FREQUENCY AND TIME SYNCHRONIZATION IN DIGITAL COMMUNICATIONS NETWORKS

M. Kihara, K. Hisadome

Abstract:	Frequency distribution performance will be improved with the installation of a new synchronization equipment (slave clock) in Nippon Telegraph and Telephone Corporation's (NTT's) network. In the slave clock system, the PLL has been optimally designed so that the total phase-time variation in the whole network is significantly less than 10 us. This phase-time variation is recommended by International Telegraph and Telephone Consultative Committee (CCITT). The design method and PLL control algorithm enable both an optimum time constant of the PLL and a frequency departure of 10-12 in a holdover operation. The functions of the frequency distribution system has the intrinsic capability of being expanded and applied to a time transfer system. Since the frequencies are synchronized, a phase-time of the standard frequency signal can be synchronized to a coordinate time scale by an initial time setting, e.g., using portable clocks. Time synchronization capability is determined by the relative phase-time variation of standard frequency signals and the time accuracy of the initial phase-time setting. Relative phase-time variation can be reduced to within 500 ns by using wand er correction. The initial time accuracy is within 0.1 us in conventional portable cesium beam standards. The time accuracy in NTT's digital networks is expected to 100 ns to 600 ns.
Published in:	Proceedings of the 20th Annual Precise Time and Time Interval Systems and Applications Meeting November 29 - 1, 1988 Sheraton Premiere Hotel Vienna, Virginia
Pages:	183 - 192
Cite this article:	Kihara, M., Hisadome, K., "FREQUENCY AND TIME SYNCHRONIZATION IN DIGITAL COMMUNICATIONS NETWORKS," Proceedings of the 20th Annual Precise Time and Time Interval Systems and Applications Meeting, Vienna, Virginia, November 1988, pp. 183-192.
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