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Self-Organization in Autonomous Sensor/Actuator Networks

[SelfOrg]Dr.-Ing. Falko Dressler

Computer Networks and Communication SystemsDepartment of Computer SciencesUniversity of Erlangen-Nürnberg

http://www7.informatik.uni-erlangen.de/~dressler/dressler@informatik.uni-erlangen.de

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Overview

Self-OrganizationIntroduction; system management and control; principles and characteristics; natural self-organization; methods and techniques

Networking Aspects: Ad Hoc and Sensor NetworksAd hoc and sensor networks; self-organization in sensor networks; evaluation criteria; medium access control; ad hoc routing; data-centric networking; clustering

Coordination and Control: Sensor and Actor NetworksSensor and actor networks; coordination and synchronization; in-network operation and control; task and resource allocation

Bio-inspired NetworkingSwarm intelligence; artificial immune system; cellular signaling pathways

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Mobile Ad Hoc and Sensor Networks

Mobile Ad Hoc Networks (MANET)Wireless Sensor Networks (WSN)

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Infrastructure-based Wireless Networks

Typical wireless network are based on infrastructureE.g., GSM, UMTS, WLAN, … Base stations connected to a wired backbone networkMobile entities communicate wirelessly to these base stationsTraffic between different mobile entities is relayed by base stations and wired backboneMobility is supported by switching from one base station to anotherBackbone infrastructure required for administrative tasks

IP backbone

ServerRouter

Gateways

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Infrastructure-based Wireless Networks – Limitations?

What if …No infrastructure is available? – E.g., in disaster areasIt is too expensive/inconvenient to set up? – E.g., in remote, large construction sitesThere is no time to set it up? – E.g., in military operations

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Possible Applications for Infrastructure-free Networks

Factory floor automation

Disaster recovery Car-to-car communication

Finding out empty parking lots in a city, without asking a serverSearch-and-rescue in an avalanche Personal area networking (watch, glasses, PDA, medical appliance, …)Military networking: Tanks, soldiers, … …

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Further Applications

Collaborative and Distributed ComputingTemporary communication infrastructureQuick communication with minimal configuration among a group of peopleExamples

A group of researchers who want to share their research findings during a conferenceA lecturer distributing notes to a class on the fly

Emergency operationsRescue, crowd control, and commando operationsConstraints

Self-configuration with minimal overheadIndependency of fixed or central infrastructureFreedom and flexibility of mobilityUnavailability of conventional communication infrastructure

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Solution: (Wireless) Ad Hoc Networks

Try to construct a network without infrastructure, using networking abilities of the participants

This is an ad hoc network – a network constructed “on demand”, “for a special purpose”

Simplest example: Laptops in a conference room –a single-hop ad hoc network

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Limited range: Multi-hopping

For many scenarios, communication with peers outside immediate communication range is required

Direct communication limited because of distance, obstacles, …Solution: multi-hop network

?

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Wireless Mesh Networks

Alternate communication infrastructure for mobile or fixed nodes/usersIndependence of spectrum reuse constraints and the requirements of network planning of cellular networksMesh topology provides many alternate data paths

Quick reconfiguration when the existing path fails due to node failuresMost economical data transfer capability coupled with the freedom of mobility

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Ad Hoc Networks vs. Infrastructure-based Networks

Infrastructure-based network

Ad hoc network

Prerequisites Pre-deployed infrastructure, e.g. routers, switches, base stations, servers

None

Node properties End system only Duality of end system and network functions

Connections Wired or wireless Usually wirelessTopology Outlined by the pre-

deployed infrastructureSelf-organized topology maintained by the nodes

Network functions Provided by the infrastructure

Distributed to all participating nodes

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Mobility: Suitable, Adaptive Protocols

In many (not all!) ad hoc network applications, participants move around

In cellular network: simply hand over to another base station

In mobile ad hoc networks (MANET):

Mobility changes neighborhood relationship Must be compensated forE.g., routes in the network have to be changed

Complicated by scaleLarge number of such nodes difficult to support

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MANET (Mobile Ad Hoc Network)

Active IETF working group

Standardization of IP routing protocol functionality suitable for wireless routing application within both, static and dynamic topologies

Approaches are intended to be relatively lightweight in nature, suitablefor multiple hardware and wireless environments, where MANETs are deployed at the edges of an IP infrastructure

Support for hybrid mesh infrastructures (e.g., a mixture of fixed and mobile routers)

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Battery-operated Devices: Energy-efficient Operation

Often (not always!), participants in an ad hoc network draw energy from batteriesDesirable: long run time for

Individual devicesNetwork as a whole

Energy-efficient networking protocolsE.g., use multi-hop routes with low energy consumption (energy/bit)E.g., take available battery capacity of devices into accountHow to resolve conflicts between different optimizations?

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Problems/Challenges for (Mobile) Ad Hoc Networks

Without a central infrastructure, things become much more difficultLack of central entity for organization availableLimited range of wireless communicationMobility of participantsBattery-operated entities

Without a central entity (like a base station), participants must organize themselves into a network Self-organization

Pertains to (among others)Medium access control – no base station can assign transmission resources, must be decided in a distributed fashionFinding a route from one participant to another

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Wireless 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 environmentNodes in the network are equipped with sensing and actuation to measure/influence environmentNodes process information and communicate it wirelessly

Wireless sensor networks (WSN)

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Wireless Sensor Networks

Multiple roles can be distinguishedSensors – measure physical phenomena, sources of measurement dataBase stations – analyze and post-process data, sinks for measurement dataActuators – perform actuation in response to received dataProcessing elements – pre-processing of transmitted data

basestation

sensornode

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Composition of Sensor Nodes – Hardware

Processor (and memory)E.g., Atmel ATmega128 microcontroller, 16 MHz, 128 kByte flash

Radio transceiverE.g., Chipcon CC1000 (315/433/868/915 MHz), CC2400 (2.4 GHz)

BatteryPossibly in combination with energy harvesting

SensorsLight, temperature, motion, …

Micro controller

Memory

Storage

Radio transceiver

Battery

Sensor 1

Sensor n…

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Composition of Sensor Nodes – Software

Event-driven operating principleE.g., TinyOS

System component

Event(Sensor)

Event(Timer)

Event(Transceiver)

…

System function…System function

Event handler

New event(Data packet)

New event(Timer)…

…

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Communication in WSN

MACEnergy-efficiency

NetworkAddress-based routingData-centric routing

TransportData aggregation

ApplicationPush vs. pull

Application layer

Transport layer

Network layer

MAC layer

Physical layer

Pow

er managem

ent plane

Mobility m

anagement plane

Task managem

ent plane

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Communication in WSN

Push vs. pull

basestation

source 1

basestation

source

basestation

source

Request (“pull”)

Transmission (“pull”)

Periodic transmission (“push”)

source 2

source 2

source 2

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Deployment Options for WSN

How are sensor nodes deployed in their environment?Dropped from aircraft Random deployment

Usually uniform random distribution for nodes over finite area is assumedIs that a likely proposition?

Well planned, fixed Regular deploymentE.g., in preventive maintenance or similarNot necessarily geometric structure, but that is often a convenient assumption

Mobile sensor nodesCan move to compensate for deployment shortcomingsCan be passively moved around by some external force (wind, water)Can actively seek out “interesting” areas

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Deployment Options for WSN

Evaluation criteria? Coverage!Radio coverage, i.e. communication relatedSensor coverage, i.e. application related

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MANET vs. WSN

Many commonalitiesSelf-organization, energy efficiency, (often) wireless multi-hop

Many differencesApplications, equipment: MANETs more powerful (read: expensive) equipment assumed, often “human in the loop”-type applications, higher data rates, more resourcesApplication-specific: WSNs depend much stronger on application specifics; MANETs comparably uniformEnvironment interaction: core of WSN, absent in MANETScale: WSN might be much larger (although contestable)Energy: WSN tighter requirements, maintenance issuesDependability/QoS: in WSN, individual node may be dispensable (network matters), QoS different because of different applications Data centric vs. id-centric networkingMobility: different mobility patterns like (in WSN, sinks might be mobile while nodes are usually static)

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WSN Application Examples

Emergency operationsDrop sensor nodes from an aircraft over a wildfireEach node measures temperatureDerive a “temperature map”

Habitat monitoringUse sensor nodes to observe wildlifeE.g., Great Duck Island, ZebraNet

Precision agricultureBring out fertilizer/pesticides/irrigation only where needed

LogisticsEquip goods (parcels, containers) with a sensor nodeTrack their whereabouts – total asset managementNote: passive readout might suffice – compare RFIDs

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WSN Application Scenarios

Home automation and health careSmart environment (smart sensor nodes and actuators in appliances learn to provide needed service)Post-operative or intensive care (telemonitoring of physiologic data)Long-term surveillance of chronically ill patients or the elderly (tracking and monitoring)

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Operation and Maintenance

Type of service of WSNNot simply moving bits like another networkRather: provide answers (not just numbers)Issues like geographic scoping are natural requirements, absent from other networks

Feasible and/or practical to maintain sensor nodes?E.g., to replace batteries?Or: unattended operation?Impossible but not relevant? Mission lifetime might be very small

Energy supply?Limited from point of deployment?Some form of recharging, energy scavenging from environment?

E.g., solar cells

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Research Objectives

Network lifetimeThe network should fulfill its task as long as possible – definition depends on applicationLifetime of individual nodes relatively unimportantBut often treated equivalently

Maintainability and fault toleranceWSN has to adapt to changes, self-monitoring, adapt operationIncorporate possible additional resources, e.g., newly deployed nodesBe robust against node failures (running out of energy, physical destruction, …)

In-network processingAgain, the network should fulfill a given task on behalf of an external userMove necessary computations into the network reduction of communication costs, speedup of operations

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Research Objectives

Quality of serviceTraditional QoS metrics do not applyStill, service of WSN must be “good”: Right answers at the right time

Software managementProgramming and re-programming of sensor nodes according to the current application demandsDebugging of distributed heterogeneous sensor nodes?From ZebraNet: “how to reboot a zebra?”

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Self-Organization in Sensor Networks

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Principles and properties

Networking functions for global connectivity and efficient resource usage

Local state

Neighbor information

Probabilistic methods

Global state (globally optimized system behavior)

Self-organizing networks Conventional networks

Implicit coordination

Explicit coordination

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Self-Organization in WSN

ObjectivesScalability – Management overhead for coordination, support for “unlimited?” number of nodesLifetime – Application dependent description of the service quality including delays and availability

Categorization in two dimensionsHorizontal, i.e. according to the necessary state informationVertical , i.e. according to the network layer

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Horizontal dimension

Location informationAbsolute or relative position, affiliation to a group of nodesUsually requires multi-hop communication

Neighborhood informationDirect neighborhood, based on local broadcasts

Local stateLocal system state, environmental factors

Probabilistic algorithmsNo state information required, stochastic processes

locationinformation

neighborhoodinformation

probabilisticalgorithms

localstate

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Vertical dimension

MAC layerMedium access, local communication

Network layerTopology control, routing tables, data-centric communication

Application layerCoordination and control, application dependent requirements (coverage, lifetime)

Application layer

Transport layer

Network layer

MAC layer

Physical layer

Control plane(e.g. mobilitymanagement) C

ross-layer optimization

(e.g. energy control)

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Mapping of Primary Self-Organization Techniques

Location information

Neighborhood information

Local state Probabilistic methods

Feedback loops Feedback is provided by observing and evaluating system parameters; this can be done either by local means (sensor readings) or with external help of neighboring systems

Interactions Information exchange among remote nodes using routing techniques

Local interaction among direct neighbors within their wireless communication range

Interactions with the environment or indirect interactions with other nodes using environmental changes (stigmergy)

Probabilistic techniques

Randomness is often exploited to prevent unwanted synchronization effects, e.g. for retrial attempts

Stochastic methods

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Further Studies

Medium access control (MAC)Problems and solutionsCase studies (S-MAC, PCM)

Ad hoc routingClassificationPrinciples of routing protocolsOptimized route stabilityAddress allocation techniques

Data-centric networkingFlooding, gossiping, and optimizationsAgent-based techniquesDirected diffusion

ClusteringPrinciples and techniquesCase studies (LEACH, HEED)

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Summary (what do I need to know)

Principles of ad hoc and sensor networksCommonalitiesDifferences

Capabilities and working behavior of WSNNode hardware and softwareCommunication principles

Self-organization in WSNTwo-dimensionsMapping to “classical” self-organization techniques

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References

I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, "Wireless sensor networks: a survey," Computer Networks, vol. 38, pp. 393-422, 2002. D. Culler, D. Estrin, and M. B. Srivastava, "Overview of Sensor Networks," Computer, vol. 37 (8), pp. 41-49, August 2004. I. Dietrich and F. Dressler, "On the Lifetime of Wireless Sensor Networks," University of Erlangen, Dept. of Computer Science 7, Technical Report 04/06, December 2006. F. Dressler, "Self-Organization in Ad Hoc Networks: Overview and Classification," University of Erlangen, Dept. of Computer Science 7, Technical Report 02/06, March 2006. H. Karl and A. Willig, Protocols and Architectures for Wireless Sensor Networks, Wiley, 2005.C. Prehofer and C. Bettstetter, "Self-Organization in Communication Networks: Principles and Design Paradigms," IEEE Communications Magazine, vol. 43 (7), pp. 78-85, July 2005. C. S. Raghavendra, K. M. Sivalingam, and T. Znati, Wireless Sensor Networks. Boston, Kluwer Academic Publishers, 2004.H. Zhang and J. C. Hou, "Maintaining Sensing Coverage and Connectivity in Large Sensor Networks," Wireless Ad Hoc and Sensor Networks: An International Journal, vol. 1 (1-2), pp. 89-123, January 2005.