As in the previous scenarios, ABS shows
the shortest identi?¬?cation delay.
0
50
100
150
200
250
300
350
400
450
No. of transmitted bits
Binary
Query
AQS
ABS
0 1 2 3 4 5
Maximum MPF (m/frame)
6 7 8 9 10
(d)
FIGURE 8.8 (continued)
(d) Tag communication overhead.
Adaptive Tag Anticollision Protocols for RFID Passive Tags 155
0
0
0.5
1
1.5
No. of collisions
2
2.5
3
3.5
8 16 24 32 40
Identical bit
48 56 64 72 80
Binary
Query
AQS
ABS
(a)
0
0
0.5
1
1.5
No. of idle cycles
2
2.5
8 16 24 32 40
Identical bit
48 56 64 72 80
Binary
Query
AQS
ABS
(b)
0
0
1
2
3
No. of reading cycles
4
5
6
7
8 16 24 32 40
Identical bit
48 56 64 72 80
Binary
Query
AQS
ABS
(c)
FIGURE 8.9
Impact of ID distribution on tag identi?¬?cation. (a) Collisions. (b) Idle cycles. (c) Identi?¬?cation delay.
156 RFID Handbook: Applications, Technology, Security, and Privacy
8.8 Conclusion
A collision caused by tags transmitting simultaneously is a major factor in deferring tag
identi?¬?cation of RFID systems. This chapter has described tree-based tag anticollision protocols
and adaptive tag anticollision protocols for passive tags. Adaptive splitting protocols
are the enhanced tree-based protocols to reduce collisions by exploiting information
obtained from the last frame of tag identi?¬?cation. The key institution behind adaptive
splitting protocols is that in most applications employing RFID tags, the set of objects
encountered in successive readings from a particular reader does not change substantially,
and information from one reading can be used for the next.
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