RFID, where are they?

This paper gives an overview of RFID technology. RFID systems are described in general and a few example cases are given. After that the paper mainly focuses on the hardware requirements for RFIDs. Also real time locationing systems (RTLS) are discussed. This gives the title of the paper a double meaning: `what is the state of the art in RFID' but also what is the available technology to come to locationing capable RFID systems. The paper gives an overview of the design challenges of different RFID systems. Also possible circuit solutions and directions are addressed.