Fast unknown tag identification in large-scale RFID systems

Unknown tags appear when tagged objects are newly moved in or wrongly placed in systems. In this paper, we investigate time-efficient protocols for collecting IDs from unknown tags. Consider the influence of unknown tag density on total recognition time, we design a high-density unknown tags identification (HUTI) protocol and a low-density unknown tags identification (LUTI) protocol, which are suitable for dense unknown tags environment and sparse unknown tags environment, respectively. Indicator vectors are constructed to help tags know expected status of selected slots. The difference between the two proposed protocols is the number of indicator vectors to be used. LUTI utilizes two indicator vectors to accurately decide each expected slot status, while HUTI only use one indicator vector to save transmitting time when the number of unknown tags is large. In order to minimize execution time, we conduct investigations on frame length and round count, of which the results are concluded as the optimal setting parameters. Simulation results demonstrate that our protocols outperform related protocols with respect to total execution time.