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Radio Frequency Identification Fundamentals and Applications, Bringing Research to Practice Part 3

Tham khảo tài liệu 'radio frequency identification fundamentals and applications, bringing research to practice part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Characterization of the Identification Process in RFID Systems 33 EPCglobal Class-1 Gen-2 works at UHF band 860MHz-930MHz . It proposes an anticollision mechanism based on a variation of FSA. Fig. 4 illustrates EPCglobal Class-1 Gen-2 operation. At a first stage the reader system is continuously monitoring the environment to detect the presence of tags by means of Broadcast packets. Tags in the coverage area are excited by the electromagnetic waves of the reader and send a reply immediately producing a multiple collision. The reader detects the collision and starts the identification cycle. During each identification cycle the time is structured as one frame which is itself divided into slots following a FSA scheme. EPCglobal Class-1 Gen-2 shows two configuration alternatives Fixed frame-length procedure All identification cycles frames have the same value number of slots . It is common to find commercial systems with this configuration. Variable frame length procedure denoted as frame-by-frame adaptation . The number of slots per frame can be changed by the reader in each identification cycle. The reader decides if increase decrease or maintain the number of slots per frame in function of some criteria. In the following subsections both procedures are overviewed as well as the implementation status of current readers. 3.3.1 Fixed frame length procedure An identification cycle starts when the reader transmits a Query packet including a field of four bits with the value Q e 0 . 15 stating that the length of the frame will be of 2Q slots. Tags in coverage receive this packet and generate a random number r in the interval 0 2Q-1 . The r value represents the slot within the frame where the tag has randomly decided to send its identification number ID r. Inside each frame the beginning of a slot is governed by the reader by transmitting the QueryRep packet excepting the slot 0 which is automatically initiated by the Query packet. The tags in coverage use an internal .