3D Tag Location Aware Scheme Based on Phase Interferometric for RFID Applications

Many indoor applications require spatial information about objects. Example applications include item finding, object level mapping and large-scale objects managing in warehouses or libraries. RFID technology enables the identification and location of objects in our daily life by integration of RFID tags. The RF signals that the tags backscatter include a lot of information about the environment of the objects which can be used to derive the objects' spatial information. In 2016, the demand for applications in the apparel industry alone exceeded 4.6 billion RFID labels. Due to the emergence of three-dimensional (3D) printing, Microsoft and Disney Research have attempted to incorporate RFID-like embedded encoding information directly into objects during the manufacturing process, which may allow objects to be uniquely identified and sensed in the future. To this end, how to additionally aware the precision spatial position of the tagged target is an important and pressing research topic. Traditional localization methods based on RF signals with backscatter tags can be classified into the following two types: (1) trilateration approaches that usually require multiple RFID readers placed in the environment, where the target position is determined by solving nonlinear equations based on the target-reader geometric relationship; and (2) scene analysis approaches that rely on the implementation of numerous tags with known positions as anchor nodes. However, both of these approaches have high implementation costs and it is difficult to apply them extensively in practice. In this paper, we propose a 3D localization scheme based on phase interferometric, named 3DinSAR. Our localization method does not need any reference tags and only one movable reader integrated with one antenna is required in order to construct the synthetic arrays to implement the locating system. The main idea is based on the 2D naive SAR localization. Rather than traversing all the spatial pixels which is time consuming and hence not efficient, we extend the naive hologram localization into a 3D scheme by using the spatial domain phase difference which relates to the wave path difference and the tags' height as additional information. Density-based spatial clustering method DBSCAN is used to give the final estimation target location to improve the accuracy. We also proposed an aperture-beam predicting method ABP to improve the real-time performance of 2D SAR method. In summary, the mainly contributions of this paper are: (1)We propose a 3D localization scheme based on phase interferometric for passive RFID system, named 3DinSAR, which is able to precisely estimate the tag's 3D location. (2)We further reduce the computational time required by using an aperture beam prediction (ABP) method, in order to improve the real-time performance. The main feature of the ABP method involves estimating the direction of arrival in order to ignore any unnecessary pixels when creating the holographic images. (3)Experiments are performed where 3DinSAR is implement with commercial off-the-shelf (COTS) RFID products. Comparing with naive 2D SAR method, the simulation results demonstrate ABP method has discount 99.4% of the time consumption. The experimental results from an indoor office environment show a spatial median error of 24 cm with minimum error 6cm for 3DinSAR, and the detection time maintain within 95 ms. © 2019, Science Press. All right reserved.