sandeep gupta arizona state university based on slides by prof. loren schwiebert, cs, wayne state...

Sandeep GuptaArizona State University

Based on Slides by Prof. Loren Schwiebert, CS, Wayne State University

Wireless Sensor Wireless Sensor Networking: Applications Networking: Applications

and Challengesand Challenges

Wireless Sensor Networks: Applications & Challenges 2

What is a Wireless Sensor Network?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


Limitations of Wireless SensorsLimitations 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


Some Sample ApplicationsSome 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


Retinal Implant Cortical Implant

Sensor-Based Visual ProsthesesSensor-Based Visual Prostheses


Organization into Ad Hoc NetworksOrganization 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.


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.

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

Current State of the ArtCurrent State of the Artin Wireless Sensorsin Wireless Sensors


Typical Sensor Node FeaturesTypical 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


Advances in Wireless Sensor NodesAdvances 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


Historical ComparisonHistorical 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


A Rosy Future for Wireless Sensors?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

Proposed Applications of Proposed Applications of Wireless SensorsWireless Sensors

Wireless Sensor Networks: Applications & Challenges 14Pervasive Computing (Smart Home / Pervasive Computing (Smart Home / Office)Office)

Sensors controlling appliances and electrical devices in the house.

Better lighting and heating in office buildings.

The Pentagon building has used sensors extensively.


Biomedical / MedicalBiomedical / Medical

Health Monitors– Glucose– Heart rate– Cancer detection

Chronic Diseases– Artificial retina– Cochlear implants

Hospital Sensors– Monitor vital signs– Record anomalies


MilitaryMilitary

Remote deployment of sensors for tactical monitoring of enemy troop movements.


Industrial & CommercialIndustrial & 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


Traffic Management & MonitoringTraffic 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

Driving Forces for AdoptingDriving Forces for AdoptingNew TechnologyNew Technology


Economic FactorsEconomic 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


NoveltyNovelty

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?


Legal / LiabilityLegal / 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??


EntertainmentEntertainment

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?


NotNot Technical Superiority 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.

Uses of New TechnologyUses of New Technology


Unexpected Killer ApplicationsUnexpected 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


Unanticipated Uses AriseUnanticipated 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

Some Technical ChallengesSome Technical Challenges


Noisy SensorsNoisy Sensors

Sensor readings can be inaccurate. Protocols need to recognize this.

GPS Sensor Accurate within

2.8 metersRelative Humidity Sensor

Accuracy of ±5%±8% at 90% Relative Humidity±2% with calibration


Wireless Channel ConditionsWireless Channel Conditions

Limitations of wireless channels– Noisy– Interference– Link Contention– Unidirectional Links

But inherently a broadcast medium


Environmental FactorsEnvironmental 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

Networking Issues in Networking Issues in Wireless Sensor NetworksWireless Sensor Networks


Specific DestinationsSpecific Destinations

Messages mostly routed to base stations– Not arbitrary

source-destination pairs

Opportunities for optimization

Network traffic is not balanced


Hop-by-Hop CommunicationHop-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.


Data Centric CommunicationData Centric Communication

Query-Response Mode of Communication

Nodes may not have unique global IdsData is retrieved by specifying some

desirable properties e.g.– What is the temperature in Room SCOB

105?


Periodic or Event-DrivenPeriodic 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.

Wireless Sensor Networks: Applications & Challenges 37In-Networking/In-Situ Processing In-Networking/In-Situ Processing (Data Aggregation)(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.


Time SynchronizationTime 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.


Scalability!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

What will Wireless Sensor What will Wireless Sensor Networks Look Like in the Networks Look Like in the

Near Future?Near Future?


Large-Scale DeploymentsLarge-Scale Deployments

Sensor networks will grow in size because of:– Lower cost

– Better protocols

– Advantages of dense networks


Heterogeneous SensorsHeterogeneous 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


Mobile SensorsMobile Sensors

Sensors with Micromachines

Low-Power Motors that Support Mobility


General Purpose SensorsGeneral 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


Overlapping Coverage AreasOverlapping 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


Mixture of Wired and WirelessMixture of Wired and WirelessWireless 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

Some Impediments toSome Impediments toCreating Future Creating Future

ApplicationsApplications


Need a Standardized InterfaceNeed 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


Service Discovery ProtocolService Discovery Protocol

Anyone need a printer?


Service Discovery Protocol (cont.)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 functionalitySupports novel interactions in the future


Security IssuesSecurity 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!


Liability and Safety ConcernsLiability 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


Software EngineeringSoftware 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.


Summary and ConclusionsSummary 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


AcknowledgmentsAcknowledgments

Professor Loren Schwiebert

Wayne State University

sandeep gupta arizona state university based on slides by prof. loren schwiebert, cs, wayne state...

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