In case an RFID
reader has to recognize tags in reader??™s range persistently, a reader continues to perform
identi?¬?cation process. ABS and AQS achieve good performance than other protocols. They
can recognize fast whether the tag is in reader??™s range or not.
Table 9.3 shows characteristics of tag anticollision protocols. A variable for maintaining a
slot number is required in probabilistic tag anticollision protocols. The binary tree protocol
should have such a variable for a counter. ABS protocol needs two variables for ASC and
PSC. The query tree protocol and AQS protocol require neither counters nor a random
number generator. As the length of query varies, the length of reader??™s message also varies.
AQS and ABS are appropriate for satisfying this evaluating factor.
9.8 Conclusions
In this chapter, we have introduced tag anticollision protocols and have presented the
performance evaluation results of them. According to the types of RFID applications, we
have considered two cases: motionless tags and moving tags. For applications employing
motionless tags, a user can determine the start as well as the end of the identi?¬?cation
process. When such applications are considered, probabilistic and deterministic tag anticollision
protocols show similar ability in identifying tags. For applications requiring
persistent observations on tags, AQS and ABS outperform any other protocols, especially
under the situation that tag population varies at low speed.
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