Sensor node: Difference between revisions

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{{primary sources|date=February 2015}}

[[Image:Sensornode.svg|thumb|300px|The typical [[Computer architecture|architecture]] of the sensor node.]]

A '''sensor node''' (also known as a '''mote''' in [[North America]]), consists of an individual [[Node (networking)|node]] from a [[sensor network]] that is capable of performing a desired action such as gathering, processing or communicating information with other connected nodes in a network.

==History==

<!-- Image with unknown copyright status removed: [[Image:MICAz.jpg|thumb|200px|MicaZ Commerical Sensor node from CrossBow Technologies]] -->Although [[Wireless Sensor Networks|wireless sensor networks]] have existed for decades and used for diverse applications such as earthquake measurements or warfare, the modern development of small sensor nodes dates back to the 1998 [[Smartdust]] project<ref>[http://robotics.eecs.berkeley.edu/~pister/SmartDust/ Smart Dust<!-- Bot generated title -->]</ref> and the NASA. [[Sensor Web]]<ref>[http://www.techbriefs.com/content/view/2227/32/ NASA Tech Brief]</ref> One of the objectives of the [[Smartdust]] project was to create autonomous sensing and communication within a cubic millimeter of space, though this project ended early on, it led to many more research projects and major research centres such as The Berkeley NEST<ref>[http://webs.cs.berkeley.edu/ Home<!-- Bot generated title -->] {{webarchive|url=https://web.archive.org/web/20011110031435/http://webs.cs.berkeley.edu/ |date=2001-11-10 }}</ref> and CENS.<ref>[http://research.cens.ucla.edu/ CENS: Center for Embedded Networked Sensing<!-- Bot generated title -->] {{webarchive|url=http://webarchive.loc.gov/all/20090407035705/http://research.cens.ucla.edu/ |date=2009-04-07 }}</ref> The researchers involved in these projects coined the term ''mote'' to refer to a sensor node. The equivalent term in the NASA Sensor Webs Project for a physical sensor node is ''pod'', although the sensor node in a Sensor Web can be another Sensor Web itself. Physical sensor nodes have been able to increase their effectiveness and it'sits capability in conjunction with [[Moore's Law]].

The chip footprint contains more complex and lower powered [[microcontrollers]]. Thus, for the same node footprint, more silicon capability can be packed into it. Nowadays, motes focus on providing the longest wireless range (dozens of km), the lowest energy consumption (a few uA) and the easiest development process for the user.<ref>[http://www.sensor-networks.org/index.php?page=0932832814 "Waspmote: a modern mote"]</ref>

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===Controller===

The controller performs tasks , processes data and controls the functionality of other components in the sensor node. While the most common controller is a [[microcontroller]], other alternatives that can be used as a controller are: a general purpose [[Desktop computer|desktop]] [[microprocessor]], [[digital signal processors]], [[Field Programmable Gate Array|FPGAs]] and [[Application-specific integrated circuit|ASICs]]. A microcontroller is often used in many [[embedded systems|sensor nodes]] due to it'sits low cost, flexibility to connect to other devices (or nodes in a network), ease of programming, and low power consumption. A general purpose microprocessor generally has a higher power consumption than a microcontroller, making it an undesirable choice for a sensor node.{{Citation needed|date=September 2010}} Digital Signal Processors may be chosen for broadband [[wireless communication]] applications, but in [[Wireless Sensor Networks]] the wireless communication is often modest: i.e., simpler, easier to process [[modulation]] and the [[signal processing]] tasks of actual sensing of data is less complicated. Therefore, the advantages of DSPs are not usually of much importance to wireless sensor nodes. FPGAs can be reprogrammed and reconfigured according to requirements, but this takes more time and energy than desired.{{Citation needed|date=September 2010}}

'''Transceiver'''

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===Power source===

A wireless sensor node is a popular solution when it is difficult or impossible to run a mains supply to the sensor node. However, since the wireless sensor node is often placed in a hard-to-reach ___location, changing the battery regularly can be costly and inconvenient. An important aspect in the development of a wireless sensor node is ensuring that there is always adequate energy available to power the system.

The sensor node [[Power consumption|consumes power]] for sensing, communicating and data processing. More energy is required for [[data communication]] than any other process. The energy cost of transmitting 1 Kb a distance of {{convert|100|m|ft}} is approximately the same as that used for the execution of 3 million instructions by a 100 million instructions per second/W processor.{{citation needed|date=March 2020}} Power is stored either in batteries or capacitors. Batteries, both rechargeable and non-rechargeable, are the main source of power supply for sensor nodes. They are also classified according to electrochemical material used for the electrodes such as [[Nickel-cadmium battery|NiCd]] (nickel-cadmium), [[Nickel-zinc battery|NiZn]] (nickel-zinc), [[Nickel-metal hydride battery|NiMH]] (nickel-metal hydride), and [[Lithium-ion battery|lithium-ion]].

Current sensors are able to renew their energy from [[Solar energy|solar]] sources, Radio Frequency(RF), [[Thermogenerator|temperature]] differences, or [[Vibration powered generator|vibration]]. Two power saving policies used are [[Dynamic Power Management]] (DPM) and [[Dynamic Voltage Scaling]] (DVS).<ref>Dynamic Power Management in Wireless Sensor Networks, Amit Sinha and Anantha Chandrakasan, IEEE Design & Test of Computers, Vol. 18, No. 2, March–April 2001</ref> DPM conserves power by shutting down parts of the sensor node which are not currently used or active. A DVS scheme varies the power levels within the sensor node depending on the non-deterministic workload. By varying the voltage along with the frequency, it is possible to obtain quadratic reduction in power consumption.

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{{Wireless Sensor Network}}

{{DEFAULTSORT:Sensor Node}}

[[Category:Wireless sensor network]]