Precise Point Positioning with Multi-constellation Satellite Systems: BeiDou、Galileo、GLONASS、GPS
REN Xiaodong, ZHANG Keke, LI Xingxing, ZHANG Xiaohong
Acta Geodaetica et Cartographica Sinica . 2015, (12): 1307 -1313 .  DOI: 10.11947/j.AGCS.2015.20140568