. Readable slot: the reading slot that only one tag replies to. The tag can be identi?¬?ed
successfully.
. Collided slot: the reading slot that has two or more tags which transmit their replies.
It is the case that the result of CRC is failed. The reader cannot recognize any tags.
. Idle slot: the reading slot that has no tag reply.
Tag anticollision protocols can be classi?¬?ed into two approaches in terms of the way of
determining the point of transmission time: (1) tree-based approach and (2) probabilistic
approach. In tree-based tag anticollision protocols, a tag determines the point of transmission
on receiving a message from a reader and making a process from the message, that is,
a decision of whether to respond to it. On the other hand, probabilistic tag anticollision
protocols use the random number generated by a tag to determine the point of transmission.
Each tag generates a random number and waits for its transmission time according to
the chosen number. Figure 9.2 shows the taxonomy of tag anticollision protocols.
Collided slot
Query Reader
Collision
detected
No reply
Tag ID Tag ID
Tag ID Tag B
Tag A
Query
rep
Query
rep
Query
rep
Continuous
wave
Continuous
wave
Idle slot Readable slot
FIGURE 9.1
Data transmission between an RFID reader and tags.
Query tree ISO/IEC 18000-3 Mode 1
ISO/IEC 18000-6 Type B
IEEE Transactions on Parallel
and Distributed Systems
BTG Super Tag,
ISO/IEC 18000-3 Mode 1 Extension
ISO/IEC 18000-3 Mode 2
ISO/IEC 1800-3 Mode 1 Extension,
ISO/IEC 18000-6 Type A,
EPC UHF class 1 Generation 2
Binary tree
Adaptive
query splitting
Adaptive
binary splitting
ALOHA
Slotted ALOHA
Framed slotted
ALOHA
Adaptive
framed slotted
ALOHA
Vogt, DFSA,
Zhen.
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