scholarly journals Multi-GNSS Relative Positioning with Fixed Inter-System Ambiguity

2019 ◽  
Vol 11 (4) ◽  
pp. 454 ◽  
Author(s):  
Hua Chen ◽  
Weiping Jiang ◽  
Jiancheng Li
Keyword(s):  
Double Difference ◽  
Relative Positioning ◽  
New Approach ◽  
Gnss Positioning ◽  
Ambiguity Fixing ◽  
Single Difference ◽  
Phase Bias ◽  
System Phase

In multi-GNSS cases, two types of Double Difference (DD) ambiguity could be formed including an intra-system ambiguity and an inter-system ambiguity, which are identified as the DD ambiguity between satellites from the same and from different GNSS systems, respectively. We studied the relative positioning methods using intra-system DD observations and using Un-Difference (UD) observations, and developed a frequency-free approach for fixing inter-system ambiguity based on UD observations for multi-GNSS positioning, where the inter-system phase bias is calculated with the help of a fixed Single-Difference (SD) ambiguity. The consistency between the receiver-end uncalibrated phase delays (RUPD) and the SD ambiguity were investigated and the positioning performance of this new approach was assessed. The results show that RUPD could be modeled as a constant if the receiver were tracking satellites continuously. Furthermore, compared to the method using DD observations with only an intra-system DD ambiguity fixed, the new ambiguity fixing approach has a better performance, especially in hard environments with a large cut-off angle or serve signal obstructions.

scholarly journals An Improved Ambiguity-Free Method for Precise GNSS Positioning with Utilizing Single Frequency Receivers

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 856 ◽  
Author(s):  
Wenhao Yang ◽  
Yue Liu ◽  
Fanming Liu
Keyword(s):  
Global Optimum ◽  
Ambiguity Function ◽  
Single Frequency ◽  
Density Estimator ◽  
New Approach ◽  
Gnss Positioning ◽  
Cycle Slips ◽  
Computation Efficiency ◽  
Ambiguity Fixing ◽  
Computation Load

The solution of carrier phase ambiguity is essential for precise global navigation satellite system (GNSS) positioning. Methods of searching in the coordinate domain show their advantage over the methods based on ambiguity fixing, for example, immune to cycle slips, far fewer epochs taken for obtaining the precise solution. However, there are still some drawbacks via using the Ambiguity Function Method (AFM), such as low computation efficiency and the existence of a false global optimum. The false global optimum is a situation where the Least Square (LS) criterion achieves minimum in another place than the point of the actual position, which restricts the application of this method to single-frequency receivers. The numerical search approach derived in this paper is based on the Modified Ambiguity Function Approach (MAFA). It focuses on eliminating the false optimum solution and reducing the computation load by utilizing single-frequency receivers without solving the ambiguity fixing problem. An improved segmented simulated annealing method is used to decrease the computation load while the Kernel Density Estimator (KDE) method is used to filter out the false optimum candidates. Static experiments were carried out to evaluate the performance of the new approach. It is shown that a precise result can be obtained by handling two epochs of data with z coordinate fixed to the referenced value. Meanwhile, the new approach can achieve a millimeter level of position accuracy after dealing with nineteen epochs of observations data when searching in x , y , z domain. The new approach shows its robustness even if the search region is broad, and the prior position is several meters away from the referenced value.

scholarly journals A Single-Difference Multipath Hemispherical Map for Multipath Mitigation in BDS-2/BDS-3 Short Baseline Positioning

2021 ◽  
Vol 13 (2) ◽  
pp. 304
Author(s):  
Chao Liu ◽  
Yuan Tao ◽  
Haiqiang Xin ◽  
Xingwang Zhao ◽  
Chunyang Liu ◽  
...  
Keyword(s):  
Satellite System ◽  
Observation Time ◽  
Double Difference ◽  
Observation Data ◽  
Multipath Mitigation ◽  
Short Baseline ◽  
Independent Variables ◽  
Positioning Errors ◽  
Single Difference ◽  
Repeat Time

The BeiDou Navigation Satellite System (BDS) features a heterogeneous constellation so that it is difficult to mitigate the multipath in the coordinate-domain. Therefore, mitigating the multipath in the observation-domain becomes more important. Sidereal filtering is commonly used for multipath mitigation, which needs to calculate the orbit repeat time of each satellite. However, that poses a computational challenge and damages the integrity at the end of the multipath model. Therefore, this paper proposes a single-difference model based on the multipath hemispherical map (SD-MHM) to mitigate the BDS-2/BDS-3 multipath in a short baseline. The proposed method is converted from double-difference residuals to single-difference residuals, which is not restricted by the pivot satellite transformation. Moreover, it takes the elevation and the azimuth angles of the satellite as the independent variables of the multipath model. The SD-MHM overcomes the unequal observation time of some satellites and does not require specific hardware. The experimental results show that the SD-MHM reduces the root mean square of the positioning errors by 56.4%, 63.9%, and 67.4% in the east, north, and vertical directions; moreover, it contributes to an increase in the baseline accuracy from 1.97 to 0.84 mm. The proposed SD-MHM has significant advantages in multipath mitigation compared with the advanced sidereal filtering method. Besides, the SD-MHM also features an excellent multipath correction capability for observation data with a period of more than seven days. Therefore, the SD-MHM provides a universal strategy for BDS multipath mitigation.

scholarly journals Estimation and evaluation of COSMIC radio occultation excess phase using undifferenced measurements

2017 ◽  
Vol 10 (5) ◽  
pp. 1813-1821
Author(s):  
Pengfei Xia ◽  
Shirong Ye ◽  
Kecai Jiang ◽  
Dezhong Chen
Keyword(s):  
Radio Occultation ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
Double Difference ◽  
Cosmic Radio ◽  
Processing Strategy ◽  
Single Difference ◽  
Excess Phase ◽  
Mean Square Errors ◽  
Better Than

Abstract. In the GPS radio occultation technique, the atmospheric excess phase (AEP) can be used to derive the refractivity, which is an important quantity in numerical weather prediction. The AEP is conventionally estimated based on GPS double-difference or single-difference techniques. These two techniques, however, rely on the reference data in the data processing, increasing the complexity of computation. In this study, an undifferenced (ND) processing strategy is proposed to estimate the AEP. To begin with, we use PANDA (Positioning and Navigation Data Analyst) software to perform the precise orbit determination (POD) for the purpose of acquiring the position and velocity of the mass centre of the COSMIC (The Constellation Observing System for Meteorology, Ionosphere and Climate) satellites and the corresponding receiver clock offset. The bending angles, refractivity and dry temperature profiles are derived from the estimated AEP using Radio Occultation Processing Package (ROPP) software. The ND method is validated by the COSMIC products in typical rising and setting occultation events. Results indicate that rms (root mean square) errors of relative refractivity differences between undifferenced and atmospheric profiles (atmPrf) provided by UCAR/CDAAC (University Corporation for Atmospheric Research/COSMIC Data Analysis and Archive Centre) are better than 4 and 3 % in rising and setting occultation events respectively. In addition, we also compare the relative refractivity bias between ND-derived methods and atmPrf profiles of globally distributed 200 COSMIC occultation events on 12 December 2013. The statistical results indicate that the average rms relative refractivity deviation between ND-derived and COSMIC profiles is better than 2 % in the rising occultation event and better than 1.7 % in the setting occultation event. Moreover, the observed COSMIC refractivity profiles from ND processing strategy are further validated using European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data, and the results indicate that the undifferenced method reduces the noise level on the excess phase paths in the lower troposphere compared to the single-difference processing strategy.

scholarly journals A Direct Attitude Determination Approach Based on GPS Double-Difference Carrier Phase Measurements

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Jianhua Cheng ◽  
Jing Wang ◽  
Lin Zhao
Keyword(s):  
Carrier Phase ◽  
Attitude Determination ◽  
Double Difference ◽  
Body Frame ◽  
Phase Equation ◽  
New Approach ◽  
Solution Approach ◽  
Relationship Of ◽  
The Relationship ◽  
Attitude Matrix

The principle of the traditional attitude solution approach based on GPS (Global Position System) is to get the attitude matrix according to the relationship of coordinates. During the progress, the error of baseline position assumed in ECEF (Earth-Centered Earth-Fixed) and the error of coordinate transform between body frame and reference frame (ENU, East-North-Up) have been included in the result, and finally the precision of attitude determination is reduced. This contribution presents a new approach of attitude determination, in which the attitude angles are calculated by the double-difference carrier phase equation of GPS according to the relationship of attitude matrix and attitude angles through least-squares estimate method. The new approach predigests the procedure of attitude determination which reduces the error assumed. According to the analysis the precision of attitude determination is higher than that of traditional method. It is shown it gets a precise attitude result with the direct attitude determination method in the simulation. A novel algorithm is proposed to solve some problems. Simulation results show the effectiveness of the proposed algorithm.

RELATIVE POSITIONING OF STROKE-BASED CLUSTERING: A NEW APPROACH TO ONLINE HANDWRITTEN DEVANAGARI CHARACTER RECOGNITION

2012 ◽  
Vol 12 (02) ◽  
pp. 1250016 ◽  
Author(s):  
K. C. SANTOSH ◽  
CHOLWICH NATTEE ◽  
BART LAMIROY
Keyword(s):  
Character Recognition ◽  
Dynamic Time Warping ◽  
Large Range ◽  
Recognition Rate ◽  
Relative Positioning ◽  
Writing Style ◽  
Time Warping ◽  
New Approach ◽  
Tip Position ◽  
Dynamic Time

In this paper, we propose a new scheme for Devanagari natural handwritten character recognition. It is primarily based on spatial similarity-based stroke clustering. A feature of a stroke consists of a string of pen-tip positions and directions at every pen-tip position along the trajectory. It uses the dynamic time warping algorithm to align handwritten strokes with stored stroke templates and determine their similarity. Experiments are carried out with the help of 25 native writers and a recognition rate of approximately 95% is achieved. Our recognizer is robust to a large range of writing style and handles variation in the number of strokes, their order, shapes and sizes and similarities among classes.

scholarly journals GNSS Precise Relative Positioning Using A Priori Relative Position in a GNSS Harsh Environment

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1355
Author(s):  
Euiho Kim
Keyword(s):  
Carrier Phase ◽  
Low Cost ◽  
A Priori ◽  
Field Tests ◽  
Satellite System ◽  
Integer Ambiguity ◽  
Double Difference ◽  
Baseline Length ◽  
Harsh Environment ◽  
Relative Positioning

To enable Global Navigation Satellite System (GNSS)-based precise relative positioning, real-time kinematic (RTK) systems have been widely used. However, an RTK system often suffers from a wrong integer ambiguity fix in the GNSS carrier phase measurements and may take a long initialization time over several minutes, particularly when the number of satellites in view is small. To facilitate a reliable GNSS carrier phase-based relative positioning with a small number of satellites in view, this paper introduces a novel GNSS carrier phase-based precise relative positioning method that uses a fixed baseline length as well as heading measurements in the beginning of the operation, which allows the fixing of integer ambiguities with rounding schemes in a short time. The integer rounding scheme developed in this paper is an iterative process that sequentially resolves integer ambiguities, and the sequential order of the integer ambiguity resolution is based on the required averaging epochs that vary for each satellite depending on the geometry between the baseline and the double difference line-of-sight vectors. The required averaging epochs with respect to various baseline lengths and heading measurement uncertainties were analyzed through simulations. Static and dynamic field tests with low cost GNSS receivers confirmed that the positioning accuracy of the proposed method was better than 10 cm and significantly outperformed a conventional RTK solution in a GNSS harsh environment.

scholarly journals High-Accuracy Attitude Determination Using Single-Difference Observables Based on Multi-Antenna GNSS Receiver with a Common Clock

2021 ◽  
Vol 13 (19) ◽  
pp. 3977
Author(s):  
Chenglong Zhang ◽  
Danan Dong ◽  
Wen Chen ◽  
Miaomiao Cai ◽  
Yu Peng ◽  
...  
Keyword(s):  
Pitch Angle ◽  
Attitude Determination ◽  
Clock Synchronization ◽  
Integer Ambiguity ◽  
Double Difference ◽  
Fiber Optic Gyroscope ◽  
Short Baseline ◽  
Practical Applications ◽  
Gnss Receiver ◽  
Single Difference

A global navigation satellite system (GNSS) receiver with multi-antenna using clock synchronization technology is a powerful piece of equipment for precise attitude determination and reducing costs. The single-difference (SD) can eliminate both the satellites and receiver clock errors with the common clock between antennas, which benefits the GNSS short-baseline attitude determination due to its lower noise, higher redundancy and stronger function model strength. However, the existence of uncalibrated phase delay (UPD) makes it difficult to obtain fixed SD attitude solutions. Therefore, the key problem for the fixed SD attitude solutions is to separate the SD UPD and fix the SD ambiguities into integers between antennas. This article introduces the one-step ambiguity substitution approach to separate the SD UPD, through which we merge the SD UPD parameter with the SD ambiguity of the reference satellite ambiguity as the new SD UPD parameter. Reconstructing the other SD ambiguities, the rank deficiency can be remedied by nature, and the new SD ambiguities can have a natural integer feature. Finally, the fixed SD baseline and attitude solutions are obtained by combining the ambiguity substitution approach with integer ambiguity resolution (IAR). To verify the effect of the ambiguity substitution approach and the advantages of the SD observables with a common clock in practical applications, we conducted static, kinematic, and vehicle experiments. In static experiments, the root mean squared errors (RMSEs) of the yaw and pitch angles obtained by the SD observables with a common clock were improved by approximately 80% and 93%, respectively, compared to double-difference (DD) observables with a common clock in multi-day attitude solutions. The kinematic results show that the dispersion of the SD-Fix in the pitch angle is two times less that of the DD-Fix, and the standard deviations (STDs) of the pitch angle for SD-Fix can reach 0.02°. Based on the feasibility, five bridges with low pitch angles in the vehicle experiment environment, which the DD observables cannot detect, were detected by the SD observables with a common clock. The attitude angles obtained by the SD observables were also consistent with the fiber optic gyroscope (FOG) inertial navigation system (INS). This research on the SD observables with a common clock provides higher accuracy.

scholarly journals 3D Modelling of Earth Kinematics in Palestine for GNSS and Geodetic Time-Dependent Positioning

2019 ◽  
Vol 8 (3) ◽  
pp. 6034-6039
Keyword(s):  
Plate Tectonics ◽  
Geodetic Network ◽  
Reference Points ◽  
Time Dependent ◽  
Relative Positioning ◽  
Jordan Valley ◽  
Local Networks ◽  
Tectonic Plates ◽  
Terrestrial Reference Frames ◽  
Gnss Positioning

The use of GNSS technologies for precise point positioning enabled the calculations for single-point observations or relative positioning of long baselines. The GNSS absolute and relative positioning techniques can be implemented between points within different tectonic plates, while the classical surveying methods start from local reference/triangulation points to near points within a few kilometers. The definition of the kinematic models of the earth has become an important role in GNSS measurements techniques and networks adjustment methods based on international terrestrial reference frames (ITRF), where the reference points can be located in different continents and tectonic plates. Thus, the position calculations in the ITRF systems are time-dependent. To satisfy the requirements of land and cadastral surveying, the bidirectional transformation between classical geodetic networks and GNSS global, regional and local networks is nowadays a primary requirement in modern geodesy. While the classical networks were defined locally assuming a static earth system, the ITRF coordinates by GNSS techniques are defined globally and directly affected by earth kinematics including plate tectonics and local crustal movements. However, Palestine has a special kinematic situation because it is located at the border between two plates; Nubia/Sinai plate and the Arabia plate along the Jordan valley line. Thus, the result is unsteady surface kinematics all over the country, which has a longitudinal shape parallel to the Jordan valley rift. Using the IGS/EUREF stations and GNSS stations data that are freely available on the internet, varying positional velocities were calculated in both magnitude and direction using years of daily available GNSS raw observations. The GNSS precise observation techniques have proven that the points of the classical networks were subjected to a kinematic situation over the years. Therefore, the Palestinian geodetic network has to be revised for kinematic effects for the integration with the modern GNSS positioning. In this work, the effect of surface movements is included in the calculations between the different ITRF coordinate systems and the classical geodetic network of Palestine. To achieve the required transformations between ITRF and the classical network, a velocities model was established and tested utilizing GIS raster interpolation. The accuracy of the modeled velocities could support 1cm in static or real-time GNSS positioning. This made it possible for the integration between geodetic measurements between different time epochs.

scholarly journals Accounting for Signal Distortion Biases for Wide-Lane and Narrow-Lane Phase Bias Estimation with Inhomogeneous Networks

2022 ◽  
Vol 14 (1) ◽  
pp. 191
Author(s):  
Chuang Shi ◽  
Yuan Tian ◽  
Fu Zheng ◽  
Yong Hu
Keyword(s):  
Large Data ◽  
Satellite System ◽  
Navigation Satellite ◽  
Signal Distortion ◽  
Bias Estimation ◽  
Data Set ◽  
Ambiguity Fixing ◽  
Wide Lane ◽  
Phase Bias ◽  
Global Navigation Satellite

Due to different designs of receiver correlators and front ends, receiver-related pseudorange biases, called signal distortion biases (SDBs), exist. Ignoring SDBs that can reach up to 0.66 cycles and 10 ns in Melbourne-Wübbena (MW) and ionosphere-free (IF) combinations can negatively affect phase bias estimation. In this contribution, we investigate the SDBs and evaluate the impacts on wide-lane (WL) and narrow-lane (NL) phase bias estimations, and further propose an approach to eliminating these SDBs to improve phase bias estimation. Based on a large data set of 302 multi-global navigation satellite system (GNSS) experiment (MGEX) stations, including 5 receiver brands, we analyze the characteristics of these SDBs The SDB characteristics of different receiver types for different GNSS systems differ from each other. Compared to the global positioning system (GPS) and BeiDou navigation satellite system (BDS), SDBs of Galileo are not significant; those of BDS-3 are significantly superior to BDS-2; Septentrio (SEPT) receivers show the most excellent consistency among all receiver types. Then, we apply the corresponding corrections to phase bias estimation for GPS, Galileo and BDS. The experimental results reveal that the calibration can greatly improve the performance of phase bias estimation. For WL phase biases estimation, the consistencies of WL phase biases among different networks for GPS, Galileo, BDS-2 and BDS-3 improve by 89%, 77%, 76% and 78%, respectively. There are scarcely any improvements of the fixing rates for Galileo due to its significantly small SDBs, while for GPS, BDS-2 and BDS-3, the WL ambiguity fixing rates can improve greatly by 13%, 27% and 14% after SDB calibrations with improvements of WL ambiguity fixing rates, the corresponding NL ambiguity fixing rates can further increase greatly, which can reach approximately 16%, 27% and 22%, respectively. Additionally, after the calibration, both WL and NL phase bias series become more stable. The standard deviations (STDs) of WL phase bias series for GPS and BDS can improve by more than 46%, while those of NL phase bias series can yield improvements of more than 13%. Ultimately, the calibration can make more WL and NL ambiguity residuals concentrated in ranges within ±0.02 cycles. All these results demonstrate that SDBs for phase bias estimation cannot be ignored and must be considered when inhomogeneous receivers are used.

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