INFORMATION PROCESSING AND ROUTING IN WIRELESS SENSOR NETWORKS
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4 Information Processing and Routing in Wireless Sensor Networks
now available to integrate a rich set of sensors onto the same CMOS chip.
Commercially available sensors now include thermal, acoustic/ultrasound,
and seismic sensors, magnetic and electromagnetic sensors, optical trans-
ducers, chemical and biological transducers, accelerometers, solar radia-
tion detectors, photosynthetically active radiation detectors, and baromet-
ric pressure detectors
[
105
]
. These sensors can be used in a broad range of
applications, including acoustic ranging, motion tracking, vibration detec-
tion, and environmental sensing.
The above technologies, along with advanced packaging techniques,
have made it possible to integrate sensing, computing, communication, and
power components into a miniaturized sensor node.
1.2.2 Wireless Networking
Besides hardware technologies, the development of WSNs also relies on
wireless networking technologies. The 802.11 protocol, the first standard
for wireless local area networks (WLANs), was introduced in 1997. It was
upgraded to 802.11b with an increased data rate and CSMA/CA mech-
anisms for medium access control (MAC). Although designed for wire-
less LANs that usually consist of laptops and PDAs, the 802.11 proto-
cols are also assumed by many early efforts on WSNs. However, the
high power consumption and excessively high data rate of 802.11 pro-
tocols are not suitable for WSNs. This fact has motivated several re-
search efforts to design energy efficient MAC protocols
[
109; 145; 189;
206
]
. Recently, the 802.15.4-based ZigBee protocol was released, which was
specifically designed for short range and low data rate wireless personal
area networks (WPAN). Its applicability to WSNs was soon supported by
several commercial sensor node products, including MicaZ
[
48
]
, Telos
[
140
]
,
and Ember products
[
58
]
.
Above the physical and MAC layers, routing techniques in wireless net-
works are another important research direction for WSNs. Some early
routing protocols in WSNs are actually existing routing protocols for wire-
less ad hoc networks or wireless mobile networks. These protocols, in-
cluding DSR
[
88
]
and AODV
[
138
]
, are hardly applicable to WSNs due
to their high power consumption. They are also designed to support
general routing requests in wireless networks, without considering spe-
cific communication patterns in WSNs. Nevertheless, the customization
of these protocols for WSNs and the development of new routing tech-
niques have become hot research topics
[
26; 51; 66; 73; 85; 95; 107; 160;