Analysis of Calibration-Free Detection Techniques for Frequency-Coded Chipless RFID

A Review of Chipless RFID Measurement Methods, Response Detection Approaches, and Decoding Techniques

“…There are also dual-polarized tags that are a special case of co-polar tags; they are designed to be read in two orthogonal polarizations that are co-polar with the polarization of the reader antenna. In the case of dual-polarized tags, the reader antenna is typically either dual-polarized, or the orientation of the reader antenna relative to the tag is changed to measure the tag in the two polarizations [69,72,[75][76][77][78]. Fig.…”

“…These features are created by the designed resonant properties of the tag, but they can vary depending on the reader architecture, how the response is viewed, and the decoding method being used. For example, while the RCS magnitude or the magnitude or phase of S-parameters are typically directly examined for decoding, in [56] and [77] the tag is measured in two orthogonal polarizations and the two responses are subtracted which creates sharp amplitude changes that can be used to identify the resonance frequencies and assign a binary code. Other examples of unique response viewing approaches include, determining the zeros in the derivative of the group delay which is itself the derivative of the phase vs. frequency response [308] and examining the pulse distortion in the response of an IR-UWB reader [275].…”

“…While some comparisons of the different methods have been attempted, they are not often one-to-one comparable due to factors, such as difference in reader hardware, tag design, reading distance, measurement environment (e.g., anechoic chamber vs. "real" environment and whether or not the tag is attached to a highly scattering object), and the design of validation experiments (i.e., the number of trials/measurements, whether misalignments and noise are considered, etc.). Additionally, many of the comparisons use subjective measurement metrics, such as ranking the complexity of a method on low-medium-high scale, without providing definitions of these classifiers [19,77,292,295,313].…”

“…DER and throughput can be evaluated as a function of reading distance and SNR, with a higher SNR corresponding to a higher throughput and therefore lower DER [77,295,305,342]. An example of this is provided in Fig.…”

“…'21 [19] MPM and Spectrogram Variation in RCS, resonance frequency, and Q-factor, and computation time as a function of window length '21 [329] Temporal Separation [245] and Differential Dual-Polarization [75] Reliability when tag is attached to different objects, memory storage, and design complexity '21 [77] compared). Another thing to note from Table V, is that some works refer to methods like background response subtraction and time gating as decoding methods, while other works may refer to these as calibration or pre-processing methods.…”