加权RAIM可用性预测方法研究

Research on Weighted Algorithm to Predict RAIM Availability

RAIM可用性预测系统是在飞机起飞前对飞机即将飞行的整个过程的机载GPS接收机的RAIM可用性进行预测,辅助空管和签派放行许可,是民航应用GPS导航的必要程序。SA(Selective Availability)取消前,SA是SPS(Standard Position Service)用户的最大误差源,各颗卫星的UERE(User Equivalent Range Error)基本接近,在进行RAIM可用性预测时可认为所有可见卫星的UERE相同;SA取消后,电离层成为SPS用户的最大误差源,与用户到卫星的仰角紧密相关,相同UERE的假设将降低RAIM的可用性。文中针对此特性,基于传统的RAIM可用性预测方法,提出了加权RAIM可用性预测方法,并对权值的选择进行分析。计算机仿真结果表明,加权方法提高了RAIM可用性,缩短了RAIM不可用时段。算法已经应用于民航的RAIM预测系统,运行良好。

RAIM Availability Prediction System is used to predict the RAIM availability of airborne GPS receiver of the whole flight phases pre-departure.SA(Selective Availability) was the most error resource for SPS(Standard Position Service) user before SA was removed for GPS.After SA was removed in 2000,ionosphere comes to be the most error resource for SPS user.Based on HPL(Horizontal Protection Level),this paper proposes a weighted HPL method to predict RAIM availability,and gives suggestions to choose the weighting value.Simulation result on computer shows that weighted HPL can improve RAIM availability distinctly and shorten the period of time that RAIM is not available.This weighted HPL method has been used in RAIM Prediction System of civil aviation.