To cope with ASC greater than TSC, the reader supports
the TSC value when a frame starts. A tag having ASC greater than TSC changes its ASC to
a random number from 0 to TSC. ABS recognizes all tags quickly through scaling ASCs of
arriving tags into the range of TSC.
Figure 8.6 illustrates an example of the operation of ABS. Assume that a reader
attempts to recognize tags A, B, and C, and there was no tag inside the reader??™s reading
range in the previous frame. Therefore all three tags are arriving tags and the TSC value
ASC/TSC
value
3
(R)
(R)
(R)
(R)(A) (A) (A)
(A) (A) (A) (A)
(B) (B) (B)
(C)
(C)
(C)
(C)
(C) (C)
(C)
(R) (R)
(R)
(R)
(A), (B),
and (C)
TSC of
reader
ASCs of
tags
PSC
Splitting
Collision
handling
Idle
handling
(B) (B) (B)
2
1
0
1 2 3 4 5 6 7 Reading
cycle
FIGURE 8.6
Tag identi?¬?cation by ABS.
150 RFID Handbook: Applications, Technology, Security, and Privacy
of the reader is 0. In this case, tag identi?¬?cation of ABS is equal to that of the binary tree
protocol because all three tags have ASCs of 0. In the ?¬?rst reading cycle, three tags
transmit simultaneously and collision occurs. Tags A and B select 0, and tag C selects 1.
In the second cycle, a collision between tags A and B occurs and both of them select 0
again. Tag C and the reader increase ASC and TSC by 1, respectively. Tags A and B are
split successfully in the third cycle, and hence the reader recognizes tags A and B in the
fourth and ?¬?fth cycles, respectively.
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