Wireless Embedded Systems (0120442x) Ad hoc and Sensor Networks

Wireless Embedded Systems(0120442x)

Ad hoc and Sensor Networks

Chaiporn [email protected]

Department of Computer EngineeringKasetsart 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 wirelesswireless

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

ad hoc

ad hoc

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

BC

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

Remotemonitoring

sensor field

Traditional Sensors

Network

Localmonitoring

Data loggers

sensor field

Wireless Sensors Sensors communicate with data

logger via radio links

radio linkRemote

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

Remotemonitoring

WSN Platforms Most are based on IEEE 802.15.4

(Wireless Low-Rate Personal Area Network)

and many others…

WSN Application Examples Agriculture

Humidity/temperaturemonitoring

Civil engineering Structural response Disaster management

Environmental sciences Habitat monitoring Conservation biology

WSN in Telemetry Applications

Sensor field

Gateway

wireless sensor node

sensor sensor

GPRSNetwork

or Internet

InformationServer

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