Wireless Embedded Systems (0120442x)
Ad hoc and Sensor Networks
Chaiporn Jaikaeo [email protected]
Department of Computer Engineering Kasetsart University
Materials taken from lecture slides by Karl and Willig
Typical Wireless Networks
Base stations connected to wired backbone
Mobile nodes communicate wirelessly to base stations
Ad hoc Networks Networks without pre-configured infrastructure
require no hubs, access points, base stations
are instantly deployable
can be wired or wireless
Initially targeted for military and emergency applications
wired multi-hop wireless wireless
802.11 Ad hoc Mode 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
Heterogeneity ― sensors, PDAs, laptops
Limited resources ― CPU, bandwidth, power
Dynamic topology due to mobility and/or failure
Mobile Ad hoc Networks (MANETs)
A
B C
Sensor Networks
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
Network is embedded in environment
Nodes in the network are equipped with sensing and actuation to measure/influence environment
Nodes process information and communicate
Remote
monitoring
sensor field
Traditional Sensors
Network
Local
monitoring
Data loggers
sensor field
Wireless Sensors
Sensors communicate with data logger via radio links
radio link
Remote
monitoring
Network
Wireless Sensor Networks Wireless sensors + wireless network
Sensor nodes (motes) deployed and forming an ad hoc network
Requires no hubs, access points
Instantly deployable
Targeted applications
Emergency responses
Remote data acquisition
Sensor network
Sensor node/mote
Internet
Gateway
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
Humidity/temperature monitoring
Civil engineering
Structural response
Disaster management
Environmental sciences
Habitat monitoring
Conservation biology
WSN in Telemetry Applications
Sensor field
Gateway
wireless sensor node
sensor
sensor
GPRS
Network
or Internet
Information
Server
Browser
Landslide Monitor
Real deployment scenario…
Sources of data: Measure data, report them “somewhere”
Typically equip with different kinds of actual sensors
Sinks of data: Interested in receiving data from WSN
May be part of the WSN or external entity, PDA, gateway, …
Actuators (actors): Control some device based on data, usually also a sink
Roles of Participants in WSN
WSN = WASN
Classifying Application Types
Interaction patterns between sources and sinks classify application types
Event detection
Periodic measurement
Function approximation
Edge detection
Tracking
Deployment Options
Dropped from aircraft
Random deployment
Well planned, fixed
Regular deployment
Mobile sensor nodes
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?
Replace batteries
Unattended operation
Impossible but not relevant
Energy supply
Limited from point of deployment
Some form of recharging / energy scavenging
Characteristic Requirements
Type of service of WSN
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
Multi-hop wireless communication
Energy-efficient operation
Both for communication and computation, sensing, actuating
Auto-configuration
Manual configuration just not an option
Collaboration & in-network processing
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
Data centric networking
Focusing network design on data, not on node identifies (id-centric networking)
To improve efficiency
Locality
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
MANET – Mobile Ad hoc Network
Self-organization
Energy efficiency
(Often) Wireless multi-hop
MANET vs. WSN - Differences
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
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
Cost reduction
For wireless communication, simple microcontroller, system on chip, sensing, batteries
Miniaturization
Some applications demand small size
“Smart dust” as the most extreme vision
Energy scavenging
Recharge batteries from ambient energy (light, vibration, …)
Conclusion
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
IWING-MRF modules from IWING LAB
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