Your local cellphone towers already provide a more accurate position beacon signal for GPS modules in most parts of the world. Additional RF beam-forming in G5+ systems also make it impractical for lamers to jam long-distances due to limited coherent signal propagation.
Indeed, amateur Hams have caught Russian ships jamming/spoofing local port traffic several years before the various official overseas conflicts started. Not sure if it is government sponsored, or just various smuggling schemes like some ships spamming China harbors. =3
Agreed about cellphone towers providing accurate position, but not with enough precision and highly dependent on the number of towers in the vicinity.
What i started building is for a highly unlikely scenario which is ; no internet + no GPS + no cell tower.
I have this idea that I'll get Bosch 9-DoF sensors onto every lane of every road, at least twice a month, then any other thing on a road can use a Shazam - like waveform lookup to determine where they are.
I didn't come up with this for dead reckoning, it's more for, um, autonomous cars to be able to avoid potholes and stuff.