this research, the GNSS precise point positioning (PPP) accuracy of the Xiaomi mi 8 smartphone is tested in post-processing and real-time modes. Raw dual-frequency observations are collected over two different time windows from both of the Xiaomi mi 8 smartphone and a Trimble R9 geodetic-quality GNSS receiver using a short baseline, due to the lack of a nearby reference station to the observation site. The data sets are first processed in differential modes using Trimble business center (TBC) software in order to provide the reference positioning solution for both of the geodetic receiver and the smartphone. An in-house PPP software is then used to process the collected data in both of post-processing and real-time modes. Precise ephemeris obtained from the multi-GNSS experiment (MGEX) is used for post-processing PPP, while the new NAVCAST real-time GNSS service, Germany, is used for real-time PPP. Additionally, the real-time PPP solution is assessed in both of static and kinematic modes. It is shown that the dual-frequency GNSS smartphone is capable of achieving decimeter-level positioning accuracy, in both of post-processing and real-time PPP modes, respectively. Meter-level positioning accuracy is achieved in the kinematic mode.

Download Full-text

Precise point positioning with decimetre accuracy using wide-lane ambiguities and triple-frequency GNSS data

Journal of Applied Geodesy ◽

10.1515/jag-2019-0068 ◽

2020 ◽

Vol 14 (3) ◽

pp. 263-284

Author(s):

Manoj Deo ◽

Ahmed El-Mowafy

Keyword(s):

Linear Combination ◽

Carrier Phase ◽

Precise Point Positioning ◽

Low Noise ◽

Positioning Accuracy ◽

The Third ◽

Triple Frequency ◽

Wide Lane ◽

Point Positioning ◽

Gnss Data

AbstractThis paper proposes precise point positioning (PPP) methods that offer an accuracy of a few decimetres (dm) with triple frequency GNSS data. Firstly, an enhanced triple frequency linear combination is presented for rapid fixing of the extra wide-lane (EWL) and wide-lane (WL) ambiguities for GPS, Beidou-2 and Galileo. This has improved performance compared to the Melbourne-Wübbena (MW) linear combination, and has 6.7 % lower measurement noise for the GPS L1/L2 signals, 12.7 % for L1/L5 and 0.7 % for L2/L5. Analysis with tested data showed a 5–6 % reduction in time required to fix the {N_{21}} and {N_{51}} ambiguities.Once the EWL/WL ambiguities are fixed with the proposed linear combinations, three methods are presented that aim to provide positioning accuracy of a few dm. In the first approach, the three EWL/WL ambiguities in their respective phase equations are used to derive a low-noise ionosphere-free (IF) linear combination. The second method uses a low noise IF combination with two carrier-phase EWL/WL equations and a single pseudorange measurement. The third method uses a low noise IF combination with a single carrier phase EWL equation and two pseudorange measurements. These proposed methods can provide dm level positioning accuracy if carrier phase measurements with mm precision is tracked by the receiver. When comparing these combinations with a combination proposed in [22], it is found that superior performance is achieved with the third method when carrier phase noise is >5–6 mm for GPS and Beidou-2 and >2–3 mm for Galileo. This model only requires the EWL ambiguity to be fixed which typically takes just one epoch of data. Thus, the user achieves instant decimetre level PPP accuracy.

Download Full-text

Single-Frequency Precise Point Positioning Using Regional Dual-Frequency Observations

Sensors ◽

10.3390/s21082856 ◽

2021 ◽

Vol 21 (8) ◽

pp. 2856

Author(s):

Junping Zou ◽

Ahao Wang ◽

Jiexian Wang

Keyword(s):

High Precision ◽

Precise Point Positioning ◽

Low Cost ◽

Deformation Monitoring ◽

Convergence Time ◽

Single Frequency ◽

Relative Positioning ◽

Dual Frequency ◽

Positioning Accuracy ◽

Point Positioning

High-precision and low-cost single-frequency precise point positioning (SF-PPP) has been attracting more and more attention in numerous global navigation satellite system (GNSS) applications. To provide the precise ionosphere delay and improve the positioning accuracy of the SF-PPP, the dual-frequency receiver, which receives dual-frequency observations, is used. Based on the serviced precise ionosphere delay, which is generated from the dual-frequency observations, the high-precision SF-PPP is realized. To further improve the accuracy of the SF-PPP and shorten its convergence time, the double-differenced (DD) ambiguity resolutions, which are generated from the DD algorithm, are introduced. This method avoids the estimation of fractional cycle bias (FCB) for the SF-PPP ambiguity. Here, we collected data from six stations of Shanghai China which was processed, and the corresponding results were analyzed. The results of the dual-frequency observations enhanced SF-PPP realize centimeter-level positioning. The difference between the results of two stations estimated with dual-frequency observations enhanced SF-PPP were compared with the relative positioning results computed with the DD algorithm. Experimental results showed that the relative positioning accuracy of the DD algorithm is slightly better than that of the dual-frequency observations enhanced SF-PPP. This could be explained by the effect of the float ambiguity resolutions on the positioning accuracy. The data was processed with the proposed method for the introduction of the DD ambiguity into SF-PPP and the results indicated that this method could improve the positioning accuracy and shorten the convergence time of the SF-PPP. The results could further improve the deformation monitoring ability of SF-PPP.

Download Full-text

Beyond three frequencies: An extendable model for single-epoch decimeter-level point positioning by exploiting Galileo and BeiDou-3 signals

10.31219/osf.io/uy5qm ◽

2020 ◽

Author(s):

Jianghui Geng ◽

Jiang Guo

Keyword(s):

High Precision ◽

Autonomous Driving ◽

Convergence Time ◽

Frequency Data ◽

Positioning Accuracy ◽

Safety Standards ◽

Triple Frequency ◽

Wide Lane ◽

Point Positioning ◽

Single Epoch

GNSS is indispensable to self-driving vehicles by delivering decimeter-level or better absolute positioning solutions. Such a high precision normally requires a convergence time spanning seconds to minutes, which is however unrealistic in extremely difficult driving conditions where GNSS signals are obstructed frequently. Such convergences, no matter how short, will greatly risk and discredit autonomous driving in satisfying stringent life-safety standards. In this study, we therefore developed an extendable GNSS precise point positioning (PPP) model to exploit the advanced Galileo/BeiDou-3 more-than-three-frequency signals with the goal of achieving instant or single-epoch 10-30 cm positioning accuracy and over 99% availability for the horizontal components over wide areas. In particular, uncombined Galileo/BeiDou-3 signals on all available frequencies were injected simultaneously into PPP to perform single-epoch wide-lane ambiguity resolution (PPP-WAR) after phase bias calibrations on raw observations. Experimenting on the Galileo five-frequency data from 36 stations in Australia, we found that instant PPP-WAR was accomplished at more than 99.5% of all epochs; we achieved an instant positioning accuracy of 0.10 and 0.11 m (1) for the east and north components, respectively, using Galileo E1/E5a/E5/E5b/E6 signals from less than 10 satellites, while 0.16 and 0.23 m using BeiDou-3 B1C/B1I/B2a/B2b/B3I signals from only 5-6 satellites per epoch observed by 10 stations within China. Moreover, we carried out vehicle-borne experiments collecting multi-frequency Galileo/BeiDou-3 signals in case of overpass and tunnel adversities. With 7 Galileo/BeiDou-3 satellites per epoch on average, instant PPP-WAR reached a mean positioning accuracy of 0.23 and 0.24 m for the horizontal components, which can be further improved to 0.14 and 0.12 m when multi-epoch filtering is preferably enabled. More encouragingly, though this positioning accuracy can also be ensured with triple-frequency data, the data redundancy favored by even more frequencies can reduce the high-precision recovery time from up to 4 s to 2 s in case of total signal blockages. With the rapidly ongoing deployment of Galileo, BeiDou-3 and other GNSS constellations, we can envision an instant global positioning service characterized by around 20-cm horizontal accuracy and over 99% availability for self-driving vehicles.

Download Full-text

Triple-Frequency GPS Precise Point Positioning Ambiguity Resolution Using Dual-Frequency Based IGS Precise Clock Products

International Journal of Aerospace Engineering ◽

10.1155/2017/7854323 ◽

2017 ◽

Vol 2017 ◽

pp. 1-11

Author(s):

Fei Liu ◽

Yang Gao

Keyword(s):

Ambiguity Resolution ◽

Carrier Phase ◽

Precise Point Positioning ◽

Free Carrier ◽

Convergence Time ◽

Dual Frequency ◽

Phase Measurements ◽

Triple Frequency ◽

Wide Lane ◽

Point Positioning

With the availability of the third civil signal in the Global Positioning System, triple-frequency Precise Point Positioning ambiguity resolution methods have drawn increasing attention due to significantly reduced convergence time. However, the corresponding triple-frequency based precise clock products are not widely available and adopted by applications. Currently, most precise products are generated based on ionosphere-free combination of dual-frequency L1/L2 signals, which however are not consistent with the triple-frequency ionosphere-free carrier-phase measurements, resulting in inaccurate positioning and unstable float ambiguities. In this study, a GPS triple-frequency PPP ambiguity resolution method is developed using the widely used dual-frequency based clock products. In this method, the interfrequency clock biases between the triple-frequency and dual-frequency ionosphere-free carrier-phase measurements are first estimated and then applied to triple-frequency ionosphere-free carrier-phase measurements to obtain stable float ambiguities. After this, the wide-lane L2/L5 and wide-lane L1/L2 integer property of ambiguities are recovered by estimating the satellite fractional cycle biases. A test using a sparse network is conducted to verify the effectiveness of the method. The results show that the ambiguity resolution can be achieved in minutes even tens of seconds and the positioning accuracy is in decimeter level.

Download Full-text