Characterization of the Identification Process in RFID Systems

Abstract

Radio Frequency Identification (RFID) is incr easingly being used to identify and track objects in supply chains, manufacturing process, product traceability, etc. These environments are characterized by a large number of items which commonly flow in conveyor belts, pallets and lorries, entering and leaving logistic installations. In these scenarios the RFID systems are installed as fo llows: one or more readers are placed in a strategic place, creating checking areas. The tags, attached to items, enter and leave the checking areas (traffic flow). The goal of RFID in these applications is to guarantee the communication with the tags as quickly and reliably as possible, ensuring that all tags are identified before they leave the checking areas (Finkenzeller, 2003). One of the main problems related to RFID in these applications is that both readers and tags share the RF spectrum. Hence, when two or mo re tags/readers transmit simultaneously a collision occurs. The collisions diminish the system performance, producing a delay in the identification, and may cause tags leaving the workspace unidentified. The parameter that measures the rate of unidentified tags is the Tag Loss Ratio (TLR). Depending on the application, even a TLR = 10-3 may be disastrous and cause thousands of items lost per day. The collisions resolution on RFID has been extensively studied during the last years, for active and passive RFID systems. In active RFID, the collision resolution is not only mandatory to reduce the identification time, but also to decrease the tag energy consumption in order to maximize the batteries lifetime. In this case, tag hardware permits to put forward sophisticated anti-collision mechanisms. Nevertheless, this complex hardware also entails high-cost-devices and, in the end, the tag price becomes the dominant factor in the final deployment. On the other hand, in passive RFID, the extreme simplicity of the tags is a hard constraint for the design of new collision resolution methods. However, the low-cost-price of passive tags is its most attractive characteristic which permits to think about a massive adoption in a near future. Several proposals have been conducted during the last years with the aim at minimizing the collision problems in passive RFID systems, suggesting new anti-collision protocols that, a priori , outperform the current standards. Most of these studies have been