This sheds new light on the technique. Apparently, they are using a mobile station (or maybe I should say a remote station) - not the base station - to track moving objects.
So if you wanted to monitor freeway traffic, you would set up these remote stations along-side the freeway at appropriate intervals.
That makes more sense to me. It would place most of the ground clutter returns after the target returns, which could be just cut off with an appropriately-timed gate window.
Nop ... they simply used a pair of converted phones to do the acquisition of the RF signal and convert that to some lower IF for digitization by the data acquistion board they have listed ...
What they appear to be doing is simple TDOA (Time Difference Of Arrival, between the 'direct ray' from the base station and the 'reflected ray' from some target) with that equipment ...
IMO that was early proof-of-concept work; it worked for an aircraft some distance out. A 'crowded' urban environment is going to require A LOT more processing hardware from multiple 'observers (receivers and data processors).