Research On Key Technology Of Context Awareness Based On RFID

It is the basis and security for context aware services systems to acquiring the real-time location and identity information exactly. Currently, in the wireless technologies domain, only RFID technology considers both the location information and the identification of users and entities. So, RFID technology has become the first choice for the context aware service system to access the "context" information. In processing of the RFID identification, when multiple tags responds to the reader at the same time, multi-tag conflict occurs and causes a huge waste of energy and bandwidth. Therefore, an effective anti-collision algorithm for RFID system is the key to ensure the identification effectively. In the aspect of location information acquisition, different application environments have different requirements for the the system cost, positioning accuracy and localization time. Therefore, it is a very complex research topic for building the appropriate RFID positioning scheme in the different applications backgrounds.In this paper, the RFID anti-collision algorithm and localization algorithm, which are the key technologies of context information acquisition in context aware information service system, are studied deeply and the main innovations are as follows:The concept of smart antenna is introduced into the RFID system and a digital multi-beamforming algorithm is designed for RFID system. On this basis, a novel tag anti-collision algorithm based on uniform linear array is also presented. The algorithm fully considers the spatial distribution of tags and divides the reader field into several subspaces. The TDBF (Twice Digital Beamforming) strategy is presented to solve the reader collision in the overlapping area between adjacent beams. In order to avoiding the tag collision within every beam, the inner anti-collision algorithm based on TDMA is adopted. Theoretical analysis and simulation results show that the algorithm could identify the numerous dense tags in the interrogation zone of reader quickly and accurately. Furthermore, it improves the recognition efficiency and reduces system traffic significantly. In addition, the planar array is used in RFID systems to solving the multi-tag problem in three-dimensional. Because of the high cost of the large area of RFID reader network in existing RFID localization system, laying a passive tag network in a wide range to localize a target with reader could maximize to reduce the system cost. And considering on the characteristics of low signal stability of passive tags, a RFID localization algorithm for multi-hop neighborhood based on proximity is presented. The algorithm localizes tags only by determining whether the tags within reader's radio range so that the additional equipment is avoided. In this paper, the main factors which affect the algorithm performance are analyzed in detail theoretically and both the simulation results and the actual tests in the system construction and the choice of system parameters are also studied in a deep-going way. Studies show that the positioning accuracy of our localization system in both stationary and mobile environment conditions is very high and not susceptible to the environment, obstacles and other disturbances.A detail analysis of the receiving signal characteristics of the mobile reader and the time-frequency characteristics by relative movement between reader and tag is given. According to different parameter settings, the Doppler frequency shift can divide into different forms and the different frequency shift estimation methods are presented. On this basis, a movement RFID localization algorithm based on instantaneous frequency estimation is presented. Different system architecture and algorithms models for different application environments were proposed. By mining the relationship among Doppler frequency shift, speed and position of reader, the estimates of position and speed of moving target has been got.