However, the existing tree-based tag
anticollision protocols cause collisions between staying tags because they do not take any
information on staying tags into consideration. At the beginning of the identi?¬?cation frame,
they make one set, which includes all the tags inside the reader??™s identi?¬?cation range, and
start the splitting procedure. To show collisions between staying tags, we measure interstaying
tag collisions through simulations of the binary tree protocol and the query tree
protocol. In our simulations, there are 50 tags in an area of 10 m310 m, and tags have
mobility following the random walk model [33]. A reader, which has the identi?¬?cation
range of 3 m, is deployed in the center of the simulation area and recognizes tags
repeatedly. To pinpoint an individual tag, we give tags virtual IDs from 1 to 50. To
make tag 1 the staying tag, we ?¬?x it in the vicinity of the reader. Figure 8.2 shows the
number of collisions caused by tag 1 and other staying tags during two consecutive
* Prominent retailers such as Wal-Mart, Target, and Best Buy, as well as logistics companies like UPS and Fed-Ex
have made this a requirement of all their operations. Manufacturers are following suite.
Adaptive Tag Anticollision Protocols for RFID Passive Tags 143
identi?¬?cation frames. Under the binary tree protocol, tag 1 suffers from more collisions
with some staying tags during the second frame in comparison with the ?¬?rst frame as
shown in Figure 8.
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