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Wireless Sensor Network Prabhakar Dhekne Bhabha Atomic Research Centre. Why Talk About Wireless?. Wireless communication is not a new technology but cell phones have brought revolution in wireless communication Wireless Technology has changed the way

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Wireless Sensor Network

Prabhakar Dhekne

Bhabha Atomic Research Centre

Talk at SASTRA

why talk about wireless
Why Talk About Wireless?
  • Wireless communication is not a new technology but cell phones have brought revolution in wireless communication
  • Wireless Technology has changed the way
    • Organizations & individuals work & live today
  • In less than 10 years
    • World has moved from fixed to wireless networks
    • Allowing people, mobile devices & computers talk to each other, connect without a cable
    • Only available option for field data acquisition
  • Interconnectivity with multiple devices
    • Using radio-waves, sometimes light
    • Frees user from many constrains of traditional computer & phone system

Talk at SASTRA

ubiquitous computing
Future State of Computing Technology?

Mobile, many computers

Small Processors

Low Power Consumption

Relatively Low Cost

Ubiquitous Computing

Talk at SASTRA

ubiquitous computing1
Ubiquitous Computing
  • Small, mobile, inexpensive computers…..everywhere!
  • Fade into the background of everyday life
  • Computers everywhere provides potential for data collection….sensors!
    • Temperature
    • Light
    • Sound
    • Motion
    • Pressure
    • Many others!!!

Talk at SASTRA

growth in wireless systems
Growth in Wireless Systems
  • Rapid growth in cellular voice services
    • Cell phones everywhere!
  • Several wireless technology options have been available for the last ~10-20 yrs
    • mini cell stations using existing standards like CDMA or GSM
    • wireless PABX using PCS standards such as DECT or PHS/PACS
    • satellite and microwave backhaul
  • Above solutions OK for voice & low-speed data, but do not meet emerging needs for broadband access and mobile data

Talk at SASTRA

mobile healthcare technologies
Mobile Healthcare Technologies

Mobile Healthcare can be regarded as the integration of technologies of medical sensors, mobile computing, and wireless communications into a system of medical assistance.

Talk at SASTRA

application examples
Application Examples
  • Monitoring of patient’s vital signs
    • Diabetes
    • Asthma
    • Hypertension
    • ECG
  • Predictive usage in order to minimize the needs for medication
  • Improving the quality of life

Talk at SASTRA

potential benefits
Potential Benefits
  • Increasing the physician productivity and efficiency.
  • Wireless sensors enable the patients’ freedom of movements and therefore promote new ways of monitoring the patient.
  • Providing clinicians remote access to patient’s information eliminates the need to manually locate and search through patient’s data.
  • Enabling telemonitoring in emergency scenarios and making remote diagnosis possible.

Talk at SASTRA


Mobile Healthcare

The provision of Real Time patient care.

  • No matter where the clinician is
  • No matter where the patient is
  • To apply physiological and medical knowledge, advanced diagnostics, simulations, and effector systems integrated with information and telecommunications for the purposes of enhancing operational and medical decision-making, improving medical training, and delivering medical treatment across all barriers

Talk at SASTRA

typical demo system
Typical Demo System
  • The patient is provided with a wearable wireless sensor. The signal from the sensor is captured in a Node situated in a mobile phone.
  • The system allows ubiquitous access to patient’s data and medical information in real-time via the mobile phone.
  • The medical data is stored & processed in a server, and can be used for establishing diagnostics and treatments.

Talk at SASTRA

application server
Application server
  • Application server centralises the received data and presents it to the user as:
    • Raw data
    • Formatted as graphs

App Server


Talk at SASTRA

wireless technology
Wireless Technology
  • Emerging mainstream wireless technologies provide powerful building blocks for next-generation applications
    • WLAN (IEEE 802.11 “WiFi”) hot-spots for broadband access, Bluetooth
      • PDAs and laptops with integrated WLANs
    • Broadband Wireless access technology- MAN (Alternative to DSL)
      • IEEE 802.16 10-30 Km 40 Mbps WiMax
    • Wide area wireless data also growing
      • SMS, GPRS, Edge, CDMA2000 1xEV-DO (2.4 Mbps data optimized)
      • Variety of interesting devices (e.g. Treo, Sidekick)
  • Networking of embedded devices
    • Smart spaces, sensor networks (IEEE 802.15.4a- ZigBee)
    • Context-aware mobile data services and web caching for information services
    • Wireless sensor nets for monitoring and control
    • VOIP for integrated voice services over wireless data networks

Talk at SASTRA


IrDA: P2P wireless

  • Infra-red Data Association
    • Based on Half Duplex Point-to-Point concept
    • Frequency below the red end of spectrum making it invisible
    • Eliminate the need for cables
    • Clear line-of-sight
    • Short-range (few meters)
  • Simplest, most prevailing wireless standard
  • No fixed speed 9.6 Kbps, 4Mbps
  • Discovery Mode to find out data rate, size
  • Token based transmission
  • IrDA ports on PDA, Laptops USB sticks
  • Remote Control in TV, VCR, Air-conditioner

Port costs less than Rs. 1000

Talk at SASTRA


Bluetooth: Wireless PAN

  • Bluetooth (Named after Danish King Harold Bluetooth)
    • Based on Master-Slave concept
    • Short-range (10 meters)
    • Eliminate the need for cables
    • Operates in 2.4 GHz ISM band
    • 720 Kbps
    • Three modes of operation park/hold/sniff
  • Piconet & Scatternet (master+7 slaves)
  • Interference due to multiple piconets and IEEE 802.15.1 home/person LAN
  • To eliminate interference frequency hoping technique used
  • Ominidirectional with both voice & data






M 1/S1

Piconet 1

Piconet 2

Port costs about Rs. 2000

Talk at SASTRA


Wi-Fi: Wireless LAN (Hot Spot)

  • Wireless Fidelity based LAN
    • Most popular on Laptops
    • Replacement to wired LAN
    • Connectivity on the move
    • Short-range (100 meters)
    • Ad Hoc and Base station mode
    • Security provided at physical layer
    • Operates in 2.4 GHz and 5 GHz
  • Collection of IEEE standards 802.11a/b/g 11 Mpbs & 54 Mbps
  • Low range, requires more power hence not suitable for PDA’s
  • Difficult to control access & security
  • Set up is expensive

Ad Hoc Net

Access Point Net

Talk at SASTRA


Wi-Max: Wireless MAN

  • Wireless Max
    • High Speed 40-70 Mbps
    • Mid-range (30 Kmeters)
    • Eliminate the need for cables
    • Saving of wired cost
    • Operates in 2.4 GHz ISM band
  • IEEE standard 802.16

Talk at SASTRA

issues in wireless networking
Issues in Wireless Networking
  • Infrastructured networks
    • Handoff
    • location management (mobile IP)
    • channel assignment

Talk at SASTRA

issues in wireless networking1
Issues in Wireless Networking

Infrastructureless networks

Wireless MAC

  • Security (integrity, authentication, confidentiality)
  • Ad Hoc Routing Protocols
  • Multicasting and Broadcasting

Talk at SASTRA

indoor environments
Indoor Environments
  • Three popular technologies

- High Speed Wireless LANs(802.11b (2.4GHz, 11 Mbps), 802.11a (5GHz, 54 Mbps & higher)

- Wireless Personal area Networks PANs (IEEE 804.14)

      • HomeRF
      • Bluetooth, 802.15

- Wireless device networks

      • Sensor networks, wirelessly networked robots

Talk at SASTRA

what is an ad hoc network
What is an Ad hoc Network
  • Collection of mobile wireless nodes forming a network without the aid of any infrastructure or centralized administration
  • Nodes have limited transmission range
  • Nodes act as a routers

Talk at SASTRA

ad hoc networks
Ad Hoc Networks
  • Disaster recovery
  • Battlefield
  • ‘Smart’ office
  • Rapidly deployable infrastructure
    • Wireless: cabling impractical
    • Ad-Hoc: no advance planning
  • Backbone network: wireless IP routers
  • Network of access devices
    • Wireless: untethered
    • Ad-hoc: random deployment
  • Edge network: Sensor networks, Personal Area Networks (PANs), etc.

Talk at SASTRA

ad hoc network
Ad Hoc Network
  • Characteristics
    • Dynamic topologies
    • Limited channel bandwidth
    • Variable capacity links
    • Energy-constrained operation
    • Limited physical security
  • Applications
    • Military battlefield networks
    • Personal Area Networks (PAN)
    • Disaster and rescue operation
    • Peer to peer networks

Talk at SASTRA

security challenges in ad hoc networks
Security Challenges in Ad Hoc Networks
  • Lack of Infrastructure or centralized control
    • Key management becomes difficult
  • Dynamic topology
    • Challenging to design sophisticated & secure routing protocols
  • Communication through Radio Waves
    • Difficult to prevent eavesdropping
  • Vulnerabilities of routing mechanism
    • Non-cooperation of nodes
  • Vulnerabilities of nodes
    • Captured or Compromised

Talk at SASTRA

  • Challenges in ad hoc network security
    • The nodes are constantly mobile
    • The protocols implemented are co-operative in nature
    • There is a lack of a fixed infrastructure to collect audit data
    • No clear distinction between normalcy and anomaly in ad hoc networks
  • Secure the Routing Mechanism
    • A mechanism that satisfies security attributes like authentication, confidentiality, non-repudiation and integrity
  • Secure the Key Management Scheme
    • Robust key certification and key distribution mechanism

Talk at SASTRA

scalable reliable consistent distributed service
Scalable, reliable, consistent, distributed service

Services while on move


Sensor services exercise monitorbiometrics traffic information

Calendar+ service Integrate dynamic traffic & schedule

Doctor prescription servicetrack health indicatorsDoctor write prescription

Follow me kiosk service receive and transmit messages

Fridge & shopping serviceFridge records stockSuggests shopping based on recipeShopping guide in store

Sensors mobile devices

Talk at SASTRA

tourist guide
Tourist guide
  • Stuttgart tourist guide
    • Like MapQuest except on mobile device
  • Mapping local interests
    • Museums historical sites
    • Shopping & restaurants Sample Data
    • Small text with description, operating hours
    • Local map

Talk at SASTRA

how it works
How it works
  • Info station
    • Island of wireless station
    • Embedded in area
    • Users have cheap low bandwidth components
    • Integrated to network with high quality connection
    • Requires some overlap to manage transition between stations for hand off
  • Scaleable by load balancing
    • Each center contains unique information
    • Overhead of communication
  • Initialize externally specified; adjusts quickly

Talk at SASTRA

map on the move
  • Provide appropriate map
  • County resolution driving in car
  • Info stations small area high bandwidth
  • Remainder lower bandwidth

Talk at SASTRA

problems in a mobile environment
Problems in a Mobile Environment
  • Variable Bandwidth
  • Disconnected Operation
  • Limited Power
  • Implications on distributed file system support?

Talk at SASTRA

constraints in mobile computing
Constraints in mobile computing
  • PDA vs. Laptop vs. cell phones
  • Cellular modem connection: Failure prone
  • Space: office vs. city vs. county
  • Not continuous connectivity required
  • Data such as pictures text files not streaming audio and video
  • Heterogeneous devices

Talk at SASTRA

manet mobile ad hoc networks
MANET: Mobile Ad hoc Networks

A collection of wireless mobile nodes dynamically forming a network without any existing infrastructure and the relative position dictate communication links (dynamically changing).

From DARPA Website

Talk at SASTRA

rapidly deployable networks
Rapidly Deployable Networks
  • Failure of communication networks is a critical problem faced by first responders at a disaster site
    • major switches and routers serving the region often damaged
    • cellular cell towers may survive, but suffer from traffic overload and dependence on (damaged) wired infrastructure for backhaul
  • In addition, existing networks even if they survive may not be optimized for services needed at site
    • significant increase in mobile phone traffic needs to be served
    • first responders need access to data services (email, www,...)
    • new requirements for peer-to-peer communication, sensor net or robotic control at the site
  • Motivates need for rapidly deployable networks that meet both the above needs ->recent advances in wireless technology can be harnessed to provide significant new capabilities

Talk at SASTRA

infostations prototype system for rapid deployment applications
Infostations Prototype: System for Rapid Deployment Applications
  • Outdoor Infostations with radio backhaul
    • for first responders to set up wireless communications infrastructure at a disaster site
    • provides WLAN services and access to cached data
    • wireless backhaul link
    • includes data cache
  • Project for development of:
    • high-speed short-range radios
    • 802.11 MAC enhancements
    • content caching algorithm & software
    • hardware integration including solar panels, antennas and embedded computing device with WLAN card

Talk at SASTRA

WINLAB’s Outdoor Infostations Prototype (2002)

ad hoc wireless network
Ad-Hoc Wireless Network
  • A flexible, open-architecture ad-hoc WLAN and sensor network testbed ...
    • open-source Linux routers, AP’s and terminals (commercial hardware)
    • Linux and embedded OS forwarding and sensor nodes (custom)
    • radio link and global network monitoring/visualization tools
    • prototype ad-hoc discovery and routing protocols





Radio Monitor


Linux PC

Forwarding Node/AP





Router network

with arbitrary topology


& storage


Sensor Node



Linux router

Talk at SASTRA

what is a wsn
What is a WSN?

Observer: The end user/computer

Sensor: The device

Phenomenon: The entity of interest to the observer

  • A network that is formed when a set of small sensor devices that are deployed in an “ad hoc fashion” no predefined routes, cooperate for sensing a physical phenomenon.
  • A Wireless Sensor Network (WSN) consists of base stations and a number of wireless sensors.
  • Is simple, tiny, inexpensive, and battery-powered

Talk at SASTRA

why wireless sensors now
Why Wireless Sensors Now?
  • Moore’s Law is making sufficient CPU performance available with low power requirements in a small size.
  • Research in Materials Science has resulted in novel sensing materials for many Chemical, Biological, and Physical sensing tasks.
  • Transceivers for wireless devices are becoming smaller, less expensive, and less power hungry (low power tiny Radio Chips).
  • Power source improvements in batteries, as well as passive power sources such as solar or vibration energy, are expanding application options.

Talk at SASTRA

typical sensor node features
Typical Sensor Node Features
  • A sensor node has:
    • Sensing Material
      • Physical – Magnetic, Light, Sound
      • Chemical – CO, Chemical Weapons
      • Biological – Bacteria, Viruses, Proteins
    • Integrated Circuitry (VLSI)
      • A-to-D converter from sensor to circuitry
    • Packaging for environmental safety
    • Power Supply
      • Passive – Solar, Vibration
      • Active – Battery power, RF Inductance

Talk at SASTRA


Sensor Node Hardware

Sensor + Actuator + ADC + Microprocessor + Powering Unit

+ Communication Unit (RF Transceiver) + GPS

  • Portable and self-sustained (power, communication, intelligence).
  • Capable of embedded complex data processing.

Talk at SASTRA

sensors and wireless radio
Sensors and Wireless Radio
  • Types of sensors:






-Strain, fatigue


  • Capable to survive harsh environments (heat, humidity, corrosion, pollution etc).
  • No source of interference to systems being monitored and/or surrounding systems.
  • Could be deployed in large numbers.

Talk at SASTRA

wireless sensor networks
Wireless Sensor Networks
  • ZigBee Wireless Communication Protocol
    • Based on the IEEE 802.15.4 standard
    • Small form factor
    • Relatively Inexpensive
    • Low Power Consumption
    • Low Data Rate of Communication
    • Self Organising, Self-Healing…multi-hop nodes
    • Integrated Sensors
    • Ideal for Wireless Sensor Network Applications

Talk at SASTRA

wsn applications
  • Potential for new intelligent applications:
    • Smart Homes
    • Process monitoring and control
    • Security/Surveillance
    • Environmental Monitoring
    • Construction
    • Medical/Healthcare
  • Implemented with Wireless Sensor Networks!

Talk at SASTRA


Medical and Healthcare Appln



Backbone Network

Net Switch

In Hospital


Net Switch

Wireless Remote


Possibility for Remote consulting

(including Audio Visual communication)

Talk at SASTRA


Medical and Healthcare


Sensors equipped

with BlueTooth

Talk at SASTRA

Source: USC Web Site

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

Talk at SASTRA

other examples
Other 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
  • VERICHIP: Miniaturised, Implanted, Identification Technology

Talk at SASTRA

structural health monitoring
Structural Health Monitoring

Accelerometer board prototype,

Ruiz-Sandoval, Nagayama & Spencer,

Civil E., U. Illinois Urbana-Champaign

Semi-active Hydraulic Damper

(SHD), Kajima Corporation, Japan

Model bridge with attached wireless sensors,

B.F. Spencer’s Lab, Civil E., U. Illinois U-C

Talk at SASTRA

application in environment monitoring


Pollutants monitored by sensors in the river

Sensors report to the base monitoring station

Application in Environment Monitoring
  • Measuring pollutant concentration
  • Pass on information to monitoring station
  • Predict current location of pollutant volume based on various parameters
  • Take corrective action

Talk at SASTRA

vmesh distributed data sensing relaying computing via vehicular wireless mesh networks
VMesh: Distributed Data Sensing, Relaying, & Computing via Vehicular Wireless Mesh Networks

Project at The University of California, Davis

US FCC allocated 5.850 to 5.925 GHz dedicated short range communication (DSRC)

Road side to Vehicle

Vehicle to vehicle communication

Talk at SASTRA

network characteristics of wsn
Network characteristics of WSN
  • Generally, the network:
    • Consists of a large number of sensors (103 to 106)
    • Spread over large geographical region (radius = 1to 103 km)
    • Spaced out in 1, 2, or 3 dimensions
    • Is self-organizing
    • Uses wireless media
    • May use intermediate “collators”

Talk at SASTRA

sensor network topology
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, theft, sabotage
  • Redeployment of additional nodes phase
    • Redeployment because of malfunctioning of units

Talk at SASTRA

organization into ad hoc net
Organization into Ad Hoc Net
  • Individual sensors are quite limited.
  • Full potential is realized only by using a large number of sensors.
  • Sensors are then organized into an ad hoc network.
  • Need efficient protocols to route and manage data in this network.

Talk at SASTRA

network topologies

Single Hop Network

All nodes communicate directly with Gateway

No router nodes

Cannot self-heal

Range 30-100m

Consumes lowest power

Network Topologies

Talk at SASTRA

network topologies1

Multi-hopping network

All nodes are routers

Self-configuring network

Node fails, network self-heals

Re-routes data through shortest path

Highly fault tolerant network

Multi-hopping provides much longer range

Higher power consumption…nodes must always listen!

Network Topologies

Talk at SASTRA

network topologies2
Star-Mesh Hybrid

Combines of star’s low power and…

…mesh’s self-healing and longer range

All endpoint sensor nodes can communicate with multiple routers

Improves fault tolerance

Increases network communication range

High degree of flexibility and mobility

Network Topologies

Talk at SASTRA

self organizing wlan
Self-Organizing WLAN
  • Opportunistic ad-hoc wireless networking concepts starting to mature…
    • Initial use to extend WLAN range in user-deployed networks
    • Based on novel auto-discovery and multi-hop routing protocols
    • extends the utility and reach of low-cost/high speed WiFi equipment

Wired Network




802.11 Access to


Ad-hoc radio link

(w/multi-hop routing




Ad-hoc access



Node (FN)

Mobile Node (MN)


Forwarding Node (FN)


Ad-hoc WLAN

Talk at SASTRA

how to get information from data centric sensor networks
How to get information from Data-centric Sensor Networks?
  • Types of Queries:
    • Historical Queries: Analysis of data collected over time
    • One Time Queries: Snapshot view of the network
    • Persistent Queries: Periodic monitoring at long and regular intervals
  • Routing required to respond to a Query:
    • Application specific
    • Data centric
    • Data aggregation capability desirable
    • Need to minimize energy consumption

Talk at SASTRA

software framework
Software Framework

MAC layer (Tiny OS, routing)

Configuration Table

Power consumption status & replacement strategy

Sensor Data Management


Application (passing parameters via API)

Talk at SASTRA

technical challenges
Technical challenges
  • Sensor design
  • Self-organizing network, that requires 0-configuration of sensors
    • Random or planned deployment of sensors, and collators
  • Auto-addressing
  • Auto-service discovery
  • Sensor localization

Talk at SASTRA

power consumption
Power Consumption
  • Limited Power Source
  • Battery Lifetime is limited
  • Each sensor node plays a dual role of data originator and data router (data processor)
  • The malfunctioning of a few nodes consumes lot of energy (rerouting of packets and significant topological changes)

Talk at SASTRA

environmental factors
Environmental Factors
  • Wireless sensors need to operate in conditions that are not encountered by typical computing devices:
    • Rain, sleet, snow, hail, etc.
    • Wide temperature variations
      • May require separating sensor from electronics
    • High humidity
    • Saline or other corrosive substances
    • High wind speeds

Talk at SASTRA

historical comparison
Historical Comparison

Consider a 40 Year Old Computer

Talk at SASTRA

advances in wireless sensor nodes
Advances in Wireless Sensor Nodes

Consider Multiple Generations of Berkeley Motes

Talk at SASTRA

  • Sensor networks will facilitate one to address several societal issues:
    • Early-warning systems
    • Disaster mitigation
  • Applications in other sectors
    • Security, transportation, irrigation
  • Technology is available today
    • Research into new sensors
    • Needs experimentation, pilot deployment
    • Lots needs to be done in Software (OS, MAC, Application)
    • While cost is an issue today, it will not be so tomorrow

Talk at SASTRA

  • Wireless & Mobile Systems Prof Dharma Prakash Agrawal and H. Deng
  • Integrating Wireless Technology in the Enterprise by Williams Wheeler, Elsevier Digital Press
  • Circuits & Systems for Wireless Communications Edited by Markus Helfenstein and George S. Moschytz, Kluwer Academic Publishers

Talk at SASTRA


Any Questions?

Talk at SASTRA