4
Tag identi?¬?cation by the query insertion procedure. (a) Communication between the reader and tags. (b) Tree of
tag identi?¬?cation.
Adaptive Tag Anticollision Protocols for RFID Passive Tags 147
. Two collision nodes: The node of query q1q2 . . . qx has two child nodes of
collision queries if and only if l(q1q2 . . . qx0) 2, l(q1q2 . . . qx1) 2, and
l(q1q2 . . . qx) 4.
. A collision node and a readable node: Two child nodes are a node of a collision query
and a node of a readable query only if l(q1q2 . . . qx0) 1, l(q1q2 . . . qx1) 1, and
l(q1q2 . . . qx) 3.
. A collision node and an idle node: Two child nodes are a node of a collision query and
a node with an idle query only if l(q1q2 . . . qx0) 0, l(q1q2 . . . qx1) 0, and
l(q1q2 . . . qx) 2.
. Two readable nodes: The node of query q1q2 . . . qx has two child nodes
of readable queries if and only if l(q1q2 . . . qx0)??1, l(q1q2 . . . qx1)??1, and
l(q1q2 . . . qx)??2.
When some tags become leaving tags, a pair of node types can be transformed into as
follows:
. A readable node and an idle node: l(q1q2 . . . qx)??1 when l(q1q2 . . . qx0)??0 and
l(q1q2 . . . qx1)??1, or l(q1q2 . . . qx0)??1 and l(q1q2 . . . qx1)??0. Therefore, query
q1q2 . . . qx is not a collision query but a readable query.
. Two idle nodes: l(q1q2 . . . qx)??0 when l(q1q2 . . . qx0)??0 and l(q1q2 .
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