ABSTRACT
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
Wireless sensors [1, 2, 5, 6, 7, 8, 11, 13, 14, 16] have received much attention in
both research and system development in recent years. With a wealth of exciting
research results obtained over the past decade, they have been continuously fueling
significant impacts and reshaping many possible areas of real-life applications in-
cluding localization [6, 11, 14, 16] or object tracking [14] for military applications,
effective event storage and distribution schemes [13, 15] in wireless sensor networks
wireless
changes in temperature, pressure or other factors in chemical plants, refinery [17] or
power lines [1] for real-time and intelligent control systems, using ultra-sound and/or
other wireless sensors as parts of embedded systems for robot navigation [2] or con-
trol, incorporating the multi-axis accelerometer or intrinsic motion sensors relative to
gravity into personal electronic devices such as the Apple iPhone R© [18], the Nokia N96 R© mobile phones [3] or Nintendo’s Wii Remote R© controller [2] for mobile gaming, or even as digital compasses to work with 3G or global positioning system
(GPS) receivers [20] on mobile devices [8, 22, 23, 25] for car or personal naviga-
tion. In many such innovative applications of wireless sensors, each sensor/node in
the system/network is employed to detect some specific event such as changes of
positions or temperature, and quickly sends the collected information to the nearest
server or sink node for further processing or concatenation of information. In many
industrial WSN applications, the automatic position determination, namely the local-
ization, of sensors is important since a sensor’s position must be known for the data
to become meaningful, especially in the location-aware sensor network communi-
cation protocols such as sensing coverage [3]. Besides, the constrained resources of
individual sensors including the maximally supported data rate, the limited battery
lifetime, and possibly the high failure rate of date transmission due to some noisy
terrains, together with the scalability, mobility or other specific requirements of the
underlying applications all pose difficult challenges to the latest research in local-
ization or WSN applications in general. Nevertheless, the innovative and suitable
uses of wireless sensors would be expected to open up many potential markets of
emergent technologies to assure a high quality of living in the future. A prominent
example is the possible integration of wireless sensors into the next-generation intel-
ligent buildings that can automatically find out the shortest path, open the involved
exit doors and guides the tenants to safe places in extreme cases of fires or natural
disasters. After a wireless sensor detects any interested event, it has to use a wireless
network such as BlueToothTM [9], the IEEE 802.11 or commonly named WiFiTM
for Wireless Fidelity [6], or the ZigBeeTM [4, 9, 21, 27, 29, 32] network. Mobile
gaming devices like the Nintendo’s Wii Remote R© controller may use BlueToothTM
network for convenient and short-range communication in personal area networks
(PANs) while popular mobile phones integrated with motion sensors, like the Apple
iPhones R© , may provide both connection functions of BlueToothTM and WiFi for users to choose. In general, the ZigBeeTM networks as defined by the IEEE 802.15.4
specification are intended to be simpler and less expensive than BlueToothTM or
IEEE 802.11 networks. This is mainly because the ZigBeeTM networks can be ac-
tivated (that is going from sleep to active mode) in 15 milliseconds or less whereas
the wake-up delays in BlueToothTM networks are typically around 3 seconds [7].
With the very low latency, devices connected to a ZigBeeTM network can be very
responsive. Besides, since ZigBeeTM devices can sleep most of the time, the aver-
age power consumption can be very low, thus resulting in a relatively longer battery
life. Overall speaking, the ZigBeeTM technology is a low-cost, low-power, wireless
mesh networking proprietary standard. The low cost allows the technology itself to
be widely deployed in wireless control and monitoring applications. The low power-
