Linear antenna arrays(LAs)can be used to accurately predict the direction of arrival(DOAs)of various targets of interest in a given area.However,under certain conditions,LA suffers from the problem of ambiguities amon...Linear antenna arrays(LAs)can be used to accurately predict the direction of arrival(DOAs)of various targets of interest in a given area.However,under certain conditions,LA suffers from the problem of ambiguities among the angles of targets,which may result inmisinterpretation of such targets.In order to cope up with such ambiguities,various techniques have been proposed.Unfortunately,none of them fully resolved such a problem because of rank deficiency and high computational cost.We aimed to resolve such a problem by proposing an algorithm using differential geometry.The proposed algorithm uses a specially designed doublet antenna array,which is made up of two individual linear arrays.Two angle observation models,ambiguous observation model(AOM)and estimated observation model(EOM),are derived for each individual array.The ambiguous set of angles is contained in the AOM,which is obtained from the corresponding array elements using differential geometry.The EOM for each array,on the other hand,contains estimated angles of all sources impinging signals on each array,as calculated by a direction-finding algorithm such as the genetic algorithm.The algorithm then contrasts the EOM of each array with its AOM,selecting the output of that array whose EOM has the minimum correlation with its corresponding AOM.In comparison to existing techniques,the proposed algorithm improves estimation accuracy and has greater precision in antenna aperture selection,resulting in improved resolution capabilities and the potential to be used more widely in practical scenarios.The simulation results using MATLAB authenticates the effectiveness of the proposed algorithm.展开更多
The Haiyang-2D altimetry mission of China is one of the first Low Earth Orbit(LEO)satellites that can receive new B1C/B2a signals from the BeiDou-3 Navigation Satellite System(BDS-3)for Precise Orbit Determination(POD...The Haiyang-2D altimetry mission of China is one of the first Low Earth Orbit(LEO)satellites that can receive new B1C/B2a signals from the BeiDou-3 Navigation Satellite System(BDS-3)for Precise Orbit Determination(POD).In this work,the achievable accuracy of the single-receiver ambiguity resolution for onboard LEO satellites is studied based on the real measurements of new BDS-3 frequencies.Under normal conditions,six BDS-3 satellites on average are visible.However,the multipath of the B1C/B2a code observations presents some patchy patterns that cause near-field variations with an amplitude of approximately 40 cm and deteriorate the ambiguity-fixed rate.By modeling those errors,for the B2a code,a remarkable reduction of 53%in the Root Mean Square(RMS)is achieved at high elevations,along with an increase of 8%in the ambiguity-fixed rates.Additionally,an analysis of the onboard antenna’s phase center offsets reveals that when compared to the solutions with float ambiguities,the estimated values in the antenna’s Z direction in the solutions with fixed ambiguities are notably smaller.The independent validation of the resulting POD using satellite laser ranging at 16 selected high-performance stations shows that the residuals are reduced by a minimum of 15.4%for ambiguity-fixed solutions with an RMS consistency of approximately 2.2 cm.Furthermore,when compared to the DORIS-derived orbits,a 4.3 cm 3D RMS consistency is achieved for the BDS-3-derived orbits,and the along-track bias is reduced from 2.9 to 0.4 cm using ambiguity fixing.展开更多
Precise point positioning with ambiguity resolution(PPP-AR)is a powerful tool for geodetic and time-constrained applications that require high precision.The performance of PPP-AR highly depends on the reliability of t...Precise point positioning with ambiguity resolution(PPP-AR)is a powerful tool for geodetic and time-constrained applications that require high precision.The performance of PPP-AR highly depends on the reliability of the correct integer carrier-phase ambiguity estimation.In this study,the performance of narrow-lane ambiguity resolution of PPP using the Least-squares AMBiguity Decorrelation(LAMBDA)and bootstrapping methods is extensively investigated using real data from 55 IGS stations over one-month in 2020.Static PPP with 24-,12-,8-,4-,2-,1-and½-h sessions using two different cutoff angles(7°and 30°)was conducted with three PPP modes:i.e.ambiguity-float and two kinds of ambiguity-fixed PPP using the LAMBDA and bootstrapping methods for narrow-lane AR,respectively.The results show that the LAMBDA method can produce more reliable results for 2 hour and shorter observation sessions com-pared with the bootstrapping method using a 7°cutoff angle.For a 30°cutoff angle,the LAMBDA method outperforms the bootstrapping method for observation sessions of 4 h and less.For long observation times,the bootstrapping method produced much more accurate coordinates compared with the LAMBDA method without considering the wrong fixes cases.The results also show that occurrences of fixing the wrong integer ambiguities using the bootstrapping method are higher than that of the LAMBDA method.展开更多
In recent years,the large Low Earth Orbit(LEO)constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems(GNSS)positioning performance.One of the important fo...In recent years,the large Low Earth Orbit(LEO)constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems(GNSS)positioning performance.One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites.The GNSS-based Precise Orbit Determination(POD)will be exclusively performed to achieve this goal,where the Integer Ambiguity Resolution(IAR)plays a key role in acquiring high-quality orbits.In this study,we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations.We perform ambiguity-fixed LEO POD for four typical missions,including Gravity Recovery and Climate Experiment(GRACE)Follow-On(GRACE-FO),Swarm,Jason-3 and Sentinel-3,using the Uncalibrated Phase Delay(UPD)products generated by our GREAT(GNSS+REsearch,Application and Teaching)software.The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits.There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias(OSB)and Integer Recovery Clock(IRC)products,indicating the good-quality of UPD products we generated.Compared to the float solution,the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites.Meanwhile,the benefit can be observed in laser ranging residuals as well,with a Standard Deviation(STD)reduction of 3–4 mm on average for the fixed solutions.Apart from the absolute orbits,the relative accuracy of the space baseline is also improved by 20–30%in the fixed solutions.The result demonstrates the superior performance of the ambiguity-fixed LEO POD,which appears as a particularly promising technique for POD of future LEO constellations.展开更多
Global navigation satellite system(GNSS)positioning depends on the correct integer ambiguity resolu-tion(AR).If the double difference equation for solving the float solution remains il-conditioned,often happening due ...Global navigation satellite system(GNSS)positioning depends on the correct integer ambiguity resolu-tion(AR).If the double difference equation for solving the float solution remains il-conditioned,often happening due to the environment complexity and the equipment mobility,the corrcct AR is difficult to achieve.Concern-ing the il-conditioned problem,methods of modifying the equation cofficient matrix are widely applied,whose effects are heavily dependent on modifying parameters.Besides,the direct inversion of the il-conditioned coef-ficient matrix can lead to a reduction in the accuracy and stability of the float solution.To solve the problem of il-conditioned matrix inversion and further improve the accuracy,the present study for the first time proves the positive definite symmetry of the coefficient matrix in AR model and employs precise integration method to the indirect inverse of cofficient matrix.AR model for the GNSS positioning and the general resolving strate-gies introduction are briefly introduced.An indirect-inversion algorithm via precise integration for il-conditioned coefficient matrix is proposed.According to the simulations and comparisons,the proposed strategy has higher precision and stability on foat solution,and less dependence on modifying parameters.展开更多
In this paper,an antenna array composed of circular array and orthogonal linear array is proposed by using the design of long and short baseline“orthogonal linear array”and the circular array ambiguity resolution de...In this paper,an antenna array composed of circular array and orthogonal linear array is proposed by using the design of long and short baseline“orthogonal linear array”and the circular array ambiguity resolution design of multi-group baseline clustering.The effectiveness of the antenna array in this paper is verified by sufficient simulation and experiment.After the system deviation correction work,it is found that in the L/S/C/X frequency bands,the ambiguity resolution probability is high,and the phase difference system error between each channel is basically the same.The angle measurement error is less than 0.5°,and the positioning error is less than 2.5 km.Notably,as the center frequency increases,calibration consistency improves,and the calibration frequency points become applicable over a wider frequency range.At a center frequency of 11.5 GHz,the calibration frequency point bandwidth extends to 1200 MHz.This combined antenna array deployment holds significant promise for a wide range of applications in contemporary wireless communication systems.展开更多
To avoid the complicated motion compensation in interferometric inverse synthetic aperture(InISAR)and achieve realtime three-dimensional(3 D)imaging,a novel approach for 3 D imaging of the target only using a single e...To avoid the complicated motion compensation in interferometric inverse synthetic aperture(InISAR)and achieve realtime three-dimensional(3 D)imaging,a novel approach for 3 D imaging of the target only using a single echo is presented.This method is based on an isolated scatterer model assumption,thus the scatterers in the beam can be extracted individually.The radial range of each scatterer is estimated by the maximal likelihood estimation.Then,the horizontal and vertical wave path difference is derived by using the phase comparison technology for each scatterer,respectively.Finally,by utilizing the relationship among the 3 D coordinates,the radial range,the horizontal and vertical wave path difference,the 3 D image of the target can be reconstructed.The reconstructed image is free from the limitation in InISAR that the image plane depends on the target's own motions and on its relative position with respect to the radar.Furthermore,a phase ambiguity resolution method is adopted to ensure the success of the 3 D imaging when phase ambiguity occurs.It can be noted that the proposed phase ambiguity resolution method only uses one antenna pair and does not require a priori knowledge,whereas the existing phase ambiguity methods may require two or more antenna pairs or a priori knowledge for phase unwarping.To evaluate the performance of the proposed method,the theoretical analyses on estimation accuracy are presented and the simulations in various scenarios are also carried out.展开更多
In order to meet the requirements of high-precision vehicle positioning in complex scenes,an observation noise adaptive robust GNSS/MIMU tight fusion model based on the gain matrix is proposed considering static zero ...In order to meet the requirements of high-precision vehicle positioning in complex scenes,an observation noise adaptive robust GNSS/MIMU tight fusion model based on the gain matrix is proposed considering static zero speed,non-integrity,attitude,and odometer constraint models.In this model,the robust equivalent gain matrix is constructed by the IGG-Ⅲmethod to weaken the influence of gross error,and the on-line adaptive update of observation noise matrix is carried out according to the change of actual observation environment,so as to improve the solution performance of filtering system and realize high-precision position,attitude and velocity measurement when GNSS signal is unlocked.A real test on a road over 600 km demonstrates that,in about 100 km shaded environment,the fixed rate of GNSS ambiguity resolution in the shaded road is 10%higher than that of GNSS only ambiguity resolution.For all the test,the positioning accuracy can reach the centimeter level in an open environment,better than 0.6 m in the tree shaded environment,better than 1.5 m in the three-dimensional traffic environment,and can still maintain a positioning accuracy of 0.1 m within 10 s when the satellite is unlocked in the tunnel scene.The proposal and verification of the algorithm model show that low-cost MIMU equipment can still achieve high-precision positioning when there are scene feature constraints,which can meet the problem of high-precision vehicle navigation and location in the urban complex environment.展开更多
Relative positioning is recognized as an important issue for vehicles in urban environments.Multi-vehicle Cooperative Positioning(CP)techniques which fuse the Global Navigation Satellite System(GNSS)and inter-vehicle ...Relative positioning is recognized as an important issue for vehicles in urban environments.Multi-vehicle Cooperative Positioning(CP)techniques which fuse the Global Navigation Satellite System(GNSS)and inter-vehicle ranging have attracted attention in improving the performance of baseline estimation between vehicles.However,current CP methods estimate the baselines separately and ignore the interactions among the positioning information of different baselines.These interactions are called’information coupling’.In this work,we propose a new multivehicle precise CP framework using the coupled information in the network based on the Carrier Differential GNSS(CDGNSS)and inter-vehicle ranging.We demonstrate the benefit of the coupled information by deriving the Cramer-Rao Lower Bound(CRLB)of the float estimation in CP.To fully use this coupled information,we propose a Whole-Net CP(WN-CP)method which consists of the Whole-Net Extended Kalman Filter(WN-EKF)as the float estimation filter,and the Partial Baseline Fixing(PBF)as the ambiguity resolution part.The WN-EKF fuses the measurements of all baselines simultaneously to improve the performance of float estimation,and the PBF strategy fixes the ambiguities of the one baseline to be estimated,instead of full ambiguity resolution,to reduce the computation load of ambiguity resolution.Field tests involving four vehicles were conducted in urban environments.The results show that the proposed WN-CP method can achieve better performance and meanwhile maintain a low computation load compared to the existing methods.展开更多
Traditional positioning methods,such as conventional Real Time Kinematic(cRTK)rely upon local reference networks to enable users to achieve high-accuracy positioning.The need for such relatively dense networks has sig...Traditional positioning methods,such as conventional Real Time Kinematic(cRTK)rely upon local reference networks to enable users to achieve high-accuracy positioning.The need for such relatively dense networks has significant cost implications.Precise Point Positioning(PPP)on the other hand is a positioning method capable of centimeter-level positioning without the need for such local networks,hence providing significant cost benefits especially in remote areas.This paper presents the state-of-the-art PPP method using both GPS and GLONASS measurements to estimate the float position solution before attempting to resolve GPS integer ambiguities.Integrity monitoring is carried out using the Imperial College Carrier-phase Receiver Autonomous Integrity Monitoring method.A new method to detect and exclude GPS base-satellite failures is developed.A base-satellite is a satellite whose measurements are differenced from other satellite’s measurements when using between-satellite-differenced measurements to estimate position.The failure detection and exclusion methods are tested using static GNSS data recorded by International GNSS Service stations both in static and dynamic processing modes.The results show that failure detection can be achieved in all cases tested and failure exclusion can be achieved for static cases.In the kinematic processing cases,failure exclusion is more difficult because the higher noise in the measurement residuals increases the difficulty to distinguish between failures associated with the base-satellite and other satellites.展开更多
Global Navigation Satellite System precise positioning using carrier phase measurements requires reliable ambiguity resolution.It is challenging to obtain continuous precise positions with a high ambiguity fixing rate...Global Navigation Satellite System precise positioning using carrier phase measurements requires reliable ambiguity resolution.It is challenging to obtain continuous precise positions with a high ambiguity fixing rate under a wide range of dynamic scenes with a single base station,thus the positioning accuracy will be degraded seriously.The Forward-Backward Combination(FBC),a common post-processing smoothing method,is simply the weighted average of the positions of forward and backward filtering.When the ambiguity fixing rate of the one-way(forward or backward)filter is low,the FBC method usually cannot provide accurate and reliable positioning results.Consequently,this paper proposed a method to improve the accuracy of positions by integrating forward and backward AR,which combines the forward and backward ambiguities instead of positions-referred to as ambiguity domain-based integration(ADBI).The purpose of ADBI is to find a reliable correct integer ambiguities by making full use of the integer nature of ambiguities and integrating the ambiguities from the forward and backward filters.Once the integer ambiguities are determined correctly and reliably with ADBI,then the positions are updated with the fixing ambiguities constrained,in which more accurate positions with high confidence can be achieved.The effectiveness of the proposed approach is validated with airborne and car-borne dynamic experiments.The experimental results demonstrated that much better accuracy of position and higher ambiguity-fixed success rate can be achieved than the traditional post-processing method.展开更多
Low-cost Global Navigation Satellite System(GNSS)devices offer a cost-effective alternative to traditional GNSS systems,making GNSS technology accessible to a wider range of applications.Nevertheless,low-cost GNSS dev...Low-cost Global Navigation Satellite System(GNSS)devices offer a cost-effective alternative to traditional GNSS systems,making GNSS technology accessible to a wider range of applications.Nevertheless,low-cost GNSS devices often face the challenges in effectively capturing and tracking satellite signals,which leads to losing the observations at certain frequencies.Moreover,the observation peculiarities of low-cost devices are in contradistinction to those of traditional geodetic GNSS receivers.In this contribution,a low-cost PPP-RTK model that considers the unique characteristics of different types of measurements is developed and its performance is fully evaluated with u-blox F9P receivers equipped with three distinctive antenna configurations:vertical dipole,microstrip patch,and helix antennas.Several static and kinematic experiments in different scenarios are conducted to verify the effectiveness of the proposed method.The results indicate that the mixed-frequency PPP-RTK model outperforms the traditional dual-frequency one with higher positioning accuracy and fixing percentage.Among the three low-cost antennas tested,the vertical dipole antenna demonstrates the best performance under static conditions and shows a comparable performance as geodetic antennas with a positioning accuracy of 0.02 m,0.01 m and 0.07 m in the east,north,and up components,respectively.Under low-speed kinematic scenarios,the helix antenna outperforms the other two with a positioning accuracy of(0.07 m,0.07 m,0.34 m).Furthermore,the helix antenna is also proved to be the best choice for vehicle navigation with an ambiguity fixing rate of over 95%and a positioning accuracy of(0.13 m,0.14 m,0.36 m).展开更多
Aiming at the problem that the traditional inter-system double-difference model is not suitable for non-overlapping signal frequencies,we propose a new inter-system double-difference model with single difference ambig...Aiming at the problem that the traditional inter-system double-difference model is not suitable for non-overlapping signal frequencies,we propose a new inter-system double-difference model with single difference ambiguity estimation,which can be applied for both overlapping and non-overlapping signal frequencies.The single difference ambiguities of all satellites and Differential Inter-System Biases(DISB)are first estimated,and the intra-system double difference ambiguities,which have integer characteristics,are then fixed.After the ambiguities are successfully fixed,high-precision coordinates and DISB can be obtained with a constructed transformation matrix.The model effectively avoids the DISB parameter filtering discontinuity caused by the reference satellite transformation and the low precision of the reference satellite single difference ambiguity calculated with the code.A zero-baseline using multiple types of receivers is selected to verify the stability of the estimated DISB.Three baselines with different lengths are selected to assess the positioning performance of the model.The ionospheric-fixed and ionospheric-float models are used for short and medium-long baselines,respectively.The results show that the Differential Inter-System Code Biases(DISCB)and Differential Inter-System Phase Biases(DISPB)have good stability regardless of the receivers type and the signal frequency used and can be calibrated to enhance the strength of the positioning model.The positioning results with three baselines of different lengths show that the proposed inter-system double-difference model can improve the positioning accuracy by 6–22%compared with the intra-system double-difference model which selects the reference satellite independently for each system.The Time to First Fix(TTFF)of the two medium-long baselines is reduced by 30%and 29%,respectively.展开更多
Integrity monitoring for precise point positioning is critical for safety-related applications.With the increasing demands of high-accuracy autonomous navigation for unmanned ground and aerial vehicles,the integrity m...Integrity monitoring for precise point positioning is critical for safety-related applications.With the increasing demands of high-accuracy autonomous navigation for unmanned ground and aerial vehicles,the integrity monitoring method of high-precision positioning has become an essential requirement.While high precision Global Navigation Satellite Systems(GNSS)positioning is widely used in such applications,there are still many difculties in the integrity monitoring method for the multi-frequency multi-GNSS undiferenced and uncombined Precise Point Positioning(PPP).The main difculties are caused by using the measurements of multiple epochs in PPP.Based on the baseline Multiple Hypothesis Solution Separation(MHSS)Advanced Receiver Autonomous Integrity Monitoring(ARAIM)algorithm,this paper discusses the feasibility of the pseudorange-based baseline ARAIM method on the single-epoch PPP based on Real-Time Kinematic(RTK)networks(PPP-RTK)framework to overcome these difculties.In addition,a new scheme is proposed to transfer the conventional PPP process into the single-epoch PPP-RTK framework.The simulation results using the proposed model are analyzed in this study.The Protection Levels(PLs)estimated by PPP Wide-lane Ambiguity Resolution(PPP-WAR)model with regional corrections can reach the meter level and the PLs estimated by PPP Ambiguity Resolution(PPP-AR)and PPP-RTK models are usually the sub-meter level.Given a horizontal Alert Limit(AL)of 1.5 m,the global coverage of availability above 99.9%for PPP-WAR,PPP-AR,and PPP-RTK can reach 92.6%,99.4%,and 99.7%respectively.The results using real kinematic data also show that tight PLs can be achieved when the observation conditions are good.展开更多
Stable and reliable high-precision satellite orbit products are the prerequisites for the positioning services with high performance.In general,the positioning accuracy depends strongly on the quality of satellite orb...Stable and reliable high-precision satellite orbit products are the prerequisites for the positioning services with high performance.In general,the positioning accuracy depends strongly on the quality of satellite orbit and clock products,especially for absolute positioning modes,such as Precise Point Positioning(PPP).With the development of real-time services,real-time Precise Orbit Determination(POD)is indispensable and mainly includes two methods:the ultra-rapid orbit prediction and the real-time filtering orbit determination.The real-time filtering method has a great potential to obtain more stable and reliable products than the ultra-rapid orbit prediction method and thus has attracted increasing attention in commercial companies and research institutes.However,several key issues should be resolved,including the refinement of satellite dynamic stochastic models,adaptive filtering for irregular satellite motions,rapid convergence,and real-time Ambiguity Resolution(AR).This paper reviews and summarizes the current research progress in real-time filtering POD with a focus on the aforementioned issues.In addition,the real-time filtering orbit determination software developed by our group is introduced,and some of the latest results are evaluated.The Three-Dimensional(3D)real-time orbit accuracy of GPS and Galileo satellites is better than 5 cm with AR.In terms of the convergence time and accuracy of kinematic PPP AR,the better performance of the filter orbit products is validated compared to the ultra-rapid orbit products.展开更多
Precise Point Positioning(PPP)with Ambiguity Resolution(AR)is an important high-precision positioning technique that is gaining popularity in geodetic and geophysical applications.The implementation of PPP-AR requires...Precise Point Positioning(PPP)with Ambiguity Resolution(AR)is an important high-precision positioning technique that is gaining popularity in geodetic and geophysical applications.The implementation of PPP-AR requires precise products such as orbits,clocks,code,and phase biases.As one of the analysis centers of the International Global Navigation Satellite System(GNSS)Service(IGS),the Wuhan University Multi-GNSS experiment(WUM)Analysis Center(AC)has provided multi-GNSS Observable-Specific Bias(OSB)products with the associated orbit and clock products.In this article,we first introduce the models and generation strategies of WUM rapid phase clock/bias products and orbit-related products(with a latency of less than 16 h).Then,we assess the performance of these products by comparing them with those of other ACs and by testing the PPP-AR positioning precision,using data from Day of the Year(DOY)047 to DOY 078 in 2022.It is found that the peak-to-peak value of phase OSBs is within 2 ns,and their fluctuations are caused by the clock day boundary discontinuities.The associated Global Positioning System(GPS)orbits have the best consistency with European Space Agency(ESA)products,and those of other systems rank in the medium place.GLObal NAvigation Satellite System(GLONASS)clocks show slightly inconsistency with other ACs’due to the antenna thrust power adopted,while the phase clocks of other GNSSs show no distortion compared with legacy clocks.With well-estimated phase products for Precise Orbit Determination(POD),the intrinsic precision is improved by 14%,17%,and 24%for GPS,Galileo navigation satellite system(Galileo),and BeiDou-3 Navigation Satellite System(BDS-3),respectively.The root mean square of PPP-AR using our products in static mode with respect to IGS weekly solutions can reach 0.16 cm,0.16 cm,and 0.44 cm in the east,north,and up directions,respectively.The multi-GNSS wide-lane ambiguity fixing rates are all above 90%,while the narrow-lane fixing rates above 80%.In conclusion,the phase OSB products at WUM have good precision and performance,which will benefit multi-GNSS PPP-AR and POD.展开更多
PPP-RTK which takes full advantages of both Real-Time Kinematic(RTK)and Precise Point Positioning(PPP),is able to provide centimeter-level positioning accuracy with rapid integer Ambiguity Resolution(AR).In recent yea...PPP-RTK which takes full advantages of both Real-Time Kinematic(RTK)and Precise Point Positioning(PPP),is able to provide centimeter-level positioning accuracy with rapid integer Ambiguity Resolution(AR).In recent years,with the development of BeiDou Navigation Satellite System(BDS)and Galileo navigation satellite system(Galileo)as well as the modernization of Global Positioning System(GPS)and GLObal NAvigation Satellite System(GLONASS),more than 140 Global Navigation Satellite System(GNSS)satellites are available.Particularly,the new-generation GNSS satellites are capable of transmitting signals on three or more frequencies.Multi-GNSS and multi-frequency observations become available and can be used to enhance the performance of PPP-RTK.In this contribution,we develop a multi-GNSS and multi-frequency PPP-RTK model,which uses all the available GNSS observations,and comprehensively evaluate its performance in urban environments from the perspectives of positioning accuracy,convergence and fxing percentage.In this method,the precise atmospheric corrections are derived from the multi-frequency and multi-GNSS observations of a regional network,and then disseminated to users to achieve PPP rapid AR.Furthermore,a cascade ambiguity fxing strategy using Extra‐Wide‐Lane(EWL),Wide-Lane(WL)and L1 ambiguities is employed to improve the performance of ambiguity fxing in the urban environments.Vehicle experiments in diferent scenarios such as suburbs,overpasses,and tunnels are conducted to validate the proposed method.In suburbs,an accuracy of within 2 cm in the horizontal direction and 4 cm in the vertical direction,with the fxing percentage of 93.7%can be achieved.Compared to the GPS-only solution,the positioning accuracy is improved by 87.6%.In urban environments where signals are interrupted frequently,a fast ambiguity re-fxing can be achieved within 5 s.Moreover,multifrequency GNSS signals can further improve the positioning performance of PPP-RTK,particularly in the case of small amount of observations.These results demonstrate that the multi-frequency and multi-GNSS PPP-RTK is a promising tool for supporting precise vehicle navigation.展开更多
The PPP–RTK method,which combines the concepts of Precise of Point Positioning(PPP)and Real-Time Kinematic(RTK),is proposed to provide a centimeter-accuracy positioning service for an unlimited number of users.Recent...The PPP–RTK method,which combines the concepts of Precise of Point Positioning(PPP)and Real-Time Kinematic(RTK),is proposed to provide a centimeter-accuracy positioning service for an unlimited number of users.Recently,the PPP–RTK technique is becoming a promising tool for emerging applications such as autonomous vehicles and unmanned logistics as it has several advantages including high precision,full flexibility,and good privacy.This paper gives a detailed review of PPP–RTK focusing on its implementation methods,recent achievements as well as challenges and opportunities.Firstly,the fundamental approach to implement PPP–RTK is described and an overview of the research on key techniques,such as Uncalibrated Phase Delay(UPD)estimation,precise atmospheric correction retrieval and modeling,and fast PPP ambiguity resolution,is given.Then,the recent efforts and progress are addressed,such as improving the performance of PPP–RTK by combining multi-GNSS and multi-frequency observations,single-frequency PPP–RTK for low-cost devices,and PPP–RTK for vehicle navigation.Also,the system construction and applications based on the PPP–RTK method are summarized.Moreover,the main issues that impact PPP–RTK performance are highlighted,including signal occlusion in complex urban areas and atmosphere modeling in extreme weather events.The new opportunities brought by the rapid development of low-cost markets,multiple sensors,and new-generation Low Earth Orbit(LEO)navigation constellation are also discussed.Finally,the paper concludes with some comments and the prospects for future research.展开更多
The BeiDou navigation satellite system with global coverage(BDS-3)has been fully operational since July 2020 and provides comprehensive services to global users.BDS-3 transmits several new navigational signals based o...The BeiDou navigation satellite system with global coverage(BDS-3)has been fully operational since July 2020 and provides comprehensive services to global users.BDS-3 transmits several new navigational signals based on the signals inherited from the BeiDou navigation satellite(regional)system(BDS-2).Previous studies focused on the positioning performance of BDS-2 plus BDS-3 and that of combining BDS-3 and other Global Navigation Satellite Systems(GNSSs),but there was no in-depth discussion on the positioning performance of the BDS-3-only.In this contribution,the BDS-3-only Real-Time Kinematic(RTK)positioning is analysed using the data collected in zero and short baselines in Wuhan,China.The RTK model based on Single-Differenced is first presented,and the BDS-3-only RTK positioning in cases of single and dual-frequencies is evaluated with the model in terms of the empirical integer ambiguity resolution success rates and positioning accuracy.Our numerical tests suggest two major findings.First,the positioning performance for the B1I and B3I retained from BDS-2 and the new frequency B1C is comparable,while that for the new frequency B2a is poorer.Second,the positioning performance of the new frequency combination of the B1C+B2a is not as good as that of the B1C only,owing to the unrealistic stochastic model used.展开更多
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 ...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.展开更多
文摘Linear antenna arrays(LAs)can be used to accurately predict the direction of arrival(DOAs)of various targets of interest in a given area.However,under certain conditions,LA suffers from the problem of ambiguities among the angles of targets,which may result inmisinterpretation of such targets.In order to cope up with such ambiguities,various techniques have been proposed.Unfortunately,none of them fully resolved such a problem because of rank deficiency and high computational cost.We aimed to resolve such a problem by proposing an algorithm using differential geometry.The proposed algorithm uses a specially designed doublet antenna array,which is made up of two individual linear arrays.Two angle observation models,ambiguous observation model(AOM)and estimated observation model(EOM),are derived for each individual array.The ambiguous set of angles is contained in the AOM,which is obtained from the corresponding array elements using differential geometry.The EOM for each array,on the other hand,contains estimated angles of all sources impinging signals on each array,as calculated by a direction-finding algorithm such as the genetic algorithm.The algorithm then contrasts the EOM of each array with its AOM,selecting the output of that array whose EOM has the minimum correlation with its corresponding AOM.In comparison to existing techniques,the proposed algorithm improves estimation accuracy and has greater precision in antenna aperture selection,resulting in improved resolution capabilities and the potential to be used more widely in practical scenarios.The simulation results using MATLAB authenticates the effectiveness of the proposed algorithm.
基金This work is partly sponsored by China Postdoctoral Science Foundation(Grant Nos.2021M702507)the National Natural Science Foundation of China(Grant Nos.42204020,42004020,42074032,41931075 and 42030109)the Key Research and Development Plan Project of Hubei Province(Grant Nos.2020BIB006).
文摘The Haiyang-2D altimetry mission of China is one of the first Low Earth Orbit(LEO)satellites that can receive new B1C/B2a signals from the BeiDou-3 Navigation Satellite System(BDS-3)for Precise Orbit Determination(POD).In this work,the achievable accuracy of the single-receiver ambiguity resolution for onboard LEO satellites is studied based on the real measurements of new BDS-3 frequencies.Under normal conditions,six BDS-3 satellites on average are visible.However,the multipath of the B1C/B2a code observations presents some patchy patterns that cause near-field variations with an amplitude of approximately 40 cm and deteriorate the ambiguity-fixed rate.By modeling those errors,for the B2a code,a remarkable reduction of 53%in the Root Mean Square(RMS)is achieved at high elevations,along with an increase of 8%in the ambiguity-fixed rates.Additionally,an analysis of the onboard antenna’s phase center offsets reveals that when compared to the solutions with float ambiguities,the estimated values in the antenna’s Z direction in the solutions with fixed ambiguities are notably smaller.The independent validation of the resulting POD using satellite laser ranging at 16 selected high-performance stations shows that the residuals are reduced by a minimum of 15.4%for ambiguity-fixed solutions with an RMS consistency of approximately 2.2 cm.Furthermore,when compared to the DORIS-derived orbits,a 4.3 cm 3D RMS consistency is achieved for the BDS-3-derived orbits,and the along-track bias is reduced from 2.9 to 0.4 cm using ambiguity fixing.
文摘Precise point positioning with ambiguity resolution(PPP-AR)is a powerful tool for geodetic and time-constrained applications that require high precision.The performance of PPP-AR highly depends on the reliability of the correct integer carrier-phase ambiguity estimation.In this study,the performance of narrow-lane ambiguity resolution of PPP using the Least-squares AMBiguity Decorrelation(LAMBDA)and bootstrapping methods is extensively investigated using real data from 55 IGS stations over one-month in 2020.Static PPP with 24-,12-,8-,4-,2-,1-and½-h sessions using two different cutoff angles(7°and 30°)was conducted with three PPP modes:i.e.ambiguity-float and two kinds of ambiguity-fixed PPP using the LAMBDA and bootstrapping methods for narrow-lane AR,respectively.The results show that the LAMBDA method can produce more reliable results for 2 hour and shorter observation sessions com-pared with the bootstrapping method using a 7°cutoff angle.For a 30°cutoff angle,the LAMBDA method outperforms the bootstrapping method for observation sessions of 4 h and less.For long observation times,the bootstrapping method produced much more accurate coordinates compared with the LAMBDA method without considering the wrong fixes cases.The results also show that occurrences of fixing the wrong integer ambiguities using the bootstrapping method are higher than that of the LAMBDA method.
基金National Natural Science Foundation of China[41974027]Sino-German mobility programme[M-0054].
文摘In recent years,the large Low Earth Orbit(LEO)constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems(GNSS)positioning performance.One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites.The GNSS-based Precise Orbit Determination(POD)will be exclusively performed to achieve this goal,where the Integer Ambiguity Resolution(IAR)plays a key role in acquiring high-quality orbits.In this study,we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations.We perform ambiguity-fixed LEO POD for four typical missions,including Gravity Recovery and Climate Experiment(GRACE)Follow-On(GRACE-FO),Swarm,Jason-3 and Sentinel-3,using the Uncalibrated Phase Delay(UPD)products generated by our GREAT(GNSS+REsearch,Application and Teaching)software.The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits.There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias(OSB)and Integer Recovery Clock(IRC)products,indicating the good-quality of UPD products we generated.Compared to the float solution,the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites.Meanwhile,the benefit can be observed in laser ranging residuals as well,with a Standard Deviation(STD)reduction of 3–4 mm on average for the fixed solutions.Apart from the absolute orbits,the relative accuracy of the space baseline is also improved by 20–30%in the fixed solutions.The result demonstrates the superior performance of the ambiguity-fixed LEO POD,which appears as a particularly promising technique for POD of future LEO constellations.
文摘Global navigation satellite system(GNSS)positioning depends on the correct integer ambiguity resolu-tion(AR).If the double difference equation for solving the float solution remains il-conditioned,often happening due to the environment complexity and the equipment mobility,the corrcct AR is difficult to achieve.Concern-ing the il-conditioned problem,methods of modifying the equation cofficient matrix are widely applied,whose effects are heavily dependent on modifying parameters.Besides,the direct inversion of the il-conditioned coef-ficient matrix can lead to a reduction in the accuracy and stability of the float solution.To solve the problem of il-conditioned matrix inversion and further improve the accuracy,the present study for the first time proves the positive definite symmetry of the coefficient matrix in AR model and employs precise integration method to the indirect inverse of cofficient matrix.AR model for the GNSS positioning and the general resolving strate-gies introduction are briefly introduced.An indirect-inversion algorithm via precise integration for il-conditioned coefficient matrix is proposed.According to the simulations and comparisons,the proposed strategy has higher precision and stability on foat solution,and less dependence on modifying parameters.
文摘In this paper,an antenna array composed of circular array and orthogonal linear array is proposed by using the design of long and short baseline“orthogonal linear array”and the circular array ambiguity resolution design of multi-group baseline clustering.The effectiveness of the antenna array in this paper is verified by sufficient simulation and experiment.After the system deviation correction work,it is found that in the L/S/C/X frequency bands,the ambiguity resolution probability is high,and the phase difference system error between each channel is basically the same.The angle measurement error is less than 0.5°,and the positioning error is less than 2.5 km.Notably,as the center frequency increases,calibration consistency improves,and the calibration frequency points become applicable over a wider frequency range.At a center frequency of 11.5 GHz,the calibration frequency point bandwidth extends to 1200 MHz.This combined antenna array deployment holds significant promise for a wide range of applications in contemporary wireless communication systems.
基金supported by the Science and Technique Commission Foundation of Fujian Province(2018H6023)。
文摘To avoid the complicated motion compensation in interferometric inverse synthetic aperture(InISAR)and achieve realtime three-dimensional(3 D)imaging,a novel approach for 3 D imaging of the target only using a single echo is presented.This method is based on an isolated scatterer model assumption,thus the scatterers in the beam can be extracted individually.The radial range of each scatterer is estimated by the maximal likelihood estimation.Then,the horizontal and vertical wave path difference is derived by using the phase comparison technology for each scatterer,respectively.Finally,by utilizing the relationship among the 3 D coordinates,the radial range,the horizontal and vertical wave path difference,the 3 D image of the target can be reconstructed.The reconstructed image is free from the limitation in InISAR that the image plane depends on the target's own motions and on its relative position with respect to the radar.Furthermore,a phase ambiguity resolution method is adopted to ensure the success of the 3 D imaging when phase ambiguity occurs.It can be noted that the proposed phase ambiguity resolution method only uses one antenna pair and does not require a priori knowledge,whereas the existing phase ambiguity methods may require two or more antenna pairs or a priori knowledge for phase unwarping.To evaluate the performance of the proposed method,the theoretical analyses on estimation accuracy are presented and the simulations in various scenarios are also carried out.
基金Youth Program of National Natural Science Foundation of China (No. 41904029)Scientific Research Project of Beijing Educational Committee (No. KM202010016009)。
文摘In order to meet the requirements of high-precision vehicle positioning in complex scenes,an observation noise adaptive robust GNSS/MIMU tight fusion model based on the gain matrix is proposed considering static zero speed,non-integrity,attitude,and odometer constraint models.In this model,the robust equivalent gain matrix is constructed by the IGG-Ⅲmethod to weaken the influence of gross error,and the on-line adaptive update of observation noise matrix is carried out according to the change of actual observation environment,so as to improve the solution performance of filtering system and realize high-precision position,attitude and velocity measurement when GNSS signal is unlocked.A real test on a road over 600 km demonstrates that,in about 100 km shaded environment,the fixed rate of GNSS ambiguity resolution in the shaded road is 10%higher than that of GNSS only ambiguity resolution.For all the test,the positioning accuracy can reach the centimeter level in an open environment,better than 0.6 m in the tree shaded environment,better than 1.5 m in the three-dimensional traffic environment,and can still maintain a positioning accuracy of 0.1 m within 10 s when the satellite is unlocked in the tunnel scene.The proposal and verification of the algorithm model show that low-cost MIMU equipment can still achieve high-precision positioning when there are scene feature constraints,which can meet the problem of high-precision vehicle navigation and location in the urban complex environment.
基金supported by the National Natural Science Foundation of China(No.61901015)。
文摘Relative positioning is recognized as an important issue for vehicles in urban environments.Multi-vehicle Cooperative Positioning(CP)techniques which fuse the Global Navigation Satellite System(GNSS)and inter-vehicle ranging have attracted attention in improving the performance of baseline estimation between vehicles.However,current CP methods estimate the baselines separately and ignore the interactions among the positioning information of different baselines.These interactions are called’information coupling’.In this work,we propose a new multivehicle precise CP framework using the coupled information in the network based on the Carrier Differential GNSS(CDGNSS)and inter-vehicle ranging.We demonstrate the benefit of the coupled information by deriving the Cramer-Rao Lower Bound(CRLB)of the float estimation in CP.To fully use this coupled information,we propose a Whole-Net CP(WN-CP)method which consists of the Whole-Net Extended Kalman Filter(WN-EKF)as the float estimation filter,and the Partial Baseline Fixing(PBF)as the ambiguity resolution part.The WN-EKF fuses the measurements of all baselines simultaneously to improve the performance of float estimation,and the PBF strategy fixes the ambiguities of the one baseline to be estimated,instead of full ambiguity resolution,to reduce the computation load of ambiguity resolution.Field tests involving four vehicles were conducted in urban environments.The results show that the proposed WN-CP method can achieve better performance and meanwhile maintain a low computation load compared to the existing methods.
文摘Traditional positioning methods,such as conventional Real Time Kinematic(cRTK)rely upon local reference networks to enable users to achieve high-accuracy positioning.The need for such relatively dense networks has significant cost implications.Precise Point Positioning(PPP)on the other hand is a positioning method capable of centimeter-level positioning without the need for such local networks,hence providing significant cost benefits especially in remote areas.This paper presents the state-of-the-art PPP method using both GPS and GLONASS measurements to estimate the float position solution before attempting to resolve GPS integer ambiguities.Integrity monitoring is carried out using the Imperial College Carrier-phase Receiver Autonomous Integrity Monitoring method.A new method to detect and exclude GPS base-satellite failures is developed.A base-satellite is a satellite whose measurements are differenced from other satellite’s measurements when using between-satellite-differenced measurements to estimate position.The failure detection and exclusion methods are tested using static GNSS data recorded by International GNSS Service stations both in static and dynamic processing modes.The results show that failure detection can be achieved in all cases tested and failure exclusion can be achieved for static cases.In the kinematic processing cases,failure exclusion is more difficult because the higher noise in the measurement residuals increases the difficulty to distinguish between failures associated with the base-satellite and other satellites.
基金the National Science Fund for Distinguished Young Scholars(Grant No.41825009)the Funds for Creative Research Groups of China(Grant No.41721003)Changjiang Scholars program.
文摘Global Navigation Satellite System precise positioning using carrier phase measurements requires reliable ambiguity resolution.It is challenging to obtain continuous precise positions with a high ambiguity fixing rate under a wide range of dynamic scenes with a single base station,thus the positioning accuracy will be degraded seriously.The Forward-Backward Combination(FBC),a common post-processing smoothing method,is simply the weighted average of the positions of forward and backward filtering.When the ambiguity fixing rate of the one-way(forward or backward)filter is low,the FBC method usually cannot provide accurate and reliable positioning results.Consequently,this paper proposed a method to improve the accuracy of positions by integrating forward and backward AR,which combines the forward and backward ambiguities instead of positions-referred to as ambiguity domain-based integration(ADBI).The purpose of ADBI is to find a reliable correct integer ambiguities by making full use of the integer nature of ambiguities and integrating the ambiguities from the forward and backward filters.Once the integer ambiguities are determined correctly and reliably with ADBI,then the positions are updated with the fixing ambiguities constrained,in which more accurate positions with high confidence can be achieved.The effectiveness of the proposed approach is validated with airborne and car-borne dynamic experiments.The experimental results demonstrated that much better accuracy of position and higher ambiguity-fixed success rate can be achieved than the traditional post-processing method.
基金National Natural Science Foundation of China,41974027,Xingxing Li42204017,Xin Li+2 种基金National Postdoctoral Program for Innovative Talents,China,BX20220239,Xin Lithe special fund of Hubei Luojia Laboratory,220100006,Xin Lithe Fundamental Research Funds for the Central Universities,2042022kf1001,Xin Li.
文摘Low-cost Global Navigation Satellite System(GNSS)devices offer a cost-effective alternative to traditional GNSS systems,making GNSS technology accessible to a wider range of applications.Nevertheless,low-cost GNSS devices often face the challenges in effectively capturing and tracking satellite signals,which leads to losing the observations at certain frequencies.Moreover,the observation peculiarities of low-cost devices are in contradistinction to those of traditional geodetic GNSS receivers.In this contribution,a low-cost PPP-RTK model that considers the unique characteristics of different types of measurements is developed and its performance is fully evaluated with u-blox F9P receivers equipped with three distinctive antenna configurations:vertical dipole,microstrip patch,and helix antennas.Several static and kinematic experiments in different scenarios are conducted to verify the effectiveness of the proposed method.The results indicate that the mixed-frequency PPP-RTK model outperforms the traditional dual-frequency one with higher positioning accuracy and fixing percentage.Among the three low-cost antennas tested,the vertical dipole antenna demonstrates the best performance under static conditions and shows a comparable performance as geodetic antennas with a positioning accuracy of 0.02 m,0.01 m and 0.07 m in the east,north,and up components,respectively.Under low-speed kinematic scenarios,the helix antenna outperforms the other two with a positioning accuracy of(0.07 m,0.07 m,0.34 m).Furthermore,the helix antenna is also proved to be the best choice for vehicle navigation with an ambiguity fixing rate of over 95%and a positioning accuracy of(0.13 m,0.14 m,0.36 m).
基金This work was jointly supported by the National Key Research Program of China Collaborative Precision Positioning Project(No.2016YFB0501900)the National Natural Science Foundation of China(Grant No.41774017).
文摘Aiming at the problem that the traditional inter-system double-difference model is not suitable for non-overlapping signal frequencies,we propose a new inter-system double-difference model with single difference ambiguity estimation,which can be applied for both overlapping and non-overlapping signal frequencies.The single difference ambiguities of all satellites and Differential Inter-System Biases(DISB)are first estimated,and the intra-system double difference ambiguities,which have integer characteristics,are then fixed.After the ambiguities are successfully fixed,high-precision coordinates and DISB can be obtained with a constructed transformation matrix.The model effectively avoids the DISB parameter filtering discontinuity caused by the reference satellite transformation and the low precision of the reference satellite single difference ambiguity calculated with the code.A zero-baseline using multiple types of receivers is selected to verify the stability of the estimated DISB.Three baselines with different lengths are selected to assess the positioning performance of the model.The ionospheric-fixed and ionospheric-float models are used for short and medium-long baselines,respectively.The results show that the Differential Inter-System Code Biases(DISCB)and Differential Inter-System Phase Biases(DISPB)have good stability regardless of the receivers type and the signal frequency used and can be calibrated to enhance the strength of the positioning model.The positioning results with three baselines of different lengths show that the proposed inter-system double-difference model can improve the positioning accuracy by 6–22%compared with the intra-system double-difference model which selects the reference satellite independently for each system.The Time to First Fix(TTFF)of the two medium-long baselines is reduced by 30%and 29%,respectively.
文摘Integrity monitoring for precise point positioning is critical for safety-related applications.With the increasing demands of high-accuracy autonomous navigation for unmanned ground and aerial vehicles,the integrity monitoring method of high-precision positioning has become an essential requirement.While high precision Global Navigation Satellite Systems(GNSS)positioning is widely used in such applications,there are still many difculties in the integrity monitoring method for the multi-frequency multi-GNSS undiferenced and uncombined Precise Point Positioning(PPP).The main difculties are caused by using the measurements of multiple epochs in PPP.Based on the baseline Multiple Hypothesis Solution Separation(MHSS)Advanced Receiver Autonomous Integrity Monitoring(ARAIM)algorithm,this paper discusses the feasibility of the pseudorange-based baseline ARAIM method on the single-epoch PPP based on Real-Time Kinematic(RTK)networks(PPP-RTK)framework to overcome these difculties.In addition,a new scheme is proposed to transfer the conventional PPP process into the single-epoch PPP-RTK framework.The simulation results using the proposed model are analyzed in this study.The Protection Levels(PLs)estimated by PPP Wide-lane Ambiguity Resolution(PPP-WAR)model with regional corrections can reach the meter level and the PLs estimated by PPP Ambiguity Resolution(PPP-AR)and PPP-RTK models are usually the sub-meter level.Given a horizontal Alert Limit(AL)of 1.5 m,the global coverage of availability above 99.9%for PPP-WAR,PPP-AR,and PPP-RTK can reach 92.6%,99.4%,and 99.7%respectively.The results using real kinematic data also show that tight PLs can be achieved when the observation conditions are good.
基金National Natural Science Foundation of China(Grand No.41904021).
文摘Stable and reliable high-precision satellite orbit products are the prerequisites for the positioning services with high performance.In general,the positioning accuracy depends strongly on the quality of satellite orbit and clock products,especially for absolute positioning modes,such as Precise Point Positioning(PPP).With the development of real-time services,real-time Precise Orbit Determination(POD)is indispensable and mainly includes two methods:the ultra-rapid orbit prediction and the real-time filtering orbit determination.The real-time filtering method has a great potential to obtain more stable and reliable products than the ultra-rapid orbit prediction method and thus has attracted increasing attention in commercial companies and research institutes.However,several key issues should be resolved,including the refinement of satellite dynamic stochastic models,adaptive filtering for irregular satellite motions,rapid convergence,and real-time Ambiguity Resolution(AR).This paper reviews and summarizes the current research progress in real-time filtering POD with a focus on the aforementioned issues.In addition,the real-time filtering orbit determination software developed by our group is introduced,and some of the latest results are evaluated.The Three-Dimensional(3D)real-time orbit accuracy of GPS and Galileo satellites is better than 5 cm with AR.In terms of the convergence time and accuracy of kinematic PPP AR,the better performance of the filter orbit products is validated compared to the ultra-rapid orbit products.
基金Hubei Luojia Laboratory(No.220100021)National Science Foundation of China(No.42025401)Fundamental Research Funds for the Central Universities(Nos.2042022kf1035,2042022kf1196).
文摘Precise Point Positioning(PPP)with Ambiguity Resolution(AR)is an important high-precision positioning technique that is gaining popularity in geodetic and geophysical applications.The implementation of PPP-AR requires precise products such as orbits,clocks,code,and phase biases.As one of the analysis centers of the International Global Navigation Satellite System(GNSS)Service(IGS),the Wuhan University Multi-GNSS experiment(WUM)Analysis Center(AC)has provided multi-GNSS Observable-Specific Bias(OSB)products with the associated orbit and clock products.In this article,we first introduce the models and generation strategies of WUM rapid phase clock/bias products and orbit-related products(with a latency of less than 16 h).Then,we assess the performance of these products by comparing them with those of other ACs and by testing the PPP-AR positioning precision,using data from Day of the Year(DOY)047 to DOY 078 in 2022.It is found that the peak-to-peak value of phase OSBs is within 2 ns,and their fluctuations are caused by the clock day boundary discontinuities.The associated Global Positioning System(GPS)orbits have the best consistency with European Space Agency(ESA)products,and those of other systems rank in the medium place.GLObal NAvigation Satellite System(GLONASS)clocks show slightly inconsistency with other ACs’due to the antenna thrust power adopted,while the phase clocks of other GNSSs show no distortion compared with legacy clocks.With well-estimated phase products for Precise Orbit Determination(POD),the intrinsic precision is improved by 14%,17%,and 24%for GPS,Galileo navigation satellite system(Galileo),and BeiDou-3 Navigation Satellite System(BDS-3),respectively.The root mean square of PPP-AR using our products in static mode with respect to IGS weekly solutions can reach 0.16 cm,0.16 cm,and 0.44 cm in the east,north,and up directions,respectively.The multi-GNSS wide-lane ambiguity fixing rates are all above 90%,while the narrow-lane fixing rates above 80%.In conclusion,the phase OSB products at WUM have good precision and performance,which will benefit multi-GNSS PPP-AR and POD.
基金supported by the National Natural Science Foundation of China(Grant 41974027 and Grant 41974029)the Sino-German mobility program(Grant No.M0054)the Technology Innovation Special Project(Major program)of Hubei Province of China(Grant No.2019AAA043).
文摘PPP-RTK which takes full advantages of both Real-Time Kinematic(RTK)and Precise Point Positioning(PPP),is able to provide centimeter-level positioning accuracy with rapid integer Ambiguity Resolution(AR).In recent years,with the development of BeiDou Navigation Satellite System(BDS)and Galileo navigation satellite system(Galileo)as well as the modernization of Global Positioning System(GPS)and GLObal NAvigation Satellite System(GLONASS),more than 140 Global Navigation Satellite System(GNSS)satellites are available.Particularly,the new-generation GNSS satellites are capable of transmitting signals on three or more frequencies.Multi-GNSS and multi-frequency observations become available and can be used to enhance the performance of PPP-RTK.In this contribution,we develop a multi-GNSS and multi-frequency PPP-RTK model,which uses all the available GNSS observations,and comprehensively evaluate its performance in urban environments from the perspectives of positioning accuracy,convergence and fxing percentage.In this method,the precise atmospheric corrections are derived from the multi-frequency and multi-GNSS observations of a regional network,and then disseminated to users to achieve PPP rapid AR.Furthermore,a cascade ambiguity fxing strategy using Extra‐Wide‐Lane(EWL),Wide-Lane(WL)and L1 ambiguities is employed to improve the performance of ambiguity fxing in the urban environments.Vehicle experiments in diferent scenarios such as suburbs,overpasses,and tunnels are conducted to validate the proposed method.In suburbs,an accuracy of within 2 cm in the horizontal direction and 4 cm in the vertical direction,with the fxing percentage of 93.7%can be achieved.Compared to the GPS-only solution,the positioning accuracy is improved by 87.6%.In urban environments where signals are interrupted frequently,a fast ambiguity re-fxing can be achieved within 5 s.Moreover,multifrequency GNSS signals can further improve the positioning performance of PPP-RTK,particularly in the case of small amount of observations.These results demonstrate that the multi-frequency and multi-GNSS PPP-RTK is a promising tool for supporting precise vehicle navigation.
基金National Science Fund for Distinguished Young Scholars(Grant No.41825009)National Postdoctoral Program for Innovative Talents,China(No.BX20220239)+1 种基金Fundamental Research Funds for the Central Universities(2042022kf1001)Project Supported by the Special Fund of Hubei Luojia Laboratory(220100006).
文摘The PPP–RTK method,which combines the concepts of Precise of Point Positioning(PPP)and Real-Time Kinematic(RTK),is proposed to provide a centimeter-accuracy positioning service for an unlimited number of users.Recently,the PPP–RTK technique is becoming a promising tool for emerging applications such as autonomous vehicles and unmanned logistics as it has several advantages including high precision,full flexibility,and good privacy.This paper gives a detailed review of PPP–RTK focusing on its implementation methods,recent achievements as well as challenges and opportunities.Firstly,the fundamental approach to implement PPP–RTK is described and an overview of the research on key techniques,such as Uncalibrated Phase Delay(UPD)estimation,precise atmospheric correction retrieval and modeling,and fast PPP ambiguity resolution,is given.Then,the recent efforts and progress are addressed,such as improving the performance of PPP–RTK by combining multi-GNSS and multi-frequency observations,single-frequency PPP–RTK for low-cost devices,and PPP–RTK for vehicle navigation.Also,the system construction and applications based on the PPP–RTK method are summarized.Moreover,the main issues that impact PPP–RTK performance are highlighted,including signal occlusion in complex urban areas and atmosphere modeling in extreme weather events.The new opportunities brought by the rapid development of low-cost markets,multiple sensors,and new-generation Low Earth Orbit(LEO)navigation constellation are also discussed.Finally,the paper concludes with some comments and the prospects for future research.
基金the National Natural Science Foundation of China(Grant Nos.41604031 and 41774042)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(Grant No.YJKYYQ20190063)+1 种基金the BDS Industrialization Project(Grant No.GFZX030302030201-2)the National Key Research Program of China Collaborative Precision Positioning Project(Grant No.2016YFB0501900).
文摘The BeiDou navigation satellite system with global coverage(BDS-3)has been fully operational since July 2020 and provides comprehensive services to global users.BDS-3 transmits several new navigational signals based on the signals inherited from the BeiDou navigation satellite(regional)system(BDS-2).Previous studies focused on the positioning performance of BDS-2 plus BDS-3 and that of combining BDS-3 and other Global Navigation Satellite Systems(GNSSs),but there was no in-depth discussion on the positioning performance of the BDS-3-only.In this contribution,the BDS-3-only Real-Time Kinematic(RTK)positioning is analysed using the data collected in zero and short baselines in Wuhan,China.The RTK model based on Single-Differenced is first presented,and the BDS-3-only RTK positioning in cases of single and dual-frequencies is evaluated with the model in terms of the empirical integer ambiguity resolution success rates and positioning accuracy.Our numerical tests suggest two major findings.First,the positioning performance for the B1I and B3I retained from BDS-2 and the new frequency B1C is comparable,while that for the new frequency B2a is poorer.Second,the positioning performance of the new frequency combination of the B1C+B2a is not as good as that of the B1C only,owing to the unrealistic stochastic model used.
基金the National Natural Science Funds of China(41874030)The Scientific and Technological Innovation Plan from Shanghai Science and Technology Committee(18511101801)+1 种基金The National Key Research and Development Program of China(2017YFA0603102)the Fundamental Research Funds for the Central Universities.
文摘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.
