Due to these characteristics, the RFID has wider range of identi?¬?cation of
tags where tags can be identi?¬?ed even when line of sight (LOS) is not obtained. Both RFID
system and bar code system readers are able to identify one object at a time. In a bar code
system, one should secure the LOS between a bar code and its reader. It is possible to
identify tags as long as they are within the reader??™s range, but the order of identi?¬?cation
should be determined.
There may be multiple tags a reader should identify. All that the tags should do is to
respond with the data corresponding to the signal received from a reader. The communication
between tags is impossible when passive tags cannot make a decision on whether
the channel is busy or not. Since a medium is shared by tags, a collision occurs at the
reader??™s side when two or more tags get transmitted simultaneously [2]. Since collisions
make collided signals be retransmitted, it increases delay for identifying tags and consumption
of energy. Therefore, the arbitration mechanism is required.
We call the protocol designed for avoiding collisions between a reader and tags an
anticollision protocol. The anticollision protocol should have the following characteristics:
. A reader should identify all the tags within its range.
. The anticollision algorithm should have a mechanism which is capable of verifying
that all the tags are identi?¬?ed.
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