Scalability in Wireless Sensor Network In the guidance ofDr Alok Nath Deemail@example.com By:- ANJANI SHANKAR TIWARI(2010JTM2385) SHASHI MANGAL (2010JTM2391)
For hardware scalability involves sensitivity and range of MEMS sensors, communication bandwidth of the radio, and power usage. The software issues include reliability of command dissemination and data transfer, management of large volume of data, and scalable algorithms for analysing the data. There are tradeoffs between the Larger numbers of nodes means increased management complexity, as well as a more complex programming model
Single Hop-single-hop networks are spatially limited by the radio range and cannot span long distances without a large power supply. Multi Hop-Multihop communication is the transfer of data and commands between two nodes that are not in the direct radio range, using intermediary nodes . Thus required less energy by a node to send data. Multihop communication is essential for scalability of low-power wireless sensor networks but at the cost of more complex routing protocols.
Routing protocols for flat WSNs1.Flooding and Gossiping2.SPIN(Sensor Protocol for Information via Negotiation)3.SAR(Sequential Assignment Routing)
LEACH(Low Energy Adaptive Clustering Hierarchy) PEGAGIS(Power-Efficient Gathering in Sensor Information Systems) TEEN (Threshold-Sensitive Energy Efficient Sensor Network Protocol)
Clustered Topology : It is more suitable to ensure scalability. In a clustered sensor network, all the nodes are organized into a hierarchy based on some clustering algorithm. In each cluster, one node is selected to act as the cluster head (CH) and collecting all the information sensed by the cluster, aggregating data and reporting to a base station. All the other sensor nodes only need to contact with their cluster head. For cluster headers, their power should be exhausted much faster so Clustering algorithms in the former usually adopt rotation of cluster heads for load balance while in the latter use fixed cluster heads.
LEACH (Low Energy Adaptive Clustering Hierarchy):- It is a hierarchical clustering-based algorithm, which includes distributed cluster formation. The main idea is to form clusters of the sensor nodes based on the received signal strength and use local cluster heads as router to the sink. LEACH uses a CDMA-TDMA hybrid communication scheme. Each cluster has unique spreading code that can minimize interference between clusters and every cluster head set up a TDMA schedule for collision-free intra-cluster communication. They use power control to set the amount of transmit power based on the distance to their cluster heads and turn off radios until their allocated transmission time. At the end of each frame, the cluster heads perform data aggregation, which can achieve considerable energy saving, and forward the aggregated data to the base station.
Drawback:- Variable number of clusters produced in each round Uneven size of clusters The cluster head far away from base station will exhaust its energy quickly LEACH does not allocate time slots to cluster heads. Hence, when cluster head transmit the aggregated data to base station and at the same time data collected by one of its members arrive, collision will happen.
In LEACH there is single-hop communication between cluster head and the base station . LEACH uses CSMA for cluster head to transmit the aggregated data, in which collision is inevitable. In EMCA we use Multihop communication from cluster heads to cluster heads and on to the base station. Time-line of EMCA is the same as LEACH, however the operation in it is different. The set-up phase is divided into four parts:- a) Cluster-formation subphase, b) Routing-establishment subphase, c) TDMA-schedule subphase and d) Synchronization subphase.
Total energy consumption for each round of sensing and transfer is =Where: -ʎ(=0.01) is poisson intensity for Randomly distributedsensor node with square area of side M; -An l bit(=500bit) packet is transmitted distance at r; -Eelec, (= 50nJ/bit)is the electronics energy; -εfs (= 10pJ/bit/m2.)is amplifier coefficient; -Probability of becoming a cluster head is p; -EDA(=5nJ/bit) be the energy consumption foraggregating one bit of data; The total energy LEACH spend in a frame is given by: