In the form of satellite ephemerides and clock parameters, the information of space datum and system time of one global navigation satellite system (GNSS) is transferred to users. With the continuously updating of satellite payload such as high precision atomic clocks, monitoring and tracking techniques such as inter-satellite links, and data processing techniques, accuracy and real-time performance of satellite ephemerides and clock products are steadily improved. Starting from December 27th, 2018, BeiDou Navigation System 3, or BDS-3 has been providing accurate and reliable basic positioning, navigation, and timing (PNT) services to the users in the countries within the ``one belt and one road'. This paper summarizes the faced challenges of precise orbit determination and time synchronization and specific solutions sought from the regional BDS-2 system to BDS-3 global system at the control segment. It is interesting to compare BDS with other GNSS systems in terms of technical characteristics. Finally, aiming at higher accuracy and more reliable PNT services, the road map of precise orbit determination and time synchronization technique for next generation navigation systems is discussed, which will be the global navigation satellite systems with higher accuracy.