Solar Radiation Pressure Modeling and Application of BDS Satellites

Solar radiation pressure(SRP)model is the basis of high precise orbit determination and positioning of navigation satellites.At present,it is common to see the study of SRP model of BDS satellites.However,the establishment and application of a comprehensive analytical SRP model based on satellite physical parameters are rare.Different from other conservative forces and non-conservative forces,SRP is closely related to the satellite’s physical parameters and in-orbit state.On the basis of the physical mechanism of solar radiation,BDS satellite physical parameters,in-orbit attitude control mode,and so on,a comprehensive analytical model has been studied in this paper.Based on precise ephemeris and satellite laser ranging(SLR)data,the precision of a comprehensive analytical model has been verified.And the precision of orbit determination is at the decimeter level using this comprehensive analytical SRP model.According to the satellite conservation theorem of angular momentum and change of in-orbit telemetry parameters,the difference between a comprehensive analytical model and the actual in-orbit interference force has been analyzed and calculated.The addition of empirical items on the comprehensive analytical model has been proposed.SLR validations demonstrated that the orbit precision of BDS C08 and C10 can be achieved at 0.078 m and 0.084 m respectively.Compared with using the improved CODE empirical model,precision orbit accuracy of them has increased by 0.021 m and 0.045 m respectively.

BDSec:Security Authentication Protocol for BeiDou-Ⅱ Civil Navigation Message

Due to the lack of authentication mechanism in BeiDou navigation satellite system(BDS),BD-Ⅱ civil navigation message(BDⅡ-CNAV) are vulnerable to spoofing attack and replay attack.To solve this problem,we present a security authentication protocol,called as BDSec,which is designed by using China’s cryptography Shangyong Mima(SM) series algorithms,such as SM2/4/9 and Zu Chongzhi(ZUC)algorithm.In BDSec protocol,both of BDⅡ-CNAV and signature information are encrypted using the SM4 algorithm(Symmetric encryption mechanism).The encrypted result is used as the subject authentication information.BDSec protocol applies SM9 algorithm(Identity-based cryptography mechanism) to protect the integrity of the BDⅡ-CNAV,adopts the SM2 algorithm(Public key cryptosystem) to guarantee the confidentiality of the important session information,and uses the ZUC algorithm(Encryption and integrity algorithm) to verify the integrity of the message authentication serial number and initial information and the information in authentication initialization sub-protocol respectively.The results of the SVO logic reasoning and performance analysis show that BDSec protocol meets security requirements for the dual user identity authentication in BDS and can realize the security authentication of BDⅡ-CNAV.

Data-Driven Heuristic Assisted Memetic Algorithm for Efficient Inter-Satellite Link Scheduling in the BeiDou Navigation Satellite System

Inter-satellite link(ISL)scheduling is required by the BeiDou Navigation Satellite System(BDS)to guarantee the system ranging and communication performance.In the BDS,a great number of ISL scheduling instances must be addressed every day,which will certainly spend a lot of time via normal metaheuristics and hardly meet the quick-response requirements that often occur in real-world applications.To address the dual requirements of normal and quick-response ISL schedulings,a data-driven heuristic assisted memetic algorithm(DHMA)is proposed in this paper,which includes a high-performance memetic algorithm(MA)and a data-driven heuristic.In normal situations,the high-performance MA that hybridizes parallelism,competition,and evolution strategies is performed for high-quality ISL scheduling solutions over time.When in quick-response situations,the data-driven heuristic is performed to quickly schedule high-probability ISLs according to a prediction model,which is trained from the high-quality MA solutions.The main idea of the DHMA is to address normal and quick-response schedulings separately,while high-quality normal scheduling data are trained for quick-response use.In addition,this paper also presents an easy-to-understand ISL scheduling model and its NP-completeness.A seven-day experimental study with 10080 one-minute ISL scheduling instances shows the efficient performance of the DHMA in addressing the ISL scheduling in normal(in 84 hours)and quick-response(in 0.62 hour)situations,which can well meet the dual scheduling requirements in real-world BDS applications.

粒子滤波算法在BDS高铁铁轨静态形变监测中的应用研究

高铁因每天清晨需要6h的空窗期维修时间而无法通行,社会的发展需要减少空窗期时间来提高高铁运转效率。传统的基于北斗卫星导航系统(BeiD ou Navigation Satellite System,BDS)的高铁铁轨路基的形变监测系统需要一天的观测时长对路基进行精确的监测,这远超高铁空窗期的观测时长无法对提高高铁运转效率起到作用。针对这种情况,在原形变监测解算算法上加入粒子滤波算法,尝试将观测时长缩减到高铁空窗期内;同时,在采样数据大幅度下降的情况下确保解算的监测点坐标值满足高铁路基的定位精度要求。本文利用广汕高铁的BDS形变监测系统的实测采样数据进行实验仿真,验证了粒子滤波算法加入后的有效性。实验结果表明,在粒子滤波算法加持下,观测时长缩减到15 min可确保监测点解算坐标值的A,B,H 3个方向精度均满足高铁路基定位的±5 mm精度要求,为减少高铁空窗期时间,提升高铁运转效率提供了有效的方法和思路。

Modeling and Prediction of Inter-System Bias for GPS/BDS-2/BDS-3 Combined Precision Point Positioning

The combination of Precision Point Positioning(PPP)with Multi-Global Navigation Satellite System(MultiGNSS),called MGPPP,can improve the positioning precision and shorten the convergence time more effectively than the combination of PPP with only the BeiDou Navigation Satellite System(BDS).However,the Inter-System Bias(ISB)measurement of Multi-GNSS,including the time system offset,the coordinate system difference,and the inter-system hardware delay bias,must be considered for Multi-GNSS data fusion processing.The detected ISB can be well modeled and predicted by using a quadratic model(QM),an autoregressive integrated moving average model(ARIMA),as well as the sliding window strategy(SW).In this study,the experimental results indicate that there is no apparent difference in the ISB between BDS-2 and BDS-3 observations if B1I/B3I signals are used.However,an obvious difference in ISB can be found between BDS-2 and BDS-3 observations if B1I/B3I and B1C/B2a signals are used.Meanwhile,the precision of the Predicted ISB(PISB)on the next day of all stations is about 0.1−0.6 ns.Besides,to effectively utilize the PISB,a new strategy for predicting the PISB for MGPPP is proposed.In the proposed strategy,the PISB is used by adding two virtual observation equations,and an adaptive factor is adopted to balance the contribution of the Observed ISB(OISB)and the PISB to the final estimations of ISB.To validate the effectiveness of the proposed method,some experimental schemes are designed and tested under different satellite availability conditions.The results indicate that in open sky environment,the selective utilization of the PISB achieves almost the same positioning precision of MGPPP as the direct utilization of the PISB,but the convergence time of MGPPP is reduced by 7.1%at most in the north(N),east(E),and up(U)components.In the blocked sky environment,the selective utilization of the PISB contributes to more significant improvement of the positioning precision and convergence time than that in the open sky environment.Compared with the direct utilization of the PISB,the selective utilization of the PISB improves the positioning precision and convergence time by 6.7%and 12.7%at most in the N,E,and U components,respectively.

北斗导航系统卫星激光测距综述

Satellite laser ranging(SLR)is an unambiguous measurement technique and generates high accuracy satellite orbit data.All satellites in the BeiDou navigation satellite system(BDS)carried laser retro-reflector arrays(LRAs),so they can be tracked by ground SLR stations in order to provide the accurate observation data.The Shanghai astronomical observatory(SHAO)designed the LRAs,and also developed the dedicated SLR systems using a 1 m-aperture telescope and a transportable cabin-based SLR system with a telescopes of 60 cm aperture.These enable BDS satellite ranging during daytime and nighttime with centimeter-level precision,allowing highly accurate estimations of satellite orbits.Moreover,some of the BDS satellites are also equipped with laser time transfer(LTT)payloads,which were developed by the SHAO and China Academy of Space Technology(CAST),providing a highly accurate time comparison between the satellites and ground clocks.This paper describes the dedicated SLR system and the design of the LRAs for BDS satellites,as well as global SLR measurements.The SLR tracking data is used for evaluating the orbit accuracy of BDS satellites and broadcast ephemeris,with an accuracy of less than 1 m.The LTT measurements to BDS satellites for a single shot have a precision of approximately 300 picoseconds,with a time stability of 20 picoseconds in 500 s.

北斗专列—LM-3A系列火箭发展回顾和未来展望

The LM-3A series launch vehicle was used for all launch missions for the BeiDou Navigation Satellite System(BDS)project,including BDS-1,BDS-2,and BDS-3.So it is known as Space Express for BDS.During the 26 years’development period for the BDS project,a series of key technological breakthroughs with the LM-3 A series of launch vehicles were made,improving the launch capability of different payloads into GTO,IGTO and MTO,from sending one satellites into transfer orbit to sending two satellites into transfer orbit,to sending two satellites into target orbit directly.A total of 59 satellites in 44 launches were launched using the LM-3 A series launch vehicle for the BDS project,achieving 100%success.

Estimation of BDS pseudorange biases with high temporal resolution:feasibility,affecting factors,and necessity

A common practice adopted for the pseudorange bias estimation and calibration assumes that Global Navigation Satellite System satellite-dependent pseudorange biases vary gently over time.Whereupon satellite pseudorange biases are routinely estimated and provided as the products with low temporal resolution,e.g.,hourly or daily,by the agencies.The story sounds unquestionably perfect under the acquainted assumption.To validate the inadequacy of the above hypothesis we herein present an approach to the estimate the BeiDou Navigation Satellite System(BDS)pseudorange biases with high temporal resolution.Its feasibility,affecting factors,and necessity are discussed.Concretely,the Geometry-Free function models are first constructed to retrieve the linear combination of the pseudorange biases;then the pseudorange Observable-specific Signal Bias(OSB)values with respect to baseline frequencies(e.g.,BDS C2I/C6I)are estimated along with the ionosphere modeling;subsequently,all multi-frequency pseudorange OSBs are determined by using the ionospheric information with constraint conditions;finally,the possible Differential Code Bias sets are attainable with the estimated pseudorange OSBs.Using the observation data of four months when the estimated BDS pseudorange biases are stable,their reliability is demonstrated with the stability at the level of sub-nanosecond and the BeiDou-3 Navigation Satellite System(BDS-3)values more stable than that of BeiDou-2 Navigation Satellite System(BDS-2).The comparison between the estimated pseudorange biases and the Chinese Academy of Sciences products reveals that the accuracy of the estimated pseudorange biases is 0.2–0.4 ns.Moreover,the large magnitude of the short-term pseudorange bias variation in the tens of nanoseconds for the BDS-2 and BDS-3 are found in years 2021 and 2022,which are affected by two types of the satellite flex power for the BDS-2 and BDS-3,respectively.We stress that it’s necessary to estimate the BDS pseudorange biases with high temporal resolution in the case of the satellite flex power and the products currently provided by the agencies cannot reflect the true quantity under the circumstance.

地基BDS/GNSS水汽精细处理及应用研究综述

随着北斗卫星导航系统/全球导航卫星系统(BeiDou navigation satellite system/global navigation satellite system,BDS/GNSS)的建设发展和地面基准站的迅猛增加,BDS/GNSS精细水汽处理及应用成为卫星导航定位和大气探测交叉融合的研究热点。围绕BDS/GNSS水汽产品高精度、高分辨率处理及气象和空间大地测量应用研究,从对流层模型、处理方法及产品构建等方面对BDS/GNSS水汽精细化处理研究现状进行了综合梳理,分析了存在的问题和发展趋势,并讨论了精细水汽产品在气候变化分析、天气预报和空间大地测量中的应用现状和前景,以期为卫星导航、气象以及空间大地测量等领域的专家学者提供借鉴和参考。

风云三号C卫星星载GPS/BDS实时定轨分析

随着北斗卫星导航系统(BeiDou navigation satellite system, BDS)的建设与运行,低轨卫星开始搭载GPS/BDS双系统接收机以实现卫星轨道确定。利用风云三号C(FengYun-3C,FY3C)卫星星载GPS/BDS双频伪距与载波相位观测数据,设置4种仿真试验方案,分别进行星载GPS/BDS在轨实时定轨数据处理,重点进行BDS观测数据对伪距实时定轨和载波相位实时定轨的精度影响分析和算法耗时分析。结果表明,采用伪距观测值,可获得1.0 m的位置精度和1.0 mm/s的速度精度;采用载波相位观测值,可获得0.3 m的位置精度和0.3 mm/s的速度精度,且引入BDS观测值后,伪距实时定轨精度降低,相位实时定轨精度有所改善。

GPS/BDS/INS tightly coupled integration accuracy improvement using an improved adaptive interacting multiple model with classified measurement update

An Extended Kalman Filter（EKF） is commonly used to fuse raw Global Navigation Satellite System（GNSS） measurements and Inertial Navigation System（INS） derived measurements. However, the Conventional EKF（CEKF） suffers the problem for which the uncertainty of the statistical properties to dynamic and measurement models will degrade the performance.In this research, an Adaptive Interacting Multiple Model（AIMM） filter is developed to enhance performance. The soft-switching property of Interacting Multiple Model（IMM） algorithm allows the adaptation between two levels of process noise, namely lower and upper bounds of the process noise. In particular, the Sage adaptive filtering is applied to adapt the measurement covariance on line. In addition, a classified measurement update strategy is utilized, which updates the pseudorange and Doppler observations sequentially. A field experiment was conducted to validate the proposed algorithm, the pseudorange and Doppler observations from Global Positioning System（GPS） and Bei Dou Navigation Satellite System（BDS） were post-processed in differential mode.The results indicate that decimeter-level positioning accuracy is achievable with AIMM for GPS/INS and GPS/BDS/INS configurations, and the position accuracy is improved by 35.8%, 34.3% and 33.9% for north, east and height components, respectively, compared to the CEKF counterpartfor GPS/BDS/INS. Degraded performance for BDS/INS is obtained due to the lower precision of BDS pseudorange observations.

Analytical long-term evolution and perturbation compensation models for BeiDou MEO satellites

The current paper establishes the analytical models of the long-term evolution and perturbation compensation strategy for Medium Earth Orbits（MEO）shallow-resonant navigation constellation,with application to the Chinese Bei Dou Navigation Satellite System（BDS）.The long-term perturbation model for the relative motion is developed based on the Hamiltonian model,and the long-term evolution law is analyzed.The relationship between the control boundary of the constellation and the offset of the orbital elements is analyzed,and a general analytical method for calculating the offset of the orbit elements is proposed.The analytical model is further improved when the luni-solar perturbations are included.The long-term evolutions of the BDS MEO constellation within 10 years are illustrated,and the effectiveness of the proposed analytical perturbation compensation calculation approach is compared with the traditional numerical results.We found the fundamental reason for the nonlinear variations of the relative longitude of ascending node and the mean argument of latitude is the long-periodic variations of the orbital inclination due to the luni-solar perturbations.The proposed analytical approach can avoid the numerical iterations,and reveal the essential relationship between the orbital element offsets and the secular drifts of the constellation configuration.Moreover,there is no need for maintaining the BDS MEO constellation within 10 years while using the perturbation compensation method.

Evaluation of strategies for the ultra-rapid orbit prediction of BDS GEO satellites

The quality of BeiDou Navigation Satellite System(BDS)Geostationary Earth Orbit(GEO)ultrarapid products is unsatisfactory because GEO satellites are nearly stationary relative to ground stations.To optimize the quality of these ultra-rapid orbit products,we investigated the effects of the fitting arc length,an a priori Solar-Radiation Pressure(SRP)model,and the along-track empirical acceleration on the prediction of BDS GEO satellite orbits.The predicted orbit arcs of 24-h were evaluated through comparisons with the corresponding observed orbit arc and Satellite Laser Ranging(SLR)observations.In both eclipse and non-eclipse seasons,accuracy of the orbit predictions obtained using a 48-h fitting arc length were better than those obtained using 24-h and 72-h fitting arc lengths.Although the overlapping precision of predicted orbits exhibited no obvious improvement when an a priori SRP model was employed,the systematic bias in the SLR residuals was significantly reduced.Specifically,the mean value of SLR residuals decreased from−0.248 m to−0.024 m during non-eclipse seasons and from−0.333 m to−0.041 m during eclipse seasons,respectively.In addition,when an empirical acceleration in the along-track direction was introduced,the three-Dimensional Root-Mean-Square(3D RMS)of overlapping orbits during eclipse seasons decreased from 2.964 to 1.080 m,which is comparable to that during non-eclipse seasons.Furthermore,the Standard Deviation(STD)of SLR residuals decreased from 0.419 to 0.221 m during eclipse seasons.The analysis of SRP estimates shows that the stability of SRP parameters was significantly enhanced after the introduction of along-track empirical acceleration in eclipse seasons.The optimal BDS GEO ultra-rapid orbit prediction products were yielded by using a 48-h fitting arc length,an a priori SRP model and an along-track empirical acceleration.

Design of a search and rescue terminal based on the dual-mode satellite and CDMA network

The current goal is to create a set of portable terminals with GPS/BD2 dual-mode satellite positioning, vital signs monitoring and wireless transmission functions. The terminal depends on an ARM processor to collect and combine data related to vital signs and GPS/BD2 location information, and sends the message to headquarters through the military CDMA network. It integrates multiple functions as a whole. The satellite positioning and wireless transmission capabilities are integrated into the motherboard, and the vital signs sensors used in the form of belts communicate with the board through Bluetooth. It can be adjusted according to the headquarters' instructions. This kind of device is of great practical significance for operations during disaster relief, search and rescue of the wounded in wartime, non-war military operations and other special circumstances.

Application of BeiDou navigation satellite system in emergency rescue of natural hazards: a case study for field geological survey of Qinghai−Tibet plateau

In recent years,geological and mineral resources exploration in China has expanded to deep hinterland of the Qinghai−Tibet Plateau and other regions with complex geological conditions.The special natural conditions of Qinghai−Tibet Plateau determine the characteristics of“life-forbidden zone”that is characterized by alpine hypoxia,changeable weather,complex road conditions,and beast attack.In particular,the work in wild depopulated zones with severe environment and poor communications imposes serious threats to the life safety of geological personnel.Therefore,how to guarantee the safety of geological personnel working on the Qinghai−Tibet Plateau and how to reduce or even avoid casualty of geological personnel have currently become the urgent challenge.In this study,an emergency rescue information system for field geological survey is constructed based on BeiDou Navigation Satellite System.A case study of emergency rescue has been conducted in the depopulated zone of the Qinghai−Tibet Plateau and good effects have been achieved,providing security assurance for personnel engaged in field geological survey on the Qinghai−Tibet Plateau and technical support for the emergency rescue in case of natural hazards on the Qinghai−Tibet Plateau.The BeiDou Navigation Satellite System(BDS)can be effectively used to locate and communicate in the emergency rescue for rigorous Geological survey task where there is no network signal for the mobile phone,and the emergency rescue guarantee system is independent,reliable,and relatively cheap.The application value of BDS is demonstrated in the geological field.

Non-Line-of-Sight Multipath Detection Method for BDS/GPS Fusion System Based on Deep Learning

Non-line-of-sight(NLOS)multipath effect is the main factor that restricts the application of global navigation satellite system(GNSS)in complex environments,especially in urban canyon.The effective avoidance of NLOS signals can significantly improve the positioning performance of GNSS receiver.In this paper,an NLOS/LOS classification model based on recurrent neural network is proposed to classify satellite signals received in urban canyon environments.The accuracy of classification is 91%,and the recognition rate of NLOS is 89%;the classification performance is better than that of traditional machine learning classification models such as support vector machine.For BeiDou navigation satellite system/global positioning system(BDS/GPS)fusion system,the least square algorithm and extended Kalman filter are used to estimate the position.The experimental results show that the three-dimensional positioning accuracy after NLOS recognition is improved about 60%on average compared with the traditional methods,and the positioning stability is also improved significantly.

Receiver Autonomous Integrity Monitoring Availability and Fault Detection Capability Comparison Between BeiDou and GPS

This paper used the statistical methods of quality control to assess receiver autonomous integrity monitoring(RAIM) availability and fault detection(FD) capability of BeiDou14(Phase II with 14 satellites),BeiDou(Phase III with 35 satellites) and GPS(with 31 satellites) for the first time. The three constellations are simulated and their RAIM performances are quantified by the global, Asia-Pacific region and temporal variations respectively. RAIM availability must be determined before RAIM detection. It is proposed that RAIM availability performances from satellites and constellation geometry configuration are evaluated by the number of visible satellites(NVS, NVS > 5) and geometric dilution of precision(GDOP, GDOP < 6) together. The minimal detectable bias(MDB) and minimal detectable effect(MDE) are considered as a measure of the minimum FD capability of RAIM in the measurement level and navigation position level respectively. The analyses of simulation results testify that the average global RAIM performances for BeiDou are better than that for GPS except global RAIM holes proportion. Moreover, the Asia-Pacific RAIM performances for BeiDou are much better than that for GPS in all indexes. RAIM availability from constellation geometry configuration and RAIM minimum FD capability for BeiDou14 are better than that for GPS in Asia-Pacific region in all cases, but the BeiDou14 RAIM availability from satellites are worse than GPS's. The methods and conclusions can be used for RAIM prediction and real-time assessment of all kinds of Global Navigation Satellite Systems(GNSS) constellation.