1. School of Aeronautic Science and Engineering, Beihang University,Beijing,P.R. China,100191
2. Institute of Unmanned System, Beihang University,Beijing,P.R. China,100191
3. School of Electronic and Information Engineering, Beihang University,Beijing,P.R. China,100191
4. School of Au-tomation Science and Electrical Engineering, Beihang University,Seventh Research Division,Beijing,P.R. China,100191