DFSA must maintain a table to return the
number of tags provided that the collision ratio and the frame size are given. It may be
burdensome to maintain a table, but DFSA makes possible to estimate the number of tags
precisely.
9.4.3 Dynamic Frame Length ALOHA
In Vogt1 protocol, we use the number of readable slots and the number of collision slots to
estimate the number of tags. The number of tags in a collision slot is at least two. If the
number of tags approaches to in?¬?nity, we can obtain the expected number of 2.39 tags in
a collision slot [13,19]. We can estimate the number of tags by using the following equation:
Zhen:Ntag ?? S ?? 2:39C (9:4)
We, in this chapter, refer to this estimation method Zhen for convenience??™s sake. This
method can easily estimate the number of tags. This is a less error-prone method that
requires only simple calculation.
9.5 Analytic Study
In this section, we analyze the performance of tag anticollision protocols. All four treebased
protocols (binary tree, query tree, ABS, and AQS) use binary search tree as their
searching method to identify tags. Therefore, we choose binary tree protocol as the
representative of tree-based protocols. On the other hand, adaptive framed slotted
ALOHA is mainly researched among the probabilistic tag anticollision protocols. Hence,
we compare the performance of adaptive framed slotted ALOHA with the binary tree
protocol.
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