| Radio frequency identification(RFID)technology uses electromagnetic induction or electromagnetic waves to transmit data wirelessly and identify objects automatically.With the popularity of RFID technology in the production chain and warehouse manage-ment,there has been widespread interest in RFID-based localization technology around the world.Compared with other technologies,the RFID localization technology based on synthetic aperture rader(SAR)has advantages in cost,accuracy and flexibility.There are two localization methods popular in SAR RFID,holographic imaging and nonlinear optimization,but neither of them has a satisfactory efficiency.On the basis of the existing work,this thesis is motivated by the intention of developing simple but efficient localization methods for two-dimension and three-dimension localization problems.This thesis gives a comprehensive explanation of the phase information of the modulated signals scattered back from the RF tag to the antenna,which helps to build the synthetic aperture RFID localization model based on phase difference.For the two-dimension localization,the localization problem is transformed into finding the solution of the hyperbolic equations by deriving the distance difference from the phase difference.For the reason that nonlinear hyperbolic equations are difficult to solve,the Taylor-series expansion is used to approximate them with linear ones.Besides,the method of choosing initial position is introduced to achieve good convergence.The experimental results show that this method not only maintains reliable performance for tags of different distances and types,but also has an average localization error of about5 cm and an average calculation time of 10 ms.For the three-dimension localization,two methods are designed for the scenarios where the antenna moves along different trajectories.When the antenna moves along straight paths,an overdetermined system of linear equations which pinpoints the location of the tag is constructed by exploiting differences of phase measurements and spatial properties of the problem’s geometry.When the antenna moves along non-straight paths,the linear equations containing the tag position and another parameter are constructed by means of phase difference,the parameter is determined through a two-step procedure and substituted into the equations to give the tag position.The performances of the two methods on accuracy and efficiency are compared with the methods of Tagoram and LM by simulation.The results show that the two methods not only achieves the localization error comparable to others,but also have an average computation time which is 99.59%lower than Tagoram and 99.36% lower than LM. |
