Just to add to this, because it's fascinating.
GPS satellites signals are about as strong as radiation from a light bulb, 20000km away. The signal that arrives on earth is 20db weaker than the noise floor, so background noise is a lot stronger than the signal is.
The way it works is that the background noise is random and the signal is repeated many times a second, so you can split the signal and add it together. The random background noise averages out and you're left with a strong signal. But due to this, it's enough to have a very weak signal that adds non random noise on the correct frequency for it to just break.
And actually what I desribed above is just the first layer of a GPS signal, it gets a lot more complicated with signals within signals, it's pretty crazy how well it works. this is an amazing write uo on how the signal actually works, in case anyone is interested