Satellite Time and Frequency Transfer and Dissemination


image of Satellite Time and Frequency Transfer and Dissemination

This is the first ITU Handbook to provide detailed information on the applied methods, technologies, algorithms, data structure and practical use of frequency and timing signals provided by satellite systems.



Communication satellite systems

The principal function of communications satellites is to transfer RF signals for communications purposes. Therefore, time and frequency transfer via communications satellites is usually accomplished by piggybacking off the communications functions. Some satellite systems, especially those utilizing timedivision multiple access systems (TDMA), require precise time for their communications functions [ITU-R Handbook, 2002; Ha, 1990]. In the majority of TDMA cases, the satellite just passes through precise timing signals from the ground, and the satellite payload itself does not require precise time for its operation. Time transfer capability is required in the satellite bus telemetry, tracking, and command system, for ranging and time tagging purposes. However, this part of the satellite system is generally not available to the leasing user. Frequency accuracy and stability requirements for commercial satellites are in general limited to that required for maintaining band allocations and for performing ranging functions. Government communications satellites tend to have much more accurate on-board frequency sources, because they are also used for navigation or other purposes that require precise time.


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