Identification of Chipless RFID Tags in the Reader

Abstract

The signal received by the antenna includes the scattered signal from the chipless RFID tag located in the reader area, reflections from background objects (clutter), and noise. Therefore, the detection process is a challenging aspect in the design of chipless RFID systems. In most situations, the reflections from background objects are stronger than the tag response. The identification can be performed based on the time-domain or frequency-domain response. In this chapter, first the time and frequency characteristics of the scattered signal from the tag are presented. It will be shown that the absolute value of the scattered field from the tag and the group delay response do not provide sufficient information about the resonant behavior of the tag. Then, a review on the time-frequency techniques, suitable for extracting the information from the signal, is presented. Two basic techniques such as short-time Fourier transform (STFT) and wavelet transform are studied in more detail. A new technique, called short-time matrix pencil method (STMPM) is introduced by which the resonant frequencies and damping factors of the CNRs are extracted from the time-domain response. It will be shown that by increasing the filtering parameter and decreasing the length of the window simultaneously, the resolution in both time and frequency domains can be improved, simultaneously. The performance of the method against noise and some important parameters such as resolution in time and frequency are studied in detail in this chapter. As an example, the time-frequency analysis of the open-ended cylinder is presented and compared to the results obtained from short-time frequency transform (STFT). Then, the application of the proposed technique in decoding the IDs of the chipless RFID tags is presented.