Collision-resilient symbol based extension of query tree protocol for fast RFID tag identification

RFID (RF based identification system) requires identification and collision avoidance schemes for tag singularization. To avoid the collision, there are two previous approaches: ALOHA based and binary tree algorithm.. They are essentially collision avoidance algorithms, and require much overhead in retransmission time. Previous research works on collision recovery protocol cannot distinguish tag collision from channel error. Because channel error significantly influences the overall performance of anti-collision protocols, we propose a robust and efficient tag collision recovery scheme using direct sequence spreading modulation; thereby we can reduce channel errors. Specifically, we propose MSQTP (multi-state query tree protocol) scheme, which is an extension of query tree protocol using modulated symbols. We experimented with two collision resilient symbols: orthogonal (Hadamard) and BIBD (balanced incomplete block design) code. MSQTP shows performance gain (decrease in iteration step for collision recovery) over previous query tree based collision recovery scheme, and shows graceful degradation in noisy environment with lower SNR.