A tag collision problem (or missed reads) in Radio Frequency Identification (RFID) system happens when multiple tags respond to a reader simultaneously. At this time, the reader cannot differentiate these tags correctly. This problem is often seen whenever a large volume of RFID tags are read together in the same radio frequency field. Tag collisions will degrade identification efficiency, and this unreliable identification will compromise the usefulness of RFID system. This chapter introduces tag collision problem and discusses tag anti-collision protocols, including ALOHA-based protocol, Binary Tree (BT) protocol, and Query Tree (QT) protocol. To date, most tag anti-collision protocols are QT protocols. Thus, in this chapter, the authors briefly describe some elegant researches on QT protocols, and also introduce their recent research results on QT protocols.
