[1]Information Engineering University Zhengzhou 450001 China;
[3]Xi’an Research Institute of Surveying and Mapping Xi’an 710054 China;
[2]State Key Laboratory of Geo-Information Engineering Xi’an 710054 China;
[4]Chang’an University Xi’an 710054 China;
[5]PLA University of Science & Technology Nanjing 210007 China;
BeiDou satellite navigation system; LEO; precise orbit determination; GEO; orbit enhancement;