..
Probabilistic
approach
Deterministic
approach
RFID tag
anticollision
FIGURE 9.2
Taxonomy of RFID tag anticollision protocols.
Comparative Performance Analysis of Anticollision Protocols in RFID Networks 163
9.3 Tree-Based Anticollision Protocols
In tree-based tag anticollision protocols, a reader divides tags into two groups. A reader
further divides each of them into two groups again. It is required that a reader be able to
distinguish each divided group. The process of dividing tags is continued until a group
contains only one tag so that each tag could be successfully identi?¬?ed. The dividing process
of a group is continued until a reader identi?¬?es all the tags.
Tree-based protocols work similar to census. The reader can recognize all tags in its
identi?¬?cation range. An identi?¬?cation process of the reader can be illustrated as a process
of creating and searching a tree where a node in the tree represents a reading slot. As stated
earlier, the result of identi?¬?cation can be classi?¬?ed into three cases: readable, idle, and
collided. After the identi?¬?cation cycle is completed, a tree is constructed. A leaf node in the
tree corresponds to either readable slot or idle slot, and an intermediate node represents a
collided slot.
Both the query tree [3,4] and binary tree [5,6] protocols represent a tree-based RFID tag
collision protocol.
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