1. Wireless Sensor Network
Prabhakar Dhekne
Bhabha Atomic Research Centre
August 24, 2006 Talk at SASTRA 1

2. 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
August 24, 2006 Talk at SASTRA 2

3. Ubiquitous Computing
 Future State of Computing Technology?
 Mobile, many computers
 Small Processors
 Low Power Consumption
 Relatively Low Cost
August 24, 2006 Talk at SASTRA 3

4. 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!!!
August 24, 2006 Talk at SASTRA 4

5. 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
August 24, 2006 Talk at SASTRA 5

6. Mobile Computing
 Identify/develop mobile
computing solutions and effector
systems integrated with existing
wireless infrastructure
 Improve health care via
enhanced training and more
effective decision making
 To maximize the amount of
medical data available for health
surveillance
August 24, 2006 Talk at SASTRA 6

7. 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.
August 24, 2006 Talk at SASTRA 7

8. 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
August 24, 2006 Talk at SASTRA 8

9. Potential Benefits
 Increasing the physician productivity and
 Wireless sensors enable the patients’ freedom
 Providing clinicians remote access to patient’s
 Enabling telemonitoring in emergency
August 24, 2006 Talk at SASTRA 9

10. 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
August 24, 2006 Talk at SASTRA 10

11. 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.
August 24, 2006 Talk at SASTRA 11

12. Application server
 Application server centralises the
received data and presents it to the
user as:
 Raw data
 Formatted as graphs
App Server
DB
August 24, 2006 Talk at SASTRA 12

13. 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
August 24, 2006 Talk at SASTRA 13

14. 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
August 24, 2006 Talk at SASTRA 14

15. Bluetooth: Wireless PAN
 Bluetooth (Named after Danish King
Harold Bluetooth)
 Based on Master-Slave concept
 Short-range (10 meters)
 Eliminate the need for cables M1
S
 Operates in 2.4 GHz ISM band S
S 2
 720 Kbps 1 S
1 M 1/S1
 Three modes of operation park/hold/sniff 2
 Piconet & Scatternet (master+7 slaves)
 Interference due to multiple piconets
and IEEE 802.15.1 home/person LAN Piconet 1 Piconet 2
 To eliminate interference frequency
hoping technique used
 Ominidirectional with both voice & data
Port costs about Rs. 2000
August 24, 2006 Talk at SASTRA 15

16. 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
Ad Hoc Access hence not suitable for PDA’s
Net Point Net  Difficult to control access & security
 Set up is expensive
August 24, 2006 Talk at SASTRA 16

17. 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
August 24, 2006 Talk at SASTRA 17

18. Issues in Wireless
Networking
 Infrastructured networks
 Handoff
 location management (mobile IP)
 channel assignment
August 24, 2006 Talk at SASTRA 18

19. Issues in Wireless
Networking
Infrastructureless networks
Wireless MAC
 Security (integrity, authentication,
confidentiality)
 Ad Hoc Routing Protocols
 Multicasting and Broadcasting
August 24, 2006 Talk at SASTRA 19

20. 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
August 24, 2006 Talk at SASTRA 20

21. 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
August 24, 2006 Talk at SASTRA 21

22. Ad Hoc Networks
• Disaster recovery
• Battlefield
• ‘Smart’ office
 Rapidly deployable
infrastructure
 Wireless: cabling
impractical
 Ad-Hoc: no advance • Network of access devices
planning • Wireless: untethered
 Backbone network : • Ad-hoc: random deployment
wireless IP routers • Edge network: Sensor networks,
Personal Area Networks (PANs), etc.
August 24, 2006 Talk at SASTRA 22

23. 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
August 24, 2006 Talk at SASTRA 23

24. 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
August 24, 2006 Talk at SASTRA 24

25. Security
 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
August 24, 2006 Talk at SASTRA 25

26. Services while on move
Sensor services services
exercise monitor
biometrics Calendar+ service
traffic information Integrate dynamic traffic & schedule
Doctor prescription service
track health indicators
Doctor write prescription
Follow me kiosk service
Sensors mobile devices receive and transmit messages
Fridge & shopping service
Fridge records stock
Scalable, reliable, consistent, Suggests shopping based on recipe
Shopping guide in store
distributed service
August 24, 2006 Talk at SASTRA 26

27. 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
August 24, 2006 Talk at SASTRA 27

28. 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
August 24, 2006 Talk at SASTRA 28

29. Map-on-the-move
 Provide appropriate map
 County resolution driving in car
 Info stations small area high bandwidth
 Remainder lower bandwidth
August 24, 2006 Talk at SASTRA 29

30. Problems in a Mobile
Environment
 Variable Bandwidth
 Disconnected Operation
 Limited Power
 Implications on distributed file
system support?
August 24, 2006 Talk at SASTRA 30

31. 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
August 24, 2006 Talk at SASTRA 31

32. 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
August 24, 2006 Talk at SASTRA 32

33. 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
August 24, 2006 Talk at SASTRA 33

34. 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 WINLAB’s Outdoor Infostations Prototype (2002)
August 24, 2006 Talk at SASTRA 34

35. 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
802.11b
Management PDA
stations
Radio Monitor
802.11b
Forwarding Node/AP Linux PC
AP (custom)
Commercial
Router network 802.11
Compute
with arbitrary topology
& storage
servers
Sensor Node
PC-based (custom)
August 24, 2006
PC
Talk at SASTRA
Linux router 35

36. What is a WSN?
Sensor: The device Observer: The end user/computer
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
August 24, 2006 Talk at SASTRA 36

37. 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.
August 24, 2006 Talk at SASTRA 37

38. 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
August 24, 2006 Talk at SASTRA 38

39. Sensor Node Hardware
Sensor + Actuator + ADC + Microprocessor + Powering Unit
+ Communication Unit (RF Transceiver) + GPS
1Kbps- 1Mbps
3m-300m
Transceiver Lossy Transmission
128Kb-1Mb
Limited Storage Memory
Embedded 8 bit, 10 MHz
Processor Slow Computation
Requires
Supervision Sensor
Multiple sensors Limited Lifetime
Battery
 Portable and self-sustained (power, communication,
intelligence).
 Capable of embedded complex data processing.
August 24, 2006 Talk at SASTRA 39

40. Sensors and Wireless Radio
 Types of sensors:
-Pressure,
-Temperature
-Light
-Biological
-Chemical
-Strain, fatigue
-Tilt
 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.
August 24, 2006 Talk at SASTRA 40

41. 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
August 24, 2006 Talk at SASTRA 41

42. 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!
August 24, 2006 Talk at SASTRA 42

43. Medical and Healthcare Appln
Remote
Databases
Backbone
Backbone
Net Switch Network
Network
In Hospital
Physician Net Switch
Wireless Remote
consultation
Possibility for Remote consulting
(including Audio Visual communication)
August 24, 2006 Talk at SASTRA 43

44. Medical and Healthcare
Applications
Sensors equipped
with BlueTooth
August 24, 2006 Talk at SASTRA Source: USC Web Site44

45. iBadge - UCLA
 Investigate behavior of children/patient
 Features:
 Speech recording / replaying
 Position detection
 Direction detection / estimation
(compass)
 Weather data: Temperature, Humidity,
Pressure, Light
August 24, 2006 Talk at SASTRA 45

46. 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
August 24, 2006 Talk at SASTRA 46

47. Structural Health Monitoring
Accelerometer board prototype,
Ruiz-Sandoval, Nagayama & Spencer,
Civil E., U. Illinois Urbana-Champaign
Semi-active Hydraulic Damper
Model bridge with attached wireless sensors, (SHD), Kajima Corporation, Japan
B.F. Spencer’s Lab, Civil E., U. Illinois U-C
August 24, 2006 Talk at SASTRA 47

48. Application in Environment
Monitoring
 Measuring pollutant
Pollutants monitored by sensors in
concentration the river
 Pass on information
to monitoring station
 Predict current ST
location of pollutant
volume based on Sensors report to the base
monitoring station
various parameters
 Take corrective action
August 24, 2006 Talk at SASTRA 48

49. August 24, 2006 Talk at SASTRA 49

50. Vehicular Traffic Control
August 24, 2006 Talk at SASTRA 50

51. 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
VMesh: Distributed Data Sensing, Relaying, & C
Networks
August 24, 2006 Talk at SASTRA 51

52. Network characteristics of WSN
 Generally, the network:
 Consists of a large number of sensors (103 to 106)
 Spread over large geographical region (radius = 1
to 103 km)
 Spaced out in 1, 2, or 3 dimensions
 Is self-organizing
 Uses wireless media
 May use intermediate “collators”
August 24, 2006 Talk at SASTRA 52

53. 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
August 24, 2006 Talk at SASTRA 53

54. 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.
August 24, 2006 Talk at SASTRA 54

55. Network Topologies
 Star
 Single Hop Network
 All nodes communicate
directly with Gateway
 No router nodes
 Cannot self-heal
 Range 30-100m
 Consumes lowest power
August 24, 2006 Talk at SASTRA 55

56. Network Topologies
 Mesh
 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!
August 24, 2006 Talk at SASTRA 56

57. Network Topologies
 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
August 24, 2006 Talk at SASTRA 57

58. 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
Wired Network
AP1 Infrastructure
Infrastructure AP2
802.11 Access to
AP
Ad-hoc radio link
(w/multi-hop routing
Ad-hoc
Infrastructure
links
Ad-hoc access
To FN
Forwarding
Node (FN)
Mobile Node (MN)
(end-user)
Forwarding Node (FN)
Self-organizing
Ad-hoc WLAN
August 24, 2006 Talk at SASTRA 58

59. 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
August 24, 2006 Talk at SASTRA 59

60. Software
Framework
MAC layer (Tiny OS, routing)
Configuration Table
Power consumption status & replacement strategy
Sensor Data Management
Middleware
Application (passing parameters via API)
August 24, 2006 Talk at SASTRA 60

61. 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
August 24, 2006 Talk at SASTRA 61

62. 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)
August 24, 2006 Talk at SASTRA 62

63. 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
August 24, 2006 Talk at SASTRA 63

64. Historical Comparison
Consider a 40 Year Old Computer
Model Honeywell H-300 Mica 2
Date 6/1964 7/2003
CPU 2 MHz 4 MHz
Memory 32 KB 128 KB
SRAM ??? 512 KB
August 24, 2006 Talk at SASTRA 64

65. Advances in Wireless
Sensor Nodes
Consider Multiple Generations of Berkeley Motes
Model Rene 2 Rene 2 Mica Mica 2
Date 10/2000 6/2001 2/2002 7/2003
CPU 4 MHz 8 MHz 4 MHz 4 MHz
Flash
8 KB 16 KB 128 KB 128 KB
Memory
SRAM 32 KB 32 KB 512 KB 512 KB
Radio 10 Kbps 10 Kbps 40 Kbps 40 Kbps
August 24, 2006 Talk at SASTRA 65

66. Summary
 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
August 24, 2006 Talk at SASTRA 66

67. References
 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
August 24, 2006 Talk at SASTRA 67

68. Any
Questions?
August 24, 2006 Talk at SASTRA 68