S05 Session of Time Frequency and Precision Timing Successfully Convened
On May 27, 2021, the Time Frequency and Precision Timing Session of the 12th China Satellite Navigation Conference (CSNC) was held in the multifunctional hall on the second floor of Greenland International Expo Center in Nanchang, Jiangxi Province. The session was chaired by Liu Ying, member of the organizing committee of CSNC, and session chairs Zhang Aimin, Wang Liang, Li Xiaohui and Du Lijun. 21 academic presentations were provided to discuss the theories, methods and technologies related to time frequency and precision timing in satellite navigation system, covering a wide range of topics including establishment and maintenance of time and frequency reference, ground atomic clock, spaceborne atomic clock, generation and maintenance of time and frequency signals, precision timing of satellite navigation system, time and frequency transmission and synchronization, evaluation of atomic clock performance, monitoring of time and frequency signal integrity, and measurement and comparison of time and frequency signals. The experts shared the current status and the latest research progress and achievements in related fields at home and abroad, engaging more than 100 experts and scholars.
First up, Research Fellow He Yuling shared the current progress and future prospects of time frequency system and payload of navigation satellite of China Academy of Space Technology Xi 'an Branch. The performance of spaceborne time-frequency product can significantly affect the navigation and positioning accuracy of the entire satellite navigation system. Benefiting from the Beidou Navigation Satellite System, China’s spaceborne high-precision time frequency technology has growing rapidly, and the spaceborne atomic clock was developed from scratch with improving performance, effectively supporting the development and steady operation of BDS system. To meet the development requirements of the next generation BDS system, it is necessary to further improve the performance of the atomic clock, study and develop new types of atomic clock, optimize the monitoring management of the atomic clock group, and improve the accuracy of inter-satellite time frequency measurement and comparison, so as to achieve higher accuracy and longer autonomous operation required by the next generation of BDS system.
Liu Tao, Research Fellow from the National Time Service Center of Chinese Academy of Sciences, presented the optical fiber time frequency transfer technology in the high-precision ground-based time service system, which uses the communication optical fiber network to build the optical fiber time frequency backbone network covering major cities and important users in China. The time transfer accuracy is better than 100 picoseconds, and the frequency transfer accuracy is better than E-19. He also briefly introduced prospect of ground-based timing system supporting the BDS system in the future.
Fang Fang, Research Fellow from the National Institute of Metrology, introduced the progress that has been made in the development of fountain clock. The cesium fountain clock, as an experimental device to reproduce defined second, has a median day stability of E-16 and a class-B uncertainty of decimal E-16. The future development of the fountain clock depends on the further improvement of performance, operation stability and reliability. The specific works include using ultra-stable microwave and optical pump to improve the stability, using low temperature sensitive vacuum-microwave cavity to improve the uncertainty index. Ms. Fang also forecasted the future development direction of fountain clock.
Dr. Patrizia Tavella, Director of the Time Department at the International Bureau of Weights and Measures (BIPM), gave an invited online presentation titled “news from the BIPM and the CCTF on time transfer and international time scale”. This presentation mainly introduced the hot issues of time and frequency currently being discussed by the Consultative Committee for Time and Frequency (CCTF), including the update of the roadmap under the modification of second definition, issues regarding leap second in UTC, considerations for the establishment of continuous time scale, and the promotion of mutual benefit between UTC and GNSS. The latest research progresses of BIPM in time frequency, including Beidou time transfer and Beidou receiver calibration, etc. were also shared by Dr. Tavella.
Lu Yun, Senior Engineer of the Beijing Institute of Tracking and Communication Technology, introduced the research on the autonomous establishment and maintenance of comprehensive atomic time for satellite navigation constellations. Wang Shichao of the Beijing Satellite Navigation Center introduced the monitoring and assessment of the time difference between the BDS and other GNSS systems and the analysis of its impacts. Guo Yanming, National Time Service Center of Chinese Academy of Sciences, introduced a method of precise time synchronization between satellite and earth and the analysis of its motion delay errors. Xu Shaoxing, the School of Electronics Engineering and Computer Science, Peking University, introduced a new method to suppress the optical frequency shift of small cesium beam atomic clock. Huang Kai, No.203 Research Institute of the Second Academy of CASIC introduced the design of a multi-channel high-precision digital phase comparator.
Sun Leyuan, Wang Wei and Huang Xinming of the National University of Defense Technology introduced the relativistic effect of the two-way time comparison between navigation satellites, the study of high precision time synchronization method of LEO based on PPP, and the research on integrity monitoring technology of atomic clocks based on Dualkalman filter. Li Junyao of the University of Chinese Academy of Sciences introduced the research on the rubidium frequency standard with stability E-15 level in atmospheric conditions. Liu Xuan of China Academy of Space Technology in Xi’an introduced the progress of the research on inter-satellite precision measurement and time-frequency synchronization technology based on USO. Li Guojun of the Beijing Satellite Navigation Center introduced the zero value calibration of Beidou common-view receiver by closuring error method.
Chen Sifei, School of Electronics Engineering and Computer Science, Peking University, Liu Shuo, No.203 Research Institute of the Second Academy of CASIC, Ma Pei, No.510 Research Institute, China Academy of Space Technology, Yang Bin, Beijing Satellite Navigation Center, Huangfu Songtao, China Academy of Space Technology (Headquarters), and Yang Jun, No. 510 Research Institute, China Academy of Space Technology also gave wonderful presentations.
