To read transmitter-only RFID tags with confidence

Radio frequency identification (RFID) enables everyday objects to be identified, tracked, and recorded. Because of expense, size, and lifetime requirements, some simple active RFID tags are designed with only a transmitter. The transmitter-only tags are unaware of each other and simply blink ID packets periodically. The question is how we can read the tags with enough confidence. The paper models the access protocol as pure ALOHA and develops a mathematical analysis to identify tag blinks within the interrogation zone without prior knowledge of the number of tags. We estimate the tag set based on the free channel in the observation window. Some simulation results and test experiments with Spider tags from RFCODE are presented.