Research On Tag Location Algorithm Of UHF RFID

As the global positioning system (GPS) gradually mature, outdoor positioningtechnology has become increasingly perfect. In indoor and some other occasions, however,GPS locate inaccurately, even can’t locate because of the limitation of some factors such assignal receiving. Bluetooth, infrared, ultrasonic and radio frequency identification (RFID)technologies were taken to locate, and RFID technology become an optimal option because ofits adventures such as non-line-of-sight, non-contact, low cost and high positioning accuracy.According to the tag power supply way, RFID system can be divided into active system andpassive system. Based on the long-distance identification of active RFID system, currenttypical RFID positioning system such as Spot ON, LANDMARC etc. adopt active tags. Areal-time positioning is unable because of the great amount of calculation, so the completeSpot ON system has not yet been built. LANDMARC well eliminate the positioning errorfrom indoor environmental factors by the implementation of reference tag position. Butinfluenced by reader, reference tag number and layout, the system response slowly and costtoo much. In order to improve the indoor positioning system performance and saving the cost,this study proposes a new method based on multilateral measurement of active radiofrequency identification (RFID) tags indoor three-dimensional localization algorithm.In this algorithm, a reader was set for receiving tag signals from four antennas.According to the received signal strength indicator (RSSI), the distance from unknown tag toeach antenna can be measured. Finally, the position of unknown tag can be calculated. Toreduce the accidental error of RSSI in single measuring and improve the positioning accuracy,each tag was positioned three times and the result of the arithmetic mean value was taken asthe final position. In order to explore the impact of antennas layout to positioning accuracy,the antenna arrangement scheme in10m x10m x10m space was studied. Simulation resultsshow that in the locating space, when choosing a specified range error, standard deviation ofthe signal strength and the appropriate antenna arrangement, the location algorithm canachieve good effect. It is also shown by simulations that the larger volumes of thetetrahedrons composed of the four antennas will result in the smaller errors of thethree-dimensional positioning. In order to further improve the precision of location, aweighted algorithm method was adopted. It was indicated that the position result ofweighted average method is more accurate than arithmetic mean method.