Formation flight of multiple Unmanned Aerial Vehicles(UAVs)is expected to bring significant benefits to a wide range of applications.Accurate and reliable relative position information is a prerequisite to safely main...Formation flight of multiple Unmanned Aerial Vehicles(UAVs)is expected to bring significant benefits to a wide range of applications.Accurate and reliable relative position information is a prerequisite to safely maintain a fairly close distance between UAVs and to achieve inner-system collision avoidance.However,Global Navigation Satellite System(GNSS)measurements are vulnerable to erroneous signals in urban canyons,which could potentially lead to catastrophic consequences.Accordingly,on the basis of performing relative positioning with double differenced pseudoranges,this paper develops an integrity monitoring framework to improve navigation integrity(a measure of reliability)in urban environments.On the one hand,this framework includes a fault detection and exclusion scheme to protect against measurement faults.To accommodate urban scenarios,spatial dependence in the faults are taken into consideration by this scheme.On the other hand,relative protection level is rigorously derived to describe the probabilistic error bound of the navigation output.This indicator can be used to evaluate collision risk and to warn collision danger in real time.The proposed algorithms are validated by both simulations and flight experiments.Simulation results quantitatively reveal the sensitivity of navigation performance to receiver configurations and environmental conditions.And experimental results suggest high efficiency and effectiveness of the new integrity monitoring framework.展开更多
Visual odometry(VO)has been widely used for many purposes in the past decade.However,the three assumptions of VO are not often met in the reality,and therefore,the uncertainty of VO output(the pose of agent)should be ...Visual odometry(VO)has been widely used for many purposes in the past decade.However,the three assumptions of VO are not often met in the reality,and therefore,the uncertainty of VO output(the pose of agent)should be estimated for safety’s sake,which can be done suitably by the integrity monitoring.To construct the integrity monitoring framework of VO,the first step is to establish the model of errors of measurements and calculate the fault rate,which has not been found in the literature to our knowledge.In response,this paper aims at establishing the model of errors of spatial points and calculating the fault rate in the stereo VO based on the feature point method.In this work,we describe the principle of stereo VO based on the feature point method in a deep and comprehensive way.The errors and faults of spatial points in stereo VO are defined,distinguished and classified in detail.The error propagation from pixel to spatial point is deduced,and the model of errors of spatial points is constructed.The KITTI odometry dataset is employed to evaluate the fault rate and standard deviation of errors of spatial points.And multiple sets of sensitive analyses are carried out to address the impact of RANdom SAmple Consensus(RANSAC)threshold,RANSAC iterations and operational scenario on spatial point error and fault rate.This paper could be a reference for constructing the integrity monitoring framework of stereo VO based on the feature point method.展开更多
With the great development of Global Navigation Satellite System(GNSS),multi-GNSS constellations(GPS,BDS,GLONASS,and Galileo)are able to provide users with more accurate positioning result.For civil aviation,to guaran...With the great development of Global Navigation Satellite System(GNSS),multi-GNSS constellations(GPS,BDS,GLONASS,and Galileo)are able to provide users with more accurate positioning result.For civil aviation,to guarantee user’s safety,multi-constellation GNSS needs to meet the integrity requirement.Using conservative error models,Multiple Hypothesis Solution Separation(MHSS)Advanced Receiver Autonomous Integrity Monitoring(ARAIM)is proposed to evaluate GNSS integrity.Current multipath error model in ARAIM algorithm is based on data of GPS Medium Earth Orbit(MEO)satellites.But BDS is a hybrid constellation.For BDS II,there has 5 Geosynchronous Earth Orbit(GEO)satellites.Previous studies have shown that the multipath effect of GEO satellites has statistical characteristics different from MEO satellites.Meanwhile,the multipath magnitude of GEO satellites is larger than that of MEO satellites.This paper mainly focuses on validating whether the multipath error model in ARAIM algorithm is conservative enough for GEO satellites.In this paper,Code Minus Carrier(CMC)residuals are calculated for BDS GEO dual-frequency signals.Then the Standard Deviation(STD)of CMC residuals can be conservatively estimated by bounded Cumulative Distribution Function(CDF).After eliminating interference from receiver noise,STD of GEO multipath can be obtained.Comparing the STD of GEO multipath effect with ARAIM multipath error model,a conclusion could be drawn that current multipath error model in ARAIM algorithm is no longer able to conservatively estimate the statistical characteristics of GEO satellites.展开更多
In recent years,multiple Unmanned Aerial Vehicle(UAV)formation flight has attracted worldwide research interest,for its potential benefits of scalability and flexibility.In complex urban environments,the successful op...In recent years,multiple Unmanned Aerial Vehicle(UAV)formation flight has attracted worldwide research interest,for its potential benefits of scalability and flexibility.In complex urban environments,the successful operation of those UAVs requires the system to provide certain safety level.As one of the key requirements,collision avoidance improves the system’s ability to accommodate operational environment variations,and to perform multiple tasks.To achieve this,artificial potential field(APF)has been recognized as one of the most suitable methods along with drone control.Although there has been substantial relevant work on the APF for single UAV in static environment,more efforts are desired to address formation maneuvers in complex environments such as urban.Most importantly,the traditional APF algorithms do not account for random errors in navigation solutions,which can bring potential risk to the UAV system.In response,this paper proposes a new APF algorithm that employs navigation information in complex urban environments,and the goal is to realize UAV formation collision avoidance.By augmenting the APF algorithm with UAV navigation information,the potential risk caused by navigation uncertainty can be mitigated,especially in the Global Navigation Satellite System(GNSS)challenged environment.The principle of the new APF approach is adaptively estimating the parameters of potential field force function,using the variance of navigation information and user-defined confidence probability.This new approach is applied in the synchronized UAV formation collision avoidance control.As a result,the UAVs can achieve fast position and attitude adjustment with high safety confidence.To verify the algorithm,quadrotors with emulated GNSS receivers are used to generate observation data.These data are incorporated into a complex urban environment simulation,where multiple sets of virtual obstacles are injected.Results show that the proposed method can achieve safe and efficient collision avoidance for cooperative formation flight in urban GNSS challenged environment.展开更多
This paper proposes a novel integrity monitoring scheme against global navigation satellite systems(GNSS)fault for civil aviation navigation.The main contributions are(a)developing an efficient user algorithm that int...This paper proposes a novel integrity monitoring scheme against global navigation satellite systems(GNSS)fault for civil aviation navigation.The main contributions are(a)developing an efficient user algorithm that integrates fault detection and exclusion(FDE)functions,and(b)deriving the analytical methods to quantify its corresponding integrity risk.The intended application of the new scheme is advanced receiver autonomous integrity monitoring(ARAIM),which is proposed by the United States(U.S.)and European Union(E.U.),and will serve as the next generation of the main aviation navigation means.In this new approach,the exclusion decision-making process is unified into the first layer detection step,thereby dramatically improving efficiency.The principle of this method is utilizing the multi-dimensional parity vector projections in parity space to extract the information of faults.In this work,we derive the projection matrix for single satellite failure modes,establish the mechanism for determining exclusion subset based on the projection magnitudes,and rigorously account for the false exclusion probabilities in the integrity risk quantification.The feasibility of the algorithm is verified and validated using Monte-Carlo simulations,and the performance is analyzed by evaluating the integrity risk.It is shown that the new FDE scheme can efficiently and effectively exclude the faulty satellites as desired,while achieving promising navigation performance.展开更多
Visual navigation systems have increasingly been adopted in many urban safety–critical applications,such as urban air mobility and highly automated vehicle,for which they must continuously provide accurate and safety...Visual navigation systems have increasingly been adopted in many urban safety–critical applications,such as urban air mobility and highly automated vehicle,for which they must continuously provide accurate and safety-assured pose estimates.Extensive studies have focused on improving visual navigation accuracy and robustness in complex environment,while insufficient attention has been paid to ensuring navigation safety in the presence of outliers.From safety perspective,integrity is the most important navigation performance criterion because it measures the trust that can be placed in the correctness of the navigation output.Through leveraging the concept of integrity,this paper develops an integrity monitoring framework to protect visual navigation system against misleading measurements and to quantify the reliability of the navigation output.We firstly present the iterative least squares(LS)-based pose estimation algorithm and derive the associated covariance estimation methodology.Then we develop a two-layer fault detection scheme through combining random sampling consensus(RANSAC)with multiple hypotheses solution separation(MHSS)to achieve high efficiency and high reliability.Finally,the framework determines the probabilistic error bound of the navigation output that rigorously captures the undetected faults and the measurement uncertainty.The proposed algorithms are validated using various simulations,and the results suggest the promising performance.展开更多
Global Navigation Satellite System(GNSS)Signal-In-Space(SIS)quality directly affects positioning integrity,which is an important metric for safety-critical applications.BeiDou Global Navigation Satellite System(BDS-3)...Global Navigation Satellite System(GNSS)Signal-In-Space(SIS)quality directly affects positioning integrity,which is an important metric for safety-critical applications.BeiDou Global Navigation Satellite System(BDS-3)broadcasts two new signals interoperable with GPS and Galileo,i.e.,B1C and B2a.They are expected to serve civil aviation applications,following the Standards and Recommended Practices(SARPs)released by International Civil Aviation Organization(ICAO).Therefore,the SIS accuracy and integrity performance of BDS-3B1C and B2a are evaluated in thiswork.The SISRange Errors(SISREs)are achieved by comparing the broadcast satellite positions and clock offsets derived from Civil NavigationMessage(CNAV)with the precise products from International GNSS Service(IGS).Specifically,given that the IGS precise products are referring to the equivalent phase center of BeiDou Regional System(BDS-2)B1I+B3I ionosphere-free combination,Differential Code Bias(DCB)from IGS is applied to realize time synchronization.This synchronization method is also meaningful to different frequencies in other constellations and supports the en-route,approaching,and landing phases.By analyzing 1-year data,an overall SIS characteristic picture of the 18 BDS-3 MEO satellites is presented here.The results show that most BDS-3 satellites are subject to an overbounding User Range Accuracy(URA)of 0.5 m to 0.85 m and a fault probability of 1.4953×10^(-5) to 1.1975×10^(-4),with an integrity performance much better than that of BDS-2 and comparable to that of GPS.BDS-3 is now ready to serve civil aviation and other safety-critical applications.展开更多
基金This study was co-supported by SJTU Global Strategic Partnership Fund(2019 SJTU–UoT)Master Research Agreement between SJTU and Honeywell Technology Solutions China(HTSC).
文摘Formation flight of multiple Unmanned Aerial Vehicles(UAVs)is expected to bring significant benefits to a wide range of applications.Accurate and reliable relative position information is a prerequisite to safely maintain a fairly close distance between UAVs and to achieve inner-system collision avoidance.However,Global Navigation Satellite System(GNSS)measurements are vulnerable to erroneous signals in urban canyons,which could potentially lead to catastrophic consequences.Accordingly,on the basis of performing relative positioning with double differenced pseudoranges,this paper develops an integrity monitoring framework to improve navigation integrity(a measure of reliability)in urban environments.On the one hand,this framework includes a fault detection and exclusion scheme to protect against measurement faults.To accommodate urban scenarios,spatial dependence in the faults are taken into consideration by this scheme.On the other hand,relative protection level is rigorously derived to describe the probabilistic error bound of the navigation output.This indicator can be used to evaluate collision risk and to warn collision danger in real time.The proposed algorithms are validated by both simulations and flight experiments.Simulation results quantitatively reveal the sensitivity of navigation performance to receiver configurations and environmental conditions.And experimental results suggest high efficiency and effectiveness of the new integrity monitoring framework.
基金supported by China Postdoctoral Science Foundation(Grant no.2019M661511)Innovation Fund from Engineering Research Center of Aerospace Science and Technology,Ministry of Education.
文摘Visual odometry(VO)has been widely used for many purposes in the past decade.However,the three assumptions of VO are not often met in the reality,and therefore,the uncertainty of VO output(the pose of agent)should be estimated for safety’s sake,which can be done suitably by the integrity monitoring.To construct the integrity monitoring framework of VO,the first step is to establish the model of errors of measurements and calculate the fault rate,which has not been found in the literature to our knowledge.In response,this paper aims at establishing the model of errors of spatial points and calculating the fault rate in the stereo VO based on the feature point method.In this work,we describe the principle of stereo VO based on the feature point method in a deep and comprehensive way.The errors and faults of spatial points in stereo VO are defined,distinguished and classified in detail.The error propagation from pixel to spatial point is deduced,and the model of errors of spatial points is constructed.The KITTI odometry dataset is employed to evaluate the fault rate and standard deviation of errors of spatial points.And multiple sets of sensitive analyses are carried out to address the impact of RANdom SAmple Consensus(RANSAC)threshold,RANSAC iterations and operational scenario on spatial point error and fault rate.This paper could be a reference for constructing the integrity monitoring framework of stereo VO based on the feature point method.
文摘With the great development of Global Navigation Satellite System(GNSS),multi-GNSS constellations(GPS,BDS,GLONASS,and Galileo)are able to provide users with more accurate positioning result.For civil aviation,to guarantee user’s safety,multi-constellation GNSS needs to meet the integrity requirement.Using conservative error models,Multiple Hypothesis Solution Separation(MHSS)Advanced Receiver Autonomous Integrity Monitoring(ARAIM)is proposed to evaluate GNSS integrity.Current multipath error model in ARAIM algorithm is based on data of GPS Medium Earth Orbit(MEO)satellites.But BDS is a hybrid constellation.For BDS II,there has 5 Geosynchronous Earth Orbit(GEO)satellites.Previous studies have shown that the multipath effect of GEO satellites has statistical characteristics different from MEO satellites.Meanwhile,the multipath magnitude of GEO satellites is larger than that of MEO satellites.This paper mainly focuses on validating whether the multipath error model in ARAIM algorithm is conservative enough for GEO satellites.In this paper,Code Minus Carrier(CMC)residuals are calculated for BDS GEO dual-frequency signals.Then the Standard Deviation(STD)of CMC residuals can be conservatively estimated by bounded Cumulative Distribution Function(CDF).After eliminating interference from receiver noise,STD of GEO multipath can be obtained.Comparing the STD of GEO multipath effect with ARAIM multipath error model,a conclusion could be drawn that current multipath error model in ARAIM algorithm is no longer able to conservatively estimate the statistical characteristics of GEO satellites.
基金supported by Shanghai Jiao Tong University(SJTU)Global Strategic Partnership Fund(2019 SJTU–UoT).
文摘In recent years,multiple Unmanned Aerial Vehicle(UAV)formation flight has attracted worldwide research interest,for its potential benefits of scalability and flexibility.In complex urban environments,the successful operation of those UAVs requires the system to provide certain safety level.As one of the key requirements,collision avoidance improves the system’s ability to accommodate operational environment variations,and to perform multiple tasks.To achieve this,artificial potential field(APF)has been recognized as one of the most suitable methods along with drone control.Although there has been substantial relevant work on the APF for single UAV in static environment,more efforts are desired to address formation maneuvers in complex environments such as urban.Most importantly,the traditional APF algorithms do not account for random errors in navigation solutions,which can bring potential risk to the UAV system.In response,this paper proposes a new APF algorithm that employs navigation information in complex urban environments,and the goal is to realize UAV formation collision avoidance.By augmenting the APF algorithm with UAV navigation information,the potential risk caused by navigation uncertainty can be mitigated,especially in the Global Navigation Satellite System(GNSS)challenged environment.The principle of the new APF approach is adaptively estimating the parameters of potential field force function,using the variance of navigation information and user-defined confidence probability.This new approach is applied in the synchronized UAV formation collision avoidance control.As a result,the UAVs can achieve fast position and attitude adjustment with high safety confidence.To verify the algorithm,quadrotors with emulated GNSS receivers are used to generate observation data.These data are incorporated into a complex urban environment simulation,where multiple sets of virtual obstacles are injected.Results show that the proposed method can achieve safe and efficient collision avoidance for cooperative formation flight in urban GNSS challenged environment.
文摘This paper proposes a novel integrity monitoring scheme against global navigation satellite systems(GNSS)fault for civil aviation navigation.The main contributions are(a)developing an efficient user algorithm that integrates fault detection and exclusion(FDE)functions,and(b)deriving the analytical methods to quantify its corresponding integrity risk.The intended application of the new scheme is advanced receiver autonomous integrity monitoring(ARAIM),which is proposed by the United States(U.S.)and European Union(E.U.),and will serve as the next generation of the main aviation navigation means.In this new approach,the exclusion decision-making process is unified into the first layer detection step,thereby dramatically improving efficiency.The principle of this method is utilizing the multi-dimensional parity vector projections in parity space to extract the information of faults.In this work,we derive the projection matrix for single satellite failure modes,establish the mechanism for determining exclusion subset based on the projection magnitudes,and rigorously account for the false exclusion probabilities in the integrity risk quantification.The feasibility of the algorithm is verified and validated using Monte-Carlo simulations,and the performance is analyzed by evaluating the integrity risk.It is shown that the new FDE scheme can efficiently and effectively exclude the faulty satellites as desired,while achieving promising navigation performance.
基金supported by Shanghai Jiao Tong University(SJTU)Global Strategic Partnership Fund(2019 SJTU–UoT).
文摘Visual navigation systems have increasingly been adopted in many urban safety–critical applications,such as urban air mobility and highly automated vehicle,for which they must continuously provide accurate and safety-assured pose estimates.Extensive studies have focused on improving visual navigation accuracy and robustness in complex environment,while insufficient attention has been paid to ensuring navigation safety in the presence of outliers.From safety perspective,integrity is the most important navigation performance criterion because it measures the trust that can be placed in the correctness of the navigation output.Through leveraging the concept of integrity,this paper develops an integrity monitoring framework to protect visual navigation system against misleading measurements and to quantify the reliability of the navigation output.We firstly present the iterative least squares(LS)-based pose estimation algorithm and derive the associated covariance estimation methodology.Then we develop a two-layer fault detection scheme through combining random sampling consensus(RANSAC)with multiple hypotheses solution separation(MHSS)to achieve high efficiency and high reliability.Finally,the framework determines the probabilistic error bound of the navigation output that rigorously captures the undetected faults and the measurement uncertainty.The proposed algorithms are validated using various simulations,and the results suggest the promising performance.
基金funded byNational Natural Science Foundation of China(Grant No.62103274).
文摘Global Navigation Satellite System(GNSS)Signal-In-Space(SIS)quality directly affects positioning integrity,which is an important metric for safety-critical applications.BeiDou Global Navigation Satellite System(BDS-3)broadcasts two new signals interoperable with GPS and Galileo,i.e.,B1C and B2a.They are expected to serve civil aviation applications,following the Standards and Recommended Practices(SARPs)released by International Civil Aviation Organization(ICAO).Therefore,the SIS accuracy and integrity performance of BDS-3B1C and B2a are evaluated in thiswork.The SISRange Errors(SISREs)are achieved by comparing the broadcast satellite positions and clock offsets derived from Civil NavigationMessage(CNAV)with the precise products from International GNSS Service(IGS).Specifically,given that the IGS precise products are referring to the equivalent phase center of BeiDou Regional System(BDS-2)B1I+B3I ionosphere-free combination,Differential Code Bias(DCB)from IGS is applied to realize time synchronization.This synchronization method is also meaningful to different frequencies in other constellations and supports the en-route,approaching,and landing phases.By analyzing 1-year data,an overall SIS characteristic picture of the 18 BDS-3 MEO satellites is presented here.The results show that most BDS-3 satellites are subject to an overbounding User Range Accuracy(URA)of 0.5 m to 0.85 m and a fault probability of 1.4953×10^(-5) to 1.1975×10^(-4),with an integrity performance much better than that of BDS-2 and comparable to that of GPS.BDS-3 is now ready to serve civil aviation and other safety-critical applications.
