| Beidou（Compass）SatelliteNavigationSystemisaglobalnavigationsatellitesystem（GNSS） constructed independently by China. Different from other GNSSs in the world,the space segment of Beidou system includes5satellites on the geostationary orbit. Thegeostationary orbital satellite features in relative stationary with earth surface and highorbit, and thus is convenient for direct and stable communications with ground stations aswellasothersatellites. AnnovaltimesynchronizationschemeforalltheclocksinBeidousystem is fully investigated. We propose the scheme to synchronize all the satellite-borneclocks via phase-locked microwave link relayed by geostationary satellites. Comparedto the conventional time synchronization scheme of synchronizing every12hours, ourscheme is able to enhance the positioning/timing precision for200times in theory. Torealize the synchronization, we evaluate in detail the frequency/time shift of all clockswithin the earth centered inertial reference frame, also the frequency/time shift of thesynchronization signal transferred between a ground station and a geostationary satelliteas well as between a geostationary satellite and other kinds of satellites. Moreover, wepoint out that by monitoring these shifts, all the satellites’ orbits can be determined withimproved accuracy. Carefully compensating the shifts, ultra-high precision time dissem-ination can be realized via the geostationary satellites, which leads to a better UniversalTime.Not only satellite-borne clocks but also clocks in ground stations must be synchro-nized with high precision to obtain high precision positioning and timing. According tothis requirement, in the second part of this thesis, research of a portable laser-cooled Cad-mium ion clock is presented; this is aimed at a transportable clock for synchronizing ofthe ground station clocks. In this part, the Cadmium ion clock system as well as resonantspectroscopy experiment on the ground-state hyperfine splitting2S1/2, F=1â†'F=0of113Cd+are introduced. The transition is measured to be15199862854.95（0.13）Hz, andconsistantwiththeresultobtainedbythegroupinJetPropulsionLaboratory, U.S.A., withimproved precision. In the experiment, ion cloud as large as105ions is trapped with a lin-ear Paul trap, and a214nm laser is used to laser cool the ions to1K. Then, two microwaveRamsey pulses are applied to the ion cloud and resonant signal with a10Hz linewidthis obtained. Based on this experiment, a transportable, high stability frequency standard with Allan deviations of2×10-14/√τ in short term and5×1015per day is feasible.This is sufficient for the synchronization of ground station clocks. |
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