Global Positioning System
(GPS) is a 24-satellite constellation owned and operated by the United
States Government as a national resource.
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CDMA cellular mobile telecommunications
network via countless CDMA system base stations scattered throughout
the world. Maintained by commercial cell phone system providers.
CDMA system timing accuracy is guaranteed to be within 10 microseconds
in order for the cell phone system to work.
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Worldwide coverage.
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Localized coverage -
extensive in North America, China, Korea, India, New Zealand, Hong Kong, and elsewhere.
Virtually absent in Europe.
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Unit requires view-of-the-sky
antenna. Sometimes not a problem, sometimes just a nuisance, sometimes
impossible. Expensive installation and maintenance costs are often
required.
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Unit works deep inside
buildings with small, integrated antenna.
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Absolute timing accuracy
of unit is under 10 nanoseconds.
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Absolute timing accuracy
of unit is typically under 10 microseconds.
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Network timing accuracy
1/2 - 2 milliseconds, typical (for NTP products).
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Network timing accuracy
is same as GPS.
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Frequency accuracy of
unit is <10-13 at 1 day.
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Frequency accuracy of
unit is <10-11 at 1 day.
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