For example, if two
mobile readers operate simultaneously in an enclosed area, there is a probability that the
two readers move near to each other at some time. The centralized LBT sensor may at that
time allocate very nearby channels to those two readers and serious interference between
those two readers may occur.
In addition, if two nearby areas are running on different RFID wireless networks and
they are uncoordinated, interference with each other will occur, and in the worst case,
cause a complete system shut down. The coordination of wireless networks in different
premises will be time and cost consuming.
A localized LBT system is as shown in Figure 7.4. Each reader has its own LBT sensor.
The LBT sensor can either be a separate antenna (Figure 7.4), or be the same antenna a
reader uses to establish communication with an RFID tag within its interrogation zone. As
compared with a centralized LBT system, a localized LBT system with wireless connectivity
enables relatively easy new reader integration into an existing system, with no additional
cabling or setup needed. However, a localized LBT system has the problem with
management of channel sharing, signal interference, and possibly creation of unwanted
shielding.
In actual fact, the connectivity of readers and the positioning of LBT sensor are closely
related. In CISC (2006), a wired system and a centralized LBT are linked together as one
con?¬?guration, whereas a wireless system and a localized LBT are linked together as
another con?¬?guration.
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