[1] [1] KOELEMEIJ J C J, DUN H, DIOUF C E V, et al. A hybrid optical-wireless network for decimetre-level terrestrial positioning[J]. Nature, 2022, 611(7936): 473-478.

[2] [2] LI H, HAN L, DUAN R, et al. Analysis of the synchronization require-ments of 5G and corresponding solutions[J]. IEEE Communications Stan-dards Magazine, 2017, 1(1): 52-58.

[4] [4] PIESTER D, SCHNATZ H. Novel techniques for remote time and fre-quency comparisons[J]. PTB Mitteilungen: Amts-und Mitteilungsblatt der Physikalisch-Technischen Bundesanstalt Braunschweig-Berlin, 2009, 119(2): 33-44.

[5] [5] LEWANDOWSKI W, THOMAS C. GPS time transfer[J]. Proceedings of the IEEE, 1991, 79(7): 991-1000.

[6] [6] ALLAN D W, WEISS M A. Accurate time and frequency transfer during common-view of a GPS satellite[C]//IEEE. 34th Annual Symposium on Frequency Control. New York: IEEE, 1980: 334-346.

[7] [7] ZUO F, CHEN Z, HU L, et al. WDM-based fiber-optic time synchroni-zation without requiring link calibration[J]. IEEE Access, 2020, 8: 114656-114662.

[8] [8] ZUO F, CHEN Z, HU L, et al. Multiple-node time synchronization over hybrid star and bus fiber network without requiring link calibration[J]. Journal of Lightwave Technology, 2021, 39(7): 2015-2022.

[10] [10] YANG H, WANG H, WANG X, et al. Picosecond-precision optical two-way time transfer in free space using flexible binary offset carrier mo-dulation[J]. OSA Continuum, 2020, 3(5): 1264-1273.

[11] [11] REN J, HOU D, LI Z, et al. Outdoor atmospheric optical two-way time transfer with serial time code[J]. Review of Scientific Instruments, 2021, 92(4): 045102-1-045102-6.

[12] [12] ZHANG Q, PANG C, WANG Y, et al. Portable system integrated with time comparison, ranging, and communication[J]. Chinese Optics Letters, 2022, 20(10): 100601-1-100601-6.

[13] [13] ZUO F, XIE K, HU L, et al. 13 134-km fiber-optic time synchroni-zation[J]. Journal of Lightwave Technology, 2021, 39(20): 6373-6380.