Military GPS

[chandin]

How does the information received by US military GPS devices vary from commercially available ones?
Is it encrypted in some way or what?
if is it possible to decode it with like a multi GPU setup or something

[PeterG]

Military GPS uses the same signal an regular GPS. Military GPS uses higher spec receiver chips for higher resolution.

Regards

[Psi]

There is some statistical error that the satellites introduce into the gps data which limits its accuracy.

The US military can set how much of this error is introduced so can vary the accuracy of consumer GPS.
From memory, one of the things president Clinton did when leaving office was to reduce this error level.

The military GPS receivers have a built in formula/key that can calculate what this error is and then apply the negative to the GPS data to cancel it out and gain the full accuracy.

I think i read somewhere that for the America's Cup boat race many years back in NZ they were able to setup a fixed gps receiver at a known point and use the error in its values to correct for the error in the positions from other gps receivers in the race boats nearby.

[the_raptor]

I am pretty sure they stopped using the deliberately lower accuracy signal (with encrypted channel for the military to get the accuracy back to spec) in the late 90's. They can still turn it back on if they need it (but it is pretty pointless with alternate positioning satellite systems).

Military GPS units just have the pretty much obsolete ability to decode the encrypted channel and better receiver chips to track more satellites.

But even with that the usual circular error probability is several meters (and likely much higher for an unstable platform like a Yacht). Land based GPS transmitters ((IIRC the military uses these a lot as well) are used to give extra accuracy over what can be achieved with just the satellites.

[sub]

Military GPS uses a second signal with a higher-rate encrypted code.  My understanding (i.e. what I've learnt from Wikipedia) is that they still have to lock to the public code (Coarse Acquisition, C/A) before attempting to lock to the military code (precision, P, P(Y) with encryption).

Some surveying equipment can improve its accuracy using P(Y) though the key is not available (called a codeless receiver).

I think i read somewhere that for the America's Cup boat race many years back in NZ they were able to setup a fixed gps receiver at a known point and use the error in its values to correct for the error in the positions from other gps receivers in the race boats nearby.

This is differential GPS (DGPS), and is used to correct for ionospheric delays.  Since these will remain constantish in the immediate vicinity of the receiver, the (accurately surveyed) station can determine a correction.  New satellites will broadcast the civilian code on several frequencies, and the relative timing will allow the propagation delay (which depends upon frequency) to be determined at the receiver.  My understanding is that P(Y) is already broadcast on this second frequency, so military receivers may (probably) already have this capability.

[chandin]

Military GPS uses a second signal with a higher-rate encrypted code.  My understanding (i.e. what I've learnt from Wikipedia) is that they still have to lock to the public code (Coarse Acquisition, C/A) before attempting to lock to the military code (precision, P, P(Y) with encryption).

Some surveying equipment can improve its accuracy using P(Y) though the key is not available (called a codeless receiver).

I think i read somewhere that for the America's Cup boat race many years back in NZ they were able to setup a fixed gps receiver at a known point and use the error in its values to correct for the error in the positions from other gps receivers in the race boats nearby.

This is differential GPS (DGPS), and is used to correct for ionospheric delays.  Since these will remain constantish in the immediate vicinity of the receiver, the (accurately surveyed) station can determine a correction.  New satellites will broadcast the civilian code on several frequencies, and the relative timing will allow the propagation delay (which depends upon frequency) to be determined at the receiver.  My understanding is that P(Y) is already broadcast on this second frequency, so military receivers may (probably) already have this capability.

has any hacker managed to break this encryption?
how tough is it compared to like for example RSA?

[johnmx]

The Galileo project will overcome the GPS. Today they launched the first 2 satellites.

http://www.businessweek.com/news/2011-10-21/europe-launches-two-galileo-satellites-to-cut-reliance-on-gps.html

[deephaven]

The Galileo project will overcome the GPS. Today they launched the first 2 satellites.

http://www.businessweek.com/news/2011-10-21/europe-launches-two-galileo-satellites-to-cut-reliance-on-gps.html

That was good timing!

[Zad]

Military GPS uses a modulation which is 10x wider in bandwidth. Normal CA code GPS uses a modulation code which is only around 1000 bits long, and therefore repeats many times a second and is easy to synch to. The military GPS modulation code repeats approximately once a day. The combination of code length and speed make it incredibly hard to crack. If it were cracked and publicised, they would change the encryption setting anyway.

The artificially degraded "selective availability" (SA) was turned off way back in 2000. It was becoming outdated anyway, with the introduction of the differential GPS network. This is basically a set of fixed ground stations, which calculate the difference between the known receiver and the transmitted location. It then broadcasts the error corrections on a set of frequencies around 300kHz.

http://www.effective-solutions.co.uk/dgps1.html

[george graves]

Not to sound like a tin-foil-hat-wearer like Dave  , but they can not only de-tune the GPS accuracy...of course they can also shut it off if need be.

[Uncle Vernon]

The Galileo project will overcome the GPS. Today they launched the first 2 satellites.

While it's easy to scoff at the organisational abilities and motives of the US military, one has to wonder about  the ultimate success of a Euro Zone focused GPS system.

The french will no doubt insist that all protocols, documentation and communications be in French. The German will assume the system to be all theirs by birth right refusing to share resources with any non blondes. the Brittish will no doubt pay the system lip service at build their own inferior and incompatible service anyway. The Italians, Greek and Spaniards will default on their repayments denying them access to the system. The Belgians will form multiple steering committee bogging the entire project indefinitely in order to meet tens of thousands of bureaucratic compliance obligations.

Don't ditch your working GPS unit just yet.   

[Zad]

Actually, by that mark, the British system would have been technically brilliant, with amazing accuracy and 20 years ahead of it's time, but governmental licensing restrictions would have dictated that only a couple of defence contractors would be able to use it, making civilian use impossible.

I don't know about these two new satellites, but the previous proof of concept satellites were engineered by a spin-off of the University of Surrey, which learned it's trade by building and flying amateur radio satellites.

[Uncle Vernon]

Actually, by that mark, the British system would have been technically brilliant, with amazing accuracy and 20 years ahead of it's time, but governmental licensing restrictions would have dictated that only a couple of defence contractors would be able to use it, making civilian use impossible.

Much like our homegrown Australian government scientific efforts. After a century of effort the only the long term most successful export product remains scientists.

[johnboxall]

The Galileo project will overcome the GPS. Today they launched the first 2 satellites.

http://www.businessweek.com/news/2011-10-21/europe-launches-two-galileo-satellites-to-cut-reliance-on-gps.html

Don't forget GLONASS - the Russians are almost there:
http://en.wikipedia.org/wiki/GLONASS
The new iPhone 4S can make use of it (Apple had no choice if they want to sell iPhones in Russia...)

[Achilles]

Military GPS uses a second signal with a higher-rate encrypted code.  My understanding (i.e. what I've learnt from Wikipedia) is that they still have to lock to the public code (Coarse Acquisition, C/A) before attempting to lock to the military code (precision, P, P(Y) with encryption).

Some surveying equipment can improve its accuracy using P(Y) though the key is not available (called a codeless receiver).

I don't know exactly where it sits, but there is already some implemented correction in GPS-Signals which corrects for Water Vapor and Temperature of the Atmopshere. We work Together with GFZ Potsdam and use GPS to estimate the Atmospheric Water Path.
http://www.oosa.unvienna.org/pdf/pres/stsc2011/tech-23.pdf    You can have a short look over here......
Maybe the Military Data uses finer/better Algorhytms for those correction estimations.

AT least Wikipedia tells us that there is a new Military Code which could be used for position aquisition. I don't know how much you can rely on secret information which is accessible in the internet..... I could imagine that not everything is true or exact here. If anymore has more insight on this topic it could be really interesting!

[rf-loop]

There is also coming Chinese next generation  Beidou II. ("Compass")
(And remember where first magnetic compass was firts find...  )

Also, nobody do not exactly know how Chinese military positioning is more accurate than it can think if look public data about they navigation systems. It can be sure that they do not use american GPS for military higher level things. They are not so stupid as all western countries who are just under "one buttonn" what is only in US hands.

And not as pentagon or nasa all doors and windows open... ... no one can find how to go inside chinese systems.........

[Bored@Work]

The Chinese were originally part-taking in the European navigation system, but were thrown out because of, well, "creative usage" of confidential project internal information.

Now guess why the Chinese try to register exactly the same frequencies for navigation that the Europeans are using with their new satellite system? I wouldn't gloat so much about the Chinese system when it is just stolen European and US technology, maybe with a few parts bought cheaply from Russia.

[rf-loop]

I wouldn't gloat so much about the Chinese system when it is just stolen European and US technology, maybe with a few parts bought cheaply from Russia.

No, they do not copy museum  of technology. But of course western propaganda do it.

Of course if you do bicycle you do it just as copy.
All is copy... as you know how you can make bicycle without copy that there is two wheels and place for sit and turning first wheel. Is it copy? Yes it is - of course it is. Yes if use same frequency area... is it copy or are there some scientific resons...
Why american pocet lighter use same light frequency as Chinese 2000 old gas lamp. Copy same frequency. Let me laugh.
You know why this frequency area is important. If use same frequency.... it meand copy...wow. I can not stop my laughing. Best of day.

*kind smile*

[Achilles]

Well, let's wait for the chinese System

It is known that China copies a lot, but we can't proof that the new system is an Galileo clone. Galileo also has nothing to do with "museum of technology". Sadly it is delayed, but because of financial problems. If the chinese System would be so great we would have a civil use for the international market and first receivers on ebay...I am very sure of that .

To the one button-us thing. That's been one of the main reasons for Europe to establish their own System which runs independent from GPS. Somehow I am a bit sad that I have to go to French Guyana next month and wasn't there for the Galileo-Sojus

[Bored@Work]

No, they do not copy museum  of technology. But of course western propaganda do it.

You can wank all the way you want about the alleged superiority of your dictatorship, and come up with the same age-old unimaginative rhetorics. It doesn't change the fact that the Chinese system is copied left, right and centered from stolen and bought technology. And your superior Chinese engineers are using the same frequencies up to six significant digits. Coincidence my arse.

[Achilles]

@ BoredAt Work:
....but it's also partly our/our Governments fault because we invite everybody and love outsourcing knowledge like hell. Sending technology and engineers to China and then wonder why the put the stuff cheaper on the market. A lot of people mentioned to me that it's not bad meant, because it's another culture. It's more like getting as good or better than the Original than copy it and make money quick.
As long as we put our money above our knowledge it will be like that....quite a nice invitation for Chinese Manufacturers

I don't know if you ever heard about our german "Transrapid". A high-speed magnetic Monorail. Completely funded my german taxes (about 1,7Billion euros) and then put it in a shelf because of the high costs.....
The Test track is being deconstructed and the only running Transrapid is serving in Shanghai right now;). Great to develop stuff with our money and then give it away....

[sub]

And your superior Chinese engineers are using the same frequencies up to six significant digits. Coincidence my arse.

To be fair, this is something of a necessity in order to allow multi-system receivers to add support without extra RF circuitry.  If you've gone to the trouble of building your own system with its own spreading codes, to change frequency and bump up the cost of your receivers would be madness unless the the systems would interfere.