Research On UHF Multi-tag Identification And Anti-collision Algorithm

Radio frequency identification (RFID) technology is a non-contact automatic identification technique. RFID do not need line-of-sight communications, able to withstand harsh physical environment, has low cost, highly efficient operation and can identify multiple tags at the same time. So it is widely applied in different fields, such as logistics, postal service, civil aviation, transport, ticketing and identity, etc. But there are still many problems need to solve in practical application. This paper concerns the multi-tag collision problem and learns the key multi-tag anti-collision algorithms of the RFID system. The main works are as follows:Firstly, this paper introduces the research background, the present situation of the RFID technology and the tag anti-collision algorithm. This paper describes the principle of RFID system and standard, the RFID air interface standards and so on. Detailed description of the principle and composition of the RFID system, RFID air interface standards. As an example, we take ISO18000-6Standard to show the way how data to decode, modulate, demodulate and communicate. Compliance with ISO18000-6C Standard for RFID systems, we used Simulink to simulate transmitter and receiver modules of readers in order to observe the signal characteristics.And then we analyzed the pure ALOHA, slotted ALOHA, frame time ALOHA and dynamic frame slotted ALOHA. For the blindness of data tags sending in ALOHA, we proposed an anti-collision algorithm based on the p-persistent CSMA in this paper. According to amount of data tags sending, the method dynamically change p values that data tags send in a slot of a data frame to improve the system throughput. In this paper, we established a mathematical model to analysis this method. The experimental results show that throughput of the system in anti-collision algorithm based on the p-persistent CSMA is significantly higher than ALOHA anti-collision algorithms when identifies multiple tags.Secondly, we analyzed the basic binary search algorithm, the recoverable binary search algorithm and dynamic binary search algorithm. For the problems of binary search algorithm need search so mang times and send large amount of information, we proposed an improved binary search anti-collision algorithm in this paper. This algorithm uses collision bits to construct quad tree, which reduces the search times and the amount of transmission information of readers to improve the system efficiency. The experimental results show that the proposed algorithm performs significantly better than the existing anti-collision algorithms．Finally, the AS3992RF module and C8051F340single-chip microcomputer was used to construct small UHF RFID system, implement multiple tags identification.