The objective of the protocol is to singulate a
tag in a multiple tag environment to read its identity or other information stored in the
tag??™s memory.
The frequency of transmissions of the RFID reader operate anywhere from 860 to 960
MHz according to local regulations, whereas in general RFID tags should be able to
operate anywhere in that frequency band, responding to locally con?¬?gured readers.
There are three frequency bands of interest:
. Region 1 (EU and Africa), typically 865??“868 MHz, 2 W ERP Frequency Agile, LBT
. Region 2 (FCC??”United States and Canada) 902??“928 MHz, 4 W EIRP Spread
Spectrum Frequency Hopping
. Region 3 (Asia). Most follow Europe, some follow FCC
Usually, the available spectrum in a local region is divided into channels or sub-bands. In
the United States, channels are 500 kHz wide, whereas in Europe sub-bands are 200 kHz
wide. In the United States, the 50 available channels, with operation at 4 W EIRP, are used
20 RFID Handbook: Applications, Technology, Security, and Privacy
according to a random selection process known as Spread Spectrum Frequency Hopping,
in which operation in one channel is limited to 400 ms after which the reader must select
another channel to transmit. In Europe, only 10 channels are available for operation at 2 W
ERP, and are used according to a Frequency Agile operation. In addition, readers must
follow a Listen before Talk operation, in which a reader must ?¬?rst listen for transmissions
in the intended sub-band of operation, and only transmit if no transmissions are detected
above a very low threshold.
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