DiSEL: A Distance Based Slot Selection Protocol for Framed Slotted ALOHA RFID Systems

This paper introduces a new medium access control (MAC) protocol for passive Radio Frequency Identification (RFID) systems. The protocol is designed as an enhancement to framed slotted ALOHA MAC protocols in which tags randomly select a slot number on a given frame size. As shown in this paper, the completely random slot selection in the framed slotted ALOHA systems is not the optimum approach to the slot selection problem. To minimize the collision probability, our protocol, named Distance Based Slot Selection (DiSEL), uses a cross- layer approach for tags to select the most appropriate time slot in a given frame. A tag in DiSEL uses the maximum and minimum received power levels of the reader-tag communications to choose a slot number. A resonant boosting network to increase the received RF power granularity and an efficient rectifier to convert the RF signal into DC introduced for the power level measurements at the tags. We test DiSEL under various tag deployment and density scenarios and show that DiSEL decreases the tag collision probability in both random uniform and evenly spaced dense tag deployments.