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Monday, 15 June 2015

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What are Wireless Sensor Networks?

Wireless technology has propagated the use of sensor networks in many applications. Sensor networks join small sized sensors and actuators with general purpose computing components. Such networks comprise of hundreds and sometimes thousands of self-functioning, low power, inexpensive wireless nodes to observe and influence the surroundings.

Wireless sensor networks usually consist of a single or multiple base stations acting as points of centralized control, whereby they provide access to other networks. These networks are unique in their dynamic network topologies. A network topology is usually selected depending on the type of application the sensors are used for or where it is situated. The types of topologies used for sensor networks include star, mesh, star-mesh etc.

Figure. Example of a Wireless Sensor Network



 In Wireless sensor networks there are two kinds of wireless nodes; sensor and base station nodes. The main function of the base station (also referred to as sinks) relies on managing the actions executed to provide reliable and efficient sensing support. It provides a gateway to other networks or acts as a data storage processing data in a powerful way. It even acts as an access point to human interface for human interaction, and is capable of broadcasting control data in the network or removes data from it. The base station node will calculate and send the even source, its position and a timestamp to the analysis centre. If an alert is received by the base station regarding a target, an identity of the target will be allocated allowing all related alerts getting appropriate management.

Every sensor within the network primarily consists of a certain amount of power and a base station that provides entrance to other networks or to the centre analysis. It is important to know that base stations have significant features over other nodes in the network. They comprise of adequate battery power to exceed the existence time of all sensor nodes, and have the capacity to save cryptographic keys, well-built processors and resources to commune with external networks. In contrast to the base stations, in a sensor network a large number of sensor nodes are connected together with radio frequency communication links, giving much significance to broadcasting in the network. Protocol procedure plays a vital role. Although they have concerns with trust assumptions, energy usage is decreased when using these protocols. The main purpose of these nodes is to gather information or events occurring from their targets.

The main functions associated with sensor nodes include: collecting information on the target with consideration to their nature and positioning, which involves the communication from nodes to base stations regarding for example sensor readings and particular alerts. Nodes should be capable of producing real-time events on detected targets using the base station node to forward an even transmission to a centre for the event to be analyzed. Base stations may request updates from sensor nodes, resulting in base station to node communication. Finally the generated events will be relayed to the base station from the sensor nodes. In this part of the communication architecture, base stations contact all of the nodes it is assigned for purposes such as routing beacons or reprogramming of the complete network. 

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