wireless sensor network (from one of my frnd who is blessed with sharp mind sukomal thnx)

Wireless Sensor Network (WSN)

·        Sensor networks are the key to gathering the information needed by smart environments, whether in buildings, utilities, industrial, and transportation systems.

·        Recent terrorist and guerilla warfare countermeasures require distributed networks of sensors that can be deployed using, e.g. aircraft, and have self-organizing capabilities.  .

·        The emerging field of wireless sensor networks combines sensing, computation, and communication into a single tiny device.

·        WSN consists of spatially distributed sensors to monitor physical or environmental conditions, such as temperature, sound, vibration or motion to pass their data through the network to a main location.

·        Wireless sensor network can be looked as an event-based system with one “sink” subscribing to specific data streams by expressing interest and queries. The remaining sensors act as “sources” to report environmental events to the subscriber sink

·        The more modern networks are bi-directional, also enabling control of sensor activity.

·        The WSN is built of "nodes" – from a few to several hundreds or even thousands, where each node is connected to one (or sometimes several) sensors.

·        Each such sensor network node has typically several parts: a radio transceiver with an internal antenna or connection to an external antenna, a microcontroller, an electronic circuit for interfacing with the sensors and an energy source, usually a battery or an embedded form of energy harvesting.

·        A sensor node might vary in size and cost depending on the complexity of the individual sensor nodes.

·        Size and cost constraints on sensor nodes result in corresponding constraints on resources such as energy, memory, computational speed and communications bandwidth.

·        The topology of the WSNs can vary from a simple star network to an advanced multi-hop wireless mesh network.

·        The propagation technique between the hops of the network can be routing.

·        Basic features of sensor networks are:

Ø  Self-organizing capabilities

Ø  Short-range broadcast communication and multi-hop routing.

Ø  Dense deployment and cooperative effort of sensor nodes

Ø  Frequently changing topology due to fading and node failures

Ø  Limitations in energy, transmit power, memory, and computing power.

·        The development of wireless sensor networks was motivated by military applications such as battlefield surveillance; today such networks are used in many industrial and consumer applications, such as industrial process monitoring and control, machine health monitoring, and so on.

Classification of Wireless Sensor Network

A simple classification of Wireless sensor networks based on their mode of functioning

• Proactive Networks

The nodes in this sort of network periodically switch on their sensors and transmitters, sense the environment and transmit the data of interest. Hence, they collect the data for the relevant parameters at regular intervals. They are well suited for applications requiring periodic data monitoring. Some instances or protocols of this kind are the LEACH (Low Energy Adaptive Clustering Hierarchy) protocol, some improvements on LEACH such as and PEGASIS (Power-efficient gathering in sensor information systems)

• Reactive Networks

The nodes of the networks according to this scheme react immediately to sudden and drastic changes in the value of a sensed attribute. They are well suited for time critical applications.

• Hybrid Networks

The nodes in such a network not only react to time-critical situations, but also give an overall picture of the network at periodic intervals in a very energy efficient manner. Such a network enables the user to request past, present and future data from the network in the form of historical, one-time and persistent queries respectively. Such kind of network takes advantages of Proactive and Reactive networks.