However, work within an ETSI Technical Group has begun to
produce a Technical Report (TR 102 436) that recommends a code of practice that will
enable RFID readers to be synchronized. EPCglobal Inc. also maintains a database of
worldwide UHF regulations (EPCglobal, 2007b).
Tags must understand three different modulation schemes; one of these would be
selected by the reader and sent to the tags that are in the reader??™s RF ?¬?eld as parameters
of the command that establishes communication with the tags. The reader selects the most
appropriate modulation scheme, based on its own operating parameters, such as regulatory
environment, received noise information, and preferences established by the system
engineer. The three different modulation schemes are
. Double Sideband Amplitude Shift Keying DSB-ASK
. Single Sideband Amplitude Shift Keying SSB-ASK
. Phase Reversal Amplitude Shift Keying PR-ASK
Data sent to the tag by the reader is encoded using a coding scheme known as pulse
interval encoding (PIE). This coding scheme de?¬?nes the duration of a zero-data bit pulse,
also known as Tari, as part of the parameters sent when communication is established with
tags by the reader. The duration of a one-data bit is at least 50% longer. This enables the
reader to specify variable data rates of 40, 80, 160, 320, and 640 kbits (kilobits per second).
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