1. Introduction to Sensor Networks Rabie A. Ramadan, PhD Cairo University http://rabieramadan.org rabie@rabieramadan.org 2

2. Do not think how hard the problem you are solving Just, “keep your eyes on the prize” 2

3. Hardware Platforms Augmented General Purpose PCs Embedded PCs (PC104), PDAs, etc.. Usually have O.S like Linux and wireless device such as Bluetooth. Dedicated Sensor Nodes Commercially off the shelf components (e.g. Berkeley Motes) System-on-chip Sensor Platform like Smart dust, PicoNode 3

4. Software Platforms Operating Systems and Language Platforms Typical Platforms are: TinyOS, nesC, TinyGALS, and Mote’ TinyOS Event Driven O.S. Requires 178 bytes of memory Supports Multitasking and code Modularity Has no file system – only static memory allocation Simple task scheduler nesC – extension of C language for TinyOS- set of language constructs TinyGALS - language for TinyOS for event triggered concurrent execution. Mote’ - Virtual machine for Berkeley Mote 4

5. Wireless Sensor Network Standards IEEE 802.15.4 Standard Specifies the physical and MAC Layers for low-rate WPANs Data rates of 250 kbps, 40 kbps, and 20 kbps. Two addressing modes: 16 - bit short and 64 - bit IEEE addressing. Support for critical latency devices, for example, joysticks. The CSMA - CA channel access. Fully handshaking protocol for transfer reliability. Power management to ensure low - power consumption. 5

6. 6 CSMA-CA Protocol How it works?

7. Wireless Sensor Network Standards IEEE 802.15.4 Standard The physical layer is compatible with current wireless standards such as Bluetooth MAC layer implements synchronization, time slot management, and basic security mechanisms. 7

8. –“the software” –Network, Security & Application layers –Brand management IEEE 802.15.4 –“the hardware” –Physical & Media Access Control layers Wireless Sensor Network Standards IEEE 802.15.4 & ZigBee In Context PHY 868MHz / 915MHz / 2.4GHz MAC Network Star / Mesh / Cluster-Tree Security 32- / 64- / 128-bit encryption Application API ZigBee Alliance IEEE 802.15.4 Customer Silicon Stack App 8

9. ZigBee Utilization 9 RESIDENTIAL/ LIGHT COMMERCIAL CONTROL INDUSTRIAL CONTROL ZigBee Wireless Control that Simply Works CONSUMER ELECTRONICS TV VCR DVD/CD remote security HVAC lighting control access control lawn & garden irrigation PC & PERIPHERALS asset mgt process control environmental energy mgt PERSONAL HEALTH CARE BUILDING AUTOMATION security HVAC lighting control access control mouse keyboard joystick patient monitoring fitness monitoring

10. Applications Example 10

11. Put tripwires anywhere—in deserts, other areas where physical terrain does not constrain troop or vehicle movement—to detect, classify & track intruders [Computer Networks 2004, ALineInTheSand webpage, ExScal webpage] Project ExScal: Concept of operation 11

12. ExScal scenarios Border Monitoring: Detect movement where none should exist, Decide target classes, e.g., foot traffic to tanks Ideal when combined with towers, tethered balloons, or UAVs 12

13. WSN Research Fields Sensors HW and Software Deployment Physical, MAC, Routing, Applications Data Aggregation and Data Mining Artificial Intelligence and data handling Self Healing Web Integration Heterogeneity Security Software Engineering (Simulators ) Cloud Computing and Sensor Networks Mobility Issues and Localization 13

14. Assignment 1 Report the main security considerations of IEEE 802.15.4 ? 14

15. Deployment, Clustering, and and Routing in WSN 15

16. Deployment Constraints Sensor Characteristics Monitored Field Characteristics Monitored/Probed Object 16

17. Sensing and Communication Range  A wireless sensor network (WSN) consists of a large number of sensor nodes (SNs)  Adequate density of sensors is required so as to void any unsensed area rsrs Sensing Area Desired Coverage Area

18. rsrs SN 1 Sensing area for SN 1 rcrc SN 2 rsrs Sensing area for SN 2 Sensing and Communication Range

19. Deployment Parameters 19

20. Deployment Parameters 20 Diffraction: passing the signal through small opening and spreading it after passing the opening Scattering: scatter the coming signal Reflection : send the signal back towards the sender

21. Deployment Parameters 21

22. Deployment Parameters 22

23. Deployment Problems and Solutions Random Deployment Virtual force Algorithm Deterministic Deployment Circle Packing Energy Mapping Movement-Assisted Sensor Deployment Sink Placement Problem Single node Multiple sink deployment Relay Node Placement in WSN 23

24. Random Deployment Virtual Force Algorithm 24

25. Virtual Force Algorithm Sensors are initially deployed randomly Objective: To maximize the Coverage Assumptions: Assume no prior knowledge about the monitored field All nodes are mobile Energy and obstacles might present in the field 25

26. Virtual Force Algorithm (Cont.) Attractive and Repulsive forces Sensors do not physically move A sequence of virtual motion paths is determined for the randomly placed sensors. Once the effective sensor positions are identified, a one-time movement is carried out to redeploy the sensors at these positions. 26

27. Virtual Force Algorithm (Semi Distributed.) Assumptions: Clustered network All clustered heads are able to communicate with the sink node The cluster head is responsible for executing the VFA and managing the one-time movement of sensors to the desired locations. 27

28. Virtual Force Algorithm (Cont.) Each sensor behaves as a “Source of force” for all other sensors. This force can be either positive (Attractive) or negative (Repulsive). The closeness and wide distance between two sensors are measured using a predefined threshold. 28

29. Virtual Force Algorithm (Cont.) Sensor Binary Model Consider an n by m sensor field grid and assume that there are k sensors deployed in the random deployment stage. s i Each sensor has a detection range r. Assume sensor s i is deployed at point (x i, y i ). s i For any point P at (x, y), we denote the Euclidean distance between s i and P as d(s i, P), The coverage of a Grid Point P can be expressed by: 29

30. Virtual Force Algorithm (Cont.) Virtual Forces Attraction force  F12 Repulsive force  F13 Zero Force  F14 Obstacle Force  preferential coverage Force  Total Force on node i = 30

31. Virtual Force Algorithm (Cont.) Using such forces, the cluster head runs the VFA After stability occurs, Sensors are ordered to move to the new positions Energy and Obstacles might be problems Any sensor will not be able to move the required distance, the moving order is discarded Obstacles need an obstacle avoidance algorithm 31

32. Think….. If some sensors are stationary, does this affect the virtual force algorithm? What other problems you see in the algorithm? Coverage might not be satisfied due to the limitation in the energy since some nodes might not be able to move to the specified place. Mobility assumption might not be the case for all WSNs 32

33. SENSOR REPLACEMENT BASED ENERGY MAPPING 33

34. The problem A set of sensors S is deployed in a monitored field F(A)for a period of time T. The field is divided into a grid of cells A. Each cell is assigned a weight where represents the importance of the cell i. The location of each sensor is assumed known; More than one sensor could be deployed in one cell. Sensors are assumed heterogeneous in terms of their energy and mobility. 34

35. Assumptions A sensor could be in different states; it could have its sensing off or on based on the field monitoring requirements. Sensing off, radio off – (sleep mode) Sensing off, radio receiving – (Receiving mode) Sensing off, radio transmitting – (Routing mode) Sensing on, radio receiving – (Sensing and Receiving mode) Sensing on, radio transmitting – (Sensing and Transmitting mode) Sensing on, radio off - (Sensing mode) 35

36. The main idea Knowing the energy map of the network : Knowing the energy map of the network : May lead to early detection to the uncovered areas. Redeploy new sensors Turn off some of the sensors due to their coverage redundancy Wake up some of the nodes when needed Move one or mobile nodes to cover the required uncovered spots 36

37. Redeployment based Energy map Step 1: Step 1: Energy dissipation rate prediction Each sensor predicts its own energy rate based on its history (e.g. Markov Chain..) Step 2: Step 2: Sensors send their initial energy and the location, predicted energy dissipation rate to the sink node through a cluster head. Sensors update their energy dissipation rate based on a specific threshold (if the new dissipation rate increased more than the given threshold, the node sends the new dissipation rate) 37

38. Redeployment based Energy map Step 3 Step 3: the sink node constructs the energy map based on the received dissipated energy rate from the sensors. The sink may move one of the mobile sensors to the uncovered spot or wake up one of the sleeping sensors 38

39. Think ……. What are the disadvantages of energy mapping algorithm ? Sensor network is an event based network. Therefore, events are not frequently or based on specific pattern. Thus, the amount of messages to be transmitted to report the energy mapping will not be expected and might play a role in sensors energy dissipation. Centralized algorithm 39

40. Movement-Assisted Sensor Deployment 40

41. The problem of sensor deployment Given the target area, how to maximize the sensor coverage with less time, movement distance and message complexity The importance of the problem Distributed instead of centralized 41

42. Voronoi Diagram Definition: Every point in a given polygon is closer to the node in this polygon than to any other node. 42

43. Overview of the proposed algorithm Sensors broadcast their locations and construct local Voronoi polygons Find the coverage holes by examining Voronoi polygons If holes exist, reduce coverage hole by moving VOR : VORonoi-based Pull sensors to the sparsely covered area 43

44. Part of Assignment 1 Given a set of sensors with limited amount of energy. Some of these sensors are assumed mobile and others are assumed stationary. Assume similar sensing and communication ranges for all sensors. Sensors are allowed to move from one place to another iff they have enough energy to move to the required destination. In addition, the borders of the monitored area is assumed known in terms of 2D coordinates. Borders may be found in the monitored area. Advice a suitable deterministic deployment algorithm for efficient deployment to the sensors given that the deployed sensors have to be connected and important areas in the field are covered. In addition, your algorithm must guarantee the coverage of the monitored field for certain period of time. You may look for an already given solution or come up with a convincing one. 44