Anti-Collision Algorithms Research For UHF RFID Systems

With the development of the CPS (Cyber Physical System, in other words it is the Internet of Things), the RFID (Radio TRequency Identification) technology, one of the important technologies for CPS, has gained more and more attentions. The RFID technology is a powerful way for automatic object identification, which enables the seamless and automatic connection between the real-world objects and their virtual representations. With the advantages of the freedom of human’s intervention, no physical contact, strong anti-jamming ability, the fast recognizing speed, the RFED technology has been referred to as the most promising one used to building the CPS, possessing broad application foreground. There are also some bottlenecks for the RFID technology, one of which is the collision of two or more tags.RFID uses radio frequency (RF) energy’s electromagnetic coupling to complete the communication between the interrogators and the tags. The communication channel is shared by different tags. when multiple tags communicates with the interrogator at the same time, a collision would occur causing a failure of that communication, in which case, each tag has to retransmit all information to the interrogator. Passive tags do not consist of an onboard power source and they must derive all of the energy required for operation from the RFID interrogator’s RF signal. So the coordination of communication cannot be carried out for themselves between each other. Therefore, the interrogators need to coordinate the different tags’ communication preventing the collision. In the RFID systems, the Dynamic Frame Slotted ALOHA (DFSA) algorithm is widely adopted to solve this collision problem. Q-algorithm, a variant for the dynamic frame-slotted ALOHA algorithm, is employed by the EPCglobal specifications for RFID air interface protocol. The parameter Q represents the number of binary bits of the frame length, and the dynamic adjustment of the frame length is completed by a constant C, in pursuit of the efficiencies of the system.This paper firstly introduces the background on the issue, describes the solved issue, illustrates EPC RFID Class-1Gen-2protocol and State of the Field. The paper adopts the EPC Class-1Generation-2UHF RFID protocol for communications at860MHz-960MHz Version1.2.0.RFID anti-collision algorithms can be categorized into two groups: tree-based and ALOHA-based ones. The DFSA (Dynamic Frame-Slotted ALOHA) algorithm is widely applied currently. The approach to estimate the number of tags also takes an important role in the anti-collision algorithm, which we also make a detailed introduction.Finally, the paper presents an approach called MF-ML to estimate the number of the tags, and design a new anti-collision algorithm. The New anti-collision algorithm reduces the frequency to adjust the frame length, decreases the communication between the interrogators and the tags, shorten the response time of device, saving the energy cost of the tags, thereby the new algorithm improve the system performance. In this paper, we will firstly compare the MF-ML approach with the existing algorithms, compare the new algorithm with the existing algorithms in adjusting frequency. Then we simulate the entire communication in matlab, The simulation result shows that our algorithm outperforms the other algorithms in the number of slots to identify all tags (identification delay),the system’s throughput and the total time to identify all tags.