Wireless Sensor Networks : Technology, Protocols, and Applications

26 INTRODUCTION AND OVERVIEW OF WIRELESS SENSOR NETWORKS
communications network interfaces; and network architecture and protocols, including
network topology and fault tolerance, scalability, self-organization, and mobility
[1.82,1.83].
Sensor networks are generally self-configuring systems. The goal is to be able to
adapt to unpredictable situations and states. Static or semidynamic topologies lend
themselves easily to preconfiguration, but highly dynamic environments require
self-configuration. In designing a sensor network, one is naturally looking for
acceptable accuracy of information (even in the presence of failed nodes and/or
links, and possibly conflicting or partial data); low network and computing latency;
and optimal resource use (specifically, power and bandwidth). Work is under way to
develop techniques that can be employed to deal with these and other pertinent
issues, such as how to represent sensor data, how to structure sensor queries,
how to adapt to changing node or network conditions, and how to manage a large
network environment where nodes have limited network management functionality.
Sensor networks often employ data processing directly in the network itself. Part
of the motivation is the potential for large pools of data being generated by the sensors.
By utilizing computation close to the source of the data for trending, averaging,
maxima and minima, or out-of-range activities, one is able to reduce the
communication throughput that would otherwise be needed. Intrinsic to this is
the development of localized algorithms that support global goals; it follows that
forms of collaborative signal processing are desired.
Researchers are looking at new system architectures to manage interactions.
Currently, many sensor systems suffer from being one-of-a-kind with piecemeal
design approaches. This predicament leads to suboptimal economics, longevity,
interoperability, scalability, and robustness. Standards will go a long way to address
a number of these concerns. A number of researchers [1.5] are taking the position
that the traditional approach and/or protocol suite is not adequate for embedded,
energy-constrained, untethered, small-form-factor, unattended systems, because
these systems cannot tolerate the communication overhead associated with the routing
and naming intrinsic in the Internet suite of protocols. Proponents are making a
pitch for special-purpose system functions in place of the general-purpose Internet
functionality designed for elastic applications. In effect, resource constraints
require a more streamlined and more tightly integrated communications layer
than that possible with a TCP–IP or ISO (International Organization for Standardization)
stack. This topic is revisited in Chapter 9 and 11.
1.2.2 Brief Historical Survey of Sensor Networks
The history of sensor networks spans four phases, described briefly below [1.13].
Phase 1: Cold-War Era Military Sensor Networks During the cold war, extensive
acoustic networks were developed in the United States for submarine surveillance;
some of these sensors are still being used by the National Oceanographic and
Atmospheric Administration (NOAA) to monitor seismic activity in the ocean. Also,
networks of air defense radars were deployed to cover North America; to handle