Wireless Embedded Systems
(0120442x)
Ad hoc and Sensor Networks
Chaiporn Jaikaeo
chaiporn.j@ku.ac.th
Department of Computer Engineering
Kasetsart University
Materials taken from lecture slides by Karl and Willig
Typical Wireless Networks
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Base stations connected to wired backbone
Mobile nodes communicate wirelessly to
base stations
Ad hoc Networks
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Networks without pre-configured infrastructure
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require no hubs, access points, base stations
are instantly deployable
can be wired or wireless
wired

wireless
multi-hop wireless
Initially targeted for military and emergency
applications
802.11 Ad hoc Mode
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IEEE 802.11 already provides support for
ad hoc mode
Computers can be connected without an
access point
Only work with single hop
Possible Applications for Ad hoc
Networks
Factory Floor
Automation
Disaster recovery
Car-to-car communication
Characteristics of Ad hoc Networks
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Heterogeneity ― sensors, PDAs, laptops
Limited resources ― CPU, bandwidth, power
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Dynamic topology due to mobility and/or failure
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Mobile Ad hoc Networks (MANETs)
C
A
B
Sensor Networks
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Participants in the previous examples were
devices close to a human user, interacting with
humans
Alternative concept:
Instead of focusing interaction on humans, focus
on interacting with environment
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Network is embedded in environment
Nodes in the network are equipped with sensing and
actuation to measure/influence environment
Nodes process information and communicate
Traditional Sensors
Network
sensor field
Remote
monitoring
Data loggers
Local
monitoring
Wireless Sensors

Sensors communicate with data logger via
radio links
sensor field
radio link
Network
Remote
monitoring
Wireless Sensor Networks
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
Wireless sensors + wireless network
Sensor nodes (motes) deployed and forming an ad hoc
network

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Requires no hubs, access points
Instantly deployable
Sensor
node/mote
Sensor network

Gateway
Targeted applications

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Emergency responses
Remote data acquisition
Internet
Remote
monitoring
WSN Platforms

Most are based on IEEE 802.15.4 (Wireless
Low-Rate Personal Area Network)
and many others…
WSN Application Examples

Agriculture
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Civil engineering
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Humidity/temperature
monitoring
Structural response
Disaster management
Environmental sciences
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Habitat monitoring
Conservation biology
WSN in Telemetry Applications
Browser
sensor
sensor
Information
Server
wireless sensor node
GPRS
Network
or Internet
Sensor field
Gateway
Landslide Monitor

Real deployment scenario…
Roles of Participants in WSN

Sources of data: Measure data, report them “somewhere”
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Sinks of data: Interested in receiving data from WSN

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Typically equip with different kinds of actual sensors
May be part of the WSN or external entity, PDA, gateway, …
Actuators (actors): Control some device based on data,
usually also a sink
WSN = WASN
Classifying Application Types

Interaction patterns between sources
and sinks classify application types
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Event detection
Periodic measurement
Function approximation
Edge detection
Tracking
Deployment Options

Dropped from aircraft
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Well planned, fixed
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Random deployment
Regular deployment
Mobile sensor nodes
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Can move to compensate for deployment
shortcomings
Can be passively moved around by some
external force (wind, water)
Can actively seek out “interesting” areas
Maintenance Options

Feasible and/or practical to maintain
sensor nodes?
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Replace batteries
Unattended operation
Impossible but not relevant
Energy supply
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Limited from point of deployment
Some form of recharging / energy scavenging
Characteristic Requirements
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Type of service of WSN
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Not simply moving bits like another network
Rather: provide answers (not just numbers)
Geographic scoping are natural requirements
Quality of service
Fault tolerance
Lifetime: node/network
Scalability
Wide range of densities
Programmability
Maintainability
Required Mechanisms
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Multi-hop wireless communication
Energy-efficient operation
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Auto-configuration
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Both for communication and computation,
sensing, actuating
Manual configuration just not an option
Collaboration & in-network processing
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Nodes in the network collaborate towards a
joint goal
Pre-processing data in network (as opposed to
at the edge) can greatly improve efficiency
Required Mechanisms
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Data centric networking
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Locality
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Focusing network design on data, not on node
identifies (id-centric networking)
To improve efficiency
Do things locally (on node or among nearby
neighbors) as much as possible
Exploit tradeoffs

E.g., between invested energy and accuracy
MANET vs. WSN - Similarities
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MANET – Mobile Ad hoc Network
Self-organization
Energy efficiency
(Often) Wireless multi-hop
MANET vs. WSN - Differences
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Equipment: MANETs more powerful
Application-specific: WSNs depend much
stronger on application specifics
Environment interaction: core of WSN,
absent in MANET
Scale: WSN might be much larger (although
contestable)
Energy: WSN tighter requirements,
maintenance issues
MANET vs. WSN - Differences

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Dependability/QoS: in WSN, individual node
may be dispensable (network matters), QoS
different because of different applications
Addressing: Data centric vs. id-centric
networking
Enabling Technologies for WSN
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Cost reduction
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Miniaturization
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For wireless communication, simple
microcontroller, system on chip, sensing,
batteries
Some applications demand small size
“Smart dust” as the most extreme vision
Energy scavenging

Recharge batteries from ambient energy (light,
vibration, …)
Conclusion
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MANETs and WSNs are challenging and
promising system concepts
Many similarities, many differences
Both require new types of architectures &
protocols compared to “traditional”
wired/wireless networks
In particular, application-specificness is a
new issue
Demonstration
Sensor Modules
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IWING-MRF modules from IWING LAB
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250 kbps 2.4GHz IEEE 802.15.4
12MHz Atmel ATMega328P microcontroller
Additional light and temperature sensors
Scenario
Monitor station
Sensor nodes measuring light intensity