The main advantage of this method is that a lot of readers can be deployed in a small
con?¬?nement area. However, reader antenna positioning can become more challenging, as
all the readers can choose any channel for transmission as long as there is no other type of
short-range device around.
7.8 Synchronization in the United States
Synchronization cannot be implemented in the United States under Part 15.247 or any
countries regulated RFID using FHSS. As discussed earlier, FHSS requires the reader to
switch (hop) from channel to channel when a collision is detected. In synchronization, the
switching or hopping is not random (or pseudorandom) in nature, and is in violation with
the regulations. However, the USA FCC has another clause with Part 15 which does not
specify FHSS. This part 15.245 allows an RF transmission to operate at 0.0375 W EIRP on a
duty cycle with a 20 dB peak to average ratio.
FIGURE 7.12
The complete frequency band allocated for
RFID operation as compared with Figure 7.7.
(From Leong, K.S., M.L. Ng, and P.H. Cole.
2006a. Synchronization of RFID readers for
dense RFID reader environments. International
Symposium on Applications and the Internet.
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.
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