The Autonomous Detection of Clock Problems in Satellite Timekeeping Systems

Y.C. Chan, J.C. Camparo, R.P. Frueholz

Abstract:	Military satellite communications (milsatcom) systems require precise timekeeping in order to take advantage of spread-spectrum communication techniques. Though the level of precise timekeeping in milsatcom is typically not as stringent as that in satellite navigation, milsatcom nevertheless poses its own unique timekeeping problems. Specifically, milsatcom timekeeping must be robust, with the ability to autonomously detect and correct timekeeping problems during protracted periods when the ground control station is either not available or burdened with other pressing tasks. Here, we consider the ability of three different space-segment timekeeping subsystems to autonomously detect the failure of a single satellite clock and to then take appropriate action to remedy the situation. These systems include a Master/Slave system, an Ensembling system, and a Kalman-Filter system. Employing Monte Carlo simulation, we consider four types of “soft” clock failure: a time-jump failure, a frequency-jump failure, a failure arising from a sudden change in the clock’s frequency aging rate, and a failure arising from an abrupt increase in the clock’s random-walk frequency noise. Our results demonstrate that the performance of the three space-segment timekeeping subsystems can be enhanced by adding general “clock failure rules” to the basic algorithms that are associated with each system. Once in place, these rules provide for robust, autonomous space-segment timekeeping,even in the presence of satellite clock failures.
Published in:	Proceedings of the 31th Annual Precise Time and Time Interval Systems and Applications Meeting December 7 - 9, 1999 Marriott's Laguna Cliffs Resort Dana Point, California
Pages:	111 - 120
Cite this article:	Chan, Y.C., Camparo, J.C., Frueholz, R.P., "The Autonomous Detection of Clock Problems in Satellite Timekeeping Systems," Proceedings of the 31th Annual Precise Time and Time Interval Systems and Applications Meeting, Dana Point, California, December 1999, pp. 111-120.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In