ABSTRACT
Ad hoc networks consist of laptops, PDAs, and other devices that can communicate in multihop fashion. Such networks emerge in conference, rescue, and battlefield environments, as well as for wireless Internet access. Ad hoc networks are often considered as mobile networks. However, this chapter is concerned with static nodes, nodes that can change activity status, or can arbitrarily fail. We are also interested in large-size networks and the design of corresponding scalable solutions. Sensor networks are a special case of ad hoc networks, with nodes that are generally densely deployed (hundreds or thousands of such nodes can be placed, mostly at random, either very close or inside the phenomenon to be studied), are small in size, static, with lower battery power, and smaller processing power. Recent technological advances have enabled the development of low-cost, low-power, and multifunctional sensor devices. These nodes are autonomous devices with integrated sensing, processing, and communication capabilities. Sensor networks consist of a large number of sensor nodes that collaborate together using wireless communication and asymmetric many-to-one data. Indeed, sensor nodes usually send their data to a specific node called the sink node or monitoring station, which collects the requested information. All nodes cannot communicate directly
with the monitoring station because such communication may be over long distances that will drain the power quickly. Hence, sensors operate in a self-organized and decentralized manner, and message communication takes place via multihop spreading. To enable this, the network must maintain the best connectivity for as long as possible. The sensor’s battery is not replaceable, and sensors can operate in hostile or remote environments. Therefore, energy consumption is considered the most important resource, and the network must be self-configured and self-organized. The best energy conservation method is to put as many sensors to sleep as possible. The network must be connected to remain functional, so that the monitoring station can receive messages sent by any of the active sensors. An intelligent strategy for selecting and updating a set of active sensors that are connected is needed to extend network lifetime. This problem is known as the connected area coverage problem, which aims to dynamically activate and deactivate sensors while maintaining full coverage of the monitoring area. Efficient solutions to the connected area coverage problem are discussed in References 1 through 3. When this coverage step is performed first, the large sensor network becomes reasonably sparse but remains connected.
