[SelfOrg] 2-1.1

Self-Organization in Autonomous Sensor/Actuator Networks

[SelfOrg]

Dr.-Ing. Falko Dressler

Computer Networks and Communication Systems

Department of Computer Sciences

University 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 infrastructure E.g., GSM, UMTS, WLAN, … Base stations connected to a wired backbone network Mobile entities communicate wirelessly to these base stations Traffic between different mobile entities is relayed by base stations and

wired backbone Mobility is supported by switching from one base station to another Backbone infrastructure required for administrative tasks

IP backbone

ServerRouter

Furth

er

network

s

Gateways

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Infrastructure-based Wireless Networks – Limitations?

What if … No infrastructure is available? – E.g., in disaster areas It is too expensive/inconvenient to set up? – E.g., in remote, large

construction sites There 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

ad ho

c

ad ho

c

Finding out empty parking lots in a city, without asking a server Search-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 Computing Temporary communication infrastructure Quick communication with minimal configuration among a group of people Examples

A group of researchers who want to share their research findings during a conference

A lecturer distributing notes to a class on the fly

Emergency operations Rescue, crowd control, and commando operations Constraints

Self-configuration with minimal overhead Independency of fixed or central infrastructure Freedom and flexibility of mobility Unavailability 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/users Independence of spectrum reuse constraints and the requirements of network

planning of cellular networks Mesh topology provides many alternate data paths

Quick reconfiguration when the existing path fails due to node failures Most 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 wireless

Topology Outlined by the pre-deployed infrastructure

Self-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 for E.g., routes in the network

have to be changed

Complicated by scale Large 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 batteries

Desirable: long run time for Individual devices Network as a whole

Energy-efficient networking protocols E.g., use multi-hop routes with low energy consumption (energy/bit) E.g., take available battery capacity of devices into account How 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 difficult Lack of central entity for organization available Limited range of wireless communication Mobility of participants Battery-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 fashion Finding 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 environment Nodes in the network are equipped with sensing and actuation to

measure/influence environment Nodes process information and communicate it wirelessly

Wireless sensor networks (WSN)

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Wireless Sensor Networks

Multiple roles can be distinguished Sensors – measure physical phenomena, sources of measurement data Base stations – analyze and post-process data, sinks for measurement

data Actuators – perform actuation in response to received data Processing 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 transceiver E.g., Chipcon CC1000 (315/433/868/915 MHz), CC2400 (2.4 GHz)

Battery Possibly in combination with energy harvesting

Sensors Light, 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 principle E.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

MAC Energy-efficiency

Network Address-based routing Data-centric routing

Transport Data aggregation

Application Push vs. pull

Application layer

Transport layer

Network layer

MAC layer

Physical layer

Pow

er managem

ent plane

Mobility m

anagement plane

Task m

anagement 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 assumed

Is that a likely proposition?

Well planned, fixed Regular deployment E.g., in preventive maintenance or similar Not necessarily geometric structure, but that is often a convenient

assumption

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

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Deployment Options for WSN

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

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MANET vs. WSN

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

Many differences Applications, equipment: MANETs more powerful (read: expensive) equipment

assumed, often “human in the loop”-type applications, higher data rates, more resources

Application-specific: WSNs depend much stronger on application specifics; MANETs comparably uniform

Environment interaction: core of WSN, absent in MANET Scale: WSN might be much larger (although contestable) Energy: WSN tighter requirements, maintenance issues Dependability/QoS: in WSN, individual node may be dispensable (network

matters), QoS different because of different applications Data centric vs. id-centric networking Mobility: different mobility patterns like (in WSN, sinks might be mobile while nodes

are usually static)

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WSN Application Examples

Emergency operations Drop sensor nodes from an aircraft over a wildfire Each node measures temperature Derive a “temperature map”

Habitat monitoring Use sensor nodes to observe wildlife E.g., Great Duck Island, ZebraNet

Precision agriculture Bring out fertilizer/pesticides/irrigation only where needed

Logistics Equip goods (parcels, containers) with a sensor node Track their whereabouts – total asset management Note: passive readout might suffice – compare RFIDs

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WSN Application Scenarios

Home automation and health care Smart 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 WSN Not simply moving bits like another network Rather: 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 lifetime The network should fulfill its task as long as possible – definition depends

on application Lifetime of individual nodes relatively unimportant But often treated equivalently

Maintainability and fault tolerance WSN has to adapt to changes, self-monitoring, adapt operation Incorporate possible additional resources, e.g., newly deployed nodes Be robust against node failures (running out of energy, physical

destruction, …)

In-network processing Again, the network should fulfill a given task on behalf of an external user Move necessary computations into the network reduction of

communication costs, speedup of operations

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Research Objectives

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

Software management Programming and re-programming of sensor nodes according to the

current application demands Debugging 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

Objectives Scalability – Management overhead for coordination, support for “unlimited?”

number of nodes Lifetime – Application dependent description of the service quality including delays

and availability

Categorization in two dimensions Horizontal, i.e. according to the necessary state information Vertical , i.e. according to the network layer

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Horizontal dimension

Location information Absolute or relative position, affiliation to a group of nodes Usually requires multi-hop communication

Neighborhood information Direct neighborhood, based on local broadcasts

Local state Local system state, environmental factors

Probabilistic algorithms No state information required, stochastic processes

locationinformation

neighborhoodinformation

probabilisticalgorithms

- topology contro

l

- clusterin

g- ta

ble-driven ro

uting

- medium access contro

l

- data ce

ntric ro

uting

- task

allocatio

n

localstate

- gossiping

- collis

ion avoidance

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Vertical dimension

MAC layer Medium access, local

communication

Network layer Topology control, routing tables,

data-centric communication

Application layer Coordination 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 solutions Case studies (S-MAC, PCM)

Ad hoc routing Classification Principles of routing protocols Optimized route stability Address allocation techniques

Data-centric networking Flooding, gossiping, and optimizations Agent-based techniques Directed diffusion

Clustering Principles and techniques Case studies (LEACH, HEED)

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Summary (what do I need to know)

Principles of ad hoc and sensor networks Commonalities Differences

Capabilities and working behavior of WSN Node hardware and software Communication principles

Self-organization in WSN Two-dimensions Mapping 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.