Wireless Sensor Networks overview Wireless Sensor Networks Introduction

Wireless Sensor Networks - overview -

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

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

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

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

Applications -general engineeringn n n n n 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

Applications -agriculture and environmental monitoringn n n n 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

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

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

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

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

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

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

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

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

Technical challenges -power supply (contd. )Power Scavenging n n Energy provided depends on how long the source is in operation Used usually to charge secondary batteries n n n Photovoltaic Cells Temperature gradient Human Power (average human body burns 10. 5 MJ of energy per day) Wind / Air flow Vibrations

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

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

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

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. n Sensor management protocol (SMP) n Task assignment and data advertisement protocol (TADAP) n 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. n No attempt thus far to propose a scheme or to discuss the issues related to the transport layer of a sensor network in literature. n

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

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

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

Technical challenges -communication architecture (contd. )Data link layer n n n The data link layer is responsible for the medium access and error control. It ensures reliable point-to-point and point-tomultipoint connections in a communication network. MAC (Medium Access Control) n Creation of the network infrastructure n Fairly and efficiently share communication resources between sensor nodes Error control n Forward Error Correction (FEC) n 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.

Technical challenges -security-

Technical challenges -designed protocols-

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

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

Examples - Berkeley Motesn n Small (under 1” square) microcontroller It consists of: n n n 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

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

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