8, No. 1 (2004) pp. 84??“97, Jan 2004.
Chapter 9
Time-Synchronization Challenges and
Techniques
Weilian Su
Department of Electrical and Computer Engineering
Naval Postgraduate School
Monterey, CA 93943
weilian@nps.edu
1 Introduction
The advancement of Micro Electro-Mechanical Systems technology, wireless
communications, and digital electronics has enabled the development of lowcost,
low-power, multifunctional sensor nodes that are small in size and communicate
untethered in short distances. The sensor nodes may be used in
military, environmental, and commercial applications [1]. Each of these applications
may require a di?®erent level of clock precision among the sensor
nodes. For example, the clock precision required for security time-stamping
and target tracking may be di?®erent. In addition, sensor nodes with a common
view of time may fuse and display voice and video data in a meaningful
way. Also, they may be able to use Time Division Multiple Access (TDMA)
to access the channel and turn o?® the radio whenever possible to save energy.
Thus, time synchronization is needed for di?®erent types of services that require
coordination and precision. If services do not require time, then time
synchronization may be an overhead for the sensor networks.
Since some applications and protocols need time synchronization, this
chapter explores the design challenges, factors influencing time precision, and
the state-of-the-art in time synchronization for wireless sensor networks.
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