GPS Spoofing... how it is done ?

[OscarH]

Hi folks,
Does anyone of you has information on how GPS Spoofing works ?
I understand GPS jamming is somehow quite easy to perform by generating a signal to muffle the receiver.
GPS Spoofing seems much more complex as you need to simulate a valid signal with shifted coordinates...
No plan to have it done, but very interested to understand how it works !
Thanks
OH

[pickit2]

just like at war... you would not want to give that information out.
your not a spy are you?

[rtm]

I think I know how to do it. At least 15 years ago, I wanted to do it by this method but had no time to try it. The idea was elementary.

You receive signals of usual GPS frequency L1 (1575.42 MHz) with a regular receiver at geographic point A, extract the amplified and filtered IF (Intermediate Frequency) signal right before the detector, then convert this spectrum band to another frequency, let's say F(144MHz) amplify it and retransmit via a communication channel to another geographic point B. There, you receive it on F(144MHz), amplify it, convert it back to the original frequency L1 (1575.42 MHz), and broadcast it there with good power. As a result, all GPS receivers will receive an amplified retransmitted signal and will show the coordinates A in point B. In practice, it will be enough to retransmit signals of L1 frequency (1575.42 MHz) all other frequencies L2 (1227.60 MHz) and L5 (1176 MHz) should be jammed in point B.

[OscarH]

just like at war... you would not want to give that information out.
your not a spy are you?

I'm not a spy - and not willing to be - but as Electronic Engineer, I am interested in the technical aspect behind the effect.
May be I need to better understand GPS operation first.
I also understand this may not be a shareable information as too sensitive in the current environment...
Cheers - OH