1. A Framework for Energy- Saving Data Gathering Using Two-Phase Clustering in Wireless Sensor Networks Wook Chio, Prateek Shah, and Sajal K. Das Center for Research in Wireless Mobility and Networking(CReWMaN) Department of Computer Science and Engineering University of Texas at Arlington IEEE MobiQuitous 2004 jenchi

2. Outline Introduction Related work Two-Phase Clustering Phase I ： Cluster Formation Phase II ： Cluster Restructuring Experimental Study Conclusion

3. Introduction A high-density wireless sensor network can be deployed for specific information-gathering Multiple sensors generating and transmitting redundant sensed data results in unnecessary power consumption Designing sensor data gather algorithms is to minimize the energy consumption for network longevity The network should be designed to seek local optimization which makes optimum use of the limited energy

4. Introduction Goal of this paper The clustering optimization problem To eliminate network-wide flooding for control information delivery To reduces the number of data transmissions with the help of its network hierarchy

5. Related work The methods of cluster schemes to elect a cluster head A self-declaration method A first-declaration-win rule Data packets are exploited using a piggy back technique ex: ： LEACH A nomination method Each node to nominate the largest indexed node in its radio range as a cluster head The above schemes don’t consider energy metric as a main factor in maintaining cluster configuration

6. Two-Phase Clustering We proposed a two phase clustering (TPC) scheme in multihop wireless sensor networks It is very likely for closely-located sensors to generate redundant sensed data Hence, data aggregation eliminates unnecessary data transmissions To provide an energy-saving delay-adaptive data gathering platform

7. Two-Phase Clustering Phase I ： Cluster Formation To partitioning the network into clusters Phase II ： Cluster Restructuring Cluster members are required to search for a neighbor closer than the cluster head within the same cluster to set up a data relay link To obtain further improvement on energy conservation by restructuring the intra-cluster node-connectivity

8. Two-Phase Clustering — Phase I ： Cluster Formation 1. Every node schedule a CH advertisement with t (0~x) sec. delay 3 10 76 15 9 12 5 11 8 4 5 13 Radius R Sensor node

9. Two-Phase Clustering — Phase I ： Cluster Formation Cluster member Direct link Cluster Head

10. Two-Phase Clustering — Phase I ： Cluster Formation Only one cluster head in a radio range To choose the nearest CH advertisement

11. Two-Phase Clustering — Phase II ： Cluster Restructuring To restructure the intra-cluster node- connectivity Every cluster member uses the data relay link instead of the direct link to send its sensed data to the cluster head Sensed data conveyed along these data relay links is aggregated at each data relay point

12. Two-Phase Clustering — Phase II ： Cluster Restructuring Purposes To minimize energy consumption in collecting sensed data while meeting delay constraints To distribute the cluster head’s workload The construction of the data relay links is launched by the cluster head’s request to search for a data relay point

13. Two-Phase Clustering — Phase II ： Cluster Restructuring Procedure for cluster head C i Mc i ： the member of C i Wc i ： have set up a data relay link : a data relay link from s i to s j with n-th forwarding index

14. Two-Phase Clustering — Phase II ： Cluster Restructuring Procedure for cluster members (s i ) of C i fix ： s i with forwarding index x rp s i ： a data relay point of s i

15. Two-Phase Clustering — Phase II ： Cluster Restructuring a Cluster member Direct link Cluster Head

16. Two-Phase Clustering — Phase II ： Cluster Restructuring a 1 Cluster member Direct link Cluster Head Data relay link

17. Two-Phase Clustering — Phase II ： Cluster Restructuring a 1 2 3 4 5 6 b Cluster member Direct link Cluster Head Data relay link

18. Two-Phase Clustering — Phase II ： Cluster Restructuring a 1 2 3 4 5 6 b 1 Cluster member Direct link Cluster Head Data relay link

19. Two-Phase Clustering — Phase II ： Cluster Restructuring a 1 2 3 4 5 6 1 b 2 3 4 5 6 Cluster member Direct link Cluster Head Data relay link

20. Two-Phase Clustering — Phase II ： Cluster Restructuring The choice of using either the data relay link or the direct link to transmit the sensed data is controlled by the cluster head The cluster head broadcasts an n-relay control message to all the cluster members Each cluster member calculates f ix mod n, if the result is zero ： to use the direct link otherwise ： to use the data relay link

21. Two-Phase Clustering — Phase II ： Cluster Restructuring The CSMA/CA is used The TPC allows cluster members to use a reduced transmission power by means of the data relay link (which is shorter than the direct link)

22. Two-Phase Clustering — Delay Adaptive Data Gathering

23. Two-Phase Clustering — Localized Cluster head Rotation The length of the time that sensors serve as a cluster head varies depending on the frequency of the sensed data transmission TPC limits the cluster head rotation to the local area, thereby saving on energy that would otherwise be consumed by unnecessary cluster head rotations

24. Two-Phase Clustering — Localized Cluster head Rotation a 1 2 3 4 5 6 1 b 2 3 4 5 6 CH broadcast Service Completion message ： SCc i

25. Two-Phase Clustering — Localized Cluster head Rotation Every cluster member schedules a CH advertisement with t sec. delay

26. a 1/3 1/2 1/37/15 3/10 1/6 2/7 3/7 2/3 4/7 1/5 1/20 Two-Phase Clustering — Localized Cluster head Rotation Delay t sec. : t←(Ei-Ec)/Ei Ei=initial energy Ec=current energy

27. a 1/3 1/2 1/37/15 3/10 1/6 2/7 3/7 2/3 4/7 1/5 1/20 Two-Phase Clustering — Localized Cluster head Rotation Delay t sec. : t←(Ei-Ec)/Ei Ei=initial energy Ec=current energy

28. Experimental Study To primarily study the effects of phase II on the energy-saving and the distribution of cluster head’s workload To present the results of the comparison of phase II to phase I The execution of phase I can be considered as the ones of LEACH in a multi-hop setting To conduct experiments using a JAVA thread-based implementation of TPC

29. Experimental Study Assumptions Homogeneous sensors 500 X 500 m 2 network space Transmission distance (sensor density) 1 sensor/200m 2, 1 sensor/300m 2, 1 sensor/400m 2, 1 sensor/500m 2 Energy consumption measurement ： 1 sensor/350m 2 Two communication radio ranges R=50m and 100m Data reporting interval ： 3 seconds Sensors are set to generate sensed data 1000 times Using radio electronics energy ： 50nJ/bit, radio amplifier energy ： 100 pJ/bit, and 512 bit-size sensed data packet A 5-relay control message to have five runs for each network density to collect the experiment result

30. Experimental Study Snapshot of an experimental result of two phase clustering with R=100m

31. Experimental Study — Effect on Transmission Distance The network density and the size of the radio range affect the transmission distance reduction radio

32. Experimental Study — Effect on Energy Saving and Cluster Head ’ s Workload To show the distribution of the remaining energy level in each sensor after 1000 rounds of sensed data transmission Relay constraint ： 5-relay

33. Experimental Study — Effect on Energy Saving and Cluster Head ’ s Workload

35. Conclusion The goal of the TPC scheme is to provide an energy-saving delay-adaptive data gathering platform to ultimately extend the network’s lifetime to meet the users’ or applications’ specific requirements such as delay constraints