"As technology progresses, an SDR can move to an almost total SR, where the digitization is at (or very near to) the antenna and all of the processing required for the radio is performed by software residing in high-speed digital signal processing elements... It is evident from inspection of these... that there is a key transition stage in the metamorphosis of SDR to SR. This metamorphosis is a function of core technology advances balanced against the full scope of design criteria and constraints applied to the wireless product."