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Atomic clocks are the core equipment aboard navigation satellites, and their performances and predictions directly determine PNT accuracy. In this paper, the on-orbit performances and prediction accuracies of atomic clocks used in new generation navigation satellites are evaluated using two-way time synchronization data. First, using clock error data preprocessed based on combined MAD gross error detection, the method used to evaluate satellite clock performance is studied. The results illustrate that gross error can be eliminated effectively and that the performances of the new generation of satellites are improved in comparison with those of regional satellites. The frequency accuracy has been enhanced from 6.91 × 10−12 to 3.29 × 10−12, and daily stability has been enhanced from 4.036 × 10−14 to 2.339 × 10−14. Second, a weighted combined clock error prediction model was designed that synthesizes polynomial and gray models using the classical weighted method. The results using the combined models show that the prediction accuracies of the new generation satellites are improved by a factor of two when compared with those for regional satellites, and the mean prediction was enhanced was from 0.77 ns to 0.38 ns. Moreover, from the research findings, it was found that prediction accuracy is significantly correlated with daily stability and frequency accuracy and has a micro-correlation with daily drift rate. Finally, in order to study the prediction accuracies of the new generation of satellites, we studied ISL and concluded that it has greatly increased the measured arc of the MEO satellites and can improve re-entry prediction accuracies from 3–4 ns to 1 ns.

A high precision multi-node clock network for multiple users was built following the precise frequency transmission and time synchronization of 120 km fiber. The network topology adopts a simple star-shaped network structure. The clock signal of a hydrogen maser (synchronized with UTC) was recovered from a 120 km telecommunication fiber link and then was distributed to 4 sub-stations. The fractional frequency instability of all substations is in the level of 10-15 in a second and the clock offset instability is in sub-ps in root-mean-square average.

In BeiDou ground-based navigation signal net, the technology of optical fiber time and frequency transfer, whose design precision excels 0.5 ns, is used to realize the time synchronization between ground stations. Limited by condition and precision, some techniques such as TWSTFT and satellite common-view are not suitable for optical fiber time synchronization testing. In this paper, the clock travel method based on cesium clock with high precision is used to test the performance of optical fiber time synchronization, and its handling process is discussed in detail. At the same time, the main error sources are analyzed in this paper. The closed-loop result of outfield testing excels 0.4 ns, which validates the feasibility of the method. Meanwhile, unilateral delay of optical fiber device is calibrated, and time delay of 100 ns level is detected, which is important for system data processing.

A precise multi-node frequency dissemination scheme for multiple users by feed-forward digital compensation technique is demonstrated. The fractional frequency instabilities of the third-level nodes were measured as 1.79×10−15/s (2.61×10−18/100s) and 1.45×10−15/s (4.58×10−18/100s).

Precision time synchronization between two remote sites is desired in many applications such as global positioning satellite systems, long-baseline interferometry, coherent radar detection and fundamental physics constant measurements. The recently developed frequency dissemination technologies based on optical fiber link have improved the transfer instability to the level of 10−19/day at remote location. Therefore it is possible to keep clock oscillation at remote locations continuously corrected, or to reproduce a “virtual” clock on the remote location. However the initial alignment and the correction of 1 pps timing signal from time to time are still required, besides the highly stabilized clock frequency transfer between distant locations. Here we demonstrate a time synchronization based on an ultra-stable frequency transfer system via 120-km commercial fiber link by transferring an optical frequency comb. Both the phase noise compensation in frequency dissemination and temporal basis alignment in time synchronization were implemented by a feed-forward digital compensation (FFDC) technique. The fractional frequency instability was measured to be 6.18 × 10−20 at 2000 s. The timing deviation of time synchronization was measured to be 0.6 ps in 1500 s. This technique also can be applied in multi-node fiber network topology.

We demonstrate feed-forward digital compensation technique applied in both precise frequency transfer and time synchronization. The fractional frequency instability was 6.18×10−20 at 2000 s and RMS variation of time synchronization was sub-40 ps.

We demonstrate precise microwave frequency dissemination of a hydrogen maser synchronized frequency comb over a 120 km commercial fiber link. The phase noise was compensated by a feed-forward digital compensation scheme, where the value of locally detected phase noise was first transmitted to the remote user end via a wavelength division multiplexing channel in the same fiber link and then compensated directly at the user end. The fractional frequency instability was measured to be at 5.28×10(-16)/s.

We demonstrate a feed-forward digital compensation scheme in an optical frequency comb based microwave frequency dissemination system over 120-km telecommunication fiber link. The dissemination fractional frequency instability (Λ-counter) was measured at 5.28×10−16/s.