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Leach & Pegasis



The LEACH & PEGASIS are the Protocols.

The LEACH & PEGASIS are the Protocols.



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Leach & Pegasis Leach & Pegasis Presentation Transcript

  • LEACH & PEGASIS PROTOCOLBy: Reena Shekar III MCA Mangalore University
  • LEACH Is a clustering based protocol to collect data from wireless network. In the network, hundreds and thousands of wireless sensors are dispersed that collects and transmit data. Also in these networks cluster heads are elected out of the sensors to transmit the data collected to base station.
  •  LEACH includes distributed cluster formation, local processing to reduce global communication, and randomized rotation of the cluster -heads. LEACH performs local data fusion to “compress” the amount of data being sent from the clusters to the base station. further reducing energy dissipation and enhancing system lifetime.
  • LEACH Network
  • The Cluster Head The LEACH Network is made up of nodes, some of which are called cluster-heads  The job of the cluster-head is to collect data from their surrounding nodes and pass it on to the base station  LEACH is dynamic because the job of cluster- head rotates
  • Existing Routing Protocols LEACH is compared against three other routing protocols:  Direct-Transmission  Single-hop  Minimum-Transmission Energy  Multi-hop  Static Clustering  Multi-hop
  • Direct-Transmission Each sensor node transmits directly to the sink, regardless of distance. Most efficient when there is a small coverage area and/or high receive cost.
  • Minimum Transmission Energy (MTE) Traffic is routed through intermediate nodes  Node chosen by transmit amplifier cost  Receive cost often ignored Most efficient when the average transmission distance is large.
  • Static Clustering Indirect upstream traffic routing Cluster members transmit to a cluster head  TDMA Cluster head transmits to the sink  Not energy-limited Does not apply to homogenous environments
  • Network Diameter LEACH vs. Direct Transmission  7x-8x energy reduction LEACH vs. MTE  4x-8x energy reduction
  • Energy and Diameter
  • LEACH’s Two Phases The LEACH network has two phases: the set-up phase and the steady-state  The Set-Up Phase  Where cluster-heads are chosen  The Steady-State  The cluster-head is maintained  When data is transmitted between nodes
  • The key featuresof LEACH are: Localized coordination and control for cluster set- up and operation. Randomized rotation of the cluster “base stations” or “cluster-heads” and the corresponding clusters. Local compression to reduce global communication.
  • An Example for LEACH Network While neither of these diagrams is the optimum scenario, the second is better because the cluster-heads are spaced out and the network is more properly sectioned
  • Future Work Extend ns to simulate LEACH, MTE, and Direct Transmission Include energy levels in self-election Implement hierarchical clustering
  • PEGASIS PEGASIS is the improved protocol where only one node is chosen a head node which sends the fused data to the BS per round. This achieves factor of 2 improvement compared to LEACH protocol It a near optimal chain-based protocol that is an improvement over LEACH. In PEGASIS, each node communicates only with a close neighbor and takes turns transmitting to the base station.
  •  PEGASIS performs better than LEACH. In sensor networks, data fusion helps to reduce the amount of data transmitted between sensor nodes and the BS. Data fusion combines one or more data packets from different sensor measurements to produce a single packet. The key idea in PEGASIS is to form a chain among the sensor nodes so that each node will receive from and transmit to a close neighbor.
  •  Gathered data moves from node to node, get fused, and eventually a designated node transmits to the BS. The PEGASIS protocol achieves between 100 to 300% improvement when 1%, 20%,50% and 100% of nodes node die compared to the LEACH protocol.
  • Step one in PEGASIS Protocol Chain construction: To construct the chain we start from the furthest node from the Base Station (BS), and then greedy approach is used to construct the chain.
  • Step two in PEGASIS Protocol Gathering data: Leader of each round is selected randomly. If N is number of nodes i mod N node is selected as head node for i round. Randomly selecting head node also provides benefit as it is more likely for nodes to die at random locations thus providing robust network. When a node dies chain is reconstructed to bypass the dead node. Head node receives all the fused data and sends to the BS.
  • PAGASIS Network
  • Advantages and DisadvantagesAdvantages of PEGASIS over LEACH: Compare to LEACH transmitting distance for most of the node reduces in PEGASIS. Messages received by each head node are at most 2 in PEGASIS is less compared to LEACH. Experimental results show that PEGASIS provides improvement by factor 2 compared to LEACH protocol for 50m * 50m network and improvement by factor 3 for 100m * 100m network. Since each node gets selected once, energy dissipation is balanced among sensor nodes.
  • Drawbacks of the PEGASIS protocol: When a head node is selected, there is consideration how far the BS is located from the head node. When a head node is selected its energy level is not considered. Since there is only one node head, it may be the bottle neck of the network causing delay. Redundant transmission of data as only one head node is selected.
  • Performance results for a 100m x 100m network with initial energy .5J/node
  • Performance results for a 50m x 50m network with initial energy .25J/node
  • Conclusions and Future Work PEGASIS, a greedy chain protocol that is near optimal for a data-gathering problem in sensor networks. PEGASIS outperforms LEACH by eliminating the overhead of dynamic cluster formation, minimizing the distance non leader-nodes must transmit,limiting the number of transmissions and receives among all nodes, and using only one transmission to the BS per round.
  •  In order to verify our assumptions about PEGASIS, we will extend the network simulator ns-2 to simulate PEGASIS, LEACH, and direct transmission protocols. Based on our C simulations, we expect that PEGASIS will outperform the other two protocols in terms of system lifetime and the quality of the network.