A Novel Update to Dynamic Q Algorithm and a Frequency-fold Analysis for Aloha-based RFID Anti-Collision Protocols

Radio frequency identification (RFID) systems are increasingly used for a wide range of applications from supply chain management to mobile payment systems. In a typical RFID system, there is a reader/interrogator and multiple tags/transponders, which can communicate with the reader. If more than one tag tries to communicate with the reader at the same time, a collision occurs resulting in failed communications, which becomes a significantly more important challenge as the number of tags in the environment increases. Collision reduction has been studied extensively in the literature with a variety of algorithm designs specifically tailored for low-power RFID systems. In this study, we provide an extensive review of existing state-of-the-art time domain anti-collision protocols which can generally be divided into two main categories: 1) aloha based and 2) tree based. We explore the maximum theoretical gain in efficiency with a 2-fold frequency division in the ultra-high frequency (UHF) band of 902-928 MHz used for RFID systems in the United States. We analyze how such a modification would change the total number of collisions and improve efficiency for two different anti-collision algorithms in the literature: a relatively basic framed-slotted aloha and a more advanced reservation slot with multi-bits aloha. We also explore how a 2-fold frequency division can be implemented using analog filters for semi-passive RFID tags. Our results indicate significant gains in efficiency for both aloha algorithms especially for midsize populations of tags up to 50. Finally, we propose two modifications to the Q-algorithm, which is currently used as part of the industry standard EPC Class 1 Generation 2 (Gen 2) protocol. The Q-Slot-Collision-Counter (QSCC) and Q-Frame-Collision-Counter (QFCC) algorithms change the size of the frame more dynamically depending on the number of colliding tags in each time slot with the help of radar cross section technique whereas the standard Q-algorithm uses a fixed parameter for frame adjustment. In fact, QFCC algorithm is completely independent of the variable C which is used in the standard protocol for modifying the frame size. Through computer simulations, we show that the QFCC algorithm is more robust and provide an average efficiency gain of more than 6% on large populations of tags compared to the existing standard