Wireless Sensor Networks

1. Wireless Sensor Networks - overview -

2. Wireless Sensor Networks • Introduction • Terminology • Applications • Technical Challenges • Examples • Conclusion

3. Introduction A Wireless sensor network (WSN) is a network that is formed when a set of small sensor devices that are deployed in an ad hoc fashion cooperate for sensing a physical phenomenon. Wireless Sensor Network consists of base stations and a number of wireless sensors.

4. Wireless Sensor Network

5. Introduction-basic features- • Self-organizing capabilities • Short-range broadcast communication and multihop routing • Dense deployment and cooperative effort of sensor nodes • Frequently changing topology due to fading and node failure • Limitation in energy, transmit power, memory, and computing power

6. Terminology • Sensor: The device • Observer: The end user/computer • Phenomenon: The entity of interest to the observer

7. Applications • General engineering • Agriculture and enivronmental monitoring • Civil engineering • Military applications • Health monitoring and surgery

8. Applications-general engineering- • Automotive telematics (cars networked) • Fingertip accelerometer virtual keybords • Sensing and maintenance in industrial plants • Aircraft drag reduction • Smart office spaces • Tracking of goods in retail stores • Tracking of containers and boxes • Social studies (human interaction and social behavior) • Commercial and residential security

9. Applications-agriculture and environmental monitoring- • Precision agriculture (crop and livestock management) • Planetary exploration (inhospitable environments) • Geophysical monitoring (seismic activity) • Monitoring of freshwater quality • Zebranet project • Habitat monitoring • Disaster detection (forest fires and floods) • Contaminant transport

10. Applications -civil enginneering- • Monitoring of structures • Urban planing (groundwater paterns, percent of CO2 cities are expelling,...) • Disaster recovery (locating signs of life after earthquake)

11. Applications -military applications- • Asset monitoring and management • Surveillance and battle-space monitoring • Urban warfare (sensors in buildings, movement of friend and foe, localizing snipers,...) • Protection (for sensitive objects) • Self-healing minefields

12. Applications -health monitoring and surgery- • Medical sensing (physiological data transmitted to a computer or physician, wireless sensing bandages worn of infection, sensors in the blood stream which prevent coagulation and thrombosis) • Micro-surgery (swarm of MEMS-based robots)

13. Technical challenges-performance metrics- • Energy efficiency/System Lifetime • Latency • Accuracy • Fault tolerance • Scalability • Transport capacity/throughput • Production costs • Sensor network topology • Transmission media • Power supply • Communication architecture • Security

14. Technical challenges-sensor network topology- • Hundreds of nodes require careful handling of topology maintenance. • Predeployment and deployment phase • Numerous ways to deploy the sensors (mass, individual placement, dropping from plane..) • Postdeployment phase • Factors are sensor nodes’ position change, reachability due to jamming, noise, obstacles etc, available energy, malfunctioning • Redeployment of additional nodes phase • Redeployment because of malfunctioning of units

15. Technical challenges- transmission media - • In a Multihop sensor network nodes are linked by Wireless medium • Radio Frequency (RF) • Most of the current sensor node HW is based on it • Do not need Line of Sight • Can hide these sensors • Infrared (IR) • License free • Robust to interference • Cheaper and easier to build • Require line of sight • Short Range Solution • Optical media • Require Line of sight

16. Technical challenges-power supply- • Power supply usually the limiting factor in terms of size and cost and life time • Power sources can be classified as • Energy Reservoir (Energy storage in form of chemical energy; batteries) • Power Distribution methods • Power Scavenging methods

17. Technical challenges-power supply (contd.)- Power distribution • Distribution of power to nodes from a nearby energy rich source • Wires (defeats purpose of wireless communication) • Acoustic waves (very low power level) • Light or lasers (Directed laser beams to large number of nodes very complicated ) • Electromagnetic (RF) power distribution • Example: µ- chip developed by Hitachi for RFID devices

18. Technical challenges-power supply (contd.)- Power Scavenging • Energy provided depends on how long the source is in operation • Used usually to charge secondary batteries • Photovoltaic Cells • Temperature gradient • Human Power (average human body burns 10.5 MJ of energy per day) • Wind / Air flow • Vibrations

19. Technical challenges- power consumption - • Sensing • Communication • Data processing Components of a sensor node

20. Technical challenges- power consumption (contd.)- • Key to Low Duty Cycle Operation: • Sleep – majority of the time • Wakeup – quickly start processing • Active – minimize work & return to sleep

21. Technical challenges-Communication architecture- • Combines power and routing awareness, • Integratesdata with networking protocols, • Communicatespower efficiently through the wireless medium • promotes cooperative efforts of sensor nodes. The sensor network protocol stack

22. Technical challenges-communication architecture (contd.)- 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)

23. Technical challenges-communication architecture (contd.)- 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.

24. Technical challenges-communication architecture (contd.)- Network layer Routing the data supplied by the transport 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.

25. Technical challenges-communication architecture (contd.)- Routing • Flooding : • Broadcast based • -High Overhead • -Data aggregation to reduce the overhead • -Less complex • Unicast: • Sensors can communicate with the observer directly or with the cluster head using one to one unicast. • MultiCast: • Sensors form application-directed groups and use multicast to communicate among group members.

26. Technical challenges-communication architecture (contd.)- Selecting an energy efficient route • 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

27. Technical challenges-communication architecture (contd.)- 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. • MAC (Medium Access Control) • Creation of the network infrastructure • Fairly and efficiently share communication resources between sensor nodes • Error control • Forward Error Correction (FEC) • Automatic Repeat Request (ARQ).

28. Technical challenges-communication architecture (contd.)- Physical layer The physical layer is responsible for frequency selection, frequency generation, signal detection, modulation and data encryption.

29. Technical challenges-security-

30. Technical challenges-designed protocols-

31. Examples • MIT d'Arbeloff Lab – The ring sensor • Monitors the physiological status of the wearer and transmits the information to the medical professional over the Internet • Oak Ridge National Laboratory • Nose-on-a-chip is a MEMS-based sensor • It can detect 400 species of gases and transmit a signal indicating the level to a central control station

32. Examples- iButton - • A 16mm computer chip armored in a stainless steel can • Up-to-date information can travel with a person or object • Types of i-Button • Memory Button • Java Powered Cryptographic iButton • Thermochron iButton Applications • Caregivers Assistance • Do not need to keep a bunch of keys. Only one iButton will do the work • Elder Assistance • They do not need to enter all their personal information again and again. Only one touch of iButton is sufficient • They can enter their ATM card information and PIN with iButton • Vending Machine Operation Assistance

33. Examples- Berkeley Motes- • Small (under 1” square) microcontroller • It consists of: • Microprocessor • A set of sensors for temperature, light, acceleration and motion • A low power radio for communicating with other motes • C compiler Inclusion • Development ongoing

34. Examples-iBadge – UCLA- Investigate behavior of children/patient Features: Speech recording / replaying Position detection Direction detection /estimation (compass) Weather data: Temperature, Humidity, Pressure, Light

35. Conclusion • Wireless Sensor Networks are ideal for remote sensing in various applications • Due to the severe power constraints there is a need for a new set of protocols for WSN • Power consumption in hardware and OS must be minimal • Data redundancy can be exploited to reduce power consumption • Technology of the future!!!!