Research On Anti-Collision For UHF RFID System

Radio Frequency Identification (RFID) is a burgeoning and advanced technology to non-contacting identify and track objects automatically using radio waves to exchange data between a reader and electronic tags which are attached to objects. With the advantages of farther distance identification and quick operation etc, UHF (Ultra High Frequency) RFID system is able to achieve the multi-object identification and motion object identification, and thereby becomes the most the most advanced automatic identification technology. The system of Internet of Things based on ultra high frequency RFID usually needs multiple readers to work simultaneously in the same area. Multi-reader collision happens. Besides, there are few research achievements on this collision. Thus, doing research on reader collision in UHF RFID dense environment is more important and in urgent need. This paper only focuses on the UHF multi-reader collision, and proposes some strategies for anti-collision.The domestic and foreign literatures were studied deeply, and the cause of multi-readers collision which divided into reader-to-reader collision (RRC) and reader-to-tag collision (RTC), was analyzed. Based on the above research, two anti-collision algorithms were proposed:Firstly, a new reader anti-collision approach by making use of graph coloring and genetic algorithm was proposed in this paper. By modeling a reader collision graph, this preset algorithm converts time slot assignment into the problem of k-vertex graph coloring, and optimizes genetic algorithms to solve the problem of K-vertex graph coloring, in order to find out the minimum time slot number and its optimal assignment. The simulation showed that the reader anti-collision algorithm is effective, practical and feasible for UHF RFID reader.Secondly, based on backscatter system, a power control algorithm based on SIR is proposed for multi-reader anti-collision in this paper. In the anti-collision process, readers dynamically adjust their transmission power according to SIR, to reduce redundancy of their coverage area, and thereby minimize multi-reader collision. Considering that some target SIR may not be achieved yet when the transmit power is adjusted to maximum, a novel backoff algorithm is proposed. The backoff time is mapped into the proportion of target SIR iteration for the fairness of channel occupation. The simulation results show the reader anti-collision algorithm based on power control and backoff algorithm converges fast, effectively reduces redundancy of their coverage area and thereby minimizes the reader collision, but also can ensure the detection range and thereby enhance read rate. Besides, the backoff algorithm can reduce the power consumption, which is important for mobile readers.Finally, some new research method and thinking were proposed in this paper, which is valuable for the research on development of UHF RFID technology.