The reader which receives a data from a tag
sends a synchronizing message. Deterministic protocols have also similar data transmission
structure. After reader??™s transmission, tags try to transmit their data to a reader.
9.6.1 Identi?¬?cation of Motionless Tags
Mobility of tags varies accordingly as the kinds of RFID applications are employed. For
some applications, one can locate objects in front of a reader, which then are identi?¬?ed.
Such a scenario happens when a reader is deployed at an entrance or an exit of a store
where products are disposed of. In this case, a user should determine the starting point and
wait until all tags are identi?¬?ed. We perform a simulation study to investigate how long a
user should wait for in each protocol. As we assume that mobility of tags is not considered,
a reader performs identi?¬?cation process without changes on tags??™ sample during its
identi?¬?cation.
Figure 9.10a shows the relationship between the number of tags and the time taken to
identify all tags by each protocol. Probabilistic tag anticollision protocols are independent
of each round, and they keep three slots: the readable, the collided, and the idle slots, all of
which follow the identical probabilistic distribution.
Reader
Tag
Inventory
request
Preamble
detect
Preamble
detect
Data
CRC
Header
Data
CRC
Reader
message
Preamble
detect
Tag reply
Header
Data
CRC
3100 ?µs
800 ?µs
800 ?µs or
variable
3100 ?µs
Preamble
detect
Data
CRC
Tag reply
FIGURE 9.
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