Retwork: Exploring Reader Network with COTS RFID Systems

Radio frequency identification has been gaining popularity in a variety of applications from shipping and transportation to retail industry and logistics management. With a limited reader-tag communication range, multiple readers (or reader antennas) must be used to provide full coverage to any deployment area beyond a few meters across. However, reader contention can seriously degrade the performance of the system or even block out some tags from being read. Most prior work on this problem requires hardware and protocol support that is incompatible with the EPC Gen2 standard. Moreover, they assume the knowledge of a reader network that precisely describes the contention relationship among all readers, but the efficient acquisition of the reader network in a practical system with commercial-off-the-shelf (COTS) tags is an open problem. This study fills the gap by proposing a novel protocol Retwork, which works under the limitations imposed by commercial Gen2-compatible tags and identifies all possible reader contentions efficiently through careful protocol design that exploits the flag-setting capability of these tags. We have implemented a prototype with 8,000 commercial tags. Extensive experiments demonstrate that Retwork can reduce communication overhead by an order of magnitude, in comparison to an alternative solution.