A Space–Time–Frequency Anticollision Algorithm for Identifying Chipless RFID Tags

Abstract

In this paper, the short-time matrix pencil method (STMPM) is efficiently employed as a time-frequency analysis methodology for the identification of multiple chipless radio-frequency identification (RFID) tags presented in the main beam of the reader antenna. Each tag represents a unique ID in the backscattered signal. Here, the data are embedded on the tag as the complex natural resonances (CNRs) of the structure. In the cases where more than one tag exist in the main beam of the reader antenna, the frequency-domain response is not sufficient to successfully distinguish the IDs of the tags. By applying the STMPM technique to the time-domain response, the poles and their residues are obtained at each snapshot of time. In order to obtain the exact values of the turn-on times of the poles, which are the roundtrip time of the tags to the antenna, high resolution in the time domain is needed which deteriorates the resolution in the frequency domain. Using mathematical descriptions, a simple formulation is derived which exhibits a duality between late-time response in the time domain and early-time response in the frequency domain. Therefore, a space-frequency representation can be simply obtained from the application of the short-frequency matrix pencil method (SFMPM) to the frequency-domain response of the tags. By possessing the exact values of the turn-on times and pole/residues of the tags, their backscattered responses can be reconstructed and associated IDs can be retrieved. With the proposed method in this paper, some scenarios are studied and discussed. As an experimental result, three 3-bit tags with different IDs (ID1:101, ID2:111, and ID3:011) are fabricated and placed away from each other. Exploiting the presented technique, the IDs of the tags and their locations are successfully distinguished. The simulation results are validated by the measured ones. The ranging error obtained by the proposed method is less than 1 cm.