We can also ?¬?nd that there exists a linear relationship between the number of tags and
the identi?¬?cation.
9.6.2 Identi?¬?cation of Moving Tags
This section presents performance of tag anticollision protocols in the applications with
high mobility of tags. We consider a situation where objects with an RFID tag move toward
a reader through a conveyer belt. There can be >200 tags within its reader??™s range. We
measured performance by changing the velocity of a conveyer belt. Figure 9.11 shows the
identi?¬?ed number of objects for each anticollision protocol when 5000 objects get moved.
The main purpose of this application is to identify tags passing by a reader.
In such an application, if tags are woken up in advance before an identi?¬?cation process
by a reader, we can have the advantage of adapting quiet state of tags because the tag that
has been already identi?¬?ed does not need to perform that process again. We show
evaluation of both cases in Zhen and DFSA in Figure 9.11a.
As the speed of conveyer belt increases, the interval entering the reader??™s range is
reduced. In other words, the larger the interval becomes, the slower the conveyer belt
moves. Among probabilistic protocols, only Zhen and DFSA using quiet state succeed
in identifying all tags of 5000 even with the fastest condition. ABS is the second best in
adaptability of the speed of a conveyer belt.
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