An Introduction to Cyber-Physical Systems

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INF5910/INF9910

Outline

• What is Cyber-Physical Systems (CPS)?• Applications• Research Challenges

2Cyber Physical CPS

Cyber Systems

• Cyber is…– More than just software– More than just networking– More than just embedded computing

• “Cyber” implies the integration of…– Computation,– Communication– Control

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Computation

Physical Systems

• Physical – natural and human-made systems governed by the laws of physics and operating in continuous time

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Power

Highway

FactoryAirline

What are Cyber-Physical Systems?

• Cyber-Physical Systems –systems in which the cyber and physical systems are tightly integrated at all scales and levels

• CPS – Integrates computation and

physical processes– uses embedded computers

and networks to compute, communicate, and control the physical processes

– receives feedbacks on how physical processes affect computations and vice versa.

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Information

Systems

Computation

A CPS Architecture

Vincenzo Liberatore, Networked Cyber‐Physical Systems: An Introduction, 2007 6

Start from an example: Cooling Data Center

• In 2006, data centers in the US– Use 59 billion kilowatt-hours of electricity– Cost US$4.1 billion– 2% of total USA energy budget

• In 2010, expected 3% of total USA energy budget

• Cooling equipment uses at least 50% total energy cost.

• A key challenge is to minimize the cooling requirement and improve the overall energy efficiency, toward optimizing the operations of data center

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Cooling data center: Cyber-physical approach

• Observation: different workloads generate different power consumption– Some locations in data center

are easier to cool than others

• Solution: moving tasks from Zone A to Zone B– lower overall power

consumption

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R.K.Sharma etal. “Balance of Power: Dynamic Thermal Management of Internet Data Centers”. Jan.2005

A

B

Temperature distribution in data center

CPS Approach: distribute tasks among the servers to minimize the temperature

cyber physicalcoupled

Two definitions for CPS

• ʺA cyber-physical system (CPS) integrates computing , communication and storage capabilities with monitoring and / or control of entities in the physical world, and must do so dependably, safely, securely, efficiently and in real-time.“– S. Shankar Sastry, UC Berkeley

• Cyber-physical systems will transform how we interact with the physical world just like the Internet transformed how we interact with one another.– NSF CPS Workshop, Austin, TX, Oct. 16‐17, 2006

CPS characteristics

• Cyber capability in every physical component• Networked• Sensing technology• Pervasive networking• Predictable behavior• Real-time operation & close loop control• High confidence software & systems• Cyber and physical components are integrated

for: learning and adaptation, higher performance, self-organization, self assembly

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Outline

• What is cyber-physical systems?• Applications• Research Challenges

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CPS applications

CPS interact with the physical world, they must operate dependably, safely, securely, efficiently and in real-time.

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Car-to-Car Communications

• Safety: vehicles broadcast their physical state information over a wireless network to allow their neighbors to track them and predict possible collisions, trigger speed-limit reminder, accident warning

• Traffic information: share information on the traffic on-road for traffic congestion alarm, get map updates

• Entertainment: search for places of interest via the Internet

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Healthcare

• Electronic Patient Record– Medical records at any point of service

• Home care: monitoring and control– Heart rate, blood pressure– wearable networks

• Operating Room– Closed loop monitoring and control; multiple

treatment stations– System coordination

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Power Grid/Smart Grid

• Current picture:– Reactive equipment protection– Power outage over the world

• 25 July 2010, Washington D.C., 250000 people lost power

• 22 March 2010, Malta, nation-wide blackout

• Better future?– Real-time cooperative control

of protection devices– Homes and offices are more

energy efficient to operate

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Outline

• What is cyber-physical systems?• Applications• Research Challenges

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A New Research Area• Artificial intelligence

– Can machines think?– By A. Turing in “Computing Machinery and Intelligence”, 1950

• Ubiquitous Computing– Computers everywhere– By Mark Weiser, XEROX PARC, 1990

• Pervasive Computing– 6As Model, The “authorized access to anytime-anywhere-any

device-any network-any data”– Industry vision (1999, IBM, etc.)

• Cyber-Physical Systems– Computation and networking integrated with physical processes

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Research Challenges

• Build the interface between the cyber world and the physical world?

• Why this is hard:– No clear boundaries between cyber and physical

worlds.– Boundaries are always changing.– No perfect digitization of the continuous world– Inpredicable complex systems– Essentially multi-disciplinary

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Multi-disciplinary

• Sensing technologies• Distribute computing and networking• Real-time computing• Control theory• Signal processing• Embedded systems

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This seminar will cover some basic material from these areas, but focus on advanced research papers related to CPS and its sub-areas.

Introduction to Wireless Sensor Networks

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Outline

• What is Wireless Sensor Networks (WSN)?• Applications• Research challenges

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Sensor nodes

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Sensor node model• Low-power processor

– Limited processing.• Memory

– Limited storage• Mobility

– No or limited movement• Communication

– Low-power.– Low data rate.– Limited range.

• Sensors– Scalar sensors: temperature, light, etc.– Cameras, microphones.

• Power– Powered by battery with long-time operation in unattended areas

Sensor Unit

CPU

Communication

Storage

POWER

Real World

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What are Wireless Sensor Networks (WSNs)?

• Networks of typically small, battery-powered, wireless devices.– On-board processing,– Communication – Sensing

• R: transmission range• V: the set of sensor nodes

Wireless Sensor Network

Sensor node

A

B

1-hop neighborhoodR

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Outline

• What is Wireless Sensor Networks (WSN)?• Applications• Research challenges

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Engineering, civilian, enterprise applicationswill eventually dominate

WSN in building environment• WSN is deployed at the

Golden Gate Bridge to monitor structural health

• Structural vibrations are measured and collected by sensors

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Golden Gate Bridge – San Francisco

http://www.cs.berkeley.edu/~binetude/ggb/

Forest observation, fire detection

• WSN is deployed in a forest to collect data including temperature, humidity, illumination, and CO2 etc.

• Applications, e.g. forest surveillance, forestry observation, fire risk27

http://greenorbs.org/

Volcano monitoring

• Use WSN to monitor active and hazardous volcanoes• Challenge: how to maximize the data collecttion,

subject to resource constraints. 28

http://fiji.eecs.harvard.edu/Volcano

Military Operation: Shooter localization

• WSN determines the shooter location and the bullet trajectory

• Red circle: the estimated shooter position

• Red line: the shot direction• Green dots: sensor locations.

• Basic idea: using the arrival times of the acoustic events at different sensor locations, the shooter position can be accurately calculated using the speed of sound and the location of the sensors.

http://w3.isis.vanderbilt.edu/projects/nest/applications.html

Urban Sensing

• Use WSN to measure city pollutants

• Put sensors on taxi• When the taxi are

moving around in a city, the sensors on the taxi can sense and transmit the air quality to a data processing center

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Carbon monoxide (CO)

http://www.escience.cam.ac.uk/mobiledata/

Oceanic Environment

• British Petroleum oil spill at the Gulf of Mexico and its huge environment damage in 2010

• monitor the environmental conditions/pollution of the ocean surface

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Wildlife behavior analysis and interaction modeling

• Put a camera (i.e. video sensor) on each deer.

• The captured video will be transmitted to a remote monitoring center for real-time viewing, control; and wildlife behavior analysis

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Body Sensor Networks

• WSN can be on/beside/in body• Medical monitoring, e.g. heart rate, blood pressure• Remote monitoring and localization for aged people at

home; patient at hospital33

http://www.iet.ntnu.no/nb/taxonomy/term/10?page=1

Outline

• What is Wireless Sensor Networks (WSN)?• Applications• Research challenges

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Challenges

• Generally, severely energy constrained.– Limited energy sources (e.g., batteries).– Trade-off between performance and lifetime.

• Resource-constrained systems– Power– Computation– Bandwidth

• Unstable wireless link quality• Scalable.

– potentially large number of nodes

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Lifetime in WSN• Objective: how to maximize the lifetime of whole network?• Different lifetime definition based on the number of alive

nodes, coverage, connectivity, QoS• Based on Number of alive nodes

– the time until the first sensor is drained of its energy

– the time until all nodes have been drained of their energy

– the time until the fraction of alive nodes falls below a predefined threshold β

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Tnn=minv 2 V TvTnn: network lifetime; Tv: the lifetime of node v

Tnn=maxv 2 V Tv

Research Topics• Energy models, energy efficiency• Routing/packet forwarding• Medium access control• Localization• Data fusion• Clustering • Topology control• Security• Novel applications• QoS

– Delay, throughput, packet delivery ratio, packet error rate– Real-time transmission in body sensor networks, wireless video sensor

networks

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Routing in Wireless Sensor Networks

• Objective: choose multi-hop routing path from source node A to the sink

• Constraints:– Energy efficiency– QoS (delay, packet

delivery ratio)

Sensor node

Source node A

Sink node

B

C

D

Wireless Sensor Network38

Medium Access Control in WSN

• Role: coordinate access to and transmission over a medium common to all nodes.

• Challenge:– Interference, Limited energy, Limited bandwidth,

Fading channel, Decentralized• Causes for energy consumption

– Packet collision, overhead, idle listening• Performance metrics

– Throughput– Energy consumption– Access delay

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Localization in WSN• Objective: determine a node’s

position

• Challenges:

– Limited communication range

– All the measurements are inaccurate because of multi-path fading.

– Interferences

– Node mobility

• Applications

– Tracking patient, old people, children who need help in case

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Clustering in WSN• Role: nodes are partitioned into a

number of small groups (clusters) to facilitate communications, management and data aggregation

• A cluster has – A cluster head: the coordinator in a

cluster– Members: nodes within a cluster

• Clustering results in two-tier hierarchy– Intercluster: cluster heads form the

higher tier– Intracluster: member nodes form

the lower tier

41Intercluster communication

Intracluster communication

Cluster head Member node

Mobile Social Networks (MSN)

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MSN

Not just using mobile phone to access Facebook!

Mobile Social Networks (MSN)

• MSN: mobile users of similar interests cooperate to establish network connectivity and communicate with each other in the absence of network infrastructure

• Properties:– mobile users usually move around several well-visited

locations– Regular user’s dwell time at each community

• Research challenges:– Social-aware information sharing and dissemination– Exploiting social science concepts (e.g. degree)

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Common interest, e.g.skiing, StarCraft, travel, music

RFID Systems; Internet of Things

Presented by Sabita

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