ABS also has a mechanism for deallocating cycles of leaving tags. A transmission of
an arriving tag is decided by a random number selected among possible values inside a
reader??™s range. Tag transmissions are aligned in the increasing order of countervalues.
ABS achieves fast identi?¬?cation by diminishing not only collisions but also unnecessary
idle cycles.
8.6.1 Tag Transmission Control
A tag has two counters, a progressed slot counter (PSC) and an allocated slot counter (ASC).
PSC signi?¬?es a numerical order of the readable cycle in a frame. Tags and readers initialize
their PSC to 0 at the beginning of the frame and increase by only 1 in the readable cycle.
ASC indicates which reading cycle the tag can transmit its ID to the reader. That is, the tag
is allowed to transmit when its ASC is equal to PSC. If the tag has ASC less than PSC, it
does not attempt the transmission until the completion of the frame, because it has already
been recognized in the ongoing frame. To control PSC and ASC, the reader informs tags of
the type of the last reading cycle by transmitting a feedback. According to the contents
of the reader??™s feedback, every tag acts as follows:
. Idle (number of tag responses??0): The tag which has not been recognized in the
current frame yet, that is, the tag which has ASC greater than PSC decreases ASC
by 1.
.
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