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
The Global Position System(GPS)satellites of Block IIR-M and later versions can turn on the signal power enhancement if needed.In recent years,this power enhancement has been triggered several times when the U.S force...The Global Position System(GPS)satellites of Block IIR-M and later versions can turn on the signal power enhancement if needed.In recent years,this power enhancement has been triggered several times when the U.S force was involved in local conflicts,which was observed by the monitoring receivers at International GNSS Service(IGS)/international GNSS Monitoring and Assessment System(iGMAS)stations or the high-gain antennas at monitoring ground stations.The specific power enhancement magnitudes with these two observation methods are different.The observations of L1/L2 P(Y)power with a high-gain antenna are accurate,while the observations at IGS/iGMAS stations contain biases.This paper analyses the reasons for the observation biases with monitoring receivers at IGS/iGMAS stations and proposes a method verifying the accurate relation between the observed carrier-to-noise ratio(C/N_(0))data and the real power enhancement magnitudes.When the power enhancement event happens,the observed L1/L2 P(Y)C/N_(0) data at IGS/iGMAS stations can be corrected using the model proposed in this paper.In the analysis,this paper concludes that the power of L1P(Y)increases by about 4.3–5.3 dB and the power of L2P(Y)by about 4.6–5.2 dB in power enhancement events,which matches the designed capability of GPS satellites as well.The results are also verified by the data of high-gain antennas.展开更多
Currently,Global Navigation Satellite System(GNSS)Real-Time Kinematic positioning(RTK)and Precise Point Positioning(PPP)techniques are widely employed for real-time monitoring of landslides.However,both RTK and PPP mo...Currently,Global Navigation Satellite System(GNSS)Real-Time Kinematic positioning(RTK)and Precise Point Positioning(PPP)techniques are widely employed for real-time monitoring of landslides.However,both RTK and PPP monitoring techniques have their limitations,such as limited service coverage or long convergence times.PPP-RTK technique which integrates RTK and PPP is a novel approach for monitoring landslides with the advantages of rapid convergence,high-precision,and a wide service area.This study summarizes the limitations of RTK,PPP,and PPP-RTK monitoring techniques and suggests some improved strategies.Their performances are compared and analyzed using real monitoring data.The experiment results demonstrate that RTK is the best option for small-scale(the baseline distance<15 km)and real-time landslide monitoring without considering the cost.PPP technique converges to centimeter-level accuracy in tens of minutes,only suitable for the stability analysis of reference stations.Over a large area(the baseline distance<100 km),PPP-RTK can provide excellent horizontal accuracy and adapt the service range in response to the demand for monitoring accuracy,as the vertical accuracy is signifcantly impacted by the service range and elevation diference.Finally,the characteristics of three techniques are integrated to form a comprehensive landslide monitoring technique that considers intelligence,robustness,and real-time.展开更多
Several Wireless Fidelity(WiFi)fingerprint datasets based on Received Signal Strength(RSS)have been shared for indoor localization.However,they can’t meet all the demands of WiFi RSS-based localization.A supplementar...Several Wireless Fidelity(WiFi)fingerprint datasets based on Received Signal Strength(RSS)have been shared for indoor localization.However,they can’t meet all the demands of WiFi RSS-based localization.A supplementary open dataset for WiFi indoor localization based on RSS,called as SODIndoorLoc,covering three buildings with multiple floors,is presented in this work.The dataset includes dense and uniformly distributed Reference Points(RPs)with the average distance between two adjacent RPs smaller than 1.2 m.Besides,the locations and channel information of pre-installed Access Points(APs)are summarized in the SODIndoorLoc.In addition,computer-aided design drawings of each floor are provided.The SODIndoorLoc supplies nine training and five testing sheets.Four standard machine learning algorithms and their variants(eight in total)are explored to evaluate positioning accuracy,and the best average positioning accuracy is about 2.3 m.Therefore,the SODIndoorLoc can be treated as a supplement to UJIIndoorLoc with a consistent format.The dataset can be used for clustering,classification,and regression to compare the performance of different indoor positioning applications based on WiFi RSS values,e.g.,high-precision positioning,building,floor recognition,fine-grained scene identification,range model simulation,and rapid dataset construction.展开更多
In order to facilitate high-precision and real-time Precise Point Positioning(PPP),the International GNSS(Global Navigation Satellite System)Service(IGS),BDS-3(BeiDou-3 Navigation Satellite System),and Galileo navigat...In order to facilitate high-precision and real-time Precise Point Positioning(PPP),the International GNSS(Global Navigation Satellite System)Service(IGS),BDS-3(BeiDou-3 Navigation Satellite System),and Galileo navigation satellite system(Galileo)have provided real-time satellite clock correction,which is updated at a high-frequency.However,the frequent updates pose the challenges of increasing the computational burden and compromising the timeliness of these correction parameters.To address this issue,an improved Real-Time Service(RTS)method is developed using an extrapolation algorithm and a linear model.The results indicate that a 1 h arc length of the satellite clock correction series is optimal for fitting a linear model of the RTS.With this approach,the 1 h extrapolation results for BDS-3 and Galileo are superior to 0.09 ns.Moreover,when these model coefficients are transmitted and updated at the intervals of 1,2,5,and 10 min,the corresponding PPP can converge at the centimeter-level.It is evident that these improved RTS methods outperform the current approach with high-frequency interval transmission,as they effectively mitigate the challenges associated with maintaining the timeliness of correction parameters.展开更多
The implementation of Intelligent Transport System (ITS) technology is expected to significantly improve road safety and traffic efficiency. One of the key components of ITS is precise vehicle positioning. Positioning...The implementation of Intelligent Transport System (ITS) technology is expected to significantly improve road safety and traffic efficiency. One of the key components of ITS is precise vehicle positioning. Positioning with decimetre to sub-metre accuracy is a fundamental capability for self-driving, and other automated applications. Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) is an attractive positioning approach for ITS due to its relatively low-cost and flexibility. However, GNSS PPP is vulnerable to several effects, especially those caused by the challenging urban environments, where the ITS technology is most likely needed. To meet the high integrity requirements of ITS applications, it is necessary to carefully analyse potential faults and failures of PPP and to study relevant integrity monitoring methods. In this paper an overview of vulnerabilities of GNSS PPP is presented to identify the faults that need to be monitored when developing PPP integrity monitoring methods. These vulnerabilities are categorised into different groups according to their impact and error sources to assist integrity fault analysis, which is demonstrated with Failure Modes and Effects Analysis (FMEA) and Fault Tree Analysis (FTA) methods. The main vulnerabilities are discussed in detail, along with their causes, characteristics, impact on users, and related mitigation methods. In addition, research on integrity monitoring methods used for accounting for the threats and faults in PPP for ITS applications is briefly reviewed. Both system-level (network-end) and user-level (user-end) integrity monitoring approaches for PPP are briefly discussed, focusing on their development and the challenges in urban scenarios. Some open issues, on which further efforts should focus, are also identified.展开更多
The BeiDou global navigation satellite system(BDS-3)constellation deployment has been completed on June 23,2020,with a full constellation comprising 30 satellites.In this study,we present the performance assessment of...The BeiDou global navigation satellite system(BDS-3)constellation deployment has been completed on June 23,2020,with a full constellation comprising 30 satellites.In this study,we present the performance assessment of single-epoch Real-Time Kinematic(RTK)positioning with tightly combined BeiDou regional navigation satellite system(BDS-2)and BDS-3.We first investigate whether code and phase Differential Inter-System Biases(DISBs)exist between the legacy B1I/B3I signals of BDS-3/BDS-2.It is discovered that the DISBs are in fact about zero for the baselines with the same or different receiver types at their endpoints.These results imply that BDS-3 and BDS-2 are fully interoperable and can be regarded as one constellation without additional DISBs when the legacy B1I/B3I signals are used for precise relative positioning.Then we preliminarily evaluate the single-epoch short baseline RTK performance of tightly combined BDS-2 and the newly completed BDS-3.The performance is evaluated through ambiguity resolution success rate,ambiguity dilution of precision,as well as positioning accuracy in kinematic and static modes using the datasets collected in Wuhan.Experimental results demonstrate that the current BDS-3 only solutions can deliver comparable ambiguity resolution performance and much better positioning accuracy with respect to BDS-2 only solutions.Moreover,the RTK performance is much improved with tightly combined BDS-3/BDS-2,particularly in challenging or harsh conditions.The single-frequency single-epoch tightly combined BDS-3/BDS-2 solution could deliver an ambiguity resolution success rate of 96.9%even with an elevation cut-off angle of 40°,indicating that the tightly combined BDS-3/BDS-2 could achieve superior RTK positioning performance in the Asia-Pacific region.Meanwhile,the three-dimensional(East/North/Up)positioning accuracy of BDS-3 only solution(0.52 cm/0.39 cm/2.14 cm)in the kinematic test is significantly better than that of the BDS-2 only solution(0.85 cm/1.02 cm/3.01 cm)due to the better geometry of the current BDS-3 constellation.The tightly combined BDS-3/BDS-2 solution can provide the positioning accuracy of 0.52 cm,0.22 cm,and 1.80 cm,respectively.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
The BeiDou Navigation Satellite System(BDS)employs a hybrid constellation including GEO(Geosynchronous Earth Orbit),IGSO(Inclined Geosynchronous Orbit),and MEO(Medium Earth Orbit)satellites,where the GEO and IGSO sate...The BeiDou Navigation Satellite System(BDS)employs a hybrid constellation including GEO(Geosynchronous Earth Orbit),IGSO(Inclined Geosynchronous Orbit),and MEO(Medium Earth Orbit)satellites,where the GEO and IGSO satellites are critical to providing continuous and reliable Positioning,Navigation,and Timing(PNT)services in the Asia–Pacifc region.To handle the inconsistency between the satellite orbits and clocks in the broadcast ephemeris,which are determined by the Orbit Determination and Time Synchronization(ODTS)and the Two-way Satellite Time Frequency Transfer(TWSTFT)technique,respectively,we present the strategies using ground-satellite-link observations to improve the accuracy of broadcast ephemeris.The clock diferences between the ODTS and TWSTFT techniques are used for correcting the radial orbit component to derive the refned orbits,which are used to generate the refned broadcast ephemeris.The test results show the precision of the refned orbits is improved by 50–60%in the 3-h to 12-h predicted arcs for the GEO satellites,and by 40–50%for the IGSO satellites.Moreover,the validation using satellite laser ranging observations shows the mean precision of the refned broadcast ephemeris is improved by 27%compared to the original one.Applying the proposed strategies in the BDS Operational Control Segment(OCS),the time evolution of BDS Single Point Positioning(SPP)in the period from Jan.2016 to April 2021 is evaluated.The SPP accuracy is improved from 1.94,2.06 and 3.29 m to 1.39,1.85,and 2.39 m in the north,east,and up components,respectively.Further update with the inclusion of BDS-3 satellites improve the corresponding SPP precision to 0.68,0.70 and 1.91 m.展开更多
The last satellite of BeiDou Navigation Satellite System with Global Coverage(BDS-3)constellation was successfully launched on June 23rd,2020,and the entire system began to provide Positioning,Navigation,and Timing(PN...The last satellite of BeiDou Navigation Satellite System with Global Coverage(BDS-3)constellation was successfully launched on June 23rd,2020,and the entire system began to provide Positioning,Navigation,and Timing(PNT)services worldwide.We evaluated the performance of location services using BDS with a smartphone that can track the Global Navigation Satellite System(GNSS)satellites in Nottingham,UK.The static and kinematic experiments were conducted in an open meadow and a lakeside route covered by trees,respectively.Experimental results show that BDS has good visibility,and its overall signal carrier-to-noise density ratio(C/N0)is comparable to that of Global Positioning System(GPS).The average C/N0 of BDS-3 satellites with elevation angles above 45°on B1 band is the highest among all systems,reaching 40.0 dB·Hz.The noise level of the BDS pseudorange measurements is within 0.5 m,and it has a good consistency among satellites.In the static experiment,the standard deviations of BDS position-ing in the east,north and up directions are 1.09,1.16,and 3.02 m,respectively,and the R95 value of the horizontal position is 2.88 m.In harsh environments,the number of BDS satellites tracked by the smartphone is susceptible to environmental factors.The bias Root Mean Squares(RMS)in the three directions of the whole kinematic positioning are 6.83,6.68,11.67 m,in which the positioning bias RMS values in a semi-open environment are only 2.81,1.11,3.29 m.Furthermore,the inclusion of BDS in multiple GNSS systems can significantly improve the positioning precision.This study intends to provide a reference for the further improvements of BDS global PNT services,particularly for Location-Based Services(LBS).展开更多
Obtaining high-precision,long-term sequences of vegetation water content(VWC)is of great significance for assessing surface vegetation growth,soil moisture,and fire risk.In recent years,the global navigation satellite...Obtaining high-precision,long-term sequences of vegetation water content(VWC)is of great significance for assessing surface vegetation growth,soil moisture,and fire risk.In recent years,the global navigation satellite system-interferometric reflection(GNSS-IR)has become a new type of remote sensing technology with low cost,all-weather capability,and a high temporal resolution.It has been widely used in the fields of snow depth,sea level,soil moisture content,and vegetation water content.The normalized microwave reflectance index(NMRI)based on GNSS-IR technology has been proven to be effective in monitoring changes in VWC.This paper considers the advantages and disadvantages of remote sensing technology and GNSS-IR technology in estimating VWC.A point-surface fusion method of GNSS-IR and MODIS data based on the GA-BP neural network is proposed to improve the accuracy of VWC estimation.The vegetation index products(NDVI,GPP,LAI)and the NMRI that unified the temporal and spatial resolution were used as the input and output data of the training model,and the GA-BP neural network was used for training and modeling.Finally,a spatially continuous NMRI product was generated.Taking a particular area of the United States as a research object,experiments show that(1)a neural network can realize the effective fusion of GNSS-IR and MODIS products.By comparing the GA-BP neural network,BP neural network,and multiple linear regression(MLR),the three models fusion effect.The results show that the GA-BP neural network has the best modeling effect,and the r and RMSE between the model estimation result and the reference value are 0.778 and 0.0332,respectively;this network is followed by the BP neural network,in which the r and RMSE are 0.746 and 0.0465,respectively.MLR has the poorest effect,with r and RMSE values of 0.500 and 0.0516,respectively.(2)The spatiotem-poral variation in the 16 days/500 m resolution NMRI product obtained by GA-BP neural network fusion is consistent with that in the experimental area.Through the testing of GNSS stations that did not participate in the modeling,the r between the estimated value of the NMRI and the reference value is greater than 0.87,and the RMSE is less than 0.049.Therefore,the method proposed in this paper is optional and effective.The spatially continuous NMRI products obtained by fusion can reflect the changes in VWC in the experimental area more intuitively.展开更多
This paper reviews the state of the art and future trends of indoor Positioning,Localization,and Navigation(PLAN).It covers the requirements,the main players,sensors,and techniques for indoor PLAN.Other than the navig...This paper reviews the state of the art and future trends of indoor Positioning,Localization,and Navigation(PLAN).It covers the requirements,the main players,sensors,and techniques for indoor PLAN.Other than the navigation sensors such as Inertial Navigation System(INS)and Global Navigation Satellite System(GNSS),the environmental-perception sensors such as High-Definition map(HD map),Light Detection and Ranging(LiDAR),camera,the fifth generation of mobile network communication technology(5G),and Internet-of-Things(IoT)signals are becoming important aiding sensors for PLAN.The PLAN systems are expected to be more intelligent and robust under the emergence of more advanced sensors,multi-platform/multi-device/multi-sensor information fusion,self-learning systems,and the integration with artificial intelligence,5G,IoT,and edge/fog computing.展开更多
Inertial navigation represents a unique method of navigation,in which there is no dependency on external sources of information.As opposed to other position fixing navigation techniques,inertial navigation performs th...Inertial navigation represents a unique method of navigation,in which there is no dependency on external sources of information.As opposed to other position fixing navigation techniques,inertial navigation performs the navigation in a relative sense with respect to the initial navigation state of the moving platform.Hence,inertial navigation systems are not prone to jamming,or spoofing.Inertial navigation systems have developed vastly,from their occurrence in the 1940s up to date.The accuracy of the inertial sensors has improved over time,making inertial sensors sufficient in terms of size,weight,cost,and accuracy for navigation and guidance applications.Within the past few years,inertial sensors have developed from being purely mechanical into incorporating various technologies and taking advantage of numerous physical phenomena,from which the dynamic forces exerted on a moving body could be computed accurately.Besides,the evolution of inertial navigation scheme involved the evolution from stable-platform inertial navigation system,which were mechanically complicated,to computationally demanding strap-down inertial navigation systems.Optical sensory technologies have provided highly accurate inertial sensors,at smaller sizes.Besides,the vibratory inertial navigation technologies enabled the production of Micro-electro-machined inertial sensors that are extremely low-cost,and offer extremely low size,weight and power consumption,making them suitable for a wide range of day-to-day navigation applications.Recently,advanced inertial sensor technologies have been introduced to the industry such as nuclear magnetic resonance technology,coldatom technology,and the reintroduction of fluid-based inertial sensors.On another note,inertial sensor errors constitute a huge research aspect in which it is intended for inertial sensors to reach level in which they could operate for substantially long operation times in the absence of updates from aiding sensors,which would be a huge leap.Inertial sensors error modeling techniques have been developing rapidly trying to ensure higher levels of navigation accuracy using lower-cost inertial sensors.In this review,the inertial sensor technologies are covered extensively,along the future trends in the inertial sensors’technologies.Besides,this review covers a brief overview on the inertial error modeling techniques used to enhance the performance of low-cost sensors.展开更多
Global Navigation Satellites Systems(GNSS)is frequently used for positioning services in various applications,e.g.,pedestrian and vehicular navigation.However,it is well-known that GNSS positioning performs unreliably...Global Navigation Satellites Systems(GNSS)is frequently used for positioning services in various applications,e.g.,pedestrian and vehicular navigation.However,it is well-known that GNSS positioning performs unreliably in urban environments.GNSS shadow matching is a method of improving accuracy in the cross-street direction.Initial position and classification of observed satellite visibility between line-of-sight(LOS)and non-line-of-sight(NLOS)are essential for its performance.For the conventional LOS/NLOS classification,the classifiers are based on a single feature,extracted from raw GNSS measurements,such as signal noise ratio,pseudorange,elevation angle,etc.Especially in urban canyons,these measurements are unstable and unreliable due to the signal reflection and refraction from the surrounding buildings.Besides,the conventional least square approach for positioning is insufficient to provide accurate initialization for shadow matching in urban areas.In our study,shadow matching is improved using the initial position from robust estimator and the satellite visibility determined by support vector machine(SVM).The robust estimator has an improved positioning accuracy and the classification rate of SVM classification can reach 91.5%in urban scenarios.An important issue is related to satellites with ultra-high or low elevation angles and satellites near the building boundary that are very likely to be misclassified.By solving this problem,the SVM classification shows the potential of about 90%classification accuracy for various urban cases.With the help of these approaches,the shadow matching has a mean error of 10.27 m with 1.44 m in the cross-street direction;these performances are suitable for urban positioning.展开更多
Communication,positioning,navigation,and decision-making abilities have evolved into Positioning,Navigation,and Timing(PNT)intelligence during the long process of human migration and hence promoted human evolution.Thi...Communication,positioning,navigation,and decision-making abilities have evolved into Positioning,Navigation,and Timing(PNT)intelligence during the long process of human migration and hence promoted human evolution.This article defines intelligence and smartness from the perspective of biological intelligence.New requirements as a result of the development of communication,navigation,time service,and decision making are identified in this study.The article points out that there are many radio PNT service methods,such as 5G,the new-generation high-speed communication networks and the low-latency and ubiquitous mobile communication networks as well as Global Navigation Satellite System(GNSS),but the integrated application is especially important in providing technical support for the adjustment and control of the physical world by intelligent sensing,cognition,decision-making,and precise coordination.The fusion of 5G and GNSS[including BeiDou Navigation Satellite System(BDS)]information with the corresponding equipment can be embedded into a machine to make it intelligent.Furthermore,the fused information of 5G and GNSS together with the environment information may extend human perception and physical world control ability in terms of time and space scale.It will help to develop critical information infrastructure in the age of intelligence,which will also extend the definition of artificial intelligence.Additionally,the“5G+BDS/GNSS”fusion path is analyzed explicitly herein in terms of realization methods,information processing,and new application services.On the whole,the application of“5G+BDS/GNSS+satellite-based communication”as a critical infrastructure for land,sea,air,space and network spatiotemporal control rights is proposed.展开更多
Smartphone-based vehicle navigation has become the primary choice in everyday life due to low cost and real-time traffic updates.However,for vehicle navigation applications in the Global Navigation Satellite System(GN...Smartphone-based vehicle navigation has become the primary choice in everyday life due to low cost and real-time traffic updates.However,for vehicle navigation applications in the Global Navigation Satellite System(GNSS)-denied scenario such as parking lot and tunnel,it is quite difficult to maintain robust and continuous positioning based on consumer-grade sensors.In this paper,a novel method is proposed for accurate vehicular dead-reckoning based only on a smartphone inertial measurement unit.Robust vehicle dead reckoning can improve positioning performance in GNSS-degraded areas or where high-precision positioning sources are available at low-frequencies.The key components of the method are a Kalman filter with data-driven parameters adapter and a deep neural network that provides data-driven measurement estimation.A combined convolutional neural network and gated recurrent unit deep learning network,termed AVNet,is proposed to estimate the attitude and velocity of the vehicle.The learned measurements are integrated into an invariant Kalman filter to estimate Three-Dimensional(3D)attitude,velocity and position.The method was tested on custom datasets collected in a parking lot,and a 0.4%relative horizontal translation error was achieved on average.展开更多
To provide competitive global positioning and timing services under the condition that monitoring stations are confined to Chinese territory,inter-satellite link(ISL)technology is used by the third-generation BeiDou N...To provide competitive global positioning and timing services under the condition that monitoring stations are confined to Chinese territory,inter-satellite link(ISL)technology is used by the third-generation BeiDou Navigation Satellite System(BDS-3).The ISL,together with the dual one-way links between satellites and anchor stations,may enable autonomous navigation for BDS-3.In this paper,we propose a general observation model for orbit determination(OD)and time synchronization(TS)directly using non-simultaneous observations,such as raw ISL pseudoranges.With the proposed model,satellite orbits,clocks,and hardware delay biases of ISL equipment can be determined simultaneously by jointly processing inter-satellite one-way pseudorange data and observation data from ground monitoring stations.Moreover,autonomous OD and TS are also achievable with one-way pseudorange data from anchor stations and satellites.Data from eight BDS-3 satellites,two anchor stations,and seven monitoring stations located in China were collected to validate the proposed method.It is shown that by jointly processing data from the ISL and seven monitoring stations,the RMS of overlap orbit differences in radial direction is 0.019 m,the overlap clock difference(95%)is 0.185 ns,and the stability of the estimated hardware delay biases for each satellite is greater than 0.5 ns.Compared with the results obtained with the seven stations,the improvements of orbits in radial direction and clocks are 95.7%and 90.5%,respectively.When the hardware delay biases are fixed to predetermined values,the accuracies of orbits and clocks are further improved.By jointly processing pseudoranges from the satellites and the two anchor stations,the RMS of overlap orbit differences is 0.017 m in the radial direction,and the overlap clock difference(95%)is 0.037 ns.It has also been demonstrated that under the condition of one-way ranging links,the accuracies of orbits and clocks obtained by the above two modes are still significantly better than those obtained by using the data from the monitoring stations alone.展开更多
Unmanned clusters can realize collaborative work,fexible confguration,and efcient operation,which has become an important development trend of unmanned platforms.Cluster positioning is important for ensuring the norma...Unmanned clusters can realize collaborative work,fexible confguration,and efcient operation,which has become an important development trend of unmanned platforms.Cluster positioning is important for ensuring the normal operation of unmanned clusters.The existing solutions have some problems such as requiring external system assistance,high system complexity,poor architecture scalability,and accumulation of positioning errors over time.Without the aid of the information outside the cluster,we plan to construct the relative position relationship with north alignment to adopt formation control and achieve robust cluster relative positioning.Based on the idea of bionics,this paper proposes a cluster robust hierarchical positioning architecture by analyzing the autonomous behavior of pigeon focks.We divide the clusters into follower clusters,core clusters,and leader nodes,which can realize fexible networking and cluster expansion.Aiming at the core cluster that is the most critical to relative positioning in the architecture,we propose a cluster relative positioning algorithm based on spatiotemporal correlation information.With the design idea of low cost and large-scale application,the algorithm uses intra-cluster ranging and the inertial navigation motion vector to construct the positioning equation and solves it through the Multidimensional Scaling(MDS)and Multiple Objective Particle Swarm Optimization(MOPSO)algorithms.The cluster formation is abstracted as a mixed direction-distance graph and the graph rigidity theory is used to analyze localizability conditions of the algorithm.We designed the cluster positioning simulation software and conducted localizability tests and positioning accuracy tests in diferent scenarios.Compared with the relative positioning algorithm based on Extended Kalman Filter(EKF),the algorithm proposed in this paper has more relaxed positioning conditions and can adapt to a variety of scenarios.It also has higher relative positioning accuracy,and the error does not accumulate over time.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
Satellite Based Augmentation System (SBAS) provides the corrections and integrity information to users, but as its signal format is opened to the public and Global Navigation Satellite System (GNSS) spoofing technolog...Satellite Based Augmentation System (SBAS) provides the corrections and integrity information to users, but as its signal format is opened to the public and Global Navigation Satellite System (GNSS) spoofing technology becomes more realistic, more feasible and cheaper. It’s foreseeable that there will be risks of spoofing threats against SBAS in the future. SBAS signal authentication technology provides a system-level solution to spoofing threats by adding special markers to SBAS signals so that receivers can verify whether the SBAS signals are from the on-orbit Geostationary Earth Orbit (GEO) satellites or whether the signal information has been forged and tampered with. First, this article introduces the existing anti-spoofing methods that can be applied to SBAS, especially the Elliptic Curve Digital Signature Algorithm (ECDSA) and Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocols. Then it discusses four possible solutions in a combination with the existing SBAS Interface Control Document (ICD). Two main Key Performance Indicators (KPIs), Time Between Authentication (TBA) and Authentication Latency (AL), obtained in the four main scenarios are compared. By analyzing the EGNOS Authentication Security Testbed (EAST) test simula-tion results of European Geostationary Navigation Overlay Service (EGNOS) in Europe, the impact of SBAS after joining the authentication service is obtained.展开更多
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.
基金National Natural Science Foundation of China(Grant Nos:U20A0193,62003354).
文摘The Global Position System(GPS)satellites of Block IIR-M and later versions can turn on the signal power enhancement if needed.In recent years,this power enhancement has been triggered several times when the U.S force was involved in local conflicts,which was observed by the monitoring receivers at International GNSS Service(IGS)/international GNSS Monitoring and Assessment System(iGMAS)stations or the high-gain antennas at monitoring ground stations.The specific power enhancement magnitudes with these two observation methods are different.The observations of L1/L2 P(Y)power with a high-gain antenna are accurate,while the observations at IGS/iGMAS stations contain biases.This paper analyses the reasons for the observation biases with monitoring receivers at IGS/iGMAS stations and proposes a method verifying the accurate relation between the observed carrier-to-noise ratio(C/N_(0))data and the real power enhancement magnitudes.When the power enhancement event happens,the observed L1/L2 P(Y)C/N_(0) data at IGS/iGMAS stations can be corrected using the model proposed in this paper.In the analysis,this paper concludes that the power of L1P(Y)increases by about 4.3–5.3 dB and the power of L2P(Y)by about 4.6–5.2 dB in power enhancement events,which matches the designed capability of GPS satellites as well.The results are also verified by the data of high-gain antennas.
基金the National Key Research and Development Program of China(Grants No.2021YFC3000503).
文摘Currently,Global Navigation Satellite System(GNSS)Real-Time Kinematic positioning(RTK)and Precise Point Positioning(PPP)techniques are widely employed for real-time monitoring of landslides.However,both RTK and PPP monitoring techniques have their limitations,such as limited service coverage or long convergence times.PPP-RTK technique which integrates RTK and PPP is a novel approach for monitoring landslides with the advantages of rapid convergence,high-precision,and a wide service area.This study summarizes the limitations of RTK,PPP,and PPP-RTK monitoring techniques and suggests some improved strategies.Their performances are compared and analyzed using real monitoring data.The experiment results demonstrate that RTK is the best option for small-scale(the baseline distance<15 km)and real-time landslide monitoring without considering the cost.PPP technique converges to centimeter-level accuracy in tens of minutes,only suitable for the stability analysis of reference stations.Over a large area(the baseline distance<100 km),PPP-RTK can provide excellent horizontal accuracy and adapt the service range in response to the demand for monitoring accuracy,as the vertical accuracy is signifcantly impacted by the service range and elevation diference.Finally,the characteristics of three techniques are integrated to form a comprehensive landslide monitoring technique that considers intelligence,robustness,and real-time.
基金National Natural Science Foundation of China(No.42001397)National Key Research and Development Program of China(No.2016YFB0502102)+2 种基金Introduction and Training Program of Young Creative Talents of Shandong Province(No.0031802)Doctoral Research Fund of Shandong Jianzhu University(No.XNBS1985)National College Student Innovation and Entrepreneurship Training Program(No.S202110430036).
文摘Several Wireless Fidelity(WiFi)fingerprint datasets based on Received Signal Strength(RSS)have been shared for indoor localization.However,they can’t meet all the demands of WiFi RSS-based localization.A supplementary open dataset for WiFi indoor localization based on RSS,called as SODIndoorLoc,covering three buildings with multiple floors,is presented in this work.The dataset includes dense and uniformly distributed Reference Points(RPs)with the average distance between two adjacent RPs smaller than 1.2 m.Besides,the locations and channel information of pre-installed Access Points(APs)are summarized in the SODIndoorLoc.In addition,computer-aided design drawings of each floor are provided.The SODIndoorLoc supplies nine training and five testing sheets.Four standard machine learning algorithms and their variants(eight in total)are explored to evaluate positioning accuracy,and the best average positioning accuracy is about 2.3 m.Therefore,the SODIndoorLoc can be treated as a supplement to UJIIndoorLoc with a consistent format.The dataset can be used for clustering,classification,and regression to compare the performance of different indoor positioning applications based on WiFi RSS values,e.g.,high-precision positioning,building,floor recognition,fine-grained scene identification,range model simulation,and rapid dataset construction.
基金This research is supported by the National Natural Science Foundation of China(NSFC)(Nos.42174019 and 41974025)the Fundamental Research Funds for the Central Universities.
文摘In order to facilitate high-precision and real-time Precise Point Positioning(PPP),the International GNSS(Global Navigation Satellite System)Service(IGS),BDS-3(BeiDou-3 Navigation Satellite System),and Galileo navigation satellite system(Galileo)have provided real-time satellite clock correction,which is updated at a high-frequency.However,the frequent updates pose the challenges of increasing the computational burden and compromising the timeliness of these correction parameters.To address this issue,an improved Real-Time Service(RTS)method is developed using an extrapolation algorithm and a linear model.The results indicate that a 1 h arc length of the satellite clock correction series is optimal for fitting a linear model of the RTS.With this approach,the 1 h extrapolation results for BDS-3 and Galileo are superior to 0.09 ns.Moreover,when these model coefficients are transmitted and updated at the intervals of 1,2,5,and 10 min,the corresponding PPP can converge at the centimeter-level.It is evident that these improved RTS methods outperform the current approach with high-frequency interval transmission,as they effectively mitigate the challenges associated with maintaining the timeliness of correction parameters.
基金the Australian Research Council(ARC)Project No.DP170103341.
文摘The implementation of Intelligent Transport System (ITS) technology is expected to significantly improve road safety and traffic efficiency. One of the key components of ITS is precise vehicle positioning. Positioning with decimetre to sub-metre accuracy is a fundamental capability for self-driving, and other automated applications. Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) is an attractive positioning approach for ITS due to its relatively low-cost and flexibility. However, GNSS PPP is vulnerable to several effects, especially those caused by the challenging urban environments, where the ITS technology is most likely needed. To meet the high integrity requirements of ITS applications, it is necessary to carefully analyse potential faults and failures of PPP and to study relevant integrity monitoring methods. In this paper an overview of vulnerabilities of GNSS PPP is presented to identify the faults that need to be monitored when developing PPP integrity monitoring methods. These vulnerabilities are categorised into different groups according to their impact and error sources to assist integrity fault analysis, which is demonstrated with Failure Modes and Effects Analysis (FMEA) and Fault Tree Analysis (FTA) methods. The main vulnerabilities are discussed in detail, along with their causes, characteristics, impact on users, and related mitigation methods. In addition, research on integrity monitoring methods used for accounting for the threats and faults in PPP for ITS applications is briefly reviewed. Both system-level (network-end) and user-level (user-end) integrity monitoring approaches for PPP are briefly discussed, focusing on their development and the challenges in urban scenarios. Some open issues, on which further efforts should focus, are also identified.
基金the National Natural Science Foundation of China(Nos.41774031,41904035,91638203)Hubei Provincial Natural Science Foundation of China(No.2019CFB261)+1 种基金the National Science Fund for Distinguished Young Scholars(No.41825009)Key Laboratory of Geospace Environment and Geodesy,Ministry of Education,Wuhan University(No.19-01-06).
文摘The BeiDou global navigation satellite system(BDS-3)constellation deployment has been completed on June 23,2020,with a full constellation comprising 30 satellites.In this study,we present the performance assessment of single-epoch Real-Time Kinematic(RTK)positioning with tightly combined BeiDou regional navigation satellite system(BDS-2)and BDS-3.We first investigate whether code and phase Differential Inter-System Biases(DISBs)exist between the legacy B1I/B3I signals of BDS-3/BDS-2.It is discovered that the DISBs are in fact about zero for the baselines with the same or different receiver types at their endpoints.These results imply that BDS-3 and BDS-2 are fully interoperable and can be regarded as one constellation without additional DISBs when the legacy B1I/B3I signals are used for precise relative positioning.Then we preliminarily evaluate the single-epoch short baseline RTK performance of tightly combined BDS-2 and the newly completed BDS-3.The performance is evaluated through ambiguity resolution success rate,ambiguity dilution of precision,as well as positioning accuracy in kinematic and static modes using the datasets collected in Wuhan.Experimental results demonstrate that the current BDS-3 only solutions can deliver comparable ambiguity resolution performance and much better positioning accuracy with respect to BDS-2 only solutions.Moreover,the RTK performance is much improved with tightly combined BDS-3/BDS-2,particularly in challenging or harsh conditions.The single-frequency single-epoch tightly combined BDS-3/BDS-2 solution could deliver an ambiguity resolution success rate of 96.9%even with an elevation cut-off angle of 40°,indicating that the tightly combined BDS-3/BDS-2 could achieve superior RTK positioning performance in the Asia-Pacific region.Meanwhile,the three-dimensional(East/North/Up)positioning accuracy of BDS-3 only solution(0.52 cm/0.39 cm/2.14 cm)in the kinematic test is significantly better than that of the BDS-2 only solution(0.85 cm/1.02 cm/3.01 cm)due to the better geometry of the current BDS-3 constellation.The tightly combined BDS-3/BDS-2 solution can provide the positioning accuracy of 0.52 cm,0.22 cm,and 1.80 cm,respectively.
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.
基金supported by the Program of Shanghai Academic Research Leaderthe National Key R&D Program of China(No.2018YFB0504300)+2 种基金Key R&D Program of Guangdong province(No.2018B030325001)the National Natural Science Foundation of China(No.11673050)the Key Program of Special Development funds of Zhangjiang National Innovation Demonstration Zone(Grant No.ZJ2018-ZD-009).
文摘The BeiDou Navigation Satellite System(BDS)employs a hybrid constellation including GEO(Geosynchronous Earth Orbit),IGSO(Inclined Geosynchronous Orbit),and MEO(Medium Earth Orbit)satellites,where the GEO and IGSO satellites are critical to providing continuous and reliable Positioning,Navigation,and Timing(PNT)services in the Asia–Pacifc region.To handle the inconsistency between the satellite orbits and clocks in the broadcast ephemeris,which are determined by the Orbit Determination and Time Synchronization(ODTS)and the Two-way Satellite Time Frequency Transfer(TWSTFT)technique,respectively,we present the strategies using ground-satellite-link observations to improve the accuracy of broadcast ephemeris.The clock diferences between the ODTS and TWSTFT techniques are used for correcting the radial orbit component to derive the refned orbits,which are used to generate the refned broadcast ephemeris.The test results show the precision of the refned orbits is improved by 50–60%in the 3-h to 12-h predicted arcs for the GEO satellites,and by 40–50%for the IGSO satellites.Moreover,the validation using satellite laser ranging observations shows the mean precision of the refned broadcast ephemeris is improved by 27%compared to the original one.Applying the proposed strategies in the BDS Operational Control Segment(OCS),the time evolution of BDS Single Point Positioning(SPP)in the period from Jan.2016 to April 2021 is evaluated.The SPP accuracy is improved from 1.94,2.06 and 3.29 m to 1.39,1.85,and 2.39 m in the north,east,and up components,respectively.Further update with the inclusion of BDS-3 satellites improve the corresponding SPP precision to 0.68,0.70 and 1.91 m.
基金the National Natural Science Foundation of China(41774027)the National Key Research and Development Program(2016YFB0502101)+1 种基金the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX19_0067)the CoDRIVE demonstration project funded under the European Space Agency’s Business Applications initiatives(ESA CoDRIVE Contract Number:4000126688/19/NL/FGL).
文摘The last satellite of BeiDou Navigation Satellite System with Global Coverage(BDS-3)constellation was successfully launched on June 23rd,2020,and the entire system began to provide Positioning,Navigation,and Timing(PNT)services worldwide.We evaluated the performance of location services using BDS with a smartphone that can track the Global Navigation Satellite System(GNSS)satellites in Nottingham,UK.The static and kinematic experiments were conducted in an open meadow and a lakeside route covered by trees,respectively.Experimental results show that BDS has good visibility,and its overall signal carrier-to-noise density ratio(C/N0)is comparable to that of Global Positioning System(GPS).The average C/N0 of BDS-3 satellites with elevation angles above 45°on B1 band is the highest among all systems,reaching 40.0 dB·Hz.The noise level of the BDS pseudorange measurements is within 0.5 m,and it has a good consistency among satellites.In the static experiment,the standard deviations of BDS position-ing in the east,north and up directions are 1.09,1.16,and 3.02 m,respectively,and the R95 value of the horizontal position is 2.88 m.In harsh environments,the number of BDS satellites tracked by the smartphone is susceptible to environmental factors.The bias Root Mean Squares(RMS)in the three directions of the whole kinematic positioning are 6.83,6.68,11.67 m,in which the positioning bias RMS values in a semi-open environment are only 2.81,1.11,3.29 m.Furthermore,the inclusion of BDS in multiple GNSS systems can significantly improve the positioning precision.This study intends to provide a reference for the further improvements of BDS global PNT services,particularly for Location-Based Services(LBS).
基金the National Natural Science Foundation of China(Grant Nos.41901409,41461089)the Guangxi Young and Middle-aged Teacher Basic Ability Improvement Project(Grant No.2018KY0247).
文摘Obtaining high-precision,long-term sequences of vegetation water content(VWC)is of great significance for assessing surface vegetation growth,soil moisture,and fire risk.In recent years,the global navigation satellite system-interferometric reflection(GNSS-IR)has become a new type of remote sensing technology with low cost,all-weather capability,and a high temporal resolution.It has been widely used in the fields of snow depth,sea level,soil moisture content,and vegetation water content.The normalized microwave reflectance index(NMRI)based on GNSS-IR technology has been proven to be effective in monitoring changes in VWC.This paper considers the advantages and disadvantages of remote sensing technology and GNSS-IR technology in estimating VWC.A point-surface fusion method of GNSS-IR and MODIS data based on the GA-BP neural network is proposed to improve the accuracy of VWC estimation.The vegetation index products(NDVI,GPP,LAI)and the NMRI that unified the temporal and spatial resolution were used as the input and output data of the training model,and the GA-BP neural network was used for training and modeling.Finally,a spatially continuous NMRI product was generated.Taking a particular area of the United States as a research object,experiments show that(1)a neural network can realize the effective fusion of GNSS-IR and MODIS products.By comparing the GA-BP neural network,BP neural network,and multiple linear regression(MLR),the three models fusion effect.The results show that the GA-BP neural network has the best modeling effect,and the r and RMSE between the model estimation result and the reference value are 0.778 and 0.0332,respectively;this network is followed by the BP neural network,in which the r and RMSE are 0.746 and 0.0465,respectively.MLR has the poorest effect,with r and RMSE values of 0.500 and 0.0516,respectively.(2)The spatiotem-poral variation in the 16 days/500 m resolution NMRI product obtained by GA-BP neural network fusion is consistent with that in the experimental area.Through the testing of GNSS stations that did not participate in the modeling,the r between the estimated value of the NMRI and the reference value is greater than 0.87,and the RMSE is less than 0.049.Therefore,the method proposed in this paper is optional and effective.The spatially continuous NMRI products obtained by fusion can reflect the changes in VWC in the experimental area more intuitively.
基金Canada Research Chairs programs(Grant No.RT691875).
文摘This paper reviews the state of the art and future trends of indoor Positioning,Localization,and Navigation(PLAN).It covers the requirements,the main players,sensors,and techniques for indoor PLAN.Other than the navigation sensors such as Inertial Navigation System(INS)and Global Navigation Satellite System(GNSS),the environmental-perception sensors such as High-Definition map(HD map),Light Detection and Ranging(LiDAR),camera,the fifth generation of mobile network communication technology(5G),and Internet-of-Things(IoT)signals are becoming important aiding sensors for PLAN.The PLAN systems are expected to be more intelligent and robust under the emergence of more advanced sensors,multi-platform/multi-device/multi-sensor information fusion,self-learning systems,and the integration with artificial intelligence,5G,IoT,and edge/fog computing.
基金Dr.Naser El-Sheimy research funds from NSERC and Canada Research Chairs programs(Grant No.RT691875).
文摘Inertial navigation represents a unique method of navigation,in which there is no dependency on external sources of information.As opposed to other position fixing navigation techniques,inertial navigation performs the navigation in a relative sense with respect to the initial navigation state of the moving platform.Hence,inertial navigation systems are not prone to jamming,or spoofing.Inertial navigation systems have developed vastly,from their occurrence in the 1940s up to date.The accuracy of the inertial sensors has improved over time,making inertial sensors sufficient in terms of size,weight,cost,and accuracy for navigation and guidance applications.Within the past few years,inertial sensors have developed from being purely mechanical into incorporating various technologies and taking advantage of numerous physical phenomena,from which the dynamic forces exerted on a moving body could be computed accurately.Besides,the evolution of inertial navigation scheme involved the evolution from stable-platform inertial navigation system,which were mechanically complicated,to computationally demanding strap-down inertial navigation systems.Optical sensory technologies have provided highly accurate inertial sensors,at smaller sizes.Besides,the vibratory inertial navigation technologies enabled the production of Micro-electro-machined inertial sensors that are extremely low-cost,and offer extremely low size,weight and power consumption,making them suitable for a wide range of day-to-day navigation applications.Recently,advanced inertial sensor technologies have been introduced to the industry such as nuclear magnetic resonance technology,coldatom technology,and the reintroduction of fluid-based inertial sensors.On another note,inertial sensor errors constitute a huge research aspect in which it is intended for inertial sensors to reach level in which they could operate for substantially long operation times in the absence of updates from aiding sensors,which would be a huge leap.Inertial sensors error modeling techniques have been developing rapidly trying to ensure higher levels of navigation accuracy using lower-cost inertial sensors.In this review,the inertial sensor technologies are covered extensively,along the future trends in the inertial sensors’technologies.Besides,this review covers a brief overview on the inertial error modeling techniques used to enhance the performance of low-cost sensors.
基金the support of The Hong Kong PolyU startup fund on the project 1-ZVKZ,“Navigation for Autonomous Driving Vehicle using Sensor Integration.”。
文摘Global Navigation Satellites Systems(GNSS)is frequently used for positioning services in various applications,e.g.,pedestrian and vehicular navigation.However,it is well-known that GNSS positioning performs unreliably in urban environments.GNSS shadow matching is a method of improving accuracy in the cross-street direction.Initial position and classification of observed satellite visibility between line-of-sight(LOS)and non-line-of-sight(NLOS)are essential for its performance.For the conventional LOS/NLOS classification,the classifiers are based on a single feature,extracted from raw GNSS measurements,such as signal noise ratio,pseudorange,elevation angle,etc.Especially in urban canyons,these measurements are unstable and unreliable due to the signal reflection and refraction from the surrounding buildings.Besides,the conventional least square approach for positioning is insufficient to provide accurate initialization for shadow matching in urban areas.In our study,shadow matching is improved using the initial position from robust estimator and the satellite visibility determined by support vector machine(SVM).The robust estimator has an improved positioning accuracy and the classification rate of SVM classification can reach 91.5%in urban scenarios.An important issue is related to satellites with ultra-high or low elevation angles and satellites near the building boundary that are very likely to be misclassified.By solving this problem,the SVM classification shows the potential of about 90%classification accuracy for various urban cases.With the help of these approaches,the shadow matching has a mean error of 10.27 m with 1.44 m in the cross-street direction;these performances are suitable for urban positioning.
基金The Major Consulting Research Project of Chinese Academy of Engineering(No.2018-ZD-02-07)The Wuhan Science and Technology Project(No.2018010401011271)+1 种基金The Major Consulting Research project of China Academy of Engineering(No.2020-ZD-16)China’s Engineering Science and Technology Development Strategy Hubei Research Institute Wuhan Branch Consulting Project.
文摘Communication,positioning,navigation,and decision-making abilities have evolved into Positioning,Navigation,and Timing(PNT)intelligence during the long process of human migration and hence promoted human evolution.This article defines intelligence and smartness from the perspective of biological intelligence.New requirements as a result of the development of communication,navigation,time service,and decision making are identified in this study.The article points out that there are many radio PNT service methods,such as 5G,the new-generation high-speed communication networks and the low-latency and ubiquitous mobile communication networks as well as Global Navigation Satellite System(GNSS),but the integrated application is especially important in providing technical support for the adjustment and control of the physical world by intelligent sensing,cognition,decision-making,and precise coordination.The fusion of 5G and GNSS[including BeiDou Navigation Satellite System(BDS)]information with the corresponding equipment can be embedded into a machine to make it intelligent.Furthermore,the fused information of 5G and GNSS together with the environment information may extend human perception and physical world control ability in terms of time and space scale.It will help to develop critical information infrastructure in the age of intelligence,which will also extend the definition of artificial intelligence.Additionally,the“5G+BDS/GNSS”fusion path is analyzed explicitly herein in terms of realization methods,information processing,and new application services.On the whole,the application of“5G+BDS/GNSS+satellite-based communication”as a critical infrastructure for land,sea,air,space and network spatiotemporal control rights is proposed.
基金supported by the National Key Research and Development Program of China(grant nos.2023YFB3906600)the NSFC(grant no.42201460).
文摘Smartphone-based vehicle navigation has become the primary choice in everyday life due to low cost and real-time traffic updates.However,for vehicle navigation applications in the Global Navigation Satellite System(GNSS)-denied scenario such as parking lot and tunnel,it is quite difficult to maintain robust and continuous positioning based on consumer-grade sensors.In this paper,a novel method is proposed for accurate vehicular dead-reckoning based only on a smartphone inertial measurement unit.Robust vehicle dead reckoning can improve positioning performance in GNSS-degraded areas or where high-precision positioning sources are available at low-frequencies.The key components of the method are a Kalman filter with data-driven parameters adapter and a deep neural network that provides data-driven measurement estimation.A combined convolutional neural network and gated recurrent unit deep learning network,termed AVNet,is proposed to estimate the attitude and velocity of the vehicle.The learned measurements are integrated into an invariant Kalman filter to estimate Three-Dimensional(3D)attitude,velocity and position.The method was tested on custom datasets collected in a parking lot,and a 0.4%relative horizontal translation error was achieved on average.
基金the National Natural Science Foundation of China(Grant Nos.41704035 and 42774012)Office of China Navigation Satellite System(Project No.GFZX03010403).
文摘To provide competitive global positioning and timing services under the condition that monitoring stations are confined to Chinese territory,inter-satellite link(ISL)technology is used by the third-generation BeiDou Navigation Satellite System(BDS-3).The ISL,together with the dual one-way links between satellites and anchor stations,may enable autonomous navigation for BDS-3.In this paper,we propose a general observation model for orbit determination(OD)and time synchronization(TS)directly using non-simultaneous observations,such as raw ISL pseudoranges.With the proposed model,satellite orbits,clocks,and hardware delay biases of ISL equipment can be determined simultaneously by jointly processing inter-satellite one-way pseudorange data and observation data from ground monitoring stations.Moreover,autonomous OD and TS are also achievable with one-way pseudorange data from anchor stations and satellites.Data from eight BDS-3 satellites,two anchor stations,and seven monitoring stations located in China were collected to validate the proposed method.It is shown that by jointly processing data from the ISL and seven monitoring stations,the RMS of overlap orbit differences in radial direction is 0.019 m,the overlap clock difference(95%)is 0.185 ns,and the stability of the estimated hardware delay biases for each satellite is greater than 0.5 ns.Compared with the results obtained with the seven stations,the improvements of orbits in radial direction and clocks are 95.7%and 90.5%,respectively.When the hardware delay biases are fixed to predetermined values,the accuracies of orbits and clocks are further improved.By jointly processing pseudoranges from the satellites and the two anchor stations,the RMS of overlap orbit differences is 0.017 m in the radial direction,and the overlap clock difference(95%)is 0.037 ns.It has also been demonstrated that under the condition of one-way ranging links,the accuracies of orbits and clocks obtained by the above two modes are still significantly better than those obtained by using the data from the monitoring stations alone.
基金Science and Technology on Complex System Control and Intelligent Agent Cooperative Laboratory foundation(201101).
文摘Unmanned clusters can realize collaborative work,fexible confguration,and efcient operation,which has become an important development trend of unmanned platforms.Cluster positioning is important for ensuring the normal operation of unmanned clusters.The existing solutions have some problems such as requiring external system assistance,high system complexity,poor architecture scalability,and accumulation of positioning errors over time.Without the aid of the information outside the cluster,we plan to construct the relative position relationship with north alignment to adopt formation control and achieve robust cluster relative positioning.Based on the idea of bionics,this paper proposes a cluster robust hierarchical positioning architecture by analyzing the autonomous behavior of pigeon focks.We divide the clusters into follower clusters,core clusters,and leader nodes,which can realize fexible networking and cluster expansion.Aiming at the core cluster that is the most critical to relative positioning in the architecture,we propose a cluster relative positioning algorithm based on spatiotemporal correlation information.With the design idea of low cost and large-scale application,the algorithm uses intra-cluster ranging and the inertial navigation motion vector to construct the positioning equation and solves it through the Multidimensional Scaling(MDS)and Multiple Objective Particle Swarm Optimization(MOPSO)algorithms.The cluster formation is abstracted as a mixed direction-distance graph and the graph rigidity theory is used to analyze localizability conditions of the algorithm.We designed the cluster positioning simulation software and conducted localizability tests and positioning accuracy tests in diferent scenarios.Compared with the relative positioning algorithm based on Extended Kalman Filter(EKF),the algorithm proposed in this paper has more relaxed positioning conditions and can adapt to a variety of scenarios.It also has higher relative positioning accuracy,and the error does not accumulate over time.
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(61601009,41974041)the Young Talent Supporting Program of the China Association for Science and Technology(2019QNRC001).
文摘Satellite Based Augmentation System (SBAS) provides the corrections and integrity information to users, but as its signal format is opened to the public and Global Navigation Satellite System (GNSS) spoofing technology becomes more realistic, more feasible and cheaper. It’s foreseeable that there will be risks of spoofing threats against SBAS in the future. SBAS signal authentication technology provides a system-level solution to spoofing threats by adding special markers to SBAS signals so that receivers can verify whether the SBAS signals are from the on-orbit Geostationary Earth Orbit (GEO) satellites or whether the signal information has been forged and tampered with. First, this article introduces the existing anti-spoofing methods that can be applied to SBAS, especially the Elliptic Curve Digital Signature Algorithm (ECDSA) and Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocols. Then it discusses four possible solutions in a combination with the existing SBAS Interface Control Document (ICD). Two main Key Performance Indicators (KPIs), Time Between Authentication (TBA) and Authentication Latency (AL), obtained in the four main scenarios are compared. By analyzing the EGNOS Authentication Security Testbed (EAST) test simula-tion results of European Geostationary Navigation Overlay Service (EGNOS) in Europe, the impact of SBAS after joining the authentication service is obtained.
