GPS and similar satellite navigation systems revolutionized how you keep track of where you are and what time it is. However, it isn’t without its problems. For one, it generally doesn’t work very well indoors or in certain geographic or weather scenarios. It can be spoofed. Presumably, a real or virtual attack could take the whole system down.
Addressing these problems is a new system called Broadcast Positioning System (BPS). It uses upgraded ATSC 3.0 digital TV transmitters to send exact time information from commercial broadcast stations. With one signal, you can tell what time it is within 100 ns 95% of the time. If you can hear four towers, you can not only tell the time, but also estimate your position within about 100 m.
The whole thing is new — we’ve read that there are only six transmitters currently sending such data. However, you can get a good overview from these slides from the National Association of Broadcasters. They point out that the system works well indoors and can work with GPS, help detect if GPS is wrong, and stand in for GPS if it were to go down suddenly.
If all digital TV stations adopt this, the presentation mentions that there would be 516 VHF stations operating with up to 10 kW over two widely separated bands. That adds to 1,526 UHF stations running between 100 kW to 1000 kW. So lots of power and very diverse in terms of frequencies. Coverage is spotty in some parts of the country, though. A large part of the western United States would lack visibility of the four stations required for a position fix. Of course, currently there are only five or six stations ..
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