With permission.
Reader 1
Reader 2
"Listen" "Talk"
"Listen"
Reader N "Listen"
"Talk"
"Talk"
Time FIGURE 7.2
Synchronization of all readers: all the readers start to ??????Listen??™??™ at the same
time and ?¬?nish ??????Listen??™??™ at the same time. (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.)
RFID Reader Synchronization 129
7.4 Actual Implementation
7.4.1 Connectivity
In actual implementation, RFID readers must be able to communicate with each other to
enable synchronization of RFID readers. There are basically two ways in connecting all the
readers; either using wired (physical) connection or using wireless connection.
A physically connected system or wired system cannot support mobile readers. In
addition, a wired connection may suffer from data latency in the network. Skeie et al.
(2001) show that time synchronization in a wired network is possible, but will require
additional hardware and system recon?¬?guration. In the best case, the time difference
achievable can be better than 1 ms. A wired system is often considered more reliable and
a more secure communication method than a wireless communication.
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