Passive RFID systems require that a reader emit energy that is then harvested by a tag and is used to reflect back a signal to the interrogator. Automatic Power Stepping is a means by which to reduce power consumption, which can improve battery life in handheld readers and reduce overall energy costs for an RFID system. IEEE offers an excellent paper on this subject: More With Less: An Adaptive Approach to Energy-Efficient RFID Systems.
According to the authors: “APS dynamically estimates the number of tags to be read, incrementally adjusts the transmission power level to use sufficient but not excessive power for communication, and consequently reduces both the energy consumption for reading a set of tags and the possibility of collisions.”
—Mark Roberti, Founder and Editor, RFID Journal