Abstract:With the emergence of autonomous navigation systems such as robots and unmanned vehicles,positioning and navigation technology has developed rapidly in the past 20 years.However,new user requirements have been raised for update of positioning and navigation,which include reliable positioning and navigation ability in any environment at any time and on any platform.Multi-source fusion positioning algorithm is the only feasible way to achieve this goal.Based on the sensor model,scene model and vehicle dynamics model,we summarize positioning methods of GNSS,inertial navigation,visual sensor,and LiDAR.Then we analyze the influence that the positioning scene and vehicle dynamics pose on the multi-source fusion positioning.Finally,the multi-source fusion positioning algorithms are detailed under two fusion framework categories of optimization and filtering.

Abstract:Aiming at the low positioning accuracy of the GNSS positioning chip of the smart phone in occluded environment,this paper uses the RTK/PDR fusion method to solve the position results.Considering that the GNSS signal is susceptible to environment noise,different expansion coefficients are set to amplify the measurement noise variance matrix R in Kalman fusion filtering to realize the weight reduction of GNSS position information in occluded environment,so as to obtain better fusion results.The experimental test shows that in open environment,the positioning accuracies were identical between RTK and RTK+PDR for both two test mobile phones.While in the slightly occluded environment,compared with the RTK single positioning,the RTK+PDR fusion positioning improved the plane lifting effect of the two test mobile phones by 6.24% and 3.97%,and improved the elevation lifting effect by 20.44% and 32.56%.In the severely occluded environment,the RTK+PDR fusion positioning improved the plane lifting effect of the two test mobile phones by 47.65% and 42.90% compared with the RTK single positioning,and improved the elevation lifting effect by 39.78% and 67.98%.The experimental results show that the RTK + PDR fusion positioning method,which dynamically sets the GNSS information weight according to the average satellite carrier to noise ratio,can partially compensate for the reduction of positioning accuracy caused by environment occlusion for mobile phones using RTK.

Abstract:This paper investigates the accuracy of BDS3 PPP-B2b corrections,the service scope,and the performance of precise point positioning (PPP).The results show that PPP-B2b improves the broadcast orbit by 4.3%,6.2% and 16.1% in radial,cross-track and along-track directions respectively;while the satellite clock errors are decreased by 81.8%,showing a standard deviation of 0.22 ns.In terms of service coverage,the availability of PPP-B2b service reaches more than 80% in China and more than 70% in the whole Asian area.In terms of positioning performance,the use of PPP-B2b signal for PPP solution reaches centimeter level for static PPP solution,and decimeter level for kinematic PPP solution with average convergence time of 22.9 min.

Abstract:In this paper,BP neural network and random forest regression algorithm are used to correct the temperature profile data of FY-3C GNSS radio occultation in 2017.The results show that both methods can correct FY-3C radio occultation temperature data,but the performance of the random forest regression is better than that of the neural network.For the random forest regression algorithm and the neural network,the mean absolute errors between the corrected results and the reanalysis data are 0.03 K and 0.32 K,respectively,and the mean square errors are 0.09 K² and 1.02 K²,respectively.When the globe is divided into 324 grids of 10°×10°,the random forest regression algorithm yields positive returns of 97.53% and 92.9% for average absolute error and mean square error corrections,respectively,and neural network produces positive returns of 75.61% for average absolute error correction and 67.9% for mean square error correction.

Abstract:To comprehensively evaluate the services provided by the BeiDou Navigation Satellite System(BDS-3),a concept of Quality of Service(QoS) in network communication is introduced and then a QoS hierarchical model is proposed.A preliminary classified evaluation index design is given,covering BDS-3 services of Radio Navigation Satellite Service(RNSS),Satellite-Based Augmentation System(SBAS),Precise Point Positioning(PPP),Regional Short Message Communication(RSMC),Global Short Message Communication(GSMC),Search and Rescue(SAR) and Ground Augmentation System(GAS).Then the service guarantee mechanism and parameters mapping relationship are analyzed,thus to provide a way to optimize multiple QoS indicators in complex conditions and quickly locate the source of the fault in abnormal conditions.The research results are expected to provide references for the comprehensive evaluation of BDS performance.

Abstract:The correct fixation of the ambiguity has a vital impact on GNSS high-precision positioning and navigation.To address the threshold determination problems existed in conventional difference tests,this paper proposes a threshold determination method based on fixed correct rates under the framework of integer aperture estimation.This method can not only select a reasonable difference test threshold according to the ambiguity's dimension,but also ensure a reliable accuracy,which has certain theoretical significance and practical value.

Abstract:The accurate survey is of great significance to water resources in terms of efficient utilization,ecological environment protection and resource management.However,most of the current water resource investigation researches were based on high-resolution satellite data,which cannot meet the accuracy requirement for survey of water resources in underlying surface of complex plain urban region.Here,an investigation method is proposed for water resources quantity,which is based on UAV(unmanned aerial vehicle) remote sensing,SWAT model and geographic information technology.In this method,the accurate distribution of surface water can be obtained by field investigation,and the total quantity of water resource including groundwater and duplicated amount between surface water and groundwater are estimated by the hydrological model with underlying surface data from the third National Land Survey.Then this method is applied to a plain city of Pizhou,where the river network is complex,to verify its feasibility and accuracy as well as analyze Pizhou's water resource characteristics.The results illustrate that,compared to conventional approaches,the proposed method considers more factors and has less uncertainty,thus can provide a highly reliable methodology for urban water resources investigation.

Abstract:In view of the difficulties in data processing and adjustment of coordinate calculation perplexed large-scale GNSS reference station network,this paper proposes a coordinate calculation method.The method is elaborated in four aspects including selection of global framework sites,division of reference station network subnets,single-day data processing of base stations,and global network adjustment calculation.Finally,the internal and external consistence accuracies of the calculation results are evaluated.The analysis results show that the method can solve reference coordinates for network with more than 3 000 stations,and the RMSE of the results is better than 3 mm in both north-south and east-west directions,and better than 6 mm in elevation.The accuracy of the calculation is higher than those of most IGS analysis centers.

Abstract:A baseline field test equipment which can rotate automatically is introduced in this paper.Comprehensively integrated with technologies of advanced MEMS inertial navigation,ARM embedding,Wi-Fi wireless transmission,high stability motor drive and high-efficiency power management,this equipment can realize automatic measurement of antenna phase center deviation as well as real time north pointing function.The test results show that the rotation error of the turntable is within 0.1° and the north pointing error is within 1°.This research shows that the automatic measurement system of antenna phase center deviation has advantages of high accuracy,high efficiency and high automation,and has solved the problems of low automation level and the lack of automatic north seeking perplexed tradition measurement methods.Furthermore,the system is integrated into a 35 cm×30 cm×30 cm portable suitcase and weighed less than 10 kg,which makes it easy to use and maintain.

Abstract:The accuracy of stochastic model directly affects the precision and reliability of GNSS precision positioning.With 10-day observation data of CUT0,CUT2 and CUTA stations in MEGX observation network,the residuals time series of GNSS were solved by single-difference model using short baseline method.According to the statistically observed noises changing with the elevation angle,a refined stochastic model is established via the least-square method.The results show that the range of pseudo-range observation precision lies in 20-50 cm,30-50 cm and 42-63 cm for Galileo,BDS and GPS,respectively;and the carrier phase observation precision falls within the scope of 1-3 mm for Galileo and BDS,and on 3 mm for GPS.For the four frequencies of Galileo,E5 is most accurate in both pseudo-range observation and carrier phase;the accuracies of B1,B2,B3 of BDS are roughly the same;the L2 of GPS is more accurate in pseudo-range observation with precision of 42 cm than L1 of 63 cm,and both L1 and L2 have carrier phase precision of 3 mm.From the above precision estimations based on single-difference model,it can be concluded that in case of short baseline,BDS/GPS/Galileo have roughly same precision in carrier phase observation values,while Galileo E5 outperforms the other satellite systems in pseudo-range observations.Residual analysis of satellite observations provides a basis for the establishment of stochastic models in positioning.

Abstract:Mobile phone RTK is vulnerable to interferences from complex environment,and the heading angle of inertial navigation data is easily divergent in scenario of mobile phone vehicle positioning.To address these problems,this paper proposes an RTK/DR loose combination positioning method combined with OSM map data.In the process of dead reckoning,based on the OSM data,combined with the information of combined positioning results and vehicle motion state,a geometric matching method from point to line was designed,and the matched road direction was used to correct heading angle.In the loose combination stage,the standard Kalman filter was used to estimate the position and velocity.In order to reduce the influence of large drift or jump of RTK on the results of loose combination,a loose combination switch was set,which can comprehensively judge whether to update the measurement by combining the covariance matrix,the vehicle's moving direction and the change of RTK positioning heading angle in RTK robust Kalman solution.Then six groups of experiment were carried out by using P30 and P40 smart phones.The results show that the introduction of OSM data can effectively solve the accumulation of heading angle error,which makes dead reckoning trajectory more consistent with the benchmark.Compared with mobile RTK,the proposed RTK/DR loose combination with switch improves positioning performance,and effectively suppresses error points of large jumps.

Abstract:All observations inevitably contain outliers.Outlier detection is a particularly tough problem under the complex conditions of the combination of multi-frequency and multi-constellation and urban canyon environments.Here,outlier detection is studied to ensure accurate and reliable positioning performance of BDS/GNSS data.The outlier detection schemes with different thresholds were proposed based on mean shift and variance inflation.Then dedicated experiments under complex conditions were carried out to evaluate the performance of the proposed outlier detection schemes.The experimental results show that the RMSE of the mean shift based small threshold(U_1/2α2(0,1)) scheme is improved by 0.059 m,0.017 m,and 0.062 m in the E,N,and U directions,respectively.The RMSE of the combined large iterative threshold(ω) and small threshold (k₀、k₁) scheme based on variance inflation is improved by 0.098 m,0.055 m,and 0.209 m in the E,N,and U directions,respectively.The results show that the above two schemes can detect and identify outliers under complex conditions.

Abstract:Based on the PPP-B2b service provided by the new BDS3 satellite navigation system,the performance of PPP including convergence time and positioning accuracy is analyzed via receivers with different pseudo-range accuracies.The results show that the accuracy of BDS3-only system after convergence(about 30 min) is better than 0.15 m in horizontal and 0.17 m in vertical direction,respectively.While the accuracy of BDS3/GPS dual system after convergence(about 20 min) is 0.11 m in horizontal and 0.13 m in vertical direction,respectively,both of which are better than the BDS3-only solution.The accuracy of BDS3/GPS solution is improved by 26.7% and 23.5% in horizontal and vertical direction,respectively,when compared with BDS3-only solution.In addition,it also shows that the receiver A with average pseudo-range accuracy of 1.681 m can reach 3D accuracy of 0.331 m(BDS3-only) after convergence of 30 min,and realize 3D accuracy of 0.250 m(BDS3/GPS) after convergence of 20 min in static mode.For the receiver B with average pseudo-range accuracy of 0.873 m,the 3D accuracy is improved from 0.221 m(BDS3-only) with convergence time of 30 min,to 0.167 m(BDS3/GPS) with convergence time of 20 min in static mode.From the above comparisons,it is clearly shown that the receiver B with pseudo-range improved by 0.808 m,can improve positioning accuracy by 33.4% after convergence in BDS3-only solution and 33.2% in BDS3/GPS solution,respectively.

Abstract:Based on data from BeiDou ground-based augmentation monitoring station in Shaanxi province,a Shaanxi regional ionospheric total electron content(TEC) model is established using the fourth-order spherical harmonic function to generate regional TEC grid products.The experimental results show that the accuracy of the Shaanxi regional ionospheric products obtained from BDS-3 data is 2.54 TECu,which is comparable to the nominal accuracy of the Global Ionospheric Map(GIM) product of the Center for Orbit Determination(CODE).In terms of single frequency precise point positioning(SF-PPP) performance,the BDS-3 regional ionospheric product improves the positioning accuracy by 35%,which is better than the correction performance of the CODE global ionospheric product(27%).Overall,the BDS-3 single system has superior performance in regional ionospheric modeling.

Abstract:To deal with the contact force for industrial robots,this paper reviewed the existing traditional control strategies including impedance control,position/force hybrid control and adaptive control,and overviewed intelligent control strategies such as fuzzy control,neural network and optimal control.This paper detailed the basic principles of each robot force control algorithm,then enumerated some application results,and prospected the future development of robot force control.

Abstract:Traditional protocols are perplexed by complex testing equipment and long development cycle,thus are not appropriate for protocol testing and evaluation in a certain field of aerospace.The HDLC protocol has been widely used in applications demanding of high reliability because of its excellent performance.Here,we propose a scheme to build HDLC protocol transceiver based on LabVIEW software,with the aim of rapid system integration and flexible configuration of protocol parameters.The HDLC core transceiver module is designed,on which a complete test system is formed.This paper introduces the HDLC protocol processing as well as the program design of receiving and sending,and elaborates the realization of the Cyclic Redundancy Check(CRC) module and the bit insert & delete module in the transceiver.Meanwhile,the main function modules of the transceiver are simulated and tested.The results show that the proposed HDLC transceiver is light in weight,efficient and flexible in operation.It can be applied to scenarios such as the testing of HDLC protocol equipment and protocol performance analysis to improve the data communication system in scalability,real-time performance and stability.