1. A method comprising: transmitting ultra-wide band (UWB) radio frequency (RF) signals at, and receiving echo signals from, an environment including at least one human, processing the received echo signals to yield a range-bin-based slow signal that is spatio-temporally characterized over a plurality of spatial range bins and a plurality of temporal sub-frames, respectively, and deriving, from the range-bin-based slow signal, a Doppler signature and a range-time energy signature as motion characteristics of the at least one human.