By continuing the splitting procedure until each set has only one tag, tree-based
protocols are capable of recognizing all the tags in the reader??™s range.
An identi?¬?cation frame in tree-based protocols can be represented by a tree structure as
shown in Figure 8.1a. Each node in the tree corresponds to a reading cycle and a number in
a node is the number of tag transmissions in that reading cycle. According to the number of
3
2
2
1
1 1
0
Tag Tag C Tag
1011
Collision cycle
Readable cycle
Idle cycle
Tag
0010
Tag
0001
000 001
01 00
0 1
Tag A Tag B
1 0
0
0 1
1
Tag
(a) (b) (c)
Tag
FIGURE 8.1
Tag identi?¬?cation of tree-based protocols. (a) Tree expression of tag identi?¬?cation. (b) Tag identi?¬?cation of the
binary tree protocol. (c) Tag identi?¬?cation of the query tree protocol.
Adaptive Tag Anticollision Protocols for RFID Passive Tags 141
tag transmissions in a reading cycle, reading cycles can be divided into three types as
follows:
. Idle cycle: No transmission is attempted. The idle cycle does not make the reader
fail to notice a tag, but it is a source of an unnecessary increment of identi?¬?cation
delay.
. Readable cycle: Exactly one transmission is attempted. The reader recognizes a tag
successfully.
. Collision cycle: More than one transmission is attempted. A tag collision occurs and
the reader is unable to recognize any tags.
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