Rfid tag readers switchable between interrogator and listener modes

Abstract

Radio-frequency identification (RFID) systems use readers to query and locate passive RFID tags in stores, warehouses, and other environments. A signal from the reader powers up the tag, which modulates and backscatters the signal toward the reader. Unfortunately, the maximum permitted RF signal power, self-interference at the reader, tag sensitivity, and channel loss limit the range at which readers can detect and locate tags. Using multiple readers simultaneously circumvents these limits. When used together, each reader transmits a signal to a tag in turn, and all of the readers listen for each of the tag's responses. The readers that are not transmitting do not experience self-interference and so can detect responses at lower power levels (longer ranges). Because the readers are at different locations, they measure different angles of arrival (AOAs) for each response. These simultaneous measurements can be used to locate each tag faster and with higher fidelity.