Objectives  As a complex and giant system, the BeiDou satellite navigation system (BDS) demands scientific, complete and efficient design and engineering implementation of time-frequency system.

  Methods  For the designation of time and frequency architecture for BDS-3, the first step is the realization of establishment, maintenance and synchronization of time and frequency architecture, and the second step is the unification of BDS time (BDT) and other navigation systems. The internal time synchronization for BDS-3 is designed as the methods of time comparison and synchronization among clocks of satellites based on inter satellite link, precise time comparison and synchronization between satellites and ground based on satellite-ground link, and comparison and precise synchronization between master station on ground, and its subsystem based on satellite two-way and ground wired two-way time comparison link. The generation of BDT signal is realized by combined clock group and integrated atomic time method. Finally, the unification of BDT and other navigation systems is realized through direct or indirect traceability comparison and time difference monitoring technology.

  Results  The long-term monitoring results of BDS-3's signals indicated that the frequency stability per day of BDT reached 4.6×10^-15, the local time accuracy of satellite clocks reached 1.25×10^-11, the 1 000 s frequency stability of satellite clocks reached 1.65×10^-14, and the time difference between BDS and other navigation satellite system maintained within 50 ns.

  Conclusions  Within the operation of BDS-3, it is further proved that the time and frequency architecture for BDS-3 is complete in function design, scientific in organizational structure and advanced in system index, which can fully support the global service capability of BDS-3.