A Precise and Stable Space-Based Time System for Navigation in Smart Cities.

The high-accuracy and high-stability space-based time system is necessary for satellite navigation systems to achieve high quality of service (QoS) on navigation and positioning in smart city applications. This paper proposes a precise and high-stability space-based time system established under the autonomous time scale of navigation satellites. The generation, maintenance, and transfer of high-precision space-based time references are researched.

A Method for Autonomous Generation of High-Precision Time Scales for Navigation Constellations.

The time maintenance accuracy of the navigation constellation determines the user positioning and timing performance. Especially in autonomous operation scenarios, the performance of navigation constellation maintenance time directly affects the duration of constellation autonomous navigation. Among them, the frequency stability of the atomic clock onboard the navigation satellite is a key factor.

Improving the short-term frequency stability of a magnetic-state-selected cesium beam clock with optical detection.

The microwave spectrum line shape and the signal-to-noise ratio of a compact optically detected magnetic-state-selection cesium beam clock are analyzed in this paper. As the noise analysis shows, the performance is related to the atomic utilization ratio and locking parameters when the laser frequency noise is the dominant noise source. Methods are adopted for realizing better short-term frequency stability of the clock, including using a highly efficient state-selection cesium beam tube, optimizing the locking parameters, and stabilizing the microwave power to maximize the error signal.

Compressing the fluctuation of the magnetic field by dynamic compensation.

We present a dynamic compensation method to compress the spatial fluctuation of the static magnetic field (C-field) that provides a quantization axis in the atomic fountain clock. The coil current of the C-field is point-by-point modulated in accordance with the atoms probing the magnetic field along the flight trajectory. A homogeneous field with a 0.