| Radio frequency identification (RFID) is the key technology to achieve "Internet of Things" (IOT) and "Ubiquitous Networ" (UN). Ultra high frequency (UHF) RFID is obtaining more and more widespread applications in social life, such as logistic supply chain management, item tracking, asset management, ETC, etc., because of its outstanding characteristic of small size antenna, high data rate, multi-tag read, great identification range, and it also has become the hot spot in automatic identification and data capture (AIDC) research area. The work of this dissertation are based on a project of the High-tech Research Project of China ("863" research project) "Research on the Communication Test Technologies in Applications of Radio Frequency Identification" with the funded number 2006AA04A106. Several key technology problems on implementation and application of UHF RFID are studied in this dissertation, and the purpose is to resolve a set of bottleneck problems which restrict the implementation of RFID applications and development of RFID industry, furthermore, provide reference for RFID evolution and other related key technologies under UC&N framework.Methods of theoretical analysis, simulation comparison, pratical measurement are used on the research of different issues in this dissertation. The main contents of this dissertation are as follows:a) Design of high efficiency multi-tag identification method; b) Study on reader collision at tag problems; c) Study on the environmental impact on performance of RFID system; d) Interference analysis and coexistence strategy design for RFID coexists with other wireless communication systems. The main innovations of this dissertation are as follows:1) A novel tag anti-collision algorithm which has much higher efficiency, stability, and security than present algorithms is creatively proposed. This algorithm breaks the limit of present algorithms and obtains a new high level of multi-tag identification efficiency. After detailedly analyzing on previous tag anti-collision algorithms, a novel algorithm is proposed, and mathematic calculations and simulation comparisons show that the efficiency and stability of multi-tag identification process is greatly improved.2) The "Reader Collision at Tag" problem is detailedly discussed and described by a probability-based theoretical model in this dissertation, which fills the gap in the relevant research area. So far, how the tags act when they received commands from more than one reader at the same time is still a mystery and it is still blank on this research spot. However, in this dissertation, every possible outcome under the "Reader Collision at Tag" scenario is detailedly analyzed. Firstly, the capability of tags to communicate with more than one reader at the same time is analyzed based on present international air interface standard of RFID. Then detailed descriptions of the "multiple readers read public tags" scenario and the information transaction process between tags and readers are carried out. Finally, the probability-based theoretical model is proposed, which clarifies the ambiguous assumption made by some researchers that "when more than one reader try to interrogate the same tag, the tag can not reply to any reader".3) Mathematical formulated theoretical models for UHF RFID indoor and outdoor signal propagation and estimation method on converage quality of RFID system are proposed in this dissertation. In order to assess the environmental impact in practical RFID applications, new mathematical models for UHF RFID indoor and outdoor signal propagation based on Friis formula considering main reflection paths in the typical environments of RFID applications are proposed. For the first time, terms "Effective Interrogation Area", "Gray Area", and "Identification Hole" are defined in this dissertation, and the mathematical methods to estimate the location and size of both "Gray Area" and "Identification Hole" are also detailedly presented in this dissertation.4) A new conception "Cognitive Radio Frequency Identification" (CRFID) is proposed in this dissertation, and a simple spectrum detection method and dynamic spectrum allocation mechanism are designed for RFID reader, which can effectively resolve the spectrum limit and interference problems faced by RFID nowadays. The CRFID ends are able to detect the air spectrum situation automatically and adaptively change its operation frequency to avoid interference. Therefore, the CRFID system can harmonicly coexistence with other wireless communication systems within the same frequency band without obvious interference, in other words, CRFID can dispel the current embarrassment in most countries that few frequency available left for RFID. Moreover, mathematical computation and simulation comparisons are carried out on the interference level produced by CRFID system and RFID system, the results of researches prove the effective interference reduction performance of CRFID.Several key problems on implementation and application of UHF RFID systems are studied in this dissertation, and methods to enhance the reliability, stability, and effenciency of RFID application system are creatively proposed. The evolution of RFID in future are also studied in this dissertation, which will be the main research area of author in the next phase of research.
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