Readable (number of tag responses??1): All the tags increase PSC by 1. The
recognized tag does not react to the reader??™s feedback and does not transmit its
ID to the reader before the start of the next identi?¬?cation frame.
. Collision (number of tag responses 2): Con?¬‚icting tags (tags which have ASCs
equal to PSC) randomly select one of two binary numbers, 0 and 1, and then add it
to ASC. The tag which has ASC greater than PSC adds 1 to ASC.
During a frame, PSC does not decrease, and an ASC value is not changed in such a way
that ASC becomes smaller than PSC. Therefore, a tag recognized by the reader gets to
obtain a unique ASC which implies the allocation of the cycle to the tag for the next
identi?¬?cation frame. The decrement of ASCs in the idle cycle deallocates cycles corresponding
to ASCs of leaving tags. A set of con?¬‚icting tags is separated into two subsets by the
tag??™s random binary number selection after tag collision; the ?¬?rst subset includes tags
Adaptive Tag Anticollision Protocols for RFID Passive Tags 149
which select 0 and the second subset includes tags which select 1. Since PSC is not changed
in the collision cycle, the ?¬?rst subset tries to retransmit in the following cycle. The second
subset transmits after the ?¬?rst subset is recognized. The increment in ASC values of
unrecognized tags in the collision cycle prevents the second subset from combining with
another set (tags which have already had ASC of 1).
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