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

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