[alphaBetaGamma]

What your suggesting is going to be tricky to implement. First you can only add delay, not subtract delay, so your specific example will not work: you can not "rebroadcast at the drone's antenna" before the original signal reach the drone.

To overcome this, could record all the gps signals, and rebroadcast them with carefully timed delays. But than gps time as determined by the drone will be different from what a clock in the drone gives, so it could be detected. If you are quick enough it might work, but it's non trivial.

And if the drone uses carrier-phase gps measurements you have a whole bunch of other problems.

Not saying it can't be done, but it's not easy.

[michaelt]

There are commercial products for less than $100 that do this for the L1 C/A signal - such as [1].

You can rebroadcast at substantially higher power than the signal coming directly from the satellite, so the direct signal gets drowned out. After all, the satellite has to broadcast to cover half the world, while you only have to cover a few square meters.

Now, I'll grant the receiver may see a change in signal strength, some cycle slips, and an increase in clock skew. But you get those in normal GPS operation anyway. If you're going to detect GPS attacks and self-destruct your drone you'll want a very low false-positive rate, and I'm not sure that's feasible.

[1] http://www.diplomat.co.uk/products/hardware-products/active-...