顾及频率间卫星钟偏差的北斗多频融合精密单点定位研究

The convergence time of precise point positioning (PPP) is as long as 20-30 minutes, which significantly limits its applications in time-critical fields. The BeiDou Navigation Satellite System (BDS) with multi-frequency transmissions is booming, which opens new prospects for the rapid convergence of PPP. But at the same time, there are many problems that need to be solved, such as the inconsistent use of IGS dual-frequency satellite clocks for multi-frequency combinations. This project will focus on the theory and method of BDS multi-frequency integrated PPP in consideration of inter-frequency clock bias (IFCB). We will propose the precise estimation approach for BDS IFCB, in which the robust estimation is introduced to refine the stochastic models. We will establish the high-accuracy models for BDS IFCB based on the internal relations between modeling coefficients and relative sun-spacecraft-earth geometry. After fully investigating the mechanisms of mutual coupling between IFCB and estimated parameters including receiver clock offset, satellite clock offset, ionospheric delay and phase ambiguity, we will propose the IFCB correction method compatible with various multi-frequency PPP models. We will develop the rapid partial ambiguity resolution, in which the negative effects of influence factors on the successful ambiguity-fixing rates are avoided and the advantages of multi-frequency integration are used, so as to reach the goal of converging to centimeter-level positioning accuracy on a global scale within a few minutes for PPP. The research findings mean a significant performance improvement for the BDS precise positioning services.

精密单点定位（PPP）收敛时间长达20~30分钟，极大限制了其在时效性要求较高领域的应用。多频率北斗卫星导航系统的迅速发展，为PPP快速收敛带来了新的前景，但同时也产生了一系列需要解决的难题，如IGS双频卫星钟差并不适用于多频组合。本项目拟开展顾及频率间卫星钟偏差（IFCB）的北斗多频融合PPP理论与方法研究。具体地，引入抗差估计精化随机模型，提出北斗卫星IFCB估计方法，根据模型系数和太阳-卫星-地球相对几何之间的内在联系，建立高精度的IFCB模型；研究IFCB和接收机钟差、卫星钟差、电离层延迟、相位模糊度等参数的相互耦合机制，提出能兼容多种观测值组合的IFCB改正方法；研究模糊度固定成功率的影响因素，并利用多频数据的优势，发展部分模糊度快速固定方法，使PPP技术在全球范围内具备快速收敛到厘米级精度的定位能力。研究成果对于提升北斗精密位置服务性能具有重要意义。

精密单点定位（PPP）技术较长的收敛时间严重限制了其在实用化方向的发展。着眼于多频率北斗卫星导航系统迅速发展这一重要契机，本项目在对频率间卫星钟偏差（IFCB）的精确估计、建模和改正基础上，利用多频数据的优势以快速固定整周模糊度，从而显著提高PPP收敛速度。在北斗IFCB高精度估计与建模方法方面，基于全球分布的275个测站长时间观测值，采用高度角相关定权策略和抗差估计，得到了各颗北斗二号卫星高精度的IFCB估值序列，通过对长时间IFCB序列严密的谐波分析分别确定了三种轨道类型卫星IFCB的周期项，在此基础上建立了考虑卫星轨道重复周期的IFCB模型，建模精度可达2~4mm，预报时间为一周时模型预报精度可达4~6mm，应用IFCB模型预报值后，三频PPP精度得到了显著改善；在兼容多种观测值组合的IFCB改正方法方面，对于北斗三号六频可用信号，根据噪声放大情况选取了四组无几何距离且消电离层（GFIF）三频组合用于估计IFCB，在对得到的IFCB序列时变特性进行了详细分析后，证明了振幅可达1dm的显著IFCB来自于接收机端，在此基础上推导了这类IFCB与其他参数的相互耦合关系，提出了多频定位时的IFCB改正方法，该方法能够兼容任意频率非组合和消电离层组合PPP模型，应用IFCB改正值后载波相位观测值残差显著减小；在多频融合PPP快速模糊度固定方法方面，发展了一种适用于北斗三号全部六频信号的非组合相位小数偏差（UPD）估计方法，分析了UPD估计过程中估计残差、数据利用率与稳定性等方面的特性,还提出了一种适用于北斗三号多频观测值的部分模糊度快速固定方法，该方法可以满足短时间内厘米级定位的需求，显著提高了多频PPP性能。研究成果在推动我国北斗卫星导航系统精密位置服务发展方面具有重要意义。在本项目的资助下，共发表学术论文15篇，授权国家发明专利2项，申请软件著作权1项，培养硕士研究生5名。