Enhanced collision arbitration protocol utilizing multiple antennas in RFID systems

In this paper, we present an enhanced collision arbitration protocol that operates over multiple antennas in RFID systems. An RFID system consists of a reader and tags, and all tags have to be quickly recognized by a reader. Due to a contention based tag transmission, collision arbitration is a very important issue in tag identification. However, collision always happens in the existing single antenna based collision arbitration scheme when more than one tag simultaneously transmit message. In order to reduce the number of collisions, we propose to use multiple antennas at the reader such that the reader can recognize multiple tags simultaneously by utilizing multi-user receiver at the reader and multiple orthogonal preambles used by each tag. In this scheme, only the tags that are not identified retransmit in the next time slot while the identified tags keep silent. Then the identification delay significantly decreases because the number of retransmissions decreases in comparison with the single antenna scheme. We analyze the performance of this proposed scheme and conduct simulations to confirm the validity of the mathematical modeling. According to the analytical and simulation results, the proposed scheme outperforms the existing single antenna scheme.