08-10-2010, 11:55 AM
Wireless sensor networks: technology, protocols, and applications
INTRODUCTION
A sensor network is an infrastructure comprised of sensing (measuring), computing, and communication elements that gives an administrator the ability to instrument, observe, and react to events and phenomena in a specified environment. The administrator typically is a civil, governmental, commercial, or industrial entity. The environment can be the physical world, a biological system, or an information technology (IT) framework. Network(ed) sensor systems are seen by observers as an important technology that will experience major deployment in the next few years for a plethora of applications, not the least being national security . Typical applications include, but are not limited to, data collection, monitoring, surveillance, and medical telemetry. In addition to sensing, one is often also interested in control and activation. There are four basic components in a sensor network: (1) an assembly of distributed or localized sensors; (2) an interconnecting network (usually, but not always, wireless-based); (3) a central point of information clustering; and (4) a set of computing resources at the central point (or beyond) to handle data correlation, event trending, status querying, and data mining. In this context, the sensing and computation nodes are considered part of the sensor network; in fact, some of the computing
may be done in the network itself. Because of the potentially large quantity of data collected, algorithmic methods for data management play an important role in sensor networks. The computation and communication infrastructure associated with sensor networks is often specific to this environment and rooted in the deviceand application-based nature of these networks. For example, unlike most other settings, in-network processing is desirable in sensor networks; furthermore, node power (and/or battery life) is a key design consideration. The information collected is typically parametric in nature, but with the emergence of low-bit-rate video [e.g., Moving Pictures Expert Group 4 (MPEG-4)] and imaging algorithms, some systems also support these types of media. In this book we provide an exposition of the fundamental aspects of wireless sensor networks (WSNs). We cover wireless sensor network technology, applications, communication techniques, networking protocols, middleware, security, and system management. There already is an extensive bibliography of research on this topic; the reader may wish, for example, to consult for an up-todate list. We seek to systematize the extensive paper and conference literature that has evolved in the past decade or so into a cohesive treatment of the topic. The book is targeted to communications developers, managers, and practitioners who seek to understand the benefits of this new technology and plan for its use and deployment.
Background of Sensor Network Technology
Researchers see WSNs as an ‘‘exciting emerging domain of deeply networked systems of low-power wireless motes2 with a tiny amount of CPU and memory, and large federated networks for high-resolution sensing of the environment’’ . Sensors in a WSN have a variety of purposes, functions, and capabilities. The field is now advancing under the push of recent technological advances and the pull of a myriad of potential applications. The radar networks used in air traffic control, the national electrical power grid, and nationwide weather stations deployed over a regular topographic mesh are all examples of early-deployment sensor networks; all of these systems, however, use specialized computers and communication protocols and consequently, are very expensive. Much less expensive WSNs are now being planned for novel applications in physical security, health care, and commerce. Sensor networking is a multidisciplinary area that involves, among others, radio and networking, signal processing, artificial intelligence, database management, systems architectures for operator-friendly infrastructure administration, resource optimization, power management algorithms, and platform technology (hardware and software, such as operating systems) .The applications, networking principles, and protocols for these systems are just beginning to be developed . The near-ubiquity of the Internet, the advancements in wireless and wireline communications technologies, the network build-out (particularly in the wireless case), the developments in IT (such as high-power processors, large random-access memory chips, digital signal processing, and grid computing), coupled with recent engineering advances, are in the aggregate opening the door to a new generation of low-cost sensors and actuators that are capable of achieving high-grade spatial and temporal resolution. The technology for sensing and control includes electric and magnetic field sensors; radio-wave frequency sensors; optical-, electrooptic-, and infrared sensors; radars; lasers; location/navigation sensors; seismic and pressure-wave sensors; environmental parameter sensors (e.g., wind, humidity, heat); and biochemical national security–oriented sensors. Today’s sensors can be described as ‘‘smart’’ inexpensive devices equipped with multiple onboard sensing elements; they are low-cost low-power untethered multifunctional nodes that are logically homed to a central sink node. Sensor devices, or wireless nodes (WNs), are also (sometimes) called motes . A stated commercial goal is to develop complete microelectromechanical systems (MEMSs)–based sensor systems at a volume of 1 mm3 . Sensors are internetworked via a series of multihop short-distance low-power wireless links (particularly within a defined sensor field); they typically utilize the Internet or some other network for long-haul delivery of information to a point (or points) of final data aggregation and analysis. In general, within the sensor field, WSNs employ contention-oriented random-access channel sharing and transmission techniques that are now incorporated in the IEEE 802 family of standards; indeed, these techniques were originally developed in the late 1960s and 1970s expressly for wireless (not cabled) environments and for large sets of dispersed nodes with limited channel-management intelligence . However, other channelmanagement techniques are also available.
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