RSAA: Reliable Splitting Aware ALOHA to capture passing tags

The Radio Frequency Identification (RFID) technology has been widely applied to labeling moving objects. In some RFID application scenarios, e.g., product checking on conveyor belt, the tags labeled on the products need to be identified and accessed before moving out of the reader´s probing range. Due to the uncertainty of ALOHA protocol and unreliability of wireless links, passing tags will suffer from collisions and link failures, and then move away without successful response. One important requirement for RFID systems is to reliably identify and access all the tags. There is naturally a tradeoff between system throughput and reliability, e.g., tag may have no chance to successfully respond in high moving speed and system throughput drops in low tag moving speed. In this paper, we introduce an integrated software system Reliable Splitting Aware ALOHA (RSAA), which is used to improve system throughput while maintaining a threshold of tag loss probability. Given a tag loss probability, RSAA is able to approach to the optimal system throughput. We implement RSAA on our NI EPC Class 1 Generation 2 UHF RFID Reader Emulator to read and access commercial tags. Experiments in indoor and outdoor scenarios are conducted to demonstrate the efficiency of RSAA. Compared with moving unaware schemes, RSAA can reliably enhance the throughput by 50%~100%. We further use trace-driven simulation to show that RSAA is able to support diverse tag density and large-scale UHF RFID systems.