1. Wireless Sensor Networks: A Survey I. F. Akyildiz, W. Su, Y. Sankarasubramaniam and E. Cayirci

2. 2 Outline Introduction Applications of sensor networks Factors influencing sensor network design Communication architecture of sensor networks Conclusion

3. 3 Introduction A sensor network is composed of a large number of sensor nodes, which are densely deployed either inside the phenomenon or very close to it. Random deployment Cooperative capabilities

4. 4 Introduction Sensor networks VS ad hoc networks: The number of nodes in a sensor network is orders of magnitude higher than the nodes in an ad hoc network. Densely deployed. Sensor nodes are limited in power, computational capacities and memory. Sensor nodes are prone to failures. The topology of a sensor network changes frequently. Sensor nodes mainly use broadcast, most ad hoc networks are based on peer-to-peer. Sensor nodes may not have global ID.

5. 5 Factors Influencing Sensor Network Design

6. 6 Factors influencing sensor network design

7. 7 Fault Tolerance Scalability Hardware Constrains Sensor Network Topology Environment Transmission Media Power Consumption

8. 8 Factors influencing sensor network design Fault tolerance is the ability to sustain sensor network functionalities without any interruption due to sensor node failures. The fault tolerance level depends on the application of the sensor networks.

9. 9 Factors influencing sensor network design The number of sensor nodes deployed in studying a phenomenon may be hundreds or thousands. Depending on the application, the number may reach an extreme value of millions. New schemes must be able to work with this number of nodes. Scalability

10. 10 Factors influencing sensor network design Production costs The cost of a single node is very important to justify the overall cost of the networks. The cost of a sensor node is a very challenging issue given the amount of functionalities with a price of much less than a dollar.

11. 11 Factors influencing sensor network design Hardware constraints

12. 12 Factors influencing sensor network design Sensor network topology Pre-deployment and deployment phase Post-deployment phase Re-deployment of additional nodes phase

13. 13 Factors influencing sensor network design Environment Busy intersections Interior of a large machinery Bottom of an ocean Surface of an ocean during a tornado Biologically or chemically contaminated field Battlefield beyond the enemy lines Home or a large building Large warehouse Animals Fast moving vehicles Drain or river moving with current.

14. 14 Factors influencing sensor network design Transmission media In a multihop sensor network, communicating nodes are linked by a wireless medium. To enable global operation, the chosen transmission medium must be available worldwide. Radio infrared optical media

15. 15 Factors influencing sensor network design Power Consumption Sensing Communication Data processing

16. 16 Communication architecture of sensor networks

17. 17 Communication architecture of sensor networks Combine power and routing awareness Integrates data with networking protocols Communicates power efficiently through the wireless medium Promotes cooperative efforts among sensor nodes.

18. 18 Communication architecture of sensor networks Physical layer: Address the needs of simple but robust modulation, transmission, and receiving techniques. frequency selection carrier frequency generation signal detection and propagation signal modulation and data encryption.

19. 19 Communication architecture of sensor networks Data link layer: The data link layer is responsible for the multiplexing of data stream, data frame detection, the medium access and error control. Medium Access Control Power Saving Modes of Operation Error Control

20. 20 Communication architecture of sensor networks Medium access control Creation of the network infrastructure Fairly and efficiently share communication resources between sensor nodes Existing MAC protocols (Cellular System, Bluetooth and mobile ad hoc network)

21. 21 Communication architecture of sensor networks Power Saving Modes of Operation Sensor nodes communicate using short data packets The shorter the packets, the more dominance of startup energy Operation in a power saving mode is energy efficient only if the time spent in that mode is greater than a certain threshold.

22. 22 Communication architecture of sensor networks Network layer: Power efficiency is always an important consideration. Sensor networks are mostly data centric. Data aggregation is useful only when it does not hinder the collaborative effort of the sensor nodes. An ideal sensor network has attribute-based addressing and location awareness.

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24. 24 Communication architecture of sensor networks Maximum available power (PA) route: Route 2 Minimum energy (ME) route: Route 1 Minimum hop (MH) route: Route 3 Maximum minimum PA node route: Route 3 Minimum longest edge route: Route 1 Energy Efficient Routes

25. 25 Communication architecture of sensor networks Interest Dissemination Sinks broadcast the interest Sensor nodes broadcast the advertisements Attribute-based naming “ The areas where the temperature is over 70 o F ” “ The temperature read by a certain node ”

26. 26 Communication architecture of sensor networks Data aggregation Solve implosion and overlap Problem Aggregation based on same attribute of phenomenon Specifics (the locations of reporting sensor nodes) should not be left out

27. 27 Communication architecture of sensor networks Several Network Layer Schemes for Sensor Networks

28. 28 Communication architecture of sensor networks Open research issues New protocols need to be developed to address higher topology changes and higher scalability. New internet working schemes should be developed to allow easy communication between the sensor networks and external networks.

29. 29 Communication architecture of sensor networks Transport layer: Needed when the system is planned to be accessed through Internet or other external networks. TCP/UDP (user datgram protocol) type protocols meet most requirements (not based on global addressing). Little attempt thus far to propose a scheme or to discuss the issues related to the transport layer of a sensor network in literature.

30. 30 Communication architecture of sensor networks Application layer: Management protocol makes the hardware and software of the lower layers transparent to the sensor network management applications. Sensor management protocol (SMP) Task assignment and data advertisement protocol (TADAP) Sensor query and data dissemination protocol (SQDDP)

31. 31 Communication architecture of sensor networks Sensor management protocol (SMP) Introducing the rules related to data aggregation, attribute- based naming, and clustering to the sensor nodes Exchanging data related to the location finding algorithms Time synchronization of the sensor nodes Moving sensor nodes Turning sensor nodes on and off Querying the sensor network configuration and the status of nodes, and reconfiguring the sensor network Authentication

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