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Chipless radio-frequency identification (RFID) has been studied as an alternative technique to conventional chipped RFID. However, chipless RFID tag backscatter signals are affected by motion and especially when they are attached to different objects. In this paper, we performed a comprehensive analysis of the backscattered chipless tag signal in two different stages. At the first stage, we performed an analysis of the backscattered signal in the nonanechoic environment when the frequency-coded tags were moving at different stepped positions. Then we continued to identify the response of signal where the chipless tag was attached to highly scattering objects. The results showed the variation in amplitude and shifting in the frequency of tag resonant when the tag was moving at different stepped positions. The variation was more prominent when the tag was attached to random objects. In order to address the issue, we conducted an experiment on orientation insensitive ground plane tag to solve the frequency shifting problem and proposed a robust detection method based on mother wavelet for the detection of tag IDs. The overall results show that the proposed technique reduces uncertainty in frequency-based chipless RFID tag signal response due to the variation in amplitude. The technique also helps in detecting the tag data bits with better resolution and has a good arrangement between time and frequency resolution for high-frequency signal components. The throughput of 90% is obtained even when the tag is attached to highly scattering objects. Finally, to validate the performance, a ground plane tag is implemented and the proposed algorithm is experimentally demonstrated. INDEX TERMS Chipless RFID, radar cross section (RCS), horn antennas, backscattered signal, detection algorithm, continuous wavelet transforms.

Radio-frequency identification (RFID) is a tracking technology that enables immediate automatic object identification and rapid data sharing for a wide variety of modern applications using radio waves for data transmission from a tag to a reader. RFID is already well established in technical areas, and many companies have developed corresponding standards and measurement techniques. In the construction industry, effective monitoring of materials and equipment is an important task, and RFID helps to improve monitoring and controlling capabilities, in addition to enabling automation for construction projects. However, on construction sites, there are many tagged objects and multiple RFID tags that may interfere with each other’s communications. This reduces the reliability and efficiency of the RFID system. In this paper, we propose an anti-collision algorithm for communication between multiple tags and a reader. In order to suppress interference signals from multiple neighboring tags, the proposed algorithm employs the time-division (TD) technique, where tags in the interrogation zone are assigned a specific time slot so that at every instance in time, a reader communicates with tags using the specific time slot. We present representative computer simulation examples to illustrate the performance of the proposed anti-collision technique for multiple RFID tags.

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