RF and EE here. This is nothing new. Or at least a motivated junior/senior in college would stumble upon this simple application of wave propagation theory pretty early on.
This is notable because it's an actual implemented system. Yes it works in theory, on the exact same principle that a radar speed gun works, but these researchers have shown that it is possible to implement in the 2.4GHz band. That's the first step to making it smaller and cheaper.
I know there has been tons of see-thru-the-walls work done over many years... But that used UWB and required specialized equipment and antennas, IIRC, whereas this uses "commodity" USRPs. Could you provide examples of the type of work you're talking about?
