BPS is a GPS alternative that nobody's heard of

“Because accurate timing is critical in many areas, from media, to the power grid, to 5G and communications, having a reliable terrestrial backup to GPS—especially one that can be hardened against different types of jamming attempts—may be important to our economy, communications and power grid.”

Broadcast TV towers can deliver timing within 10 nanoseconds of GPS. A terrestrial signal is much harder to jam than a satellite. About 1,700 US stations could carry it. Only a few are testing it.