Baseband Signals and Power in Load-Modulated Digital Backscatter

Passive digital backscatter signals in systems like radio frequency identification (RFID) are usually received along with strong interference from a leaked carrier. The simplest way to quantify the “useful” communication signal is to separate it as an amplitude-shift keying (ASK) or biphase-shift keying (BPSK) component. These definitions give different power normalizations, posing some complexity in comparison of link quantities. This letter investigates their suitability in terms of basic signal theory and conservation of energy to clarify relationships between the baseband signals and “backscattered power.” Defining received backscatter as BPSK guarantees energy conservation for arbitrary tag modulation loads.