Although each of them has different dividing algorithms and tree
maintenance methods, they are very similar with respect to constructing a searching
tree in an identi?¬?cation cycle. The main advantage of tree-based tag anticollision protocol
is that all tags in identi?¬?cation range of the reader can be identi?¬?ed. An identi?¬?cation cycle
is a process that constructs a tree from root node to leaf nodes. When the next identi?¬?cation
cycle begins, information of tree in the previous cycle is initialized. AQS protocol [7] and
ABS protocol [7] can improve the performance by using the information of tree in the
previous cycle.
9.3.1 Query Tree
A reader transmits a query to tags using a query tree protocol. The query contains the
pre?¬?xes of the tag identi?¬?cation (ID) codes. All tags within the range of a reader compare
the query of the reader with their ID codes and transmit their ID codes to the reader when
the result of the comparison is true. This protocol uses a query of reader and pre?¬?xes of tag
ID codes to divide tags into two groups. Tags in one group transmit their ID codes to the
reader while tags in the other group wait for the next query of the reader.
The content of a query is the identi?¬?er of each group. The reader repeats dividing tags
into two groups until the number of tags in a group is one. When the number of tags in a
group is one, the reader is successful in identifying the tag.
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