An Energy-Efficient Unequal Clustering Mechanism for Wireless Sensor Networks

1. An Energy-Efficient Unequal Clustering Mechanismfor 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. Outline • Introduction • The EEUC Mechanism • Simulation • Conclusions

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

6. Introduction --- LEACH BS Cluster header 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)

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

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

15. EEUC --- Unequal Clustering Algorithm • If Si becomes a tentative CH, Si has a competition range Rcomp • If Si becomes a CH at the end of the competition, there will not be another CH within Si ‘s competition diameter R4 S3 or S4 can be a CH R3 S4 S3 R1 R2 S1and S2 can be CHs S1 S2

16. EEUC --- Unequal Clustering Algorithm • The node’s Rcomp 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 Rcomp range d (si, BS) dmax : si.Rcomp= dmin : si.Rcomp=

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. Rj Rj Ri Ri Sj Sj Si Si EEUC --- Unequal Clustering Algorithm • Each tentative CH maintains a set SCHof its “adjacent” tentative CH • Tentative head sjis an “adjacent” node of si sjis in si’s competition diameter or si is in sj’s competition diameter

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

20. EEUC --- Unequal Clustering Algorithm A B C • If Areceives a FINAL_HEAD_MSG from B, A will give up the competition immediately • A informs all nodes in its SCHby broadcasting a QUIT_ELECTION_MSG

21. EEUC --- Unequal Clustering Algorithm A B C • C receives a QUIT_ELECTION_MSG form A • C will remove A from its SCH

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

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. Simulation

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

28. Simulation The first node dies The last node dies

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