Wireless Sensor Networks - overview -

Wireless Sensor Networks Introduction Introduction Terminology Terminology Applications Applications Technical Challenges Technical Challenges Examples Examples Conclusion Conclusion

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.

Wireless Sensor Network

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

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

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

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

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

Applications -civil enginneering- Monitoring of structures Monitoring of structures Urban planing (groundwater paterns, percent of CO 2 cities are expelling,...) Urban planing (groundwater paterns, percent of CO 2 cities are expelling,...) Disaster recovery (locating signs of life after earthquake) Disaster recovery (locating signs of life after earthquake)

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

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) 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) Micro-surgery (swarm of MEMS-based robots)

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

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

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

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

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

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

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

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

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

Technical challenges -communication architecture (contd.)- Application layer An application layer management protocol makes the 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) Sensor management protocol (SMP) Task assignment and data advertisement protocol (TADAP) Task assignment and data advertisement protocol (TADAP) Sensor query and data dissemination protocol (SQDDP) Sensor query and data dissemination protocol (SQDDP)

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. 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. No attempt thus far to propose a scheme or to discuss the issues related to the transport layer of a sensor network in literature.

Technical challenges -communication architecture (contd.)- Network layer Routing the data supplied by the transport layer. Power efficiency is always an important consideration. Power efficiency is always an important consideration. Sensor networks are mostly data centric. Sensor networks are mostly data centric. Data aggregation is useful only when it does not hinder the collaborative effort of the sensor nodes. 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. An ideal sensor network has attribute-based addressing and location awareness.

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

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

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

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

Technical challenges -security-

Technical challenges -designed protocols-

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

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

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

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

Conclusion Wireless Sensor Networks are ideal for remote sensing in various applications 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 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 Power consumption in hardware and OS must be minimal Data redundancy can be exploited to reduce power consumption Data redundancy can be exploited to reduce power consumption Technology of the future!!!! Technology of the future!!!!