I'm wondering if there's some doppler-shift assessment possible to detect (and possibly reject) spoofing/jamming? A fixed ground-based spoofer/jammer will be too consistent in its doppler-shift, unless it varies its frequency slightly, but that would only work well against specific targets, not broad areas.
> Radio waves experience Doppler shifts the same as sound waves do as objects move. The Doppler shifts for the real satellites will all be different as the object moves either towards or away from them depending on their position in the sky. However, the Doppler shift caused by the object’s motion due to a spoofer is the same for all the satellites signals because they are all arriving from the same direction. This uniformity of Doppler is another indication of spoofing. Again, only the most sophisticated spoofer can account for an object’s motion to adjust its Doppler shift for each individual satellite, and to do so requires tracking the object’s course.
https://safran-navigation-timing.com/resiliency-in-pnt-gps-g...
