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.
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
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.
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.