Grouping Based Dynamic Framed Slotted ALOHA for Tag Anti-Collision Protocol in the Mobile RFID Systems

Dynamic framed slotted ALOHA (DFSA) protocol has been widely used in many RFID systems. According to the information from last frame (e.g. the number of idle, success and collision slots), DFSA dynamically adjusts the next frame size so as to reach higher identification efficiency. The process is known as tag estimation of DFSA. Similar to most existing tag anti-collision protocols, The DFSA initially aims at tag identification in static environments where all tags keep still during the tag identification process. However, in many real scenarios (called mobile RFID systems), tags usually move along a fixed path in the reader coverage area. That is, tags enter and leave the area continuously. This easily leads to serious errors of tag estimation because the tag estimation of almost existing DFSA variants do not consider new arrival tags. The errors in turn cause very low tag identification rate and eventually make some tag leave the area unidentified. In this paper, we propose a grouping based dynamic framed slotted ALOHA protocol (GBDFSA) which is very suitable for mobile RFID systems. Through tag grouping in their arrival time order, the tag estimation algorithm in GBDFSA can eliminate the influence of new arrival tags. Simulation results show that GBDFSA can significantly reduce the numbers of lost tags in mobile RFID systems. The idea of the paper is used in various existing DFSA variants so as to make these protocols adapt to mobile RFID systems.