What’s to prevent a potential enemy from setting up a Differential GPS base station to achieve 10-meter accuracy? Can the US selectively deny GPS service to a certain geographic area of the world while still ensuring that friendly forces in the same area continue to receive GPS service?
By: Distiller - 13th December 2006 at 08:56
The range limit of DGPS is usually given as 200 nautical miles. But that is seldom achieved. Both the DGPS station and the user have to be in direct line of sight of the same GPS-satellite, topographic and metereological conditions play a role.
DGPS operates on long wave frequencies.
Look here for more. The USCG has a network of these stations.
http://www.navcen.uscg.gov/dgps/default.htm
http://www.navcen.uscg.gov/dgps/coverage/CurrentCoverage.htm
By: mabie - 13th December 2006 at 00:51
The commercial frequencies can be shut down, or slightly distorted time codes can be transmitted. Such effects can be limited to certain parts of the orbit.
D-GPS only works in a limited geographical area, or you need a lot of D-GPS stations. That is what China actually does. They are errecting hundreds or probably thousands of reference transmitters.
As I understand it, a D-GPS transmitter with enough power could actually be more trhan a thousand miles away from a client-receiver so a single unit could cover a vast area.. as far as distorting the time codes to cause inaccuracies, DGPS should be able to compensate because it knows its true position geographically and would transmit the corrected position data to all its clients as well.
By: Distiller - 4th December 2006 at 15:30
The commercial frequencies can be shut down, or slightly distorted time codes can be transmitted. Such effects can be limited to certain parts of the orbit.
D-GPS only works in a limited geographical area, or you need a lot of D-GPS stations. That is what China actually does. They are errecting hundreds or probably thousands of reference transmitters.
By: ELP - 29th November 2006 at 07:53
“potential enemy”…. don’t know… current enemies are using GPS against us now in any number of ways. About the only thing we have a handle on is the secure variant of our military only GPS receivers which have secure/anti-spoof/anti-jam abilities. We run exercises to practice killing off jammers. We are good about protecting what we have on the military GPS side so it isn’t denied for our use, but seem to be limited…. ( funding / manpower / such a huge task ) of doing anything to limit the civilian segment of GPS ( which for a lot of uses is good enough ) from being used against us.
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November 29, 2006 at 6:57 am