Abstract
Radio Frequency IDentification (RFID) has enabled a wide range of automated tracking and monitoring applications. However, RFID tags share a wireless communication medium to deliver their information to the RFID reader which results in tag collisions and, hence, a significant energy consumption and delay in the interrogation process. Handling tag collisions is a challenging task because of the limited capabilities available to passive RFID tags. In classical anti-collision schemes, the RFID reader interrogates all tags in its range at once using its maximum transmission range, which results in many collisions and wastes energy. In a previous work, we proposed a novel approach in which the interrogation zone of an RFID reader is divided into a number of ring-shaped clusters, and tags of different clusters are read separately. We also proposed a method that finds the optimal clustering scheme assuming an ideal setting in which the transmission range of the RFID reader can be tuned with high precision. In this paper, we consider a more practical scenario in which the RFID reader has a finite set of discrete transmission ranges rather than continuous ones. This suits currently existing commercial RFID readers that come with configurable output power. We present a delay mathematical analysis for this optimization problem and devise an algorithm that finds the optimal clustering efficiently. The proposed approach can be integrated with any existing anti-collision scheme to improve its performance and, hence, meet the demand of large scale RFID applications. Simulation results show that our approach is able to make significant improvements in saving energy and time by reducing collisions.