1. 1 Wireless Networks Lecture 34 Wireless Sensor Networks Part I Dr. Ghalib A. Shah

2. 2 Outline  Introduction to WSN  Applications of WSN  Factors Influencing Performance of WSN ►Power consumption, fault tolerance, scalability, topology, cost  Architecture and Communication Protocols  Challenges in WSNs.

3. 3 Last Lecture Review  Motivation ►Fixed-end systems, fixed wired network, window-based, slow-start, loss-based congestion control  TCP Variants ►Slow start ►Fast Retransmit/Recovery (TCP Reno)  Issues in Heterogeneous Wireless Networks ►BER, Bandwidth, variable RTT, Mobility, Power  TCP Schemes for Wireless ►Revolve around distinguishing congestion loss, error loss, delay bounds, dup Acks ►Pure Link-level Approaches (FEC/ARQ) ►Soft-state Transport Layer Caching Approaches (SNOOP) ►Soft-state Cross Layer Signalling Approaches (ECN, EBSN, ELN, ATCP) ►Hard-state Transport Layer Approaches (I-TCP, Mobile TCP)

4. 4 Introduction to WSNs  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.  Features: ►Random deployment ►Self-organizing ►Cooperative capabilities ►Local computation

5. 5 What is a Sensor ?  Sensor is a small sized, low power, low cost, Micro-Electro- Mechanical Systems (MEMS)  which is capable of sensing, computing and communicating. Processor Speed8 MHz Flash512K bytes SRAM8k bytes Radio Frequency916 MHz/ 2.4 GHz (ISM) Data Rate40 Kbits/Sec (Max) Radio Range100 feet Power2 x AA batteries

6. 6 Networking Open Experimental Platform Small microcontroller 8 kB code 512 B data Simple, low-power radio 10 kbps ASK EEPROM (32 KB) Simple sensors WeC 99 “Smart Rock” Mica 1/02 NEST open exp. Platform 128 kB code, 4 kB data 40kbps OOK/ASK radio 512 kB Flash Rene 11/00 Designed for experimentation -sensor boards -power boards TinyOS Services Dot 9/01 Demonstrate scale Spec 6/03 “Mote on a chip” Telos 4/04 Robust Low Power 250kbps Easy to use Mica2 12/02 38.4kbps radio FSK Commercial Off The Shelf Components (COTS)

7. 7 Introduction Sensor networks VS ad hoc networks:  Scalability ►The number of nodes in a sensor network can be several orders of magnitude higher than the nodes in an ad hoc network.  Deployment ►Sensor nodes are densely deployed.  Failure Rate ►Sensor nodes are prone to failures.  Highly Dynamic topology ►The topology of a sensor network changes very frequently?  Communication Paradigm ►Sensor nodes mainly use broadcast, most ad hoc networks are based on p2p.  Power Limitation ►Sensor nodes are limited in power, computational capacities and memory.  Unique IDs ►Sensor nodes may not have global ID.

8. 8 Applications of sensor networks  temperature  humidity  vehicular movement  lightning condition  pressure  soil makeup  noise levels  the presence or absence of certain kinds of objects

9. 9 Applications of sensor networks (Cntd.)  Military applications ►Monitoring friendly forces, equipment and ammunition ►Battlefield surveillance ►Reconnaissance of opposing forces and terrain ►Battle damage assessment ►Nuclear, biological and chemical attack detection and reconnaissance  Environmental applications ►Forest fire detection ►Biocomplexity mapping of the environment ►Flood detection ►Precision agriculture

10. 10 Applications of sensor networks (Cntd.)  Health applications ►Telemonitoring of human physiological data ►Tracking and monitoring patients and doctors inside a hospital ►Drug administration in hospitals  Home applications ►Home automation ►Smart environment

11. 11 Applications of sensor networks Other commercial applications  Environmental control in office buildings  Interactive museums  Managing inventory control  Vehicle tracking and detection  Detecting and monitoring car thefts

12. 12 Factors influencing sensor network design  Fault tolerance ►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.  Scalability ►Scalability measures the density of the sensor nodes. ►Density = (R) = (N R 2 )/A  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.

13. 13 Factors influencing sensor network design Hardware constraints

14. 14 Factors influencing sensor network design  Sensor network topology ►Pre-deployment and deployment phase ►Post-deployment phase ►Re-deployment of additional nodes phase  Power consumption ►Sensing ►Communication 3000 instructions can be executed for the same energy cost of sending a bit 100m by radio. ►Data processing

15. 15 Energy Consumption  Sensor node has limited energy supply  Nodes may not be rechargeable  3000 instructions can be executed for the same energy cost of sending a bit 100m by radio. Power consumption of a typical senor node 0 5 10 15 20 Power (mW) SensingCPUTXRXIDLESLEEP

16. 16 Factors influencing sensor network design Environment  Busy intersections  Interior of a large machinery  Bottom of an ocean  Inside a twister  Biologically or chemically contaminated field  Battlefield beyond the enemy lines  Home or a large building  Large warehouse  Fast moving vehicles  Drain or river moving with current.

17. 17 Communication architecture of sensor networks

18. 18 Communication architecture of sensor networks

19. 19 Protocol Stack  Power Management Plan ►Turning off the receiver after a msg is received from neighbor in order to avoid getting duplicate msg and conserving energy. ►Informing neighbor nodes during low battery power.  Mobility Management Plan ►The mobility management plane detects and registers the movement of sensor nodes, so a route back to the user is always maintained, and the sensor nodes can keep track of who are their neighbor sensor nodes.  Task Management Plan ►The task management plane balances and schedules the sensing tasks given to a specific region. Not all sensor nodes in that region are required to perform the sensing task at the same time. As a result, some sensor nodes perform the task more than the others depending on their power level.

20. 20 Communication architecture of sensor networks  Application layer ►An 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)  Transport layer ►This layer is especially needed when the system is planned to be accessed through Internet or other external networks. ►No attempt thus far to propose a scheme or to discuss the issues related to the transport layer of a sensor network in literature.

21. 21 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.

22. 22 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

23. 23 Communication architecture of sensor networks Data aggregation

24. 24 Communication architecture of sensor networks  Data link layer ►The data link layer is responsible for the medium access and error control. It ensures reliable point-to-point and point-to- multipoint connections in a communication network.  Medium access control ►Creation of the network infrastructure ►Fairly and efficiently share communication resources between sensor nodes  Power saving modes of operation ►Operation in a power saving mode is energy efficient only if the time spent in that mode is greater than a certain threshold.

25. 25 Communication architecture of sensor networks Error control  Forward Error Correction (FEC)  Automatic Repeat Request (ARQ). Simple error control codes with low-complexity encoding and decoding might present the best solutions for sensor networks.

26. 26 Challenges in WSN  Cross-layer approach: A Grand Challenge ►Traditional layered approach is not suitable for WSNs ►Good for design, abstraction & debugging ►Bad for energy efficiency, overhead & performance

27. 27  How to realize mapping?  User/Applications Requirements  ►Arch. & Topology or Communication Protocols ►E.g. reliability ?

28. 28 Research Directions  Topology Control  Coverage  Data Aggregation  Temporal/Spatial Correlation  Localization / Synchronization  Energy Efficient Data Dissemination  QoS Framework  Network Monitoring and Management  How to integrate WSNs into NGWI ?

29. 29 Simulation for Sensor Networks Simulation provides :  Controlled, Reproducible testing environment  Cost – effective alternative  Means to explore and improve design space

30. 30 TinyOS  The role of any operating system (OS) is to promote development of reliable application software by providing a convenient and safe abstraction of hardware resources.  Wireless sensor networks (WSNs) are embedded but general-purpose, supporting a variety of applications, incorporating heterogeneous components, and capable of rapid deployment in new environments  An open-source development environment ►A programming language and model (NesC)  TOSSIM for simulating TinyOS  TinyDB for Sensor DB in TinyOS

31. 31 Summary  Introduction to WSN  Applications of WSN  Factors Influencing Performance of WSN  Architecture and Communication Protocols  Challenges in WSNs.