1. 1 An Energy-Efficient Unequal Clustering Mechanism for Wireless Sensor Networks Chengfa Li, Mao Ye, Guihai Chen State Key Laboratory for Novel Software Technology Nanjing University Jie Wu Department of Computer Science and Engineering Florida Atlantic University MASS 2005 Speaker: Sheng-Wen Chang

2. 2 Outline Introduction The EEUC Mechanism Simulation Conclusions

3. 3 Introduction --- Background Clustering provides an effective way for prolong the lifetime of the WSNs Using equal size of clusters to balance traffic overhead

4. 4 Introduction --- Background Within a clustering organization Intra-cluster communication can be single-hop or multi-hop Inter-cluster communication Single-hop: LEACH Multi-hop: HEED (Infocom 2004)

5. 5 Introduction --- LEACH CHs farther away from the BS must transmit packets over long distances than those of CHs closer to the BS Cluster Head Cluster member BS

6. 6 Introduction --- LEACH M. Ye, C. Li, G. H. Chen, and J. Wu, "EECS: An Energy Efficient Clustering Scheme in Wireless Sensor Networks (International Journal of Ad Hoc & Sensor Wireless Networks, 2005) Cluster header BS

7. 7 Introduction --- HEED The initial probability for each node to become a tentative CH depends on its residual energy Final CHs are selected according to the cost Cluster Head Cluster member BS

8. 8 Introduction --- HEED The role of cluster head is usually periodically rotated among nodes Not balance the energy consumption among CHs Cluster Head Cluster member BS

9. 9 Introduction --- HEED Hop spots problem In each round, CHs closer to the BS are burdened with heavy relay traffic and tend to die early Cluster Head Cluster member BS

10. 10 Introduction --- Motivations and Goals Motivations Using unequal clustering mechanism to solve hot spot problem among CHs in each round Clusters closer to the BS have smaller sizes than those farther away form the BS Goals Balances the energy consumption Prolong network lifetime

11. 11 EEUC --- Assumptions Sensors uniformly deploy over a sensor field Sensors and a BS are all stationary Sensors can use power control A node can compute the approximate distance to another node Based on the received signal strength

12. 12 EEUC --- Overview CHs closer to the BS support smaller cluster sizes More clusters are produced closer to the BS

13. 13 EEUC --- Overview Unequal Clustering Algorithm CHs are selected by localized competition Inter-cluster Multi-hop Routing A CH chooses a relay CH Adjacent CH ’ s residual energy Its distance to the BS

14. 14 EEUC --- Unequal Clustering Algorithm The BS broadcasts a “ hello ” message to all nodes Each node computes the distance to the BS Several tentative CHs are selected to compete for final CHs

15. 15 EEUC --- Unequal Clustering Algorithm If S i becomes a tentative CH, S i has a competition range R comp If S i becomes a CH at the end of the competition, there will not be another CH within S i ‘s competition diameter S3S3 S4S4 R4R4 R3R3 S2S2 S1S1 R2R2 R1R1 S 1 and S 2 can be CHs S 3 or S 4 can be a CH

16. 16 EEUC --- Unequal Clustering Algorithm The node ’ s R comp should be decrease as its distance to the BS decreases is the maximum competition radius c is a constant coefficient between 0 and 1 and controls R comp range d (s i, BS) d max : s i.R comp = d min : s i.R comp =

17. 17 EEUC --- Unequal Clustering Algorithm The broadcast radius of every control message is Each tentative CH broadcasts a COMPETE_HEAD_MSG Competition radius Residual energy

18. 18 EEUC --- Unequal Clustering Algorithm Each tentative CH maintains a set S CH of its “adjacent” tentative CH Tentative head s j is an “adjacent” node of s i SiSi SjSj RjRj RiRi SjSj SiSi RjRj RiRi s j is in s i ’s competition diameter or s i is in s j ’s competition diameter

19. 19 EEUC --- Unequal Clustering Algorithm Each tentative CH checks its S CH and makes a decision whether it can the final CH S i ’s residual energy is more than all the nodes in its S CH It will win the competition Broadcast a FINAL_HEAD_MSG to inform its adjacent tentative CHs

20. 20 EEUC --- Unequal Clustering Algorithm AB If A receives a FINAL_HEAD_MSG from B, A will give up the competition immediately A informs all nodes in its S CH by broadcasting a QUIT_ELECTION_MSG C

21. 21 EEUC --- Unequal Clustering Algorithm AB C receives a QUIT_ELECTION_MSG form A C will remove A from its S CH C

22. 22 EEUC --- Unequal Clustering Algorithm Each CH broadcasts a CH_ADV_MSG across the network area Node ID Residual energy Distance to the BS Each ordinary node joins its closest CH

23. 23 EEUC --- Inter-cluster Multi-hop Routing A threshold TD_MAX into our multi-hop forwarding model If a CH ’ s distance to the BS is smaller than TD_MAX It transmits its data to the BS directly

24. 24 EEUC --- Inter-cluster Multi-hop Routing A CH chooses a node to forwarding its data from its candidate set R CH More residual energy Smallest distance between the CH and the Relay

25. 25 Simulation Network coverage: (0,0)~(200,200)m BS location: (100,250)m Number of nodes: 400 : 90m c=0.5 TD_MAX=150m

26. 26 Simulation

27. 27 Simulation Too many clusters will be produced closer to the BS

28. 28 Simulation The first node dies The last node dies

29. 29 Conclusions Propose a novel energy-efficient clustering mechanism for WSNs The hot spots problem between CHs is solved The EEUC mechanism improves the lifetime over LEACH and HEED