SAINT, Phoenix, Arizona, USA, #
2006 by IEEE. With permission; Leong, K.S., M.L.
Ng, A. Grasso, and P.H. Cole. 2006d. J. Commun., 1,
9, # 2006 by IEEE. With permission.)
RFID Reader Synchronization 135
are assigned to be the reader transmitting channels while the tag reply channels are the
four channels beside the transmitting channels (Impinj, 2006). For example, transmitting
channel 4 uses channels 2, 3, 5, and 6 for tag reply (Figure 7.13).
Although the transmitting channels are reduced from a total of ?¬?ve down to four, the
transmitting channels are placed two channels away rather than one channel away. From
the transmit mask shown in Figure 7.14, an improvement of 5 dB can be obtained. Hence
with the reduction of interference between transmitting channels, readers can be placed
nearer to each other.
7.7.2 Separation of RFID and Non-RFID Signals
Another variation of synchronization is to differentiate an RFID signal from a non-RFID
signal. A method using signal recognition is presented in Intermec (2006). The idea is that
all the RFID readers in a certain region can be treated as a single entity in the regulation as
outlined in the ETSI 302 208. Hence, it is only required to avoid the signal interference
between all the RFID readers and the rest of the short-range devices. If this concept is valid,
the interrogation signals of RFID readers are not treated as a signal in a channel when an
LBT test is carried out.
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