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sci.geo.satellite-nav (Global Satellite Navigation) (sci.geo.satellite-nav) Discussion of global navigation satellite systems (GNSS). Topics include the technical aspects of GNSS operation, user experiences in the use of GNSS, information regarding GNSS products and discussion of GNSS policy (such as GPS selective availability).

Ubiquitous PNT and Sequestration: The World Runs on GPS Time



 
 
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Old November 18th 13, 10:39 PM posted to sci.geo.satellite-nav
Sam Wormley[_2_]
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Default Ubiquitous PNT and Sequestration: The World Runs on GPS Time

Ubiquitous PNT and Sequestration: The World Runs on GPS Time
http://gpsworld.com/ubiquitous-pnt-a...s-on-gps-time/


Quick as lightning, before I even had a chance to challenge the
response or thought process, a grizzled old E9, who proved his
operational savvy that day, interjected, “Beg your pardon, but all of
our radios, computers, networks and communications gear are
referenced and synchronized to GPS time. A GPS jammer would take us
out of business until we brought up our backup atomic reference
system. So, initially a Coke-can jammer activated in our facility
would be catastrophic, but we would soon be back in business because
we have backup atomic reference systems.”


Fast-forward, and today that transition between GPS and atomic
reference system is seamless. There is no down time, and yet the
systems still run on GPS time. But during that initial visit, I could
tell by the looks on the junior communications officers faces that
surrounded us that, while they appreciated the save by the old chief,
they were also still wondering, just how pervasive is the actual
impact of GPS time for computers, networks and communications?

The answer is simple. The world as we know it today runs on GPS
time.


  #2  
Old November 22nd 13, 02:29 PM posted to sci.geo.satellite-nav
Alan Browne
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Default Ubiquitous PNT and Sequestration: The World Runs on GPS Time

On 2013.11.18, 17:39 , Sam Wormley wrote:

Fast-forward, and today that transition between GPS and atomic
reference system is seamless. There is no down time, and yet the
systems still run on GPS time. But during that initial visit, I could
tell by the looks on the junior communications officers faces that
surrounded us that, while they appreciated the save by the old chief,
they were also still wondering, just how pervasive is the actual
impact of GPS time for computers, networks and communications?

The answer is simple. The world as we know it today runs on GPS
time.


Risk management is required and should suit the needs of the organization:

- internet sources - 10ms (possibly better if the client network and is
engineered carefully).

- GPS disciplined clock. A Rubidium clock that is 'disciplined' with a
GPS input (many hours time constant) can then coast accurately when GPS
time is lost and until the jammer is defeated. 1 ns. The same clock
can be used as primary NTP for the organization in any case.

- alternate satellite sources (Galileo, Glonass - though so close in
frequency, a "coke can" jammer would likely hit them as well. (100 ns
or better).

- CRPA antennas: more complex and expensive. You need to determine the
direction of the jammer and steer a null in that direction.

The level of mitigation depends on how critical time is to the
operation, the likelihood that internet might be cut off (best alternate
source of time) is pretty low and the other solutions are more expensive
and technically demanding.

--
"The radio was once expected to promote international understanding and
co-operation;
it has turned out to be a means of insulating one nation from another."
-George Orwell, 1945

 




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