How Manufacturers Can Easily Improve Working Range of Passive RFIDs

Radio-Frequency IDentification (RFID) technology permits a reader to wirelessly query a tag for its embedded globally unique identifier. Passive RFID tags, which are small, low-cost (a few cents each), and batteryless, can be reliably read only when they are within a few meters of the reader since the tag must power up itself by harvesting energy from the reader. Past work attempts to increase the RFID range by providing them with more energy, such as by synchronizing multiple custom design RFID readers and performing beamforming. However, we demonstrate that a passive tag's range is limited not only by the need for the tag to harvest energy but also by the need for the tag to decode the reader's transmission, and vice versa. Thus, instead of modifying readers, we ask if a tag's manufacturer can increase passive RFIDs' range by lowering the data rate. Our results show that the working range can be increased by a factor of about 10 by simply using a low data rate. Our real-world experiments using customized tag prototypes have a range of ~40 m, with an SNR exceeding 12 dB.