1. On Efficient Clustering of Wireless Sensor Networks Mohamed Younis, Poonam Munshi, Gaurav Gupta (Univ. of Maryland) Sameh M. Elsharkawy( Catholic Univ.) Presented by HCLiang

2. Visual Communication-Laboratory, NTHU 2 Outline Introduction System Model Multi-Gateway Clustered Architecture Multi-tier Sensor Network Architecture Simulation Conclusion and Future Work

3. Visual Communication-Laboratory, NTHU 3 Introduction-Sensors attributes Sensors – tiny devices that are capable of gathering physical information like heat, light, or motion of an object etc... Application – civil, Military, Combat field surveillance etc…. Energy – very scarce resource for sensors and has to be managed wisely.

4. Visual Communication-Laboratory, NTHU 4 Introduction-Sensors basic functions Collect information – probe the surrounding environment and generate reports of the collected readings. Transmit data – transmit reports to command center (usually a gateway) via radio transmitter. Mode transition – can change to sleep mode for power saving.

5. Visual Communication-Laboratory, NTHU 5 Introduction-Sensors ’ energy issue Main consumer of energy – signal processing and communication. Save energy – appropriate selection of only subset of sensors to be turned on and thus avoid wasting sensors energy. Effective operate sensors – gateway has to monitor sensors’ health status and remaining energy.

6. Visual Communication-Laboratory, NTHU 6 Introduction- problems when deploy sensors(1/2) Obstacles – the region we want to deploy sensors may exist many obstacles (tree, buildings, etc…) Terrain – terrain may not always be flat.

7. Visual Communication-Laboratory, NTHU 7 Introduction- problems when deploy sensors(2/2)

8. Visual Communication-Laboratory, NTHU 8 Introduction- 2 methods to solve previous problems Multi-Gateway Clustered Architecture – multiple gateway nodes are placed and sensors are grouped around them forming a network clusters. Multi-tier Sensor Network Architecture – we introduce an additional tier in the network by forming groups of sensors. Each group we select an agent node to help the nodes can’t be directly reached by the gateway in this group.

9. Visual Communication-Laboratory, NTHU 9 Outline Introduction System Model Multi-Gateway Clustered Architecture Multi-tier Sensor Network Architecture Simulation Conclusion and Future Work

10. Visual Communication-Laboratory, NTHU 10 System Model-Gateway A gateway is responsible for only a subset of the entire sensors population. Gateway node is assumed to know the geographical locations of sensors deployed in its vicinity. Gateway and sensors are assumed to be stationary.

11. Visual Communication-Laboratory, NTHU 11 System Model-Sensors The sensors is assumed to be capable of reporting its remaining energy and operating in an active mode or a low-power mode. Sensors are also assumed can act as a relay to forward data form another sensors.

12. Visual Communication-Laboratory, NTHU 12 System Model- Estimate communication energy consumption of a sensor node Reference: W.Heinzelman “ Energy-efficient Communication Protocol for Wireless Sensor Networks ” M.Bhardwaj, et. Al, “ Upper Bounds on the Lifetime of Sensor Networks ” R.Min, et. al, “ An Architecture for a Power-aware Distributed Microsensor Node ”

13. Visual Communication-Laboratory, NTHU 13 Outline Introduction System Model Multi-Gateway Clustered Architecture Multi-tier Sensor Network Architecture Simulation Conclusion and Future Work

14. Visual Communication-Laboratory, NTHU 14 Multi-Gateway Clustered Architecture Employs multiple gateway nodes to increase sensor reachability and minimize sensor to gateway communication related energy. Network setup is performed in two stage  Bootstrapping  Clustering

15. Visual Communication-Laboratory, NTHU 15 Multi-Gateway Clustered Architecture- Overview

16. Visual Communication-Laboratory, NTHU 16 Multi-Gateway Clustered Architecture- Bootstrapping phase(1/3) Gateways discover the nodes that are located within their communication range. Gateways broadcast a message called “probe” to reveal their identity and location. Each gateway starts the bootstrapping at a different instance of time in order to avoid collision. In reply, Sensors broadcast a message called “heartbeat”

17. Visual Communication-Laboratory, NTHU 17 Multi-Gateway Clustered Architecture- Bootstrapping phase(2/3) Nodes discovered in this phase is included in a RSet. (Range Set) A sensor ‘ ‘ belongs to RSet of gateway ‘ ‘ if it satisfies the following criteria

18. Visual Communication-Laboratory, NTHU 18 Multi-Gateway Clustered Architecture- Bootstrapping phase(3/3) Using the energy model mentioned before, the cost calculated by gateway. Construct two kind of nodes in Gateway, the first one is ‘Exclusive nodes’, the second one is the nodes that can communicate with more than one gateway. Construct ‘ESet’ satisfies

19. Visual Communication-Laboratory, NTHU 19 Multi-Gateway Clustered Architecture- Clustering phase 1. Calculate RSet and ESet for every gateway 2. Nodes in ESet allocated to their respective gateway. 3. Each unassigned sensor node is associated with the gateway with minimal communication cost.

20. Visual Communication-Laboratory, NTHU 20 Outline Introduction System Model Multi-Gateway Clustered Architecture Multi-tier Sensor Network Architecture Simulation Conclusion and Future Work

21. Visual Communication-Laboratory, NTHU 21 Multi-tier Sensor Network Architecture- Overview

22. Visual Communication-Laboratory, NTHU 22 Multi-tier Sensor Network Architecture- Bootstrapping phase Gateway establishes the following attributes for every sensor.  Gateway-link-status  Neighbor-list  Hop-list

23. Visual Communication-Laboratory, NTHU 23 Multi-tier Sensor Network Architecture- Group Formation phase(1/3) AgentID: 0 if belong Group-list: Gateway designate for every potential agent sensor to track members of its group.

24. Visual Communication-Laboratory, NTHU 24 Multi-tier Sensor Network Architecture- Group Formation phase(2/3) Step 1: For each sensor, the gateway calculate the Hop-list of sensors by picking neighbors that belong to the set.Sensors in are sorted in ascending order according to the cardinality of their Hop-list. Step 2: Starting form the sensors with lowest cardinality of the Hop-list, we assign an agent sensor in for every sensor

25. Visual Communication-Laboratory, NTHU 25 Multi-tier Sensor Network Architecture- Group Formation phase(3/3)

26. Visual Communication-Laboratory, NTHU 26 Outline Introduction System Model Multi-Gateway Clustered Architecture Multi-tier Sensor Network Architecture Simulation Conclusion and Future Work

27. Visual Communication-Laboratory, NTHU 27 Simulation-Environment A set of sensors is randomly placed in a 1000*1000 m square area. Gateway is randomly positioned within the boundaries of the deployment region. Some link among sensors in close proximity and between the gateway and some sensors are randomly selected to be broken to simulate terrain effects.

28. Visual Communication-Laboratory, NTHU 28 Simulation

29. Visual Communication-Laboratory, NTHU 29 Simulation

30. Visual Communication-Laboratory, NTHU 30 Outline Introduction System Model Multi-Gateway Clustered Architecture Multi-tier Sensor Network Architecture Simulation Conclusion and Future Work

31. Visual Communication-Laboratory, NTHU 31 Conclusion and Future Work Simulation results have demonstrated the superiority of the multi-tier architecture in terms of node reachability. if multiplicity of gateway nodes is not restrained, it would be beneficial to increase the number of deployed gateways in order to extend the lifetime of sensors.

32. Visual Communication-Laboratory, NTHU 32 Conclusion and Future Work Future work:  Optimal placement of gateways.  The effect of the different network clustering methods on the network’s energy consumption.  Life span of different types of nodes.