1. Globecom 2004 Energy-Efficient Self-Organization for Wireless Sensor Networks: A Fully Distributed approach Liang Zhao, Xiang Hong, Qilian Liang Department of Electrical Engineering University of Texas at Arlington

2. Globecom 2004 Outline Introduction to Cluster-based Sensor Networks LEACH Protocol Review Problem Formulation Expellant Self-Organization Scheme Simulation Conclusion

3. Cluster-based Sensor networks(1/2) Homogeneous versus Heterogeneous Single hop versus Multi-hop BS Advantage: Robust to node failures. Drawbacks: (1)High load on cluster head (2)The hardware has to support (a) long range transmissions (b) complex data computations (c) co-ordination of MAC (d) routing within a cluster. Advantage: Sensor nodes only requires simple hardware support. Drawbacks: (1)Less robust to node failure (2)Sensors far from cluster head have highest energy expenditure (3)Uniform clustering has to be considered. Single hop homogeneous networks Single hop heterogeneous networks BS

4. Cluster-based Sensor networks(2/2) BS Multi-hop homogeneous networksMulti-hop heterogeneous networks BS  Sensors near cluster head have highest energy expenditure Distance from cluster head Energy Single hop Multi hop [ Infocom04, Globecom04 ] [ 2 * Globecom04 ]

5. Globecom 2004 LEACH Protocol 1. Single hop homogeneous networks 2. Random cluster head rotation 3. Perfect data correlation model – All individual packets from members of the same cluster can be combined into a single representative packet.

6. LEACH Protocol In LEACH, each node i elects itself to be a head at the beginning of round r+1 with probability P i (t). (1) (a) C i (t) is the indicator function determining whether or not node i has been a head in the most recent (r mod ( N/c )) rounds. (b) c is the desired number of clusters

7. Globecom 2004 (2) E i (t) is the current energy of node i

8. Problem Formulation 1. N in (1) and E total in (2) are global information 2. Too few or too many cluster heads [  ][  ] 3. Non-uniform distribution of cluster heads

9. Random election (1) Suppose (2) All nodes have equal amount of energy, if N nodes want to elect c heads, then the self-electing probability for each node is [back]

10. Globecom 2004 Expellant Self-Organization Scheme Contribution: Turn the question about “how many clusters should the nodes be partitioned? “ into “What is the appropriate cluster size?”

11. [Example]

12. Expellant Self-Organization Scheme Example Step 1: Each node broadcasts vital information (energy, location,…etc) at cluster radius R c (R c is a predetermined system parameter) RcRc Step 2: Each node counts its neighbors and broadcasts the number of its neighbors at cluster radius R c 2 1 2 3 1 1 0 N is the set of neighbors B(i) is the number of neighbors of the ith neighbor r = 0.8 in this paper Step 3: Each node decides to become cluster head according to its potential and broadcast its claim ( Using random back-off to avoid collision) Potential:

13. Globecom 2004 Expellant Self-Organization Scheme Step 4: Nodes sends “Joint” message to join the nearest cluster head 2 1 2 3 1 1 0 Step 5: Nodes that are outside the neighborhood of existing cluster head forces itself to be a cluster head “Joint” [back]

14. Globecom 2004 Simulation 100 nodes Each has 2J initial energy Evenly distributed in a circular region with diameter 100m Base station located at (125m, 0)

15. Radio Energy Dissipation Model

16. Optimal c (1/2)

17. Optimal c (2/2)

18. Globecom 2004 ESO versus LEACH (1/2)

19. Globecom 2004 ESO versus LEACH (2/2)