Intentional GPS Jamming On the Increase 243
benst writes "Here's yet another way to measure the success of GPS: by the efforts to negate it. While unintentional jamming continues to rise, intentional jamming by both foreign military forces and at-home miscreants of various stripes has shown increased vigor in the past six months. Related here are recent instances of intentional jamming on each side of the border, and (briefly outlined) one initiative mounted by the National Geospatial Intelligence Agency (NGA) to counteract it. Also, here are some ways to detect and prevent jamming."
Re:This must be an urban legend (Score:3, Informative)
I didn't get this at first, so here [youtube.com]. Its from space balls
Re:Domestic jammers (Score:3, Informative)
GPS not critical to JDAM delivery (Score:2, Informative)
GPS is only necessary to obtain current location of the JDAM once along the flight path. Once the position is known to a reasonable degree of accuracy, the on-board AHRS can take over and still deliver the payload to within about 1mm/km of distance traveled.
Re:Ways to prevent jamming. (Score:5, Informative)
> Just put loads of debris in the same orbit at a greatly different speed
Unfortunately, the same orbit means the same speed - different speeds, different orbits.
You need to create an orbit that crosses the satellite's orbit at some point and wait until your debris and the satellite meet at the crossing (since their orbiting times are different, they will, if you wait long enough).
Re:Domestic jammers (Score:2, Informative)
Re:Good. (Score:1, Informative)
You don't need a GPS jammer.
If your bridge is 8 feet high, you simply need a metal arch 9 feet high, and a 'low bridge' sign suspended from it by two one-foot pieces of chain.
http://www.flickr.com/photos/barelyfitz/17874114/in/photostream/
Galileo (Score:3, Informative)
Don't forget the huge disagreement [newscientist.com] between the US and Europe over the Galileo satellite system. The EU intended to use the GPS military band carrier frequencies for Galileo, so that the US couldn't jam it without also jamming the signal used by their own armed forces. Eventually the EU backed down and agreed to use separate frequencies.
Re:secret signals (Score:3, Informative)
Check Wikipedia on GPS.
GPS signals are currently using direct sequence spread spectrum signals to enable every sattelite to transmit on the same frequency. There are two signals, the "free-to-everyone" C/A code, and the military-only P-code (transmitted on two frequencies). The C/A code has a relatively short ss-word and the P-code has a very long ss-word, making it hard to jam...
I would guess most of the jamming mentioned in TFA is aimed at commercial GPS receivers. Now if the Chinese make something that can jam the military GPS receivers, that is something worth writing about, but TFA doesn't mention it.
Re:This must be an urban legend (Score:3, Informative)
NVM... i'm a moran.
it looked like the slashdot ad was in your sig.
Re:secret signals (Score:5, Informative)
Um, no, it isn't. It's owned, lock, stock and barrel, by the US military. Civilian devices are allowed to access it, but the satellites are not commercially owned.
Or they could just ring up the CO of the US Air Force's 50th Space Wing, since that's who owns and maintains the current "boatload of satellites".
Re:Good. (Score:5, Informative)
They already do this for the bridges on Storrow Drive that runs along the Charles River in Boston (they would get jammed under the bridge). Problem was that truckers hit it so much they were regularly destroying the sign. You also need to place it in a spot where the truckers can take an exit instead of trying to reverse up a busy road.
Re:secret signals (Score:3, Informative)
The GPS satellites already use spread-spectrum signals. Each satellite is given a unique Pseudo-random Noise (PRN) code (along with a Space Vehicle number). The PRN code allows each satellite to generate a unique code for the spread-spectrum signals. This both puts the signal below the noise floor and increases jamming difficulty. The civil code generation procedure is well known, and will allow you to build a single-frequency receiver. The military P/Y code generation is classified or restricted information (only a few receiver manufacturers can make true dual-frequency receivers).
The "black" signal available to the military is the P/Y code on L2. This is theoretically unknown to non-military users, but it can still be tracked with by some very fancy receivers.
There are a couple new signals (BOC encoded this time) that Block 2RMs and Block 3 satellites will be transmitting, including improved military and civil codes, and a code expressly for safety-of-life purposes (i.e. aircraft landing). These new signals have a spectral shape (because of the BOC encoding, which gives 2 large peaks side by side, rather than 1 large peak and sidelobes). This will improve anti-jam properties as well.
The nice thing about spread-spectrum signals and jamming is that the jammer has to put out a HUGE amount of power across several MHz of spectrum to wipe out just one of the GPS signals, and either or both can used for > 5 m positioning in civil applications. It would certainly degrade the targeting solution for a missile to the point where it might hit the right building, but certainly not the window. (High rate kinematic solutions of this type would need a dual-frequency measurement, IMHO.)
See "Global Positions System Signals Measurements and Performance" by Misra and Enge for more information. It is an excellent text for an introduction to the GPS system.
Re:Good. (Score:4, Informative)
his type reminds of the people who think it's okay to drive 61 mph in a 65 mph zone in the FAST LANE.
Yeah, sure they are technically correct but intentionally and more than a bit arrogantly lack any pragmatic approach to driving on the road.
In Wisconsin at least, left lane squatters are not "technically correct". The statute requires vehicles traveling "at less than the normal speed of traffic at the time and place and under the conditions" to be driven in the right-hand lane. It doesn't matter what the speed limit is. Since this behavior tends to provoke unsafe driving by others if not outright road rage, I think citing more people for it would definitely make the roads safer.
Re:Good. (Score:3, Informative)
there is a so called "rechtsfahrgebot" in germany. it is a rule of the german road traffic regulations that (more or less) states that on the roads out of a town you always have to drive at the rightmost lane possible.
Re:Very worrisome (Score:3, Informative)
IMHO, neither WAAS [wikipedia.org] nor DGPS [wikipedia.org] are solutions to the jamming problem.
WAAS signals are uploaded to the GPS satellites and broadcast as part of the GPS signals. Thus, when GPS is jammed, WAAS is jammed too.
DGPS ground based transmitters send signals that are potentially strong enough to overcome jamming. However, DGPS transmits the difference between local and GPS estimates. If neither the DGPS, nor your local GPS can receive the GPS signals due to jamming, then DGPS is no help.
Re:Good, where can I buy a 50cm rad jammer. (Score:1, Informative)
I believe the power button is within your 40-50cm jamming requirement
Re:GPS satellites are hard to hit (Score:3, Informative)
GPS satellites are between LEO and GEO. Communications satellites are in GEO.
Since you need your GPS constellation to have birds over higher latitudes than "0, all the time" there's no advantage to GEO, and a very important benefit to reception and payload mass in using lower orbits.
Re:secret signals (Score:3, Informative)