Rfid-based Indoor Positioning System Research And Design

Global Positioning System (GPS) is the most successful and well-know system in the field of wireless position-location. However, it doesn't work well inside building because of the weak satellite signal. So it is important in practice and theory to develop a position-fixing system to suit indoor environment. RFID technique becomes a primary candidate for low-cost, high performance and large scale indoor location-sensing system because of its advantages such as non-line-of-sight (NLOS) identification and the low cost nature.Landmark and SpotON are RFID-based indoor position-location system. SpotON develops a relationship between radio signal strength and identified distance according to experimental data, which fixes the position of item in three-dimension by using the triangulation algorithm, and its performance depends on the environment. Landmark improves the accuracy of position-location system by using the nearest-neighbor algorithm and reference tags. The density and the number of tags affect the accuracy of the system.Theoretical basics of wireless position-location system are described in this paper, and the RFID-based indoor position-location system is researched and developed.At first, it has been demonstrated in practice and theory that there is no line-of-sight path indoor, which affects the accuracy of time of arrival (TOA),time difference of arrival (TDOA) and angle of arrival (AOA) method seriously. In this paper, the advantage and disadvantage of the location-sensing system is described in detail and the distance between reader and tags is calculated by using the path loss model. The reference tag is introduced to estimate the path loss index to improve the accuracy of the location-sensing system.Secondly, the nearest-neighbor algorithm, which is the key to landmark, is improved in this paper so as to reduce the unnecessary computation and improve the performance of location-sensing system.Thirdly, the final position is computed by using the Taylor series method at the initial point after the position has been estimated by utilizing the improved nearest-neighbor algorithm. The experiments prove the new algorithm improves the performance of system and decreases the reference tags.Finally, since the RFID-based location system has not time advantage because of the characteristic of RFID technique, the influence of tags collision and reader collision to the system real-time performance is analyzed and a method for small-scale system is presented in this paper.