2. Characteristics and Limitations of Conventional RFIDs

Although RFID technology has been proven to be sufficiently adequate for some applications, such as toll collection and anti-theft systems, there are numerous other applications that cannot benefit from this technology due to some of the limitations of the conventional RFID technologies. With the widespread interest and usage of RFIDs, the vulnerabilities of current RFID systems are becoming apparent. These limitations are directly related to the environment that the tags and readers ­communicate. This environment consists of both the wireless channel and the physical object that the tags are attached to. Various objects and systems in the wireless channel can cause a range of signal degradation such as attenuation, ­multipath fading, and interference to the RF signal carrying the tag information. Since the reliability of an RFID system is directly dependent on the robustness of the tag-reader RF link, the signaling scheme becomes a fundamental area of study for characterization and further performance improvement of such systems.