Basic Concepts of Wireless Sensor Networks Lina M. Pestana Leão de Brito University of Madeira, Portugal Laura M. Rodríguez Peralta University of Madeira, Portugal B INTRODUCTION As with many technologies, defense applications have been a driver for research in sensor networks, which started around 1980 due to two important programs of the Defense Advanced Research Projects Agency (DARPA): the distributed sensor networks (DSN) and the sensor information technology (SensIT) (Chong & Kumar, 2003). However, the development of sensor networks requires advances in several areas: sensing, commu- nication, and computing. The explosive growth of the personal communications market has driven the cost of radio devices down and has increased the quality. At the same time, technological advances in wireless com- munications and electronic devices (such as low-cost, low-power, small, simple yet efficient wireless com- munication equipment) have enabled the manufacturing of sensor nodes and, consequently, the development of wireless sensor networks (WSNs). Despite the fact that these networks have specific challenges, they represent a significant improvement over traditional sensor networks, concerning the cost, size, flexibility, distributed intelligence, errors (the combination of measures from different sensors can improve the measurements precision) and monitor- ing targets that otherwise would not be possible (for example, the collaboration between sensors can help monitoring low activity targets). However, the main advantage of WSNs is the possibility of being deployed anywhere, in irregular or inaccessible terrains or even in hostile environments where cable installation is not a possible solution. Furthermore, these networks require unattended operation. This means that sensor networks protocols and algorithms must possess self- organizing capabilities. The failure of sensor nodes due to lack of power, environmental interferences, or physical damage, should not affect the overall task of sensor nodes. The sensor nodes have limited capabilities, which consist of sensing, signal and data processing, and radio communication. However, these networks have a unique feature: the collaborative effort of the sensor nodes in data gathering and processing, in order to accomplish more complex tasks. WSNs combine the advantages of wireless communication with some computation capabilities and detection of some physical character- istics (typically, temperature, light, vibration, sound, radiation, etc.). Thus, the application areas of WSNs are quite numerous: environmental monitoring, health (a case where deployment of sensors has to be manual), surveillance (for example, intrusion detection), secu- rity, engineering, aviation, traffic monitoring, military, home, monitoring disaster areas, industry, etc. In this article, we present a broad survey of the communications architecture of the sensor networks, as well as the issues that influence the network design, the protocols, and algorithms proposed so far for sen- sor networks. WIRELESS SENSOR NETWORKS: MAIN CHARACTERISTICS A sensor network consists of a large number of tiny sensor nodes that are densely deployed either inside the phenomenon or very close to it. The sensors measure ambient conditions in the environment surrounding them and then transform these measurements into signals that can be processed to reveal some charac- teristics about the phenomenon. The data collected is routed to special nodes called sink nodes, by a multi- hop infrastructureless architecture, shown in Figure 1 (adapted from Lewis, 2004). Then the sink node sends data to the user via Internet or satellite through a gateway (also called base station, BS). The user can interact with the physical world (and, consequently, with WSNs) through the Internet. This is why some Copyright © 2008, IGI Global, distributing in print or electronic forms without written permission of IGI Global is prohibited.