Tags are divided into two groups: one group has 0 in their counter values; the other group
has the counter values of 1.
The group with the counter value of 0 tries to transmit and wait for the reply from the
reader. If a collision occurs, tags which tried to transmit their ID codes in the previous cycle
are divided into two groups by using a pseudo-random number, and tags that did not try
the ID transmission increase the value of their counters by 1. If there are no collisions, all
tags decrease the value of their counters by 1.
The tags identi?¬?ed successfully set the value of their counters to 0 and wait for the start
of a frame message from the reader. Since the binary tree protocol uses the random number
generator in branching out, idle slots can occur many times. However, the probability of
this is very low. As the information regarding tag ID codes is not used in the identi?¬?cation
process as in probabilistic tag anticollision protocols, the performance of the binary tree
protocol is not affected by the distribution of the ID codes of tag population.
In Figure 9.4, we provide an example of the identi?¬?cation procedure of the binary tree
protocol. Initially, all tags set the value of their counter variables to 0. The tags with the
counter value of 0 try to transmit and a collision occurs. Each tag generates random
number of 0 or 1.
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