Wireless sensor network

Published on June 2016 | Categories: Types, Books - Non-fiction | Downloads: 37 | Comments: 0 | Views: 333
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Recent Research trends in WSN Sensor nodes have finite resources such as memory, power, communication range etc. Memory: Improvising the memory requires cheap hardware. Since leading hardware companies are producing a range of sensors Communication range: In recent days a collection of sensor nodes are being deployed in a distributed area. Even though each sensor has limited communication range, a group of sensors can operate together to sense a particular environment. Power: Considerable research has been focused at overcoming these deficiencies through more energy efficient routing, localization algorithms and system design. Challenges in WSN: The unique challenges of "i# "ii# $d%hoc deployment &n%attended operation S! include

"iii# &ntethered Thus, unli'e traditional networ's, where the focus is on ma(imizing channel throughput or minimizing node deployment, the ma)or consideration in a sensor networ' is to e(tend the system lifetime as well as the system robustness. Major Research trends: [1]Reducing Energy consumption and hence reducing power: The power consumed by the sensor nodes can be reduced by developing design methodologies and architectures

which help in energy aware design of sensor networ's. The lifetime of a sensor networ' can be increased significantly if the operating system, the application layer and the networ' protocols are designed to be energy aware. *+, -ower management in radios is very important because radio communication consumes a lot of energy during operation of the system. $nother aspect of sensor nodes is that a sensor node also acts a router and a ma)ority of the pac'ets which the sensor receives are meant to be forwarded. Intelligent radio hardware that help in identifying and redirecting pac'ets which need to be forwarded and in the process reduce the computing overhead because the pac'ets are no longer processed in the intermediate nodes. *., $ path should not be used continuously to forward pac'ets regardless of how much energy is saved because this depletes the energy of the nodes on this path and there is a breach in the connectivity of the networ'. It is better that the load of the traffic be distributed more uniformly throughout the networ'. [2] Localization: In sensor networ's, nodes are deployed into an unplanned infrastructure where there is no a prior 'nowledge of location. The problem of estimating spatial%coordinates of the node is referred to as localization. *+, $n immediate solution to localization, is /-S or the /lobal -ositioning System. 0owever, there are some strong factors against the usage of /-S. 1or one, /-S can wor' only outdoors. Secondly, /-S receivers are e(pensive and not suitable in the construction of small cheap sensor nodes. $ third factor is that it cannot wor' in the presence of any obstruction li'e dense foliage etc. Thus, sensor nodes would need to have other means of establishing their positions and organizing themselves into a coordinate system without relying on an e(isting infrastructure. *., The currently deployed technique for localization is pro(imity based localization, where a sin' or base station 'nows their

position and beacons are forwarded among sensor nodes to organize themselves. *2, 3ther research trends are using signal strength and signal pattern matching. 4ut these techniques require e(pensive hardware. [3] ode placement techni!ues: 1. Random: $ny random location is chosen as a suitable candidate. 2. Max: In this case, the terrain is divided into step5step squares. The localization error is calculated at each square corner. $ beacon is added at the point which has the ma(imum localization error. Even though this approach is simple, it suffers from being overly influenced by propagation effects or random noises. 3. Grid: The /rid approach computes the cumulative localization error over each grid for several overlapping grids. $ new beacon is added at the center of the grid which has the ma(imum cumulative localization error. ["] Routing: Conventional 6outing protocols deploy flooding techniques. There are two disadvantages in this approach m!losion7 If a node is a common neighbor to nodes holding the same data item, then it will get multiple copies of the same data item. Therefore, the protocol wastes resources sending the data item and receiving it. Reso"rce management7 In conventional flooding, nodes are not resource%aware. They continue with their activities regardless of the energy available to them at a given time. 8any protocols such as S%8ac, directed diffusion, rumour based routing etc are deployed and more energy efficient protocols are needed. [#] $ime synchronization: Sensor networ' applications require collaborative e(ecution of a distributed tas' among a large set of sensor nodes.

Time synchronization is critical in sensor networ's for diverse purposes including 9The cloc's in a sensor networ' can be inconsistent due to several reasons. 9:esign issues of synchronization algorithm [%] &esign 'actors: • 1ault Tolerence • Scalability • Cost • -ower consumption #a"lt $olerance7 In sensors networ's, hundreds, and in the e(treme, hundreds of thousands of sensors are deployed in a large geographical area. In some cases dropped from airplanes, or deployed using artillery shells.6equiring that every node must wor' in order for the networ' to operate is impossible to achieve. The networ' must have a high level of fault tolerance in order to be of any practical value *++,. Scala%ilit&7 $s we mentioned above, sensor sensor networ's may include from tens to hundreds of thousands of sensors. Some times new nodes are added to the networ' after some nodes power supplies are completely e(hausted. That results in a variable number of nodes. The protocols used in the networ's must be scalable in order to survive under these circumstances. Cost7 because of the large number of nodes required,as well as the fact that in most networ's the nodes are disposable "wor' until they drain off their power supply,then, then they are disposed of#. The cost is a very important design factor for sensor networ's. 0aving a low cost for sensor nodes is a must. 'o(er cons"m!tion7 -ower consumption is the most important design factor for sensor networ's. power could be saved at the medium access control, and networ' level protocol. 8inimizing the number of collisions or the path length results also in energy saving. Transmission and reception of radio signal is another candidate for power minimization. Short distance transmission and simple circuitry for modulation;demodulation results in power saving.

Sensor Management and )os ss"es: $fter the sensor networ' is deployed in an unpredictable environment, a high%level management protocol can help notify users of resource depletion or abnormal activities.<imited energy and bandwidth resources in sensor networ's ma'e e(tracting states from each individual node infeasible. Estrin et al. *=>, have proposed an in%networ' aggregation approach of networ' states to construct abstracted scans of sensor networ' health. The ob)ective is to build an efficient monitoring infrastructure for sensor networ's, where the scans describe the geographical distribution of networ' resources or activity of a sensor filed. &sing application%level 'nowledge to optimize the networ' protocol is another goal of sensor management protocols. $pplication layer management protocols aim at seamlessly integrating sensor networ's with the Internet. Importance of supporting ?oS for sensor networ's is also gradually being realized in order to have the fle(ibility of discriminating among the type of data that the sensors are reporting . -riority%based data handling is used to reduce the reporting delay and increase the chance of reception of crucial sensor data.

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