1. A method comprising: transmitting, via at least one transmitting antenna, ultra-wide band (UWB) radio frequency (RF) signals at an environment including at least one human, and receiving, via at least one receiving antenna, echo signals from the environment, processing the received echo signals to yield a range-bin-based slow signal that is spatially characterized over a plurality of spatial range bins, estimating at least one respiration feature of the at least one human by analyzing the slow signal, and classifying the at least one respiration feature to indicate a respiration mode of the at least one human.