Fairness Matters: Identification of Active RFID Tags with Statistically Guaranteed Fairness

RFID systems with battery powered active tags are widely used in various applications such as supply chain management and object tracking. In RFID identification, tags transmit their IDs to readers over a shared wireless medium, thus, transmissions from tags often collide causing some tags to use their scarce energy resources to retransmit their IDs. Existing RFID identification protocols are unfair in the sense that some tags transmit more times compared to others and thus deplete their batteries faster. Locating tags with depleted batteries for replacement is troublesome. This paper addresses the fundamental problem of ensuring required fairness in the number of transmissions per tag while minimizing identification time in active RFID tag identification. We propose the first Fair RFID Identification Protocol (FRIP) that can achieve any required amount of fairness. The key idea behind FRIP is to bound the expected number of tags that transmit more than once by finding optimal frame sizes for the standardized frame slotted Aloha. We implemented and performed side-by-side comparisons of FRIP with all nine major existing RFID identification protocols. Our results show that FRIP can achieve arbitrarily high fairness. FRIP reduces the average number of transmissions per tag by at least 2.62 times compared to the best existing protocol. At the same time, it is faster than the existing protocols. FRIP is easy to deploy because it is compliant with the C1G2 standard, and thus, requires no modifications to tags or to the communication protocol between tags and readers. It only needs to be implemented on readers as a software module. FRIP works with multiple readers.