A tag maintains a progressed-slot counter
(PSC) as well as an allocated-slot counter (ASC). PSC maintains the number of timeslots
passed in an identi?¬?cation cycle. At the start of an identi?¬?cation cycle, PSC is initialized to 0.
In every readable slot, all tags increase their PSCs by 1. ASC determines whether a tag can
transmit its data. If a tag has the same value for both ASC and PSC, the tag can transmit.
A tag can be in one of the following three states:
. Wait state: If the tag has ASC greater than PSC, it waits for a command from the
reader.
. Active state: If a tag has ASC equal to PSC, it transmits its data to the reader.
. Sleep state: If a tag has ASC less than PSC, the tag does not transmit any data. This
tag waits for the next identi?¬?cation cycle since it has already been identi?¬?ed in the
current identi?¬?cation cycle.
Adaptive query splitting
001
011 110 111 011 110
Set of tags is changed
111
111 110 011 001 000 Medium Query
00 l 10 010 011
110 111
10 l 010 011 110
111 000 001
010 l 011 110 111
000 001
011 l 110 111
000 001
110 l 111 000 001
111 l 000 001
000 l 001
001
Collision
Idle
Idle
Readable
Readable
Readable
Readable
Readable
001 000
CQ: 00 10 010 011 110 111
010
FIGURE 9.5
An example of tag identi?¬?cation using the adaptive query splitting protocol with ?¬?ve tags.
Comparative Performance Analysis of Anticollision Protocols in RFID Networks 167
In a collided slot, the colliding tags, the tags of the active state, add a random number (0 or
1) to ASC.
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