I want to like this — I think having ground-based alternatives to GPS and other space-based PNT systems is a very good thing! But after reading the paper at
https://www.nab.org/bps/Broadcast_Positioning_System_Using_A... and other BPS information on the NAB's website, I think the NAB is being wildly optimistic about BPS:
• ATSC 3.0's physical layer can already transmit GPS time in a way that receivers could get it back out. What BPS brings to the table is a requirement and specification for accurately and consistently filling in the physical layer preamble fields containing the time data, along with a new physical layer pipe (think "low-level data stream") that contains additional information about the transmitter and, optionally, its neighboring transmitters.
• BPS is capable of producing time fixes when the receiver only has a lock on one source. This isn't surprising at all — GPS receivers can do the same thing. But either type of receiver with only one source would see a clock offset proportional to the path delay, which it wouldn't be able to compute and back out without knowing its position.
• BPS is only designed for 2-D position fixes. While that's a reasonable design decision (the vertical position error would be massive), it also makes BPS less useful for the NAB's "indoor positioning for first responders" use case, especially in areas with multi-story buildings.
• The need to receive and process/decode multiple, most likely non-adjacent 6 MHz channels for positioning increases receiver complexity and cost.
• The NAB claims that 1 kilometer of separation between two BPS transmitters is "sufficient for useful position determination." I don't buy it, especially in the face of poor transmitter geometry.
• They note that 16 TV stations in the New York City area broadcast from One World Trade Center, so for the purposes of BPS, they're effectively one station. This kind of transmitter colocation is incredibly common, both in urban areas (ten TV stations broadcast from Sutro Tower in San Francisco) and in more rural areas (six TV stations in the Roanoke-Lynchburg DMA broadcast from towers within ~1 mile of each other on the ridgeline of Poor Mountain). Even if every ATSC TV station became an ATSC 3.0 w/ BPS transmitter, bad transmitter geometries would destroy BPS's position accuracy in lots of markets.
• What's the business case for broadcasters? BPS won't be free for broadcasters to implement, and there doesn't seem to be a path to it generating revenue except for a hand-wavy "maybe one day televisions will be able to determine their locations without Internet connections using BPS, and then broadcasters can do location-targeted advertising with those TVs!"
My uncharitable take is that BPS will never be a usable standalone PNT system. A timing system in the "rebroadcasts GPS" sense? Maybe. Standalone positioning? No way. Broadcasters implementing BPS (or ATSC 3.0 at all) without being forced to by the government? I don't see it.