北斗卫星导航系统实时定轨与钟差处理策略

目前鲜有对北斗卫星导航系统（BeiDouNavigationSatelliteSystem,BDS）实时精密定轨与钟差确定的研究,文章提出了BDS实时轨道与实时钟差处理策略,包括了观测与动力学模型、实时轨道与实时钟差处理流程与评估方法。尤其对于实时钟差,为了提高计算效率,联合使用两个独立并行的线程估计非差绝对钟差和历元间相对钟差。利用多模全球卫星导航系统试验(MGEX)与全球连续检测评估系统（iGMAS）实测数据进行了北斗实时轨道与钟差解算,BDS实时轨道径向平均精度对于GEO卫星优于20cm,对于IGSO与MEO一般优于10cm;钟差精度对于GEO卫星为0.5~4.5ns,对于IGSO／MEO为0.2~2.0ns。基于目前的轨道与钟差结果,实时精密单点定位（PrecisePointPositioning,PPP）结果可以达到分米量级。     

一种高精度实时GPS卫星钟差预测算法

为获得高精度实时GPS卫星钟差,文章提出一种基于多项式和最小二乘支持向量机(Least Squares Support Vector Machines,LS-SVM)相结合的钟差预报方法.该方法采用国际GNSS服务发布的超快速观测星历建模进行短期预报,首先根据卫星钟的物理特性用附有周期项的多项式模型进行拟合以提取趋势项和周期项,然后用LS-SVM对多项式拟合残差进行建模预报,最后将预报结果加上趋势项和周期项,得到最终的钟差预报值.试验结果表明,所提算法能够实时有效地对GPS卫星钟差进行预报,且精度优于超快速预报星历.     

神经网络在导航卫星钟差预报中的应用CSCD

为提高导航卫星钟差预报精度,提出一种神经网络和多项式相结合的钟差预报方法,该方法在根据星载原子钟物理特性进行多项式模型预报后,采用神经网络对多项式模型预报误差进行建模,以实现导航卫星钟差预报精度补偿。为验证本文提出的预报模型的可行性和有效性,利用实测的COMPASS导航卫星钟差数据进行钟差预报精度分析,并与传统的多项式模型预报精度进行比较。结果表明:基于神经网络建立的组合预报模型能有效提高导航卫星钟差的预报精度。     

精密GPS卫星钟差的改正和应用

分析了GPS卫生钟差的变化特性，探讨了利用GPS地面跟踪站的观测数据估算GPS卫星钟差的可行性，建立了相应的算法和软件系统，并把由地面跟踪站的实测数据估算的卫星钟差用于星载GPS定轨计算，得到优于1m的定轨精度。     

脉冲星方位误差估计的两步卡尔曼滤波算法

为了克服钟差和卫星位置误差对脉冲星方位误差估计的影响,设计了两步卡尔曼滤波（TSKF）算法。首先,介绍了脉冲星方位误差估计的传统模型,并通过分析和仿真验证了钟差、卫星位置误差以及2种误差同时存在时会使脉冲星方位误差估计结果产生较大偏差。其次,在传统的估计模型中加入了钟差和卫星位置误差,并将钟差和钟差变化率增广为新的状态量,从而推导出包含2种误差的新模型,并证明了该模型的完全可观测性;根据该模型并按照两步卡尔曼滤波原理,得到了TSKF算法的步骤。最后,通过仿真表明:在钟差和卫星位置误差同时影响下,传统脉冲星方位误差估计算法偏差较大且发散;TSKF算法则能够有效隔离2种误差的影响,使赤经和赤纬误差估计达到0.2 mas之内的精度。      

灰色模型在卫星钟差预报中的缺陷分析

卫星钟差预报是时间同步的关键技术之一,方法繁多。针对灰色模型在卫星钟差预报中的应用,以GPS Rb钟钟差预报为实例,从模型构造上分析了该模型在卫星钟差预报中存在的缺陷,有利于该模型的改进和完善。     

星地激光时间比对在卫星导航系统中的应用

星地精密激光时间比对具有精度高、系统误差少等优点,因此利用星地精密激光时间比对,不但可以对无线电时间比对进行外部精度检验,而且可以检验并分离无线电伪距测量的系统误差,分析检测设备时延的不稳定性和卫星钟的中短期性能指标,提高卫星钟差的预报精度。     

一种高精度GPS卫星钟差预报方法

为了获得实时高精度GPS钟差,提出了采用快速星历建模进行短期预报。文章先对钟差数据提取趋势项,再利用傅里叶分析研究其周期特征以确定建模与预报时间段长度,最后利用径向基函数(Radial Basis Function,RBF)神经网络建模实时预报钟差。由于RBF神经网络用于非线性数据建模效果良好,在提取线性趋势项并合理确定建模周期后,该方法能够得到较好的预报结果。实际预报结果表明,文中方法得到的预报钟差精度高于超快速星历,能够满足分米级实时精密定位的要求。     

基于实时SSR数据的LEO卫星精密单点定位研究

对目前低轨卫星实时定位的方法进行了研究,现在通常采用GPS定位,使用广播星历和普通晶振,实时定位精度一般在10m以内,不能满足高精度实时定位的需求。IGS组织在全球范围内对GPS跟踪分析,生成精密星历、精密钟差产品、按SSR格式的广播星历和钟差修正产品并在网上发布。对这些IGS产品进行了调查,提出在现有测控支持情况下,可以通过高密度上注SSR信息流实现在轨高精度定位。以某型号低轨微小卫星在轨导航增强载荷为应用背景,用IGS03产品中的1057和1058数据对双频GPS接收机的星历和钟差进行修正,采用递推最小二乘估计和LAMDA模糊度固定过对载波相位和伪距信息进行处理,在短时间内获得亚米级定位结果。     

关于北斗卫星导航系统的被动式定位算法比较研究

我国北斗卫星导航系统空间卫星共有2或3颗,无法单独满足被动导航定位的要求．针对这种卫星稀少的情况提出了3种被动式定位算法: 2星定位算法、 3星3参数定位算法和3星4参数定位算法, 这些算法分别采用气压测高方法增加观测数据和采用数学模型描述接收机钟差的方法减少定位方程求解的未知数;探讨了北斗卫星导航系统备份星的可用性和对导航定位精度的贡献;还提出了准差分修正技术,提高了定位精度．实验证明, 3种算法都取得了100m以内的定位结果,可以满足一般用户定位需求．     

Monitoring atomic clocks on board GNSS satellites

A method for monitoring atomic clocks on board Global Navigation Satellites System (GNSS) satellites is described to address the issue of clock related signal integrity in safety–critical applications of GNSS. The carrier-phase time transfer is employed in the clock monitoring method which enables tight tracking of the satellite onboard clocks and thus improves detectability of clock anomalies. Detecting onboard clock anomalies requires the ability to monitor clocks in real time, and a Kalman filter can then be utilized to estimate the phase offsets between the satellite clocks and ground clocks. This study, using the difference between the measured and predicted phase offset as a test statistic, sets a threshold for clock anomalies based on the prediction interval approach. Finally the validity of the monitoring method is examined by processing a set of real GNSS data that includes two recent incidents of clock anomalies in GNSS satellites.     

卫星与测站钟差支持条件下的GEO卫星精密定轨

在基于伪距的GEO卫星精密定轨中, GEO卫星的静地特性导致定轨解算无法对星地组合钟差进行有效估计, 需要独立的时间同步支持. 本文讨论了卫星和测站钟差支持条件下的GEO卫星定轨原理, 利用仿真数据系统地分析了中国区域网跟踪条件下GEO卫星的定轨精度, 从定性和定量角度分析了钟差二次项、星地时间同步精度、站间时间同步精度及系统差等因素对定轨精度的影响.      

Switching and performance variations of on-orbit BDS satellite clocks

The information of the satellite clock switching and performance variations on-orbit of Chinese BeiDou-2 Navigation System (BDS) is not available for the public. In order to detect the BDS satellite clock switching and performances variation, we analyzed the precise clock offset products with a total duration of 5?years every BDS satellite equipped four atomic clocks from four different manufactures from January 2013 to October 2017. Three important contributions are concluded as follows. (1) It is found that the average time of on-orbit operation for BDS satellite clocks is about 1–2?years. There have been 22 times of clock switching for BDS satellites, of which the C05 and C08 satellites have been switched to the fourth (last) atomic clock. (2) There are frequent phase adjustments for BDS on-orbit satellite clocks, and the frequency series is relatively stable. Furthermore, there are semi-annual sinusoid cycles in the frequency drift series of C06 and C09 satellites. (3) The performances of MEO satellite clocks perform better than the IGSO and GEO satellite clocks. The average ten-thousand frequency stability of BDS satellite clocks is about 1E-13, which is worse than that of GPS and Galileo but better than that of GLONASS.     

基于遥测数据动态特征的卫星异常检测方法

基于遥测参数分析异常是保证卫星正常在轨运行的基础,通常采用阈值法判断遥测参数是否超差来判断卫星工作状态,由于其无法检测在阈值范围内变化的卫星遥测数据异常,因而会导致故障漏报.本文利用遥测参数动态变化特性,提出一种基于遥测数据变化规律检测异常的方法.利用周期图谱法求解遥测参数周期,根据遥测数据各周期之间参数值的相似性,按照遥测参数周期对数据进行采样,得到平稳差分序列,对其建立自回归移动平均混合模型,通过精确的预测结果与实测遥测数据比较来发现异常.利用该方法对实际在轨运行的某卫星2012年5月太阳能帆板转动异常故障进行验证,结果表明其能够有效避免故障漏报.      

辅助型GPS接收机中伪码相位延时及其不确定度估计算法研究

快速捕获卫星信号是研制辅助型GPS (A-GPS)接收机所必须解决的一项关键技术. 针对A-GPS接收机能从辅助数据中获取有效星历的特点, 本文提出了一种伪码相位延时及其不确定度估计算法. 该算法在对建立的信号发射时刻方程泰勒展开的基础上, 利用辅助信息建立了伪码相位延时及其不确定度估计方程. 分析和仿真表明, 提出的算法能有效压缩剩余卫星伪码相位延时不确定度, 加快A-GPS接收机的捕获速度.      

基于符号化表示相似度度量的卫星多元工程参数异常检测

随着卫星系统复杂程度的日益增加,综合分析卫星多元参数之间的相关性异常对于卫星安全运行和空间任务的正确执行具有重要意义。利用某卫星工程参数数据,基于符号聚合近似算法（SAX）,研究卫星多元工程参数的异常检测问题,解决了当前异常检测方法中多元参数融合时不考虑上下文信息造成信息丢失的问题,实现多元参数有效融合,形成一种优化的基于快速动态时间规整算法（Fast-DTW）的异常检测算法。研究结果表明,模型在某卫星电源子系统的异常检测过程中,recall,precision和F1 score分别为0.947,0.9和0.923,能够实际应用于卫星异常检测,提高卫星在轨运行的安全性。     

The GLONASS-M satellite yaw-attitude model

The proper modeling of the satellites’ yaw-attitude is a prerequisite for high-precision Global Navigation Satellite System (GNSS) positioning and poses a particular challenge during periods when the satellite orbital planes are partially eclipsed. Whereas a lot of effort has been put in to examine the yaw-attitude control of GPS satellites that are in eclipsing orbits, hardly anything is known about the yaw-attitude behavior of eclipsing GLONASS-M satellites. However, systematic variations of the carrier phase observation residuals in the vicinity of the orbit’s noon and midnight points of up to ±27 cm indicate significant attitude-related modeling issues. In order to explore the GLONASS-M attitude laws during eclipse seasons, we have studied the evolution of the horizontal satellite antenna offset estimates during orbit noon and orbit midnight using a technique that we refer to as “reverse kinematic precise point positioning”. In this approach, we keep all relevant global geodetic parameters fixed and estimate the satellite clock and antenna phase center positions epoch-by-epoch using 30-second observation and clock data from a global multi-GNSS ground station network. The estimated horizontal antenna phase center offsets implicitly provide the spacecraft’s yaw-attitude. The insights gained from studying the yaw angle behavior have led to the development of the very first yaw-attitude model for eclipsing GLONASS-M satellites. The derived yaw-attitude model proves to be much better than the nominal yaw-attitude model commonly being used by today’s GLONASS-capable GNSS software packages as it reduces the observation residuals of eclipsing satellites down to the normal level of non-eclipsing satellites and thereby prevents a multitude of measurements from being incorrectly identified as outliers. It facilitates continuous satellite clock estimation during eclipse and improves in particular the results of kinematic precise point positioning of ground-based receivers.     

Design of BDS-3 integrity monitoring and preliminary analysis of its performance

With the improvement in the service accuracy and expansion of the application scope of satellite navigation systems, users now have high demands for system integrity that are directly related to navigation safety. As a crucial index to measure the reliability of satellite navigation systems, integrity is the ability of the system to send an alarm when an abnormity occurs. The new-generation Beidou Navigation Satellite System (BDS-3) prioritized the upgrading of system integrity as an important objective in system construction. Because the system provides both basic navigation and satellite-based augmentation system (SBAS) services by the operational control system, BDS-3 adopts an integrated integrity monitoring and processing strategy that applies satellite autonomous integrity monitoring and ground-based integrity monitoring for both the basic navigation service and SBAS navigation service. BDS-3 also uses an improved and refined integrity parameter system to provide slow, fast and real-time integrity parameters for basic navigation, and provide SBAS-provided integrity information messages in accordance with Radio Technical Commission for Aeronautics (RTCA) specification and dual frequency, multi-constellation (DFMC) specification to support the SBAS signal frequency, single constellation operation and DFMC operation respectively. The performance of BDS-3 system integrity monitoring is preliminarily verified during on-orbit testing in different states, including normal operation, satellite clock failure and satellite ephemeris failure. The results show that satellite autonomous integrity monitoring, ground-based integrity monitoring and satellite-based augmentation all correctly work within the system. Satellite autonomous integrity monitoring can detect satellite clock failure but not satellite orbit failure. However, ground-based integrity monitoring can detect both. Moreover, the satellite-based augmentation integrity system monitors the differential range error after satellite ephemeris and clock error corrections based on user requirements. Compared to the near minute-level time-to-alert capability of ground-based integrity monitoring, satellite autonomous integrity monitoring reduces the system alert time to less than 4 s. With a combined satellite-ground monitoring strategy and the implementation of different monitoring technologies, the BDS-3 integrity of service has been considerably improved.