The sixth cycle is an idle cycle because there are no
tags which have ASC equal to PSC (??2). ASC of tag C and TSC of the reader are
decreased by 1 and the reader recognizes tag C in the seventh cycle. The reader
terminates the identi?¬?cation frame after the seventh cycle. By using the values of ASCs
and TSC decided in the current frame into tag identi?¬?cation of the next frame, the reader
achieves fast tag identi?¬?cation. The arriving tags in the next frame can randomly select
their ASCs among numbers ranging from 0 to 2. Especially, when there is no leaving tag
and no arriving tag in the next frame, the reader can reidentify these three tags without
any collision.
8.7 Performance Evaluation
We evaluate the performance of AQS and ABS compared with the binary tree protocol and
the query tree protocol. To measure the ef?¬?ciency of tag identi?¬?cation in the tree-based
protocols, we consider the following aspects:
. Number of collisions: We measure the number of collisions between tag-to-reader
signals. A collision defers identi?¬?cation and increases power consumption of tags.
. Number of idle cycles: The idle cycle is a factor of identi?¬?cation delay.
. Identi?¬?cation delay: We measure the total delay for recognizing all tags by the
interrogation cycle. Fast identi?¬?cation is the most signi?¬?cant factor in the treebased
anticollision protocols because they do not cause the tag starvation problem.
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