Basic performance and future developments of BeiDou global navigation satellite system

The core performance elements of global navigation satellite system include availability,continuity,integrity and accuracy,all of which are particularly important for the developing BeiDou global navigation satellite system(BDS-3).This paper describes the basic performance of BDS-3 and suggests some methods to improve the positioning,navigation and timing(PNT)service.The precision of the BDS-3 post-processing orbit can reach centimeter level,the average satellite clock offset uncertainty of 18 medium circular orbit satellites is 1.55 ns and the average signal-in-space ranging error is approximately 0.474 m.The future possible improvements for the BeiDou navigation system are also discussed.It is suggested to increase the orbital inclination of the inclined geostationary orbit(IGSO)satellites to improve the PNT service in the Arctic region.The IGSO satellite can perform part of the geostationary orbit(GEO)satellite’s functions to solve the southern occlusion problem of the GEO satellite service in the northern hemisphere(namely the“south wall effect”).The space-borne inertial navigation system could be used to realize continuous orbit determination during satellite maneuver.In addition,high-accuracy space-borne hydrogen clock or cesium clock can be used to maintain the time system in the autonomous navigation mode,and stability of spatial datum.Furthermore,the ionospheric delay correction model of BDS-3 for all signals should be unified to avoid user confusion and improve positioning accuracy.Finally,to overcome the vulnerability of satellite navigation system,the comprehensive and resilient PNT infrastructures are proposed for the future seamless PNT services.