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

Abstract

Chipless RFID systems can be considered as a special case of passive RFID systems, where the tag contains no power source and no electronics. Instead, the tag's information is stored in its structure and accessed through its electromagnetic (EM) scattering response. However, robust response detection, which is primarily a function of the measurement method, measurement equipment, and processing method used, is still a major challenge in the chipless RFID field. The consequences of not properly capturing a tag response include, incorrectly assigning an ID or incorrectly reporting a sensing parameter. Due to the criticality of these challenges, this review seeks to provide an overview of the current measurement methods, equipment architectures, and processing methods as they relate to chipless RFID tag response detection and decoding. Since chipless RFID started gaining popularity around 2005, the developments in this area have been focused on three major categories: timedomain, frequency-domain, and spatial-domain systems. Frequency-domain systems have emerged as the most popular among these three categories, and thus, this review focuses on techniques used for these systems.

Local Sensitivity Analysis and Monte Carlo Simulation to Examine the Effects of Chipless RFID Measurement Uncertainties—Part I: Misalignment-Based Uncertainty

“…As previously mentioned, a binary code can be assigned to a tag response in a number of different ways [4,13]. For this work, multiple configurations of two different coding methods with different sensitivities to response shape changes are utilized to examine the role the coding method plays in tag performance.…”

“…When the environment is relatively static, coherent subtraction of the background response can be an effective approach to remove clutter. However, this process is not very effective when the environment is dynamic or when the tag is measured at a small reading distance [4,8]. As such, it is beneficial to quantify the effects of clutter on the decoding performance of a tag through an approach that can be adjusted for different measurement configurations.…”

“…Overall, depending on the coding method used, these response changes due to misalignment may or may not create bit differences. As such, both code-based metrics (i.e., bit differences, bit error rate (BER), detection error rate (DER), and throughput) and response characteristic-based metrics (i.e., RMSE and resonant frequency shift) can be used to quantify the consequences of misalignment, as will be demonstrated throughout this paper [4].…”

“…When it comes to making chipless RFID measurements, there are a variety of factors that can affect the measured tag response. These include, tag/reader misalignments, the tag radar cross-section (RCS) level, and background reflections (i.e., clutter) and noise (e.g., reader receiver noise that contributes to measurement error) that can each overwhelm or alter the tag response [3,4]. The effects of tag/reader misalignment have been explored to varying extents.…”

“…Through these examples it can be seen that tag/reader misalignments can cause magnitude changes, response shape distortions, and resonant frequency shifts, all of which can lead to improper decoding of the tag response depending on the coding method used. While these response changes may be tolerable in ID applications depending on the coding method used, they are often not acceptable in sensing applications where changes in resonant frequency or response shape are used to determine a sensing parameter [4,13]. It should be noted that attempts have been made to mitigate the effects of tag/reader misalignment from both the tag perspective [14][15][16][17] and reader perspective [18][19][20][21].…”