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GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

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Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#61

Post by daniel-cussen »

anovikov wrote: post #35
jof wrote: post #32

Earlier quoted context omitted.

The GPS P(Y) and Military codes exist to (hopefully) prevent spoofing.

They aren't. A spoofer doesn't need to know what the signal means/be able to decrypt it. Just retransmit signal received from a different place at higher power. Only way to distinguish it from a real one is timing, but that requires an atomic clock, which is $15,000 and too expensive for most applications. But, military grade GPS receivers use virtual beam forming to achieve a very high attenuation of spoofing signal…

Atomic clocks are $2000 now. SA.45, specifically. And they're smaller.

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#62

Post by londons_explore »

beambot wrote: post #31
joering2 wrote: post #29

Earlier quoted context omitted.

This is what keeps my awake at night sometimes... that one of US drones flying over Afghanistan will be eventually fooled into thinking the target it has to drop a bomb on is actually somewhere else over the Europe.

Depending on who you believe, that GPS spoofing has already been used for military purposes: https://en.m.wikipedia.org/wiki/Iran–U.S._RQ-170_incident

One can GPS spoof with $100 worth of hardware and a few days putting together opensource software defined radio modules.

Just hook a GPS signal emulator to a software defined transmitter.

A total system bandwidth of 1 Mhz is nowhere near computational limits today. Total transmission power of a couple of watts is trivial.

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#63

Post by anovikov »

jcims wrote: post #58
lisper wrote: post #46

Earlier quoted context omitted.

Money. INS is still very expensive relative to GPS, and GPS is pretty frickin' reliable 99.99% of the time.

Would commodity six axis sensors have enough precision to do a reasonable job at INS?. Buy a pack of iPhones and use some kind of quorum protocol to reduce the risks associated with one going bad?

No, they won't, not at all.

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#64

Post by anovikov »

daniel-cussen wrote: post #61
anovikov wrote: post #35

Earlier quoted context omitted.

They aren't. A spoofer doesn't need to know what the signal means/be able to decrypt it. Just retransmit signal received from a different place at higher power. Only way to distinguish it from a real one is timing, but that requires an atomic clock, which is $15,000 and too expensive for most applications. But, military grade GPS receivers use virtual beam forming to achieve a very high attenuation of spoofing signal…

Atomic clocks are $2000 now. SA.45, specifically. And they're smaller.

Great! That is a big difference. Cheap enough for every jet aircraft, most turboprops, and some of the most expensive guided munitions (cruise missiles, or nukes like B.61 Mod 12 for sure).

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#65

Post by anovikov »

jschwartzi wrote: post #42
lisper wrote: post #40

Earlier quoted context omitted.

> Hopefully GPS isn't your sole source of information. Nowadays, in modern airplanes, it often is your only source of positional information when you're in instrument conditions (which is, of course, when it matters most). > I carry multiple navigational aids Yeah? Like what?

Compass, Altimeter, topographic maps, notes about the route that I've made. Even a watch can aid navigation if you can calculate your speed and see any terrain features. If anything doesn't jive with what I expect or what I'm seeing I try to understand why.

Maybe there is a market for civilian version of DSMAC?

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#66

Post by burntrelish1273 »

gsich wrote: post #56
jhayward wrote: post #53

Earlier quoted context omitted.

GPS and Galileo use the same frequency for their public service. Jamming one gets them both. Glonass is a couple hundred megaherz away from GPS L1.

So there is no reason NOT to support Glonass.

Except the Russians run and control it and may consider opportunities to weaponize it offensively against unsuspecting Western users.

The best bet is to use as many positing systems as possible in order to prevent attacks narrowly targeting one positioning system.

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#67

Post by patrickg_zill »

joering2 wrote: post #29
lisper wrote: post #26

It is worth noting that there are two different ways to attack GPS: jamming and spoofing. Jamming is when you broadcast a noise signal at the GPS frequency, which prevents affected receivers from receiving the GPS signal. The result is that the GPS doesn't know where it is. Spoofing is when you send out a fake GPS signal that appears genuine but has the wrong timing. The result is that the GPS thinks it knows where i…

This is what keeps my awake at night sometimes... that one of US drones flying over Afghanistan will be eventually fooled into thinking the target it has to drop a bomb on is actually somewhere else over the Europe.

They may well have other systems like inertial systems combined with GPS. See for instance https://en.wikipedia.org/wiki/GPS/INS

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#68

Post by scrumper »

derefr wrote: post #55
ianburrell wrote: post #54

Earlier quoted context omitted.

GPS receivers do not have clocks. Atomic clocks are expensive and large; there is no way you get one every device. Only the satellites have atomic clocks. The receiver get the time from the satellites. It basically compares the time delay between the satellites to determine position and time.

I didn't say they have atomic clocks. They do have clocks, though. Like most computers do. And they are high-precision, and are low-drift enough to predict the locations of satellites as long as they have been re-synchronized within the last few days or so. Which, as you say, also happens by just observing the time signatures from the satellites. You need four visible satellites to determine your own time, though, wh…

Your final point conflates icbms with cruise missiles - very different things. I don’t believe icbms use TERCOM or visual matching.

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#69

Post by manarth »

Cyph0n wrote: post #30
manarth wrote: post #21

Earlier quoted context omitted.

The feature is called "Selective Availability", and has been disabled since May 2000. https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_...

So are you saying that the US military does not have a higher accuracy positioning system? I highly doubt that.

There are well-known ways to improve GPS accuracy, such as dGPS [1], inertial guidance, and beam-riding [2].

I think it unlikely that the US military has a secret second constellation of GPS-like satellites, operating on an undetectable secret frequency. Firstly, it would be difficult to launch and operate such a constellation in secret, and secondly, because augmenting the GPS data with independent, secondary sources operating with a different approach provides more redundancy and is proven technique for increasing accuracy.

The capability to limit accuracy in the satellite signal already existed – the fact that it was shut off is a strong signal that the perceived benefit is no longer important.

[1] https://en.wikipedia.org/wiki/Differential_GPS [2] https://en.wikipedia.org/wiki/Beam_riding

Re: GPS signal disturbed at altitudes above 2000-3000 feet over Norway [pdf]

#70

Post by gsich »

burntrelish1273 wrote: post #66
gsich wrote: post #56

Earlier quoted context omitted.

So there is no reason NOT to support Glonass.

Except the Russians run and control it and may consider opportunities to weaponize it offensively against unsuspecting Western users. The best bet is to use as many positing systems as possible in order to prevent attacks narrowly targeting one positioning system.

The same can be said to NAVSTAR GPS. The only system which is not primarly built for military uses is Galileo.

Yes, that's what I am saying. Don't rely on one system. Using more also increases accuracy.

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