Study On Key Technologies Of RFID Air Interface Protocols

In recent years, with the deep application of information technology and the rapid development of the Internet of things, Radio Frequency identification (RFID) technology has been widespread concern of scholars and industry. Over the past ten years, UHF band RFID technologies become one of the fast developed directions of RFID because it can realize remote multiple objects fast recognition and tracking. The air interface protocol is one of the key technologies of UHF RFID, and also a hot problem in RFID research field. In general, the communication mouthed and its parameters between the reader and tags are specified by the air interface protocols. In this thesis, the research work is focus on the air interface protocol for the RFID system at UHF band. A systematic study of UHF passive RFID is perfumed, which includes the modulation and coding in physical layer, the system link model and performance in LOS multipath environment, and the ant-collission algorithm, and so on. The main contributions of this work can be summarized as follows:1. In order to solve the constrained energy of passive tag, a new energy efficient data coding method is proposed for the forward link (from reader to tag) in passive RFID system. By using this data coding, a reader can improve the transmission energy from reader to tag without enhancing the decoding complication in tag side. Thereby, the processing ability of tag and the system performance are improved. This data coding performance is analyzed and the time extraction is also provided.2. To decrease the energy consumption and improve performance in return link (from tag to reader) in UHF band passive RFID systems, a scheme of coded modulation is proposed. The cutoff rate is used to study the influence of encoding on system performances. Analysis results show that coded modulation is more energy efficient than encoded modulation in passive RFID return link and the system performance is improved with almost no increase in chip complexity. The gains of encoding in system information rates and communication range for different cutoff rate is analyzed and evaluated.3. The UHF passive RFID systems are often applied for the LOS environments. Wherefore, the read stability of UHF passive RFID systems is easily interfered by the multipath. In order to make an intensive comprehend on the link characteristics, and improve the link performances, a RFID system link model in LOS multipath environments is proposed. The theoretical analysis results on the proposed link model are compared with the test results in the real test environments. Finally, the suggestions on the system improvement are given.4. Anti-collision is an important key technical for RFID air interface protocols. For more effectively resolving the tag collision and reducing the tag access time delay, a variety of anti-collision algorithms are proposed in this thesis. Firstly, a tag collision detection method based on the pulses identification is proposed. Based on the collision detection method, several anti-collision algorithms are provided. As the analysis results shown, the proposed algorithms achieve good system performance, and the algorithms are very easy to be performed.5. For the capture phenomenon in the wireless environment, an optimal probability analysis model to utilize the capture effect for improving the system throughput is developed. According to this model, an optimal capture utilization method which maximizes the theoretical system throughput is also provided. Based on optimal probability model, a simple and feasible access method with capture estimation is proposed, which also yields a good capture gain when the capture occurrence is consciously introduced.