The reduction in collisions facilitates tag identi?¬?cation with a small delay and
few transmissions while recognizing all the tags inside the reader??™s reading range.
8.2 Tree-Based Tag Anticollision Protocols
Tree-based tag anticollision protocols perform tag identi?¬?cation in units of reading cycle. In
a reading cycle, a reader transmits a query (or a feedback) to tags and then one or some of
tags transmit ID to the reader. Since the passive tag cannot detect collision, the reader
detects whether or not tag collision occurs among tag responses and determines the
contents of the query (or the feedback) in the next reading cycle according to the result
of the detection. On receiving a query (or a feedback) from the reader, the tag decides
whether to transmit or not. Only if a single tag transmits in a reading cycle, the reader can
recognize it successfully.
In tree-based protocols, the reader recognizes all the tags within its reading range during
an identi?¬?cation frame, which consists of several reading cycles. The reader attempts to
recognize a set of tags in a reading cycle. A set includes tags, which transmit at the same
reading cycle. If a set has more than one tag, tag transmissions lead to collision. When tag
collision occurs, the mechanisms split the set into two subsets by tag IDs or random binary
numbers. After that, the reader attempts to recognize two subsets one by one in the same
frame.
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