Basic performance of BeiDou-2 navigation satellite system used in LEO satellites precise orbit determination

The visibility for low earth orbit（LEO） satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system（GPS）. In addition, the spaceborne receivers＇ observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satellites orbits. The precise orbit determination（POD） results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional（3D） accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about30 cm. As for the precise relative orbit determination（PROD）, the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demonstrates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit（GEO） satellites is illustrated for POD.     

北斗空间信号误差统计特征及描述方法研究

通过对比北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)广播星历与事后精密星历,提取了轨道和卫星时钟误差。基于北斗轨道误差及北斗卫星时钟误差统计特征分析,构建区别于全球定位系统(Global Positioning System,GPS)的BDS空间信号用户测距误差(Signal-In-Space User Range Error,SISRE)描述方法,对BDS广播星历中用户测距精度(User Range Accuracy,URA)进行了验证。6个月的北斗数据测试结果表明,北斗GEO、IGSO和MEO卫星的URA分别为3.0m、1.9m和1.6m。     

BDS接收机星间载波相位偏差

BDS(BeiDou satellite navigation System,北斗卫星导航系统)的MEO/IGSO (Medium Earth Orbit/Inclined Geosynchronous Satellite Orbit,中圆地球轨道/倾斜地球同步轨道)卫星在D1导航电文上调制了NH(Neumann-Hoffman,奈曼-霍夫曼)二次编码,而在GEO(Geostationary Earth Orbit,地球静止轨道)卫星上未使用.利用北斗MEO/IGSO和GEO卫星进行差分定位时,采用不同NH码符号映射规则的接收机之间会出现半周载波相位偏差的问题,严重影响RTK (Real-Time Kinematic,实时动态差分)应用.通过分析半周载波相位偏差的形成机理,从单差、双差、三差应用角度分别研究了半周载波相位偏差的影响.分析结果表明,接收机NH码符号映射规则与卫星不一致时,接收机直接用乘法器对NH码解调将存在反相,也即引入了半周载波相位偏差;在满足特定条件下,单差和双差应用时会存在半周载波相位偏差的问题;三差应用时不存在半周载波相位偏差的问题.最后,提出了需在北斗接口控制文件中明确卫星NH码调制或映射规则的修订建议.     

不同电离层模型对北斗共视的精度影响分析

GNSS共视时间传递已成为远程高精度时间同步的主要技术手段之一,我国自主研制的北斗导航系统已经服务于亚太地区,基于北斗共视进行高精度时间传递已成为我国时频领域的研究热点。为了提高导航系统定位精度,需降低或消除导航定位过程中的各类误差,其中电离层为影响北斗共视的主要误差。研究了常用的几种电离层修正算法,利用2014年7月份的观测数据分析不同电离层模型对北斗共视钟差的精度影响,给出了残差标准差和稳定度值。分析结果表明:经各种电离层修正后,钟差精度都有所提高,其中双频电离层修正最优,比VTEC格网模型和Klobuchar模型分别提高22%和30%。对于不同星座,GEO卫星计算的钟差修正后精度明显优于MEO、IGSO卫星。     

Precise orbit determination for TH02-02 satellites based on BDS3 and GPS observations

The Tianhui-2 02 (TH02-02) satellite formation, as a supplement to the microwave mapping satellite system Tianhui-2 01 (TH02-01), is the first Interferometric Synthetic Aperture Radar (InSAR) satellite formation-flying system that supports the tracking of BeiDou global navigation Satellite system (BDS3) new B1C and B2a signals. Meanwhile, the twin TH02-02 satellites also support the tracking of Global Positioning System (GPS) L1&L2 and BDS B1I&B3I signals. As the spaceborne receiver employs two independent boards to track the Global Navigation Satellite System (GNSS) satellites, we design an orbit determination strategy by estimating independent receiver clock offsets epoch by epoch for each GNSS to realize the multi-GNSS data fusion from different boards. The performance of the spaceborne receiver is evaluated and the contribution of BDS3 to the kinematic and reduced-dynamic Precise Orbit Determination (POD) of TH02-02 satellites is investigated. The tracking data onboard shows that the average number of available BDS3 and GPS satellites are 8.7 and 9.1, respectively. The carrier-to-noise ratio and carrier phase noise of BDS3 B1C and B2a signals are comparable to those of GPS. However, strong azimuth-related systematic biases are recognized in the pseudorange multipath errors of B1C and B3I. The pseudorange noise of BDS3 signals is better than that of GPS after eliminating the multipath errors from specific signals. Taking the GPS-based reduced-dynamic orbit with single-receiver ambiguity fixing technique as a reference, the results of BDS3-only and BDS3 + GPS combined POD are assessed. The Root Mean Square (RMS) of orbit comparison of BDS3-based kinematic and reduced-dynamic POD with reference orbit are better than 7 cm and 3 cm in three-Dimensional direction (3D). The POD performance based on B1C&B2a data is comparable to that based on B1I&B3I. The precision of BDS3 + GPS combined kinematic orbit can reach up to 3 cm (3D RMS), which has a more than 25% improvement relative to the GPS-only solution. In addition, the consistency between the BDS3 + GPS combined reduced-dynamic orbit and the GPS-based ambiguity-fixed orbit is better than 1.5 cm (3D RMS).     

18参数广播星历分析研究

针对18参数广播星历模型对混合星座（包含GEO（地球同步轨道）、IGSO（倾斜地球同步轨道）、MEO（中地球轨道））的拟合精度和稳定性问题,利用摄动理论中的分析方法研究18参数广播星历模型新增参数的物理意义,通过数值仿真比较分析18参数模型与16参数模型对混合星座的拟合精度和稳定性。分析研究表明,新增2个参数可以较好地逼近轨道变化的长周期项,相同拟合弧长的拟合精度比16参数提高了50%左右,但受短周期项影响,拟合不够平稳,同时由于轨道变化特征的差异,对GEO和IGSO卫星的拟合不如MEO卫星稳定。数值仿真结果表明,要保证稳定性必须增加拟合弧长,但拟合精度会有一定下降,18参数条件下,MEO卫星选用3h拟合弧长能保持很好的稳定性,GEO和IGSO卫星则需要选择5h拟合弧长。     

参考系选择对Kepler广播星历参数拟合精度的影响

通过对MEO、IGSO、GEO三类导航卫星广播星历的开普勒轨道根数拟合方法及其拟合精度的分析研究,得出结论:开普勒轨道根数拟合导航卫星广播星历的方法,能很好吸收坐标变换过程中岁差、章动、极移、地球自转等因素对卫星星历拟合精度的影响。     

地球静止卫星精密测定轨技术的现状及发展

介绍并分析了针对地球静止卫星的各种高精度测定轨跟踪技术.指出测距系统的校正误差是常规测距跟踪网定轨在沿迹方向和法向的主要误差源,为保证一致的卫星三维位置解算精度,应利用高分辨率的角度观测约束信息来有效地降低测距偏差对轨道确定的影响,或者利用天地基联合定轨的低轨卫星运动几何在轨道改进的同时精化测距偏差.     

双星定位系统及其备份星在近地卫星联合定轨建模中的应用

建立了基于双星定位系统距离和观测数据的近地卫星联合定轨模型,设计了相应的数值融合联合定轨算法;为进一步提高近地卫星定轨精度,考虑融合双星及备份星距离和观测数据,建立了基于双星和备份星的近地卫星联合定轨模型及实现算法,并针对不同仿真条件进行了联合定轨仿真实验。仿真计算结果表明,联合定轨方式较传统近地卫星精密定轨方式可以更好地抑制双星星历误差对近地卫星定轨精度的影响,近地卫星和双星的定轨精度均得到了一定程度的提高;同时,融合备份星观测数据的近地卫星联合定轨精度得到进一步改善,达到5.17m。     

面向导航增强的低轨卫星钟差确定及预报方法研究

低轨导航增强是未来导航发展的重要趋势,而高精度低轨卫星钟差是实现低轨导航增强的必要条件。基于Sentinel-6A卫星,对低轨卫星钟差特性进行了分析,给出了钟差确定方法及影响因素,介绍了顾及钟差特性的低轨卫星钟差预报方法。实验表明,低轨卫星钟差含有多个周期项,给低轨卫星建模和预报带来了困难。与使用运动学定轨模型相比,基于简化动力学的定轨模型可显著提升低轨卫星钟差精度;当基于运动学模型确定低轨卫星钟差时,相较于使用GPS单系统数据,多GNSS观测数据可提升低轨卫星钟差精度。研究表明,基于GPS和Galileo观测的Sentinel-6A卫星钟差精度相较于GPS单系统钟差精度改善了36%,同时,所使用的GNSS产品精度与低轨卫星钟差精度密切相关。利用顾及卫星钟差特性的低轨卫星钟差预报方法,当预报时长小于1 min,低轨卫星钟差预报精度（预报与解算值之差的RMSE）在0.1 ns之内,当预报时长小于5 min,预报精度在0.3 ns之内,随着预报时长的增长,预报精度显著下降。