Sandeep Gupta

1
Wireless Sensor Networking Applications and
Challenges

• Sandeep Gupta
• Arizona State University
• Based on Slides by Prof. Loren Schwiebert, CS,
  Wayne State University

2
What is a Wireless Sensor Network?

• Wireless Sensor Node Sensor Actuator ADC
  Microprocessor Powering Unit Communication
  Unit (RF Transceiver)
• An ad hoc network of self-powered and
  self-configuring sensor nodes for collectively
  sensing environmental data and performing data
  aggregation and actuation functions reliably,
  efficiently, and accurately.

GPS Sensor Node
3
Limitations of Wireless Sensors

• Wireless sensor nodes have many limitations
• Modest processing power 8 MHz
• Very little storage a few hundred kilobits
• Short communication range consumes a lot of
  power
• Small form factor several mm3
• Minimal energy constrains protocols
• Batteries have a finite lifetime
• Passive devices provide little energy

4
Some Sample Applications

• Industrial and Commercial Uses
• Inventory Tracking RFID
• Automated Machinery Monitoring
• Smart Home or Smart Office
• Energy Conservation
• Automated Lighting
• Military Surveillance and Troop Support
• Chemical or Biological Weapons Detection
• Enemy Troop Tracking
• Traffic Management and Monitoring

5
Sensor-Based Visual Prostheses
Retinal Implant
Cortical Implant
6
Organization into Ad Hoc Networks

• 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.

7
Why Wireless Sensors Now?

• Moores 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.
• Power source improvements in batteries, as well
  as passive power sources such as solar or
  vibration energy, are expanding application
  options.

8
Current State of the Artin Wireless Sensors
9
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

10
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 Memory 8 KB 16 KB 128 KB 128 KB
SRAM 32 KB 32 KB 512 KB 512 KB
Radio 10 Kbps 10 Kbps 40 Kbps 40 Kbps
11
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
12
A Rosy Future for Wireless Sensors?

• Is the effort on wireless sensor protocols a
  waste of time??
• Can we just wait 10-15 years until we have
  sensors that are very powerful??

• NO!! Will still face
• Very limited storage
• Modest power supplies

13
Proposed Applications of Wireless Sensors
14
Pervasive Computing (Smart Home / Office)

• Sensors controlling appliances and electrical
  devices in the house.
• Better lighting and heating in office buildings.
• The Pentagon building has used sensors
  extensively.

15
Biomedical / Medical

• Health Monitors
• Glucose
• Heart rate
• Cancer detection
• Chronic Diseases
• Artificial retina
• Cochlear implants
• Hospital Sensors
• Monitor vital signs
• Record anomalies

16
Military
Remote deployment of sensors for tactical
monitoring of enemy troop movements.
17
Industrial Commercial

• Numerous industrial and commercial applications
• Agricultural Crop Conditions
• Inventory Tracking
• In-Process Parts Tracking
• Automated Problem Reporting
• RFID Theft Deterrent and Customer Tracing
• Plant Equipment Maintenance Monitoring

18
Traffic Management Monitoring

• Future cars could use wireless sensors to
• Handle Accidents
• Handle Thefts

• Sensors embedded in the roads to
• Monitor traffic flows
• Provide real-time route updates

19
Driving Forces for AdoptingNew Technology
20
Economic Factors

• New technologies replace existing technologies or
  fill new niches when there are economic
  advantages.
• Wireless sensors will replace wired sensors
• No wiring lower costs
• More flexible deployments
• Wireless sensors will provide new services
• Provide cost advantages or lower overhead
• Improve product quality or product features

21
Novelty

• Some early adopters use new technology simply for
  novelty or the fun of it. Examples include
• Java rings and internet watches.
• Maybe wireless sensors for dating or meeting new
  people?
• Personal wireless sensors for fun a temperature
  monitor you carry around?

22
Legal / Liability

• New technologies are adopted because of
  government mandates
• Air bags in automobiles
• Child safety seats
• Companies employ new technologies to avoid being
  sued!!
• Temperature sensors to detect coffee that is too
  hot??

23
Entertainment

• New technology is adopted for entertainment.
• Playing games is major use of home PCs.
• So is Internet browsing.
• Games on cellular phones.
• 3D visualization for games.
• Games of tag using wireless sensors?
• Interactive role-playing games with sensors?

24
Not Technical Superiority

• Useful technologies may not dominate the
  marketplace for several reasons.
• Delay in getting to market.
• Lack of standardization.
• Limited applications.
• Consumer preference VHS vs. Betamax.
• Weaker marketing or capitalization.
• Unusual that there are no alternative
  technologies that can be used.

25
Uses of New Technology
26
Unexpected Killer Applications

• Useful applications often follow available
  technology. For example,
• PCs were available and people looked for a killer
  app Visicalc.
• The Internet was not created with these current
  applications in mind
• World Wide Web
• E-Commerce
• Peer-to-Peer Digital Music Sharing

27
Unanticipated Uses Arise

• Once technology is available, creativity leads to
  new applications
• Sims Internet world
• E-Bay auctions
• Mirror for the Palm Pilot
• Digital cameras with PC interface
• What surprising applications for wireless sensor
  networks?
• Depends on sensor node technology

28
Some Technical Challenges
29
Noisy Sensors

• Sensor readings can be inaccurate. Protocols
  need to recognize this.
• GPS Sensor
• Accurate within
• 2.8 meters
• Relative Humidity Sensor
• Accuracy of 5
• 8 at 90 Relative Humidity
• 2 with calibration

30
Wireless Channel Conditions

• Limitations of wireless channels
• Noisy
• Interference
• Link Contention
• Unidirectional Links
• But inherently a broadcast medium

31
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

32
Networking Issues in Wireless Sensor Networks
33
Specific Destinations

• Messages mostly routed to base stations
• Not arbitrary source-destination pairs
• Opportunities for optimization
• Network traffic is not balanced

34
Hop-by-Hop Communication

• Energy for wireless communication grows with
  distance d at the rate d2 d4.
• Multiple short hops are cheaper than one long
  hop.
• Scheduling many nodes leads to high contention
  not scalable.

35
Data Centric Communication

• Query-Response Mode of Communication
• Nodes may not have unique global Ids
• Data is retrieved by specifying some desirable
  properties e.g.
• What is the temperature in Room SCOB 105?

36
Periodic or Event-Driven

• Communication patterns for wireless sensor
  networks take one of two general forms
• Periodic transmissions from all sensors.
• Reports from only those sensors that observe a
  specific event.
• Based on different application requirements.
• Routing protocols have been proposed for either
  type of traffic.

37
In-Networking/In-Situ Processing (Data
Aggregation)

• Neighboring sensors observe similar phenomenon
  have similar readings.
• Better to locally combine similar readings.
• Increases accuracy and reliability.
• Decreases energy consumption.
• May be better to summarize readings.
• Avoids base station traffic implosion.
• Reduces energy consumption.

38
Time Synchronization

• Data aggregation assumes time synchronization!!!
• Need to know events at different sensors are
  temporally related.
• Allows one to distinguish multiple targets.
• Not trivial to accomplish in the constrained
  environment of sensor networks.

39
Scalability!

• Size of sensor networks will grow because
• Sensors more affordable as cost decreases
• Redundant sensors provide
• Reliability
• Fault tolerance
• Longer network lifetime
• Protocols will support large networks
• Applications will exist for larger networks

40
What will Wireless Sensor Networks Look Like in
the Near Future?
41
Large-Scale Deployments

• Sensor networks will grow in size because of
• Lower cost
• Better protocols
• Advantages of dense networks

42
Heterogeneous Sensors

• Homogeneous network of sensors is the typical
  assumption, but not the future!!
• Combining sensors with different functions
• Hierarchy of sensors a few expensive powerful
  sensors with more cheap sensors
• Useful for special communication nodes
• A few sensor nodes with expensive sensors, such
  as GPS-equipped sensors

43
Mobile Sensors

• Sensors with Micromachines
• Low-Power Motors that Support Mobility

44
General Purpose Sensors

• Single-purpose network is the typical assumption,
  but not the future!!
• Sensors for evolving applications
• Sensors that can adapt to changing objectives
• More memory and CPU will allow more complex
  applications
• Flexibility increases marketability

45
Overlapping Coverage Areas

• Sensors will be deployed for specific
  applications, but
• These deployments will overlap
• Sensors will have different properties
• Users will want to combine these different
  sensors for new applications
• Temperature sensors for fire fighting
• Location tracking for rescue operations

46
Mixture of Wired and Wireless

• Wireless sensors will become a seamless part of
  larger networks!
• Combining wired sensors with wireless sensors
• Wired sensors can have more power
• Wired sensors can run TCP/IP
• Accessing wireless sensors through the Internet
• Need a gateway to translate requests
• Uploading/downloading information remotely
• Modifying wireless sensor tasks remotely
• Increased direct user interaction

47
Some Impediments toCreating Future Applications
48
Need a Standardized Interface

• Automated interaction between sensors implies
  some standard mechanism for communication!
• Requires compatible wireless technology
• Standardization a common theme
• TCP/IP for the Internet
• Java for Internet programming
• Jini, SLP, etc. for 802.11 wireless devices
• Need a service discovery protocol
• Enables standard interface among sensors

49
Service Discovery Protocol
Anyone need a printer?
"Dear Mom...I'm sitting..."
50
Service Discovery Protocol (cont.)

• For a wireless sensor network, service discovery
  provides
• Automated calibration of new devices
• Highly dynamic system configurations
• Cooperation among resource poor devices
• Solves resource sharing device
• Storage and long-range networking services can be
  obtained from a nearby server
• Reduces duplication of functionality
• Supports novel interactions in the future

51
Security Issues

• Concerns about misuse and privacy
• Privacy issues may slow consumer adoption of
  technology
• User tracking RFID concerns
• Has not proved true on the Internet!
• Authentication and privacy are not always
  complementary objectives
• Do not want your medical sensor hacked!!
• Data tampering and computer viruses could be a
  nightmare!

52
Liability and Safety Concerns

• Companies may adopt wireless sensors to reduce
  liability, but wireless sensors could also
  increase liability
• Use in critical applications could be limited
• Imagine a medical sensor fails!!
• Or an automotive theft deterrent system failure
• Companies will be slow to adopt technology that
  increases their legal exposure
• May delay adoption

53
Software Engineering

• Imagine a heterogeneous wireless sensor network
  with complex tasks and high levels of
  interaction
• End-user level products easy to use
• Software design??
• Debugging??
• Remote software updates??
• Example Send a request over the Internet to turn
  on lights when your car reaches home. The
  request fails.

54
Summary and Conclusions

• Wireless sensor networks have a bright future
• Many applications have been proposed
• Potential to revolutionize human-computer
  interactions
• Availability of sensors will lead to new and
  exciting applications
• A lot of research remains to be done
• Many obstacles to overcome
• Wireless sensors will not evolve into traditional
  computers
• Allow realism to guide research efforts

55
Acknowledgments

• Professor Loren Schwiebert
• Wayne State University