Sensor Node Essay

A sensor node is also known as a mote (mostly in North America). This sensor node in a wireless sensor network is capable of performing some processing, gathering of sensory information and communicating with other connected nodes in the network. It must be clearly understood that a mote is a node but a node is not always a mote. Although wireless sensor nodes have existed for decades and used for applications as diverse as earthquake measurements to even warfare, the latest development of small sensor nodes dates back to the 1998 Smartdust project[1] and the NASA Sensor Webs Project[1]. One of the objectives of the Smart dust project was to create autonomous sensing and communication within a cubic millimeter of space. Though this project

The main components of a sensor are radio transceiver or optical as the communication unit, sensor as the sensing unit, a micro-controller for the processing unit and battery or solsr cells as the power unit. Several sensors may be present in the hardware device in the sensing unit. This device produces measurable response to change which acts as an Interface between motes to the environment. Theses measurable changes are sound, motion, vibration, temperature, pollutants or the pressures in environmental conditions. There are mainly two kinds of sensor used in the network. First, is the normal sensor node deployed to accuraately sense the phenomena. The second is a gateway node that interfaces sensor network to the external world so that the sensed data could reach the user. Hence the whole mechanism of wireless sensor networks works on this principle. Many types of sensor exist now-a-days such as magnetometer, accelerometer, light and others but the types of sensor being used in a sensor node will depend on the application for which it is being deployed. The processing unit in the sensor architecture is responsible for the collecting and processing of the captured signal from the sensor unit. These signals are then transmitted to the network. It determines both energy consumption as well as computational capabilities of the sensor node. The power unit consisting of battery whose main function is

It is basically interested in receiving the data from other sensor nodes. It can be either part of the wireless sensor network or an external device such as a laptop or PDA. In general there is one base station, but depending on the application multiple base stations are possible in a network. Sensory information is communicated to the Base Station through Wireless hop by hop transmissions. Interaction patterns between the source and the sink includes the following:

Event Detection: If a certain event occurs, the sensor nodes report the measurement of this event to the interested sinks. This is known as Event detection in WSN.

Periodic measurement: Periodically reporting of events to interested sinks is necessary to get the latest data about the event. Tracking: This feature of the wireless sensor network reports the position of an observed intruder in the network.

As it can be gathered that most of the data in the sensor network will be directed toward the sink and this data conveyed will pass through many intermediate nodes before reaching the sink which is interested in the data.

Communicating data directly from the node to the sink will be very energy expensive, and also very expensive so multi hop communication is preferred in wireless sensor network.

Fig1.3: Basic example of a path from node to sink in