Possible GPS Interferance

Submitted: Thursday, Mar 20, 2003 at 08:21
ThreadID: 3948 Views:1660 Replies:1 FollowUps:5
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Just came across this. With impending world trouble gps systems may not work.


http://www.theregister.co.uk/content/6/29818.html
US to disrupt GPS, satellite comms in Gulf?
By John Lettice
Posted: 19/03/2003 at 12:01 GMT


The US may pull the plugs on civilian GPS (Global Positioning System) during a war in Iraq, and could take steps to disrupt satellite communications systems, according to a Gulf News report. Quoting "senior industry sources" the report suggests that GPS - which is the simplest candidate for a switch-off - would be the first satellite service to be affected, but that it could be done "as part of a wider drive to stem the flow of information/propaganda during the conflict, especially in the initial phases."

At the moment the US is the only game in town when it comes to GPS, and just over a year ago US Deputy Secretary of Defense Paul Wolfowitz appeared to be trying to keep it that way. But clearly he couldn't have been, because the State Department was at the time spreading sweetness, light and interoperability. Possibly meaning that Galileo is cool provided we can switch that one off as well.

But even if not, it's still a couple more wars down the line. As far as today's war is concerned, disabling non- US military GPS might have some impact, not necessarily confined to the war zone, but action against satellite communications systems in general would be a more drastic step. Inmarsat yesterday said it had increased its capacity from four to nine operational satellites in the Middle East in preparation for increased demand, and helpfully quoted CNN's Nic Robertson as saying: "Videophones put you in the heart of a story." Indeed they do Nic, indeed they do.

Given that the US has indicated that users of 'freelance' sat systems may be in some personal peril, some less potentially lethal attempt to shut off the supply in general would make sense. But how? ®
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Reply By: GaryInOz - Thursday, Mar 20, 2003 at 10:39

Thursday, Mar 20, 2003 at 10:39
When GPS first came into service during Iraq mark 1, the "least significant bits" in the data stream were dithered, or made intentionally inacurate (actually scrambled) so it could not be used by other opposition forces for precision guidance.

The Miltary later removed this dithering to allow its use by commercial and private operators during peacetime after some smart people realised that by setting up a fixed land based GPS reciever/transmission point (ie building, landmark, etc), and seeing how much that was dithered, then subtracting that dither from the dither in their present location, gave them exactly the same accuracy as the undithered signal. This also limited the possibility of someone working out the algorithm they used in the scrambling, and to counter the spread of these points.

What the US may do is to turn the dithering back on The official GPS MIL-SPEC equipment has an internal program that can "unscramble" the dithereing allowing its use in precision guided uses.

In short, you will probably have reduced accuracy, I think it used to be +/-100' horizontally and 50' vertically. It is unlikely they will actually turn GPS off altogether.
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Follow Up By: plexus - Friday, Mar 21, 2003 at 01:13

Friday, Mar 21, 2003 at 01:13
Well, I haven't been able to receive any signals at all now for about 8 hours.... I was thinking that they were going to resume "Selective Availability" when they started their frolic in Iraq this afternoon, but it looks like it's been shut down altogether. Or is it just that my unit needs to download new almanacs and will be back up again soon? Who knows....
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Follow Up By: Greg Harewood - Friday, Mar 21, 2003 at 01:49

Friday, Mar 21, 2003 at 01:49
plexus - check your batteries - from what Ive heard nothing will happen - everything will work as normal. Paranoia is taking affect - beware. Stay indoors and dont drive.
Cheers
Greg
PS The Russians are coming..the Russians are coming..
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Follow Up By: plexus - Friday, Mar 21, 2003 at 01:58

Friday, Mar 21, 2003 at 01:58
My GPS runs off the aux battery in the dual-battery system.... so that means they've infiltrated my truck... bloody CIA.
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Follow Up By: Greg Harewood - Friday, Mar 21, 2003 at 02:32

Friday, Mar 21, 2003 at 02:32
plexus - has any member of your family been acting strangely lately - staying out late, a bit moody/tense, stocking up on bake beans, talking into shoes? Ring Ray Martin now - just for your own peace of mind:)
Cheers
Greg
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Follow Up By: plexus - Friday, Mar 21, 2003 at 10:58

Friday, Mar 21, 2003 at 10:58
Come to think of it, the cat *does* kinda stare at me lately....
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