对光纤陀螺随机噪声的ARMA建模及卡尔曼滤波方法进行了研究。针对ARMA(Auto-Regressive and Moving Average自回归滑动平均)模型的有色噪声在状态方程中不能通过传统的状态扩充法进行白化的问题,提出了新的噪声白化方法:采用增广最小二乘法估计ARMA模型的参数,同时提取出ARMA模型中的驱动白噪声,从而可以把ARMA模型中的有色噪声项作为控制项放入系统的状态方程,通过Sage-Husa的次优无偏MAP(Maximum A Posteriori,极大后验)噪声统计估值器对系统噪声的统计特性进行估计,实现了系统噪声的白化。在此基础上应用自适应卡尔曼滤波,有效消除了误差,得到状态值的准确估计。实验结果表明,对于随机噪声的自相关和互相关特性均呈现拖尾性质的光纤陀螺,采用新方法比传统基于AR模型的Kalman滤波降噪方法滤除噪声的效果提高了10%以上。
Advanced Receiver Autonomous Integrity Monitoring(ARAIM) is a new technology that will provide worldwide coverage of vertical guidance in aviation navigation. The ARAIM performance and improvement under depleted constellations is a practical problem that needs to be faced and researched further. It is a shortcut that improves the availability in position domain whose key idea is to replace the conventional least squares process with a non-least-squares estimator to lower the integrity risk in exchange for a slight increase in nominal position error. The contributions given in this paper include two parts: First, the impacts of one satellite outage on different constellations are analyzed and compared. The conclusion is that GPS is more sensitive and vulnerable to one satellite outage. Second, a constellation weighted ARAIM(CW-ARAIM)position estimator is proposed. The position solution is replaced by a constellation weighted average solution to eliminate the constellation difference. The new solution will move close to the constellation solutions with respect to the accuracy requirement. The simulation results under baseline GPS and Galileo dual-constellation show that the one GPS satellite outage will knock the availability from 91% to only 50%. The performance remains stable with one Galileo satellite outage. With the assistance of the CW-ARAIM method, the availability can increase from 50% to more than80% under depleted GPS configurations. Even without any satellite outage, the proposed method can effectively improve the availability from 91.29% to 98.75%. The test results under optimistic constellations further verify that a balanced constellation is more important than more satellites on orbit and the superiority of CW-ARAIM method is still effective.
