Time Synchronization of Distributed Readers for a Large-Scale Active RFID Network

Radio frequency identification (RFID) is an emerging automatic identification technology that uses radio waves to transmit information. However, it is difficult to apply in large-scale or in dense environments because of its limited radio communication range and obstacles such as water and steel infrastructure. To overcome these problems, distributed and multiple deployment of RFIDs is needed. The distributed deployment of RFID readers can reduce the labor and cost involved in data collection and various applications. In a distributed RFID environment, time synchronization is essential for efficient collection of RFIDs and to allow readers to communicate with each other. This paper proposes a method to provide time to distributed RFID readers and synchronize their time with a reference clock. The proposed time synchronization method reduces traffic needed for synchronization and provides an accurate time by correcting the drift at a lower level. Our results show that the performance of the proposed method is 2.6 times better than that of the conventional time synchronization protocol.