Research Of Outdoor Person Location System Based On RFID

Radio frequency identification is an automatic identification technology transmitting data through radio waves and it’s widely used in person position and tracking for its non line-of-sight, non-contact, large storage capacity and low cost. Compared with other position system, the biggest advantage of RFID position system is not affected by the influence of multipath effect and non line-of-sight effect, and it can make "chip- target object" one to one correspondence and obtain better position accuracy.Taking a chemical enterprise as an example, the outdoor person position system is designed in this thesis based on RFID in order to ensure personnel life and property safety. In the thesis, the person position system is divided into hardware layer, middleware layer and application layer. Hardware mainly includes readers, tags and antennas, in charge of collecting the basic data. Middleware layer includes hardware adapter module, data processing module, event engine module, location service interface module, system configuration module and security management module. Hardware adapter module takes charge of shielding the heterogeneity of readers and provides a unified interface to transmit data. According to the requirement of the localization algorithm data processing module completes data handing, including collecting, filtering, integration data and offsetting the leakage reading. Event engine module works out person location coordinates by RFID reader topology network localization algorithm. Location service interface module transmits data to upper layer in terms of the requirement of data format. System configuration module is responsible for the system upgrade, security maintenance, equipment diagnosis and condition monitoring. Safety management module is responsible for protecting people’s privacy and enterprises’ business secrets and prevents illegal person from attacking system maliciously. Application layer includes various application software, statistical inquir y, alarm, system configuration, etc.In order to meet the chemical enterprises’ demand, the accuracy of person position system must be very high, so the original RFID reader topology network localization algorithm need improve. The original algorithm’s position accuracy depends on the density of deployed readers and the reader’s effective identification range. The more readers deployed the higher position accuracy can reach. But if the density is too large, the system cost will be increased rapidly and signal interference also caused. In order to improve the position accuracy without increasing the cost of the person position system, reference tags and virtual reference tags are brought in which coordinates are known to assist orientation. In the improved algorithm, the RSSI is added to the original position vector and the strategy of reader main orientation and reference tags assistant orientation is put into effect. Deploy many tags around readers, calculate the Euclidean distance between reference tags, virtual reference tags and target tags, chooses the best k reference tags, uses the weighted residuals method to obtain target tags’ location coordinates. Compared with the original algorithm, the improved algorithm not only improves the location accuracy, but also solves following problems: poor accuracy when a tag is identified by one reader, unable to deal with the situation when a tag is identified by two or more readers at the same time, leakage read and ping-pong effect.