1. On Efficient Clustering of Wireless Sensor Networks Mohamed Younis, Poonam Munshi, Gaurav Gupta, and Sameh M. Elsharkawy Dependability and Security in Sensor Networks and Systems (IEEE DSSNS 2006)

2. Outline 1. Introduction 2. Multi-Gateway Clustered Architecture 3. Multi-tier Sensor Network Architecture – Group Formation 4. Performance Assessment 5. Conclusions

3. 1. Introduction Sensor network be use to probe environment and generate reports Cluster-head aggregates and analyzes the sensed data

4. Signal processing and communication are the main consumers of energy Ideally able to communicate with the gateway through short-haul communication

5. Nodes are not reachable by cluster-head due to obstacle

6. Nodes lie outside the transmission range

7. Main objective is enable effective monitoring of sensors’ status to management Two clustering methodologies: – Multi-gateway clustering Architecture – Multi-tier Sensor Network Architecture

8. System Model transmitter and receiver transmit op-amp loss

9. 2. Multi-Gateway Clustered Architecture Increase sensor reachability and minimize sensor to cluster-head communication Two stages: – Bootstrapping – Clustering

10. 2-1 Bootstrapping Cluster-heads broadcast a message （ probe ） to reveal their identity and location In reply the sensors broadcast a message （ heartbeat ） indicating their location and energy reserve Each node discovered included in a range set （ RSet ）

11. Each cluster-head constructs a range set of all the nodes that can communicate with it Cluster -head

12. Associated with a communication cost CSj-Gi Each cluster-head record all the nodes in its RSet and their cost Cluster exchanged all the cluster-heads to gain global knowledge

13. Cluster-heads construct set called exclusive set （ ESet ） which sensor nodes communicate a single cluster-head Cluster -head

14. The global exclusive set （ ESet ） is the union of all the cluster-heads’ exclusive sets

15. 2-2 Clustering The nodes in the NESet are allocated to their respective cluster-heads Select the minimal communication cost Cluster -head

16. 3. Multi-tier Sensor Network Architecture Propagation of radio signals weak: – Terrain – High level of signal interference Cluster-head can reach all deployed sensors in at most 2 hops Pick some 'agent‘ nodes act as communication hops

17. A group can have only the agent 1-hop

18. Respectively can and cannot directly receive messages from cluster-head Cluster-head establishes the attributes for every sensor: – Cluster-head-link-status – Neighbor-list (group-list) – Hop-list

19. 3.1 Group Formation Mainly for ensuring SUR can connect with cluster-head AgentID ： identify the agent node

20. Group formation Step 1: – Cluster-head calculates the Hop-list of sensors by picking SR and SUR be sorted ascending order Step 2: – Assign an agent starting with lowest cardinality of the hop-list

21. An agent sensor Si in SR for every sensor Sj ∈ SUR J I agentId(j)=i group-list(i)=j

22. J

23. The node of assignment cost:

24. A B C lBl=1 lAl=2 lCl=1

25. 4. Performance Assessment Experiments’ environment: 1000m ×1000 m Cluster-head is randomly positioned Cluster-head transmission range: 500 m Sensors transmission range: 50 m Values a1 and a2 are 0.6 and 0.4 Channel capacity set to 2Mbps

26. Comparison with multi-gateway architecture by varying the number of sensors

27. Comparison with multi-gateway architecture by the probability of links failure

28. 5. Conclusions Two methods achieving high node reachability Mixture of both approaches can achieve both efficient and flexible setup Future work – Optimal placement of the gateways – Different network clustering methods on the network’s energy consumption rate – life span of the different types of nodes