1. A Radio Frequency Identification (RFID) reader system for communicating with a plurality of RFID tags, the system operable to: cause to be transmitted to the RFID tags a first reader command that communicates a first value for a Q parameter, the first reader command thus causing each of the RFID tags to occupy one of a plurality of first slots that are defined by the first value; then cause a plurality of QueryRep commands to be transmitted sequentially to the RFID tags, each QueryRep command for examining a respective one of the first slots for its occupancy by causing any of the RFID tags occupying the respective first slot to backscatter a response within a tag response time window of the first slot and be silent at a tag silent period of the first slot that is outside the tag response time window of the first slot; receive an initial reference signal during one of the tag silent periods of one of the first slots; measure an aspect of the initial reference signal; set a detection threshold from the measured aspect; detect second signals during at least some of the tag response time windows of the examined first slots; determine from the second signals whether the occupancy of the examined first slots is none of at least one of the RFID tags, in which the determination for at least a certain one of the first slots is performed by comparing the detection threshold to a power of a second signal corresponding to the certain slot; decide according to the determined first slot occupancies and according to a Q-algorithm a second value for the Q parameter; and then cause to be transmitted to the RFID tags a second reader command that communicates the second value for the Q parameter, the reader second command thus causing each of the RFID tags to occupy one of a plurality of second slots that are defined by the second value.