A new tag, whose ID does not match a pre?¬?x of a readable
node in previous cycle, is quickly identi?¬?ed with pre?¬?xes of idle nodes in previous cycle
by the reader.
To prevent the growth of CQ (which carries information of leaf nodes), the query
deletion process is used. The query deletion process is the process that merges queries
Slot
Tag A
Tag B
Tag C
Tag D
Counter
0
Tag A
Tag A
Tag A
Tag A Tag B Tag D Tag C
Tag B
Tag B
Tag B
Tag C Tag C Tag C
Medium Collision Collision Collision
Tag D
Tag D Tag D
Tag B
Tag C
Tag D Tag D
Tag C Tag C
0
0
0
0
0
0 1 2 3 2
1 2
1
1
1
FIGURE 9.4
An example of tag identi?¬?cation using the binary tree protocol with four tags.
166 RFID Handbook: Applications, Technology, Security, and Privacy
that share the same query content except the last bit. Idle nodes unnecessarily disturb the
speed of identi?¬?cation, and CQ can eliminate pre?¬?xes of unnecessary idle nodes. For
example, if the nodes of the pre?¬?x p0p1 . . . pi0 and p0p1 . . . pi1 contain at least one idle
node and the non-idle node is a readable node, CQ stores the pre?¬?x p0p1 . . . pi instead of
the pre?¬?x p0p1 . . . pi0 and p0p1 . . . pi1.
9.3.4 Adaptive Binary Splitting
ABS protocol is the method by which tags remember their identi?¬?cation order in the previous
cycle by adding one to the counters in the tags.
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