Accelerating real-time PPP ambiguity resolution by incorporating multi-GNSS observations

2019 ◽  
Vol 63 (9) ◽  
pp. 3009-3017 ◽  
Author(s):  
Zhao Li ◽  
Hua Chen ◽  
Peng Yuan
Keyword(s):  
Real Time ◽  
Ambiguity Resolution ◽  
Gnss Observations

Real-time estimation of multi-GNSS and multi-frequency integer recovery clock with undifferenced ambiguity resolution

2020 ◽  
Author(s):  
Yun Xiong ◽  
Yongqiang Yuan ◽  
Jiaqi Wu ◽  
Xin Li ◽  
Jiaxin Huang
Keyword(s):  
Real Time ◽  
Ambiguity Resolution ◽  
Computation Time ◽  
Time Estimation ◽  
Global Navigation Satellite Systems ◽  
Estimation Model ◽  
Processing Efficiency ◽  
Real Time Clock ◽  
Clock Estimation ◽  
Gnss Observations

<p>Precise clock product of global navigation satellite systems (GNSS) is an important prerequisite to support real-time precise positioning service. The developments of multi-constellation and multi-frequency GNSS open new requirements for real-time clock estimation. In this contribution, the estimation model of multi-GNSS and multi-frequency integer recovery clock (IRC) is developed to improve both the accuracy and efficiency of real-time clock estimates. In the proposed method, the undifferenced ambiguities are fixed to integers, thus the integer properties of the ambiguities are recovered and the accuracy of the clock estimates is also improved. Moreover, benefitting from the removal of large quantities of ambiguity parameters, the computation time is greatly reduced which can guarantee high processing efficiency of real-time clock estimates. Multi-GNSS observations from 150 globally distributed Multi-GNSS Experiment (MGEX) tracking stations were processed with the proposed model. Compared to the float satellite clocks, the precision of the real-time IRC with respect to CODE 30 s final multi-GNSS satellite clock products were improved by 53.0%, 42.7%, 63.7% and 33.9% for GPS, BDS, Galileo and GLONASS, respectively. The average computation time per epoch with multi-GNSS observations was improved by 97.1% compared to that of standard float clock estimation. Kinematic precise point positioning (PPP) ambiguity resolution was also performed with the derived real-time IRC products. Compared to the float PPP solutions, the position accuracy of the multi-GNSS IRC-based fixed solutions was improved by 77.2%, 49.7% and 52.7% from 24.2, 13.3 and 30.7 mm to 5.5, 6.7 and 14.5 mm for the east, north and up components, respectively. The results indicate that ambiguity fixing can be successfully achieved by using the derived the IRC products. In addition, the estimation model of multi-frequency IRC products is also investigated to promote the capability and application of real-time PPP AR under multi-frequency signals.</p>

scholarly journals High-Accuracy Real-Time Kinematic Positioning with Multiple Rover Receivers Sharing Common Clock

2021 ◽  
Vol 13 (4) ◽  
pp. 823
Author(s):  
Lin Zhao ◽  
Jiachang Jiang ◽  
Liang Li ◽  
Chun Jia ◽  
Jianhua Cheng
Keyword(s):  
Real Time ◽  
Ambiguity Resolution ◽  
Temporal Stability ◽  
Estimation Method ◽  
Satellite System ◽  
Integer Ambiguity ◽  
Dual Frequency ◽  
Kinematic Positioning ◽  
Real Time Kinematic ◽  
Satellite Visibility

Since the traditional real-time kinematic positioning method is limited by the reduced satellite visibility from the deprived navigational environments, we, therefore, propose an improved RTK method with multiple rover receivers sharing a common clock. The proposed method can enhance observational redundancy by blending the observations from each rover receiver together so that the model strength will be improved. Integer ambiguity resolution of the proposed method is challenged in the presence of several inter-receiver biases (IRB). The IRB including inter-receiver code bias (IRCB) and inter-receiver phase bias (IRPB) is calibrated by the pre-estimation method because of their temporal stability. Multiple BeiDou Navigation Satellite System (BDS) dual-frequency datasets are collected to test the proposed method. The experimental results have shown that the IRCB and IRPB under the common clock mode are sufficiently stable for the ambiguity resolution. Compared with the traditional method, the ambiguity resolution success rate and positioning accuracy of the proposed method can be improved by 19.5% and 46.4% in the restricted satellite visibility environments.

scholarly journals Real-Time Kinematic Precise Orbit Determination for LEO Satellites Using Zero-Differenced Ambiguity Resolution

2019 ◽  
Vol 11 (23) ◽  
pp. 2815 ◽  
Author(s):  
Xingxing Li ◽  
Jiaqi Wu ◽  
Keke Zhang ◽  
Xin Li ◽  
Yun Xiong ◽  
...  
Keyword(s):  
Real Time ◽  
Ambiguity Resolution ◽  
Orbit Determination ◽  
Precise Orbit Determination ◽  
The Real ◽  
Precise Orbit ◽  
Ambiguity Fixing ◽  
Real Time Kinematic ◽  
Leo Satellites ◽  
Fixed Solution

The rapid growing number of earth observation missions and commercial low-earth-orbit (LEO) constellation plans have provided a strong motivation to get accurate LEO satellite position and velocity information in real time. This paper is devoted to improve the real-time kinematic LEO orbits through fixing the zero-differenced (ZD) ambiguities of onboard Global Navigation Satellite System (GNSS) phase observations. In the proposed method, the real-time uncalibrated phase delays (UPDs) are estimated epoch-by-epoch via a global-distributed network to support the ZD ambiguity resolution (AR) for LEO satellites. By separating the UPDs, the ambiguities of onboard ZD GPS phase measurements recover their integer nature. Then, wide-lane (WL) and narrow-lane (NL) AR are performed epoch-by-epoch and the real-time ambiguity–fixed orbits are thus obtained. To validate the proposed method, a real-time kinematic precise orbit determination (POD), for both Sentinel-3A and Swarm-A satellites, was carried out with ambiguity–fixed and ambiguity–float solutions, respectively. The ambiguity fixing results indicate that, for both Sentinel-3A and Swarm-A, over 90% ZD ambiguities could be properly fixed with the time to first fix (TTFF) around 25–30 min. For the assessment of LEO orbits, the differences with post-processed reduced dynamic orbits and satellite laser ranging (SLR) residuals are investigated. Compared with the ambiguity–float solution, the 3D orbit difference root mean square (RMS) values reduce from 7.15 to 5.23 cm for Sentinel-3A, and from 5.29 to 4.01 cm for Swarm-A with the help of ZD AR. The SLR residuals also show notable improvements for an ambiguity–fixed solution; the standard deviation values of Sentinel-3A and Swarm-A are 4.01 and 2.78 cm, with improvements of over 20% compared with the ambiguity–float solution. In addition, the phase residuals of ambiguity–fixed solution are 0.5–1.0 mm larger than those of the ambiguity–float solution; the possible reason is that the ambiguity fixing separate integer ambiguities from unmodeled errors used to be absorbed in float ambiguities.

scholarly journals Weighting of Multi-GNSS Observations in Real-Time Precise Point Positioning

2018 ◽  
Vol 10 (2) ◽  
pp. 84 ◽  
Author(s):  
Kamil Kazmierski ◽  
Tomasz Hadas ◽  
Krzysztof Sośnica
Keyword(s):  
Real Time ◽  
Precise Point Positioning ◽  
Point Positioning ◽  
Gnss Observations

Recent Developments in Precise Point Positioning

GEOMATICA ◽  
2012 ◽  
Vol 66 (2) ◽  
pp. 103-111 ◽  
Author(s):  
S. Bisnath ◽  
P. Collins
Keyword(s):  
Real Time ◽  
Ambiguity Resolution ◽  
Carrier Phase ◽  
Precise Point Positioning ◽  
Solution Convergence ◽  
Similar Information ◽  
Recent Developments ◽  
Significant Step ◽  
Point Positioning ◽  
New Processing

In standard Precise Point Positioning (PPP), the carrier phase ambiguities are estimated as real-valued constants, so that the carrier-phases can provide similar information as the pseudoranges. As a consequence, it can take tens of minutes to several hours for the ambiguities to converge to suitably precise values. Recently, new processing methods have been identified that permit the ambiguities to be estimated more appropriately as integer-valued constants, as they are in relative Real-Time Kinematic (RTK) positioning. Under these conditions, standard ambiguity resolution techniques can be applied to strengthen the PPP solution. The result can be a greatly reduced solution convergence and re-convergence period, representing a significant step toward improving the performance of PPP with respect to that of RTK processing. This paper describes the underlying principles of the method, why the enhancements work, and presents some results.

scholarly journals Integrity Monitoring for Carrier Phase Ambiguities

2011 ◽  
Vol 65 (1) ◽  
pp. 41-58 ◽  
Author(s):  
Shaojun Feng ◽  
Washington Ochieng ◽  
Jaron Samson ◽  
Michel Tossaint ◽  
Manuel Hernandez-Pajares ◽  
...  
Keyword(s):  
Least Squares ◽  
Real Time ◽  
Ambiguity Resolution ◽  
Carrier Phase ◽  
Integer Number ◽  
Integrity Monitoring ◽  
Level Of Confidence ◽  
F Distribution ◽  
Position Solution ◽  
T Distribution

The determination of the correct integer number of carrier cycles (integer ambiguity) is the key to high accuracy positioning with carrier phase measurements from Global Navigation Satellite Systems (GNSS). There are a number of current methods for resolving ambiguities including the Least-squares AMBiguity Decorrelation Adjustment (LAMBDA) method, which is a combination of least-squares and a transformation to reduce the search space. The current techniques to determine the level of confidence (integrity) of the resolved ambiguities (i.e. ambiguity validation), usually involve the construction of test statistics, characterisation of their distribution and definition of thresholds. Example tests applied include ratio, F-distribution, t-distribution and Chi-square distribution. However, the assumptions that underpin these tests have weaknesses. These include the application of a fixed threshold for all scenarios, and therefore, not always able to provide an acceptable integrity level in the computed ambiguities. A relatively recent technique referred to as Integer Aperture (IA) based on the ratio test with a large number of simulated samples of float ambiguities requires significant computational resources. This precludes the application of IA in real time.This paper proposes and demonstrates the power of an integrity monitoring technique that is applied at the ambiguity resolution and positioning stages. The technique has the important benefit of facilitating early detection of any potential threat to the position solution, originating in the ambiguity space, while at the same time giving overall protection in the position domain based on the required navigation performance. The proposed method uses the conventional test statistic for ratio testing together with a doubly non-central F distribution to compute the level of confidence (integrity) of the ambiguities. Specifically, this is determined as a function of geometry and the ambiguity residuals from least squares based ambiguity resolution algorithms including LAMBDA. A numerical method is implemented to compute the level of confidence in real time.The results for Precise Point Positioning (PPP) with simulated and real data demonstrate the power and efficiency of the proposed method in monitoring both the integrity of the ambiguity computation and position solution processes. Furthermore, due to the fact that the method only requires information from least squares based ambiguity resolution algorithms, it is easily transferable to conventional Real Time Kinematic (RTK) positioning.

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