[time-nuts] "The GPS navigation is the weakest point,"

Michael Costolo michael.costolo at gmail.com
Thu Dec 15 21:31:54 EST 2011


This is all very interesting. I may have missed it if it was posted previously, but here they claim what they did to dupe and land the bird.  Now how much of this is true remains to be seen. I'm curious how plausible the story is. 

Is there no way to have some validation of the integrity of a GPS signal? 

http://www.csmonitor.com/World/Middle-East/2011/1215/Exclusive-Iran-hijacked-US-drone-says-Iranian-engineer

-Mike-



On Dec 15, 2011, at 8:56 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
> 
> Put a $35 eBay rubidium on board and you would have to be sure the time solution stayed correct as the take over was implemented. 
> 
> I know strange to tie timing into a discussion like this :)….
> 
> Bob
> 
> 
> On Dec 15, 2011, at 8:20 PM, Jim Lux wrote:
> 
>> On 12/15/11 2:24 PM, Azelio Boriani wrote:
>>> There are GPS simulators for lab use (never seen live or in a picture), I
>>> suppose they have one connector to feed the GPS receiver antenna.
>>> Generating in one equipment all the signals you don't need many but only
>>> one precise timing source.
>>> 
>>> 
>> 
>> Not quite (there's a discussion of this on the list about a year or so ago)...
>> 
>> It's harder than you think to generate realistic fake signals for a moving target.
>> 
>> At work (JPL) we have a fancy Spirent GPS simulator.  And sure enough, it can generate all the signals your receiver would see given a particular path you expect your receiver to follow.
>> 
>> But, in order to use that to provide a spoofing signal, you'd need to know (fairly precisely)
>> 
>> a) the position and velocity of the victim
>> b) the position and velocity(zero) of the jamming station
>> 
>> You calculate what the expected time,code phase, and doppler of the GPS signals would be at the victim.  Then, you subtract out the time from jammer to victim and the doppler from jammer to victim, and use that generate your spoofing signal.
>> 
>> Then, the trajectory of the spoofed position has to be something that is internally consistent (i.e. the acceleration, velocity, and position all have to agree in the Kalman filter), and you have to continously update your jamming signal with continuously updated position and velocity of the victim.
>> 
>> 
>> Spoofing GPS is very hard.It was designed to be so, both for its original military purposes and because you want internal consistency checks to make sure you aren't displaying false information to a user.
>> 
>> Jamming GPS to deny it is relatively easy. A high power swept tone does it very nicely on inexpensive receivers. There are more sophisticated approaches.  You can buy them for $20 on the internet that plug into a car cigarette lighter.  You get one of these jammers, put it on an airplane with a big power amplifier and fly above your sovereign territory and you can deny GPS to pretty much everyone underneath you. There are receiver designs that can tolerate tone or swept or barrage jammers, but they are more expensive, heavier, etc, and I suspect they wouldn't bother on a UAV.
>> 
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