导航卫星参考频率的星上自主完好性监测方法研究

Adopting space atomic clock as the original reference, the onboard time/frequency generation and maintenance system utilizes related software and hardware resources to provide accurate, stable and continuous reference frequency for the navigation satellite. The performance of the reference frequency is closely related to the positioning precision of the satellite navigation system, so it is necessary to perform integrity monitoring of the reference frequency. As the conventional method of integrity monitoring, ground-based monitoring system has the drawbacks of high dependence on the ground and poor time-to-alert performance. In order to solve this problem, this project considers autonomous integrity monitoring onboard satellite, and puts forward a digital frequency measurement method based on sinusoidal beat technique, by which high-accuracy inter-comparison and measurement of the master and slave reference frequency can be carried out. Subsequently, a forecasting model based on adaptively robust filtering technique is studied and built to meet the demand of the forecast and comparison of the frequency difference，which is an important prerequisite for reference frequency anomaly detection. In addition, a method of oscillator intervention and a method of time-frequency distribution rényi entropy analysis are proposed to achieve the goal of reference frequency anomaly isolation and identification onboard the navigation satellite.

导航卫星时频生成与保持系统以星载原子钟输出频率为参考，综合相关软硬件资源为导航卫星有效载荷提供星上参考频率。导航卫星参考频率的准确性、稳定性和连续性会直接影响卫星导航系统的定位精度，因此导航卫星在轨运行期间有必要对星上参考频率实施完好性监测。对于星上参考频率的完好性监测可分为星上自主监测和地基辅助监测两种模式。依靠地基辅助技术实施星上参考频率的完好性监测可以降低卫星载荷的复杂度，但其星地闭环的处理模式会导致监测系统及时告警的能力较差。本课题拟开展导航卫星参考频率的星上自主完好性监测方法的研究，提出正弦差拍数字化测频方法实现星上参考频率主、备链路的高精度比对测量，提出自适应抗差滤波频差预测比较的方法实现星上参考频率的异常检测，提出中间振荡器介入的方法实现星上参考频率的异常隔离，提出基于时频分布Rényi熵特征分析的方法实现星上参考频率的异常识别。

导航卫星发射升空时会受到冲击振动和加速度的影响，在轨运行期间还会遭受复杂的太空热辐射、电磁辐射以及自身电路的物理性老化等危害，因此导航卫星时频生成与保持系统工作运行期间可能会出现故障，导致星上参考频率的突发性异常。而导航卫星参考频率的准确性、稳定性和连续性会直接影响卫星导航系统的定位精度，因此导航卫星在轨运行期间有必要对其参考频率实施完好性监测。为了能够准确检测异常并及时告警，导航卫星参考频率星上自主检测不可或缺。本项目开展了导航卫星参考频率的星上自主完好性监测方法的研究。具体研究了基于FPGA的正弦差拍数字化测频方法实现星上参考频率主、备链路的高精度比对测量，并研制了系统原理样机；设计了二次多项式和αβγ滤波器的频差预测模型，借此实现星上参考频率的异常检测；使用中间振荡器介入的方法实现星上参考频率的异常隔离；提出了基于时频分布Rényi熵特征分析的方法实现星上参考频率的异常识别。本项目的部分研究成果有望为导航卫星有效载荷的工程研制提供一种新思路和技术支撑。