RFID is one of the most important automatic identification techniques in the future IoT world. Compared with the other techniques, RFID has various advantages such as no requirement of line of sight, the capability of wireless communication, low cost, small size, and so on. This article discusses two types of anomaly tags, i.e., missing tags and unknown tags, which usually appear due to theft or product misplacement. Generally, there are two categories of anomaly tag pinpointing protocols: boolean detection, which aims at probabilistically determining whether there exist anomaly tags or not; and exact identification, which aims at identifying all anomaly tag IDs. This article first conducts a comprehensive survey of the existing anomaly tag pinpointing protocols, particularly emphasizing their evolution road. After that, we also conduct a taxonomy of the existing protocols and summarize their pros and cons. Finally, we discuss some technical challenges and problems that have not been covered yet, and point out the potential opportunities in RFID research and applications.

中文翻译：

---

查明异常RFID标签：情况和机会

RFID是未来物联网世界中最重要的自动识别技术之一。与其他技术相比，RFID具有各种优势，例如无需视线，无线通信能力，成本低，体积小等优点。本文讨论了两种类型的异常标签，即丢失的标签和未知的标签，它们通常是由于盗窃或产品放错位置而出现的。通常，有两种类型的异常标签定位协议：布尔检测，旨在以概率方式确定是否存在异常标签；精确识别，旨在识别所有异常标签ID。本文首先对现有的异常标签定位协议进行了全面的调查，特别强调了它们的发展之路。之后，我们还将对现有协议进行分类，并总结其优缺点。最后，我们讨论了尚未解决的一些技术挑战和问题，并指出了RFID研究和应用中的潜在机会。