(a) Collisions by the binary tree protocol. (b) Collisions by
the query tree protocol.
144 RFID Handbook: Applications, Technology, Security, and Privacy
8.4 Adaptive Tag Anticollision Protocols
In tree-based tag anticollision protocols, the tree search causes tag identi?¬?cation delay, and
the reduction in identi?¬?cation delay can be accomplished by skipping of collision cycles.
However, once a frame is started, the tree searches of the binary tree protocol and the
query tree protocol depart from the root or the level 1 nodes of the tree and investigate all
intermediate nodes wherein tag collisions occur. The unreasonable starting point of the tree
search prolongs identi?¬?cation delay.
The basic idea of adaptive splitting protocols is to adaptively decide the starting point of
the tree search with information on tags recognized in the last identi?¬?cation frame. At
every identi?¬?cation frame, the tree search of tag identi?¬?cation starts from the nodes which
were the leaf nodes of the tree in the last identi?¬?cation frame. Note that these starting nodes
were readable cycles or idle cycles in the last frame. To recognize arriving tags, the
identi?¬?cation process traces down the path of the tree by inserting two child nodes of
the current node into the tree. To handle unnecessary idle cycles induced by leaving tags,
the identi?¬?cation process traces up the path of the tree by replacing two leaf nodes with
their parent node.
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