A wireless sensor network (WSN) is a set of wireless sensor nodes that sense, process data, and communicate cooperatively. Sensor node location and network topology are typically not predetermined. Models for node deployment should thus be at least partially stochastic. WSNs have both military and civilian applications. WSN system designs need to satisfy a number of constraints simultaneously: WSN nodes typically rely on battery power, making eventual node failure inevitable. Whereas wired network protocols are usually designed to provide a high quality of service (QoS), energy conservation is often a major issue for WSN implementations. There is a trade-off between QoS and system lifetime in these systems. WSNs use low-cost radios with a high error rate and limited bandwidth. Associated protocols need to have low communications overhead and high fault tolerance. Limited on-board processors and memory prohibit the use of overly complicated protocols. Sensor node failures and possible node mobility make network topology transient. The environment also has frequent and unpredictable perturbations. These topological disturbances demand self-organizing protocols, capable of adapting to these changes. WSNs must also have distributed control architectures to maintain a level of reliability, scalability, and flexibility that is not possible for centralized control systems.
