A wireless system signals through an RF link. It can use one of the ?¬?ve guard bands,
mentioned in Section 7.2.1, for sending a synchronizing signal. A synchronizing signal can
be a signal with a special pattern. A wireless system can also use any existing wireless
protocol such as Bluetooth technology. It supports mobile readers but is inevitably vulnerable
to interference (signal integrity problem) and unauthorized signal snif?¬?ng (security
problem).
Both connectivity methods have their own advantages and disadvantages. The decision
in choosing either of these two methods is largely dependent on the positioning of the LBT
sensor, which is discussed later.
7.4.2 Positioning of LBT Sensors
An LBT sensor of an RFID reader is responsible for detecting signals in the channel of
interest before transmission in that channel. This LBT sensor must have a power sensitivity
level better than 126 dBW as speci?¬?ed in ETSI (2006). If not, this LBT sensor will not be
able to function ef?¬?ciently in determining whether there exists a signal with a power level
higher than the power level speci?¬?ed in regulations in the channel of interest. An LBT
sensor can be the RFID antenna used for transmitting and receiving signals in the communication
with RFID tags. An LBT sensor can also be a separate antenna connected to an
RFID reader.
In addition, several RFID readers could share an LBT sensor within a close vicinity.
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