Tag anticollision protocols can be grouped into two broad categories, namely ALOHAbased
protocols and tree-based protocols. ALOHA-based protocols [7??“21] reduce the
occurrence probability of tag collisions since each tag tries to transmit the ID at randomly
selected time. ALOHA-based protocols, however, cannot completely prevent collisions,
and hence they have the serious problem that a speci?¬?c tag may not be identi?¬?ed for a long
time, leading to the so-called ??????tag starvation problem.??™??™ On the other hand, in tree-based
protocols such as the binary tree protocol [20??“25] and the query tree protocol [26,27], tag
identi?¬?cation conceptually forms a tree. Based on the collision resolution algorithms
studied in Refs. [28??“31], tree-based protocols split a set of tags into two subsets at a time
and attempt to recognize the subsets one by one. By splitting until each set has only one
tag, the reader can recognize all the tags in the reader??™s reading range. Tree-based protocols
do not cause tag starvation, although they have relatively long identi?¬?cation delay as
compared with ALOHA-based protocols.
Based on the analysis earlier, a good tag collision arbitration protocol for passive RFID
tags should have the following characteristics:
. The reader ought to recognize all the tags inside its own reading range. Tag
starvation problem results in the failure of object tracking and monitoring.
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