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Handbook of Smart Antennas for RFID Systems by Nemai Chandra Karmakar

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CHAPTER 24

ANTI-COLLISION OF RFID TAGS USING CAPTURE EFFECT

QI JING TEOH and NEMAI CHANDRA KARMAKAR

Department of Electrical and Computer Systems Engineering, Monash University, Clayton, Victoria, Australia

24.1 INTRODUCTION

RFID systems operates in a complex environment where many tags reside in one or multiple readers’ reading zones. The transponders within the reading zone do not respond with the same signal strength to the reader. The signal strength varies from transponder to transponder due to their different physical location, architecture, data packet structures, and temporal variation in responding to the interrogation signal from the reader. When more than one transponder is transmitting simultaneously to an interrogator within its reading zone, it leads to a collision at the interrogator. In a real communication environment, the reader is able to successfully identify the strongest data packet in a collision. This phenomenon is called the capture effect [1–3]. However, most works on anti-collision protocols have made a simple assumption that when a collision occurred between tags, all data packets are considered lost. This assumption is ignored in capture effect calculation.

As discussed in the previous chapter, in the frame-slotted Aloha (FSA) algorithm, there are a fixed number of timeslots for each read cycle. The tags will randomly choose a timeslot from the time frame to transmit their data. Figure 24.1 illustrates the process of tag recognition in FSA for Reader#1 ...

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