3-dimensional Localization Via RFID Tag Array

Nowadays,RFID has been widely used in the applications such as warehouse,logis-tic management and industrial manufacture.In these applications,by attaching one or more RFID tags onto the objects,many novel functions such as indoor localization and smart sensing can be effectively realized.For example,with the exact locations of all items on the shelves,the robotic arm can be used to fetch the specified items in a fully automated manner,which will reduce labor cost and improve accuracy.However,most state-of-art RFID-based localization schemes mainly focus on the localization in the 2-dimensional(2D)space,e.g.,they usually provide the 2D coordinates of the objects in the indoor maps and fail to judge the 3D orientation of the objects and localize them in 3D space accurately.Besides,due to the multipath effect in the indoor environment,the RF signal will bounce off on walls,ceiling and furniture,which will distort the phase values of the tags and will further influence the 3D localization result.In this paper,we propose 3DLoc,which performs 3D localization on the tagged objects by using the RFID tag arrays.3DLoc deploys three arrays of RFID tags on three mutually orthogonal surfaces of each object.When performing 3D localization,3DLoc contin-uously moves the RFID antenna and scans the tagged objects in a 2-dimensional space right in front of the tagged objects.By referring to the fixed layout of the tag array,we use the Angle of Arrival-based schemes to accurately estimate the tagged objects' ori-entation and 3D coordinates in the 3D space.To suppress the localization errors caused by the multipath effect,we propose two methods to improve the localization accura-cy.The first one is to use the linear relationship of the AoA parameters to remove the unexpected outliers from the estimated results,and the second one calibrates the phase values based on the reference tag array.We have implemented a prototype system and evaluated the actual performance in the real complex environment.The experimental results show that 3DLoc achieves the mean accuracy of 10cm in free space and 15.7cm in the multipath environment for the tagged object.The main contributions we made in this paper are as follows:1.By deploying tag arrays on three mutually orthogonal surfaces of the object,we accurately estimate the tagged object' s orientation and 3D coordinates in the 3D space based on the AoA localization scheme.2.To suppress the localization errors caused by the multipath effect,we propose a mobile scanning-based scheme and use the linear relationship of the AoA parameters to remove the unexpected outliers from the estimated results via continuous sampling.Specially for the environment in which there exists only one reflector,we propose a phase calibration system based on reference RFID tag array.By extracting the pa-rameters of how the reflector influence the RF signal from the reference tag array,we finally calibrate the phase of the target tag,which directly improves the accuracy of the localization result.3.We have implemented a prototype system and evaluated the actual performance in the real complex environment.The experimental results show that 3DLoc achieves the mean accuracy of 10cm in free space and 15.7cm in the multipath environment for the tagged object.