北斗/GNSS多系统频间偏差的统一函数模型与估计理论方法研究

Accurate estimation of the Inter-Frequency Bias (IFB) is the key to realize deep integration of multi-frequency data for BeiDou/GNSS satellites. However, the definition and estimation method of IFBs based on observation combination of certain frequencies is difficult to apply to various observation combinations flexibly, and the causes for this problem is not recognized sufficiently. To solve this problem, we develop a unified IFB model that is suitable for various linear combinations, aiming at realizing consistent estimation for IFBs. Firstly, the parameterization and processing strategy are studied based on analysis of the time-variation characteristic of the IFBs. Then, start from the raw multi-system and multi-frequency observation equation, the equivalent transformation between the IFB derived from undifferenced and uncombined model and that from various linear combinations is studied, and a unified function model of IFBs suitable for different linear combinations is developed. Finally, based on the unified model, an estimation method for multi-frequency IFBs is proposed by fully considering the advantages of different linear combinations to improve the accuracy and reliability of IFB estimations. The innovation of this study is developing a unified model for IFB estimation, which solves the consistent problem of IFB estimation using different observation linear combinations. This research solves a difficult issue to realize deep integration of multi-frequency data for BeiDou/GNSS satellites.

频间偏差的准确估计是实现北斗/GNSS多频观测数据深度融合的关键。目前，基于特定频率观测值组合的频间偏差的定义与估计方法难以灵活应用于各类观测值组合，对这种差异性产生的原因尚认识不充分。针对这一问题，本项目提出构建频间偏差参数在不同观测值组合中的统一函数模型，实现频间偏差的一致性估计：首先，深入分析多系统频间偏差的时变特性和规律，提出频间偏差的参数化策略；然后，从多频多系统原始观测方程入手，研究采用非差非组合及不同线性组合方法估计得到的频间偏差之间的转换关系，构建适用于不同组合方法的频间偏差估计统一函数模型；最后，充分利用不同观测值组合的优势，研究基于统一函数模型的多系统频间偏差参数估计方法，提高频间偏差估值的精度和可靠性。本项目创新之处在于提出一种频间偏差估计的统一函数模型，解决不同观测值组合估计频间偏差的一致性问题，为实现北斗/GNSS多频观测数据深度融合解决一个难点问题。

21世纪以来，全球导航卫星系统（GNSS）建设呈现多频化发展趋势，多频观测值体现出来的兼容性问题成为目前制约多频信号深度融合的关键。频间偏差是影响多频数据深度融合的核心，对其中涉及到的理论、机制和方法进行深入研究并形成一套统一模型是实现频间偏差在多频终端普适性应用的基础。. 针对上述问题，项目组首先通过对不同GNSS卫星频间偏差的时域和频域特性进行了分析，提出分别引入4阶和2阶三角级数模型对GPS卫星和北斗二号卫星相位频间钟偏差（PIFCB）进行建模；而Galileo卫星和北斗三号卫星PIFCB变化量级小于观测值噪声，可以忽略。进一步，通过深入研究非差非组合和不同线性组合的函数关系，建立了一套特定基准条件下多频频间偏差统一函数模型，实现了卫星PIFCB和伪距频间钟偏差（CIFCB）的统一估计，新模型较传统的线性组合模型提高了频间偏差的估值精度。同时，项目组揭示了钟差和频间偏差参数之间的相关性及误差传递规律，精确测算了GPS卫星钟差与差分码偏差（DCB）之间的线性模型系数，建立了频间偏差的误差传递模型。最后，为了实现频间偏差在多频终端的普适性应用，项目组提出了基于统一函数模型的多频频间偏差修正方法，解决了多频用户任意频率观测值的频间偏差统一修正难题。. 基于上述理论方法创新，项目组研发了基于原始观测值的北斗/GNSS多频数据处理软件，已将其用于卫星精密轨道、卫星精密钟差、天顶对流层及梯度、电离层延迟、跟踪站坐标、地心运动参数等大地测量产品计算，并在地球参考框架、电离层监测、极端暴雨过程分析等地学研究领域得到了应用。

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