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A seminar report on data aggregation in wireless sensor networks



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  • 2. MANAGEMENT STUDIES, CHITTOOR-517127 DEC-2012S NO. TITLE PAGE NO.1 Introduction 52 Goal & Problem Definition in Data Aggregation 7 TABLE OF CONTENTS3 Data Aggregation: An Overview 8 3.1 In-Network Aggregation 3.2 Tree-Based Approach 3.3 Cluster-Based Approach 3.4 Multi-path Approach4 Query Processing 15 4.1 Query Models 4.2 Query Language in Tiny DB 4.3 Queries and Aggregates5 Simulation and Experimental Analysis 206 Security Challenges 257 Advantages and Disadvantages 298 Future Scope &Applications 30 2
  • 3. 9 Conclusion 3110 References 32 ABSTRACTSensor networks are collection of sensor nodes which co-operatively send sensed data tobase station. As sensor nodes are battery driven, an efficient utilization of power is essential inorder to use networks for long duration hence it is needed to reduce data traffic inside sensornetworks, reduce amount of data that need to send to base station. The main goal of dataaggregation algorithms is to gather and aggregate data in an energy efficient manner so thatnetwork lifetime is enhanced. Wireless sensor networks (WSN) offer an increasingly Sensornodes need less power for processing as compared to transmitting data. It is preferable to do innetwork processing inside network and reduce packet size. One such approach is dataaggregation which attractive method of data gathering in distributed system architectures anddynamic access via wireless connectivity.Wireless sensor networks have limited computational power and limited memory and batterypower, this leads to increased complexity for application developers and often results inapplications that are closely coupled with network protocols. In this paper, a data aggregationframework on wireless sensor networks is presented. The framework works as a middleware foraggregating data measured by a number of nodes within a network.The aim of the proposed work is to compare the performance of TAG in terms of energyefficiency in comparison with and without data aggregation in wireless sensor networks and toassess the suitability of the protocol in an environment where resources are limited. 3
  • 4. 1. INTRODUCTIONSensor Networks:The wireless sensor network is ad-hoc network. It consists small light weighted wireless nodescalled sensor nodes, deployed in physical or environmental condition. And it measured physicalparameters such as sound, pressure, temperature, and humidity. These sensor nodes deployed inlarge or thousand numbers and collaborate to form an ad hoc network capable of reporting todata collection sink (base station). Wireless sensor network have various applications like habitatmonitoring, building monitoring, health monitoring, military survivallance and target tracking.However wireless sensor network is a resource constraint if we talk about energy, computation,memory and limited communication capabilities. All sensor nodes in the wireless sensor networkare interact with each other or by intermediate sensor nodes.With advance in technology, sensor networks composed of small and cost effective sensingdevices equipped with wireless radio transceiver for environment monitoring have becomefeasible. The key advantage of using these small devices to monitor the environment is that itdoes not require infrastructure such as electric mains for power supply and wired lines forInternet connections to collect data, nor need human interaction while deploying. These sensornodes can monitor the environment by collecting information from their surroundings,and workcooperatively to send the data to a base station, or sink, for analysis. 4
  • 5. Figure 1 Architecture of the Sensor networkA sensor nodes that generates data, based on its sensing mechanisms observation and transmitsensed data packet to the base station (sink). This process basically direct transmission since thebase station may located very far away from sensor nodes needs. More energy to transmit dataover long distances so that a better technique is to have fewer nodes send data to the basestation.These nodes called aggregator nodes and processes called data aggregation in wireless sensornetwork. 5
  • 6. 2. GOALS AND PROBLEM DEFINITIONGOAL:The main goal of data aggregation algorithms is to gather and aggregate data in an energyefficient manner so that network lifetime is enhanced. Wireless sensor networks (WSN) offer anincreasingly attractive method of data gathering in distributed system architectures and dynamicaccess via wireless connectivity.PROBLEM DEFINITION:Data aggregation protocols aims at eliminating redundant data transmission and thus improve thelifetime of energy constrained wireless sensor network. In wireless sensor network, datatransmission took place in multi-hop fashion where each node forwards its data to the neighbornode which is nearer to sink. Since closely placed nodes may sense same data, above approachcannot be considered as energy efficient. An improvement over the above approach would beclustering where each node sends data to cluster-head (CH) and then cluster-head performaggregation on the received raw data and then send it to sink. Performing ag homogeneoussensor network cluster-head will soon die out and again re-clustering has to be done which againcause energy consumption. 6
  • 7. 3. DATA AGGREGATION:AN OVERVIEWData aggregation is a process of aggregating the sensor data using aggregation approaches. Thegeneral data aggregation algorithm works as shown in the below figure. The algorithm uses thesensor data from the sensor node and then aggregates the data by using some aggregationalgorithms such as centralized approach, LEACH(low energy adaptive clusteringhierarchy),TAG(Tiny Aggregation) etc. This aggregated data is transfer to the sink node byselecting the efficient path 7
  • 8. Fig:General architure of algorithm3.1 In-Network Aggregation:In-network aggregation is the global process of gathering and routing information through amulti-hop network, processing data at intermediate nodes with the objective of reducing resourceconsumption (in particular energy), thereby increasing network lifetime. There are two approaches for in-network aggregation: 1) with size reduction 2) without size reduction.With size reduction: In-network aggregation with size reduction refers to the process of combiningand compressing the data packets received by a node from its neighbors in order to reduce thepacket length to be transmitted or forwarded towards sinkWithout size reduction:In-network aggregation without size reduction refers to the process merging data packetsreceived from different neighbors in to a single data packet but without processing the value ofdata. 8
  • 9. 3.2 Tree Based Approach:The tree based approach is defining aggregation from constructing an aggregation tree. The formof tree is minimum spanning tree, sink node consider as a root and source node consider as aleaves. Information flowing of data start from leaves node up to root means sink(basestation).Disadvantage of this approach, as we know like wireless sensor network are not freefrom failure .in case of data packet loss at any level of tree, the data will be lost not only forsingle level but for whole related sub tree as well.This approach is suitable for designing optimalaggregation techniques data centric protocol know as Tiny aggregation (TAG) approach. Fig:Tree-based aggregation in wireless sensor networks 9
  • 10. The working of TAG is depending on two phases: 1) distributed phase 2) collection phaseDistributed Phase:In distributedphase, in which aggregate queries are pushed down into the network.Collection Phase:A collectionphase, where the aggregate values are continually routed up from children to parents.Recall that our query semantics partition time into epochs of duration ,and that we must producea single aggregate value (when not grouping) that combines the readings of all devices in thenetwork during that epoch. 10
  • 11. 3.3 Cluster-Based Approach:In energy-constrained sensor networks of large size, it is inefficient for sensors to transmit thedata directly to the sink In such scenarios, Cluster based approach is hierarchical approach. Incluster-based approach, whole network is divided in to several clusters. Each cluster has acluster-head which is selected among cluster members. Cluster-heads do the role of aggregatorwhich aggregate data received from cluster members locally and then transmit the result to basestation (sink). Recently, several cluster-based network organization and data-aggregationprotocols have been proposed for the wireless sensor network. Fig:Cluster Based sensor networks.Arrow indicates wireless communication links 11
  • 12. The cluster heads can communicate with the sink directly via long range transmissions or multihopping through other cluster heads.K. Dasgupta in proposed a maximum lifetimedata aggregation (MLDA) algorithm which findsdatagathering schedule provided location of sensors node andbase-station, data packet size, andenergy of each sensornode. A data gathering schedule specifies how data packetare collectedfrom sensors node and transmitted to basestation for each round. A schedule can be thought of asacollection of aggregation trees. They proposedheuristic-greedy clustering-based MLDA basedon MLDAalgorithm. In this they partitioned the network in to clusterand referred each cluster assuper-sensor. They thencompute maximum lifetime schedule for the super-sensorsand then usethis schedule to construct aggregation treesfor the sensors. W. Choi et present a two-phaseclustering (TPC) scheme. Phase I of this scheme createsclusters with a cluster-head andeach node within thatcluster form a direct connects with cluster-head. Phase I thecluster-headrotation is localized and is done based on the remaining energy level of the sensor nodes whichminimizetime variance of sensors and this lead to energy savingfrom unnecessary cluster-headrotation. In phase II, eachnode within the cluster searches for a neighbor closer thancluster-headwhich is called data relay point and setup up adata relay link.Now the sensor nodes within a clustereither use direct link or data relay link to send their datatocluster head which is an energy efficient scheme. The datarelay point aggregates data atforwarding time to another data relay point or cluster head. In case of high networkdensity, TPCphase II will setup unnecessary data relaylink between neighbors as closely deployed sensorwillsense same data and this lead to a waste of energy. 12