Wireless Sensor Networks : Technology, Protocols, and Applications

REFERENCES 31
Standards As implied by the protocol stack of Figure 1.4, a suite of protocols and
open standards are needed at the physical, link, network, and transport layers; in
addition, other management protocols and standards are required (physical layer
standards are also known as air interface standards). Historically, sensor networks
have used network- and application-specific protocols. This has had the effect of
slowing cost-effective commercial deployment on a wide scale. Standards are
now beginning to be incorporated into sensor networks. The highest degree of standardization
has occurred at the lower layers. Within-building WSNs now tend to
look to use ZigBee/IEEE802.15.4; WSNs that are in the open (outside buildings
and over a broad geography) may find other technologies useful. In particular,
IEEE-based wireless LAN standards have been given consideration. IEEE 802.11
supports 1- or 2-Mbps transmission in the 2.4-GHz band using either frequencyhopping
spread spectrum or direct-sequence spread spectrum. IEEE 802.11a is an
extension of 802.11 that provides up to 54 Mbps in the 5-GHz band and uses orthogonal
frequency-division multiplexing encoding. IEEE 802.11b is an extension to
802.11 that provides 11-Mbps transmission in the 2.4-GHz band using DSSS. IEEE
802.11g provides up to 54 Mbps in the 2.4-GHz band. Extensions of these standards
were also under way at the time of this writing (e.g., IEEE 802.11n). Another transmission
method is free-space optics operating in the 1-mm wavelength (infrared).
Infrared is license-free line-of-sight technology that operates at short range (300
to 3000 m). The new WiMax standard (IEEE 802.16) may also be useful for metropolitan
environments, as is the application of cellular third-generation technologies.
Earlier we also mentioned the Smart Dust mote, which uses the visible optical
spectrum to communicate.
1.3 CONCLUSION
In this chapter we introduced the basic concept of WSNs and supportive technologies.
The chapters that follow address in much greater detail and technical depth
the issues that have been highlighted here.
REFERENCES
[1.1] C. S. Raghavendra, K. M. Sivalingam, T. Znati Eds., Wireless Sensor Networks, Kluwer
Academic, New York, 2004.
[1.2] E. Cayirci, R. Govindan, T. Znati, M. Srivastava, Editorial: ‘‘Wireless Sensor
Networks,’’ Computer Networks: International Journal of Computer and Telecommunications
Networking, Vol. 43, No. 4, Nov. 2003.
[1.3] T. Znati, C. Raghavendra, K. Sivalingam, Guest editorial, Special Issue on Wireless
Sensor Networks, Mobile Networks and Applications, Vol. 8, No. 4, Aug. 2003.
[1.4] B. Krishnamachari, ‘‘A Wireless Sensor Networks Bibliography,’’ Autonomous
Networks Research Group, University of Southern California–Los Angeles, http://
ceng.usc.edu/anrg/SensorNetBib.html#0103.