Dozens of policing agencies are currently using cell-site simulators (CSS) by Jacobs Technology and its Engineering Integration Group (EIG), according to newly-available documents on how that company provides CSS capabilities to local law enforcement. A proposal document from Jacobs Technology,...
As far as I understand, RF is RF. All the truck device needs to do is operate on the same RF frequencies as the tower with the correct data form and handshakes (which I'm sure the cell companies happily provide), and boom, you're connected.
Phones naturally connect to the strongest signal, which will be these things as long as its signal is stronger than the tower, and then the transceiver on the truck connects to the cell tower and is configured to MITM snoop as traffic is passed through the truck device on to the tower and vice versa.
I think the whole point is location tracking and identification. You figure if they want to go after a group of protestors, all they do is set up their tig near them and they'll instantly have every device in the immediate area that they can chase down. And let's be real here, they don't give two fucks about legality anymore, they're in full suppression mode. All the more reason to never bring a phone to a protest in the US.
If there are two or more cell towers within range of the phone and they have access to those towers they can triangulate the location of the phone already.