I think there is no need to hack the signal. It can be done by capturing and delaying signals. What you need for that is
1) the location of satellites. You can probably get it from the commercial signal.
2) transmission system, which overpowers signals from satellites. Many amateurs have it too.
3) location of the receiver you want to distract. I have no idea, how this works, but apparently it is possible.
4) program that calculates right delays for each signal so that plane will locate itself incorrectly.
Maybe the droid was programmed so, that GPS overrides other locationing devices, if it is working and the droid thought that GPS was working.
As jgrahamc says: "I realize that as a Westerner I shouldn't be rooting for the Iranians but if they did spoof GPS, jam the rest of the communications and get this thing to land thinking it was at its home base then it's at least a neat hack."
I'm not sure, if I'm thinking this way too simply, but I don't think any of those countermeasures work in this case. I don't know, if satellite gets signals from GPS-device (I don't think so), when using military signal, but anyway it will get exactly the same signal, as it would get in non-disturbed system. Similarly the droid will have exactly the same signal from satellite, only delayed.
When commercial GPS-devices begin to locate themselves, they need four satellites for the process: Three for the coordinates and one for time. I believe, that military system works the same way. If you cut down the signals for a while, the droid will, when the signal (delayed one) comes back, maybe adjust it's clock a couple of 1/10000ths of second to get GPS-locationing back in business. And after that the signal transmitter decides, where the droid will fly.
Many guesses here, but this is just one suggestion free for discussion, how the system might work...
1) the location of satellites. You can probably get it from the commercial signal.
2) transmission system, which overpowers signals from satellites. Many amateurs have it too.
3) location of the receiver you want to distract. I have no idea, how this works, but apparently it is possible.
4) program that calculates right delays for each signal so that plane will locate itself incorrectly.
Maybe the droid was programmed so, that GPS overrides other locationing devices, if it is working and the droid thought that GPS was working.
As jgrahamc says: "I realize that as a Westerner I shouldn't be rooting for the Iranians but if they did spoof GPS, jam the rest of the communications and get this thing to land thinking it was at its home base then it's at least a neat hack."