基于非合作卫星导航信号的寄生多普勒自主导航

This project proposes a new concept which is adopted to realize a kind of parasitic autonomous navigation for spacecraft in LEO by using codeless Doppler measurements which are exploited from non-cooperative signals of navigation satellite system, and the purpose is to improve the survival ability of spacecraft. The project assumes that the navigation satellite system doesn’t transmit the civilian navigation signals and only encrypted navigation signals are available in the special occasions. The autonomous navigation principles and methods put forward here can be used to accomplish autonomous navigation task for spacecraft by exploiting encrypted navigation signals. Algorithms of on-orbit identification for Doppler frequency shift and compensation will be studied to realize a self-aided PLL after analyzing the characteristics of non-cooperative navigation signal. The mathematical model and the error model of the high dynamic narrowband PLL will be established, and then optimization will be investigated. When there is no frequency overlap, the strategy of acquisition for target carrier signal will be researched, and the prior knowledge of frequency shift will be used to aid the multiple channels to achieve cooperative signal capture. A matching index based on frequency shift difference will be proposed, and frequency level matching method will be investigated to identify the navigation satellites with the specific frequency shift. When there is frequency overlapping, the navigation satellite identification is realized by matching the measuring frequency shift series and the prior frequency shift series. Measurement equations of different forms will be constructed and analysis of their characteristics will be implemented. The wild value multi-staged detecting and eliminating algorithms will be explored, and covariance analysis method and Monte-Carlo simulations will be adopted to research the autonomous performance.

项目提出了一个寄生于非合作全球卫星导航系统实现低轨航天器无码多普勒自主导航的新概念，从而提高航天器的生存能力。“非合作”指的是他方卫星导航系统在特殊条件下限制了明码信号服务，仅发送加密导航信号；“寄生”指的是项目提出的导航原理和方法能利用非合作导航信号实现低轨航天器自主导航。项目在分析非合作导航信号特点的基础上，研究利用在轨辨识补偿频移实现跟踪环路自辅助的测量机制，建立高动态窄带载波跟踪环路的数学模型和误差模型并优化；在没有频率交叠时，研究基于先验频移知识辅助多个通道协同捕获目标载波的策略，提出频移差匹配指标，研究频率级匹配方法来辨识各频移对应的导航星；在有频率交叠时，采用实测频移与先验频移整体匹配的方式实现导航星识别；建立不同形式的测量方程并分析其特点，研究野值多级检测与抑制方法，采用协方差分析法和蒙特卡洛法研究该导航方案的性能规律。

项目探索了一种寄生于非合作全球卫星导航系统实现低轨航天器无码多普勒自主导航的新方法，有助于提高航天器的生存能力。“非合作”指的是他方卫星导航系统在特殊条件下限制了明码信号服务，仅发送加密导航信号；“寄生”指的是项目提出的导航原理和方法能利用非合作导航信号实现低轨航天器自主导航。系统地研究了多种无码载波相位跟踪与恢复方案：（1）利用半公开的P码进行第一次码剥离，然后对剩余W码进行平方法获得连续载波，由于利用本地产生的P码剥离了卫星导航信号中的P码，显著改善了信噪比；（2）在分析整个信道信噪比的基础上，提出了利用可控增益天线辅助实现载波可靠恢复的方案，分别研究了串行与并行两种捕获算法。采用基于多普勒频率特征的导航星识别方法，利用实测导航星多普勒频移系列与先验导航星频率系列的对应差，以频率差的和最小作为优化指标，具体搜索算法分别是：基于频率差的和的绝对值的三分法，基于频率差的和的二分法，以及基于频率差的和的绝对值的二分法。建立了高精度的轨道动力学与计算方法，采用卫星导航接收机输出的载波相位数据实现了高精度在轨定位算法，成果应用于和德一号首颗导航增强实验卫星。开展了物理仿真研究，设计并实现了寄生导航软件接收机，采用导航模拟器、中频采样器采集与自研的软件接收机较完整地完成了基于非合作导航信号的寄生自主导航实验验证，表明了本项目方案与相关关键技术是可行的。