Self-Organization in Autonomous Sensor/Actuator Networks [ SelfOrg ]

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

2. 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 Networking Swarm intelligence; artificial immune system; cellular signaling pathways

3. Mobile Ad Hoc and Sensor Networks Mobile Ad Hoc Networks (MANET) Wireless Sensor Networks (WSN)

4. 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 Further networks Gateways Server Router

5. 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

6. Factory floor automation Possible Applications for Infrastructure-free Networks Disaster recovery Car-to-car communication • 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, … • …

7. 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

8. 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

9. 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 ?

10. 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

11. Ad Hoc Networks vs. Infrastructure-based Networks

12. 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

13. 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)

14. 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?

15. 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

16. 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)

17. 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 sensor node

18. 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, … Sensor 1 Micro controller Radio transceiver … Sensor n Memory Storage Battery

19. Composition of Sensor Nodes – Software • Event-driven operating principle • E.g., TinyOS System component Event (Sensor) System function New event (Timer) … Event (Timer) … … … System function New event (Data packet) Event (Transceiver) Event handler

20. Communication in WSN • MAC • Energy-efficiency • Network • Address-based routing • Data-centric routing • Transport • Data aggregation • Application • Push vs. pull Application layer Task management plane Transport layer Mobility management plane Power management plane Network layer MAC layer Physical layer

21. Communication in WSN • Push vs. pull basestation source 2 source Request (“pull”) basestation source 2 source 1 Periodic transmission (“push”) basestation source 2 source Transmission (“pull”)

22. 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

23. Deployment Options for WSN • Evaluation criteria? Coverage! • Radio coverage, i.e. communication related • Sensor coverage, i.e. application related

24. 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)

25. 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

26. 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)

27. 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

28. 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

29. 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?”

30. Self-Organization in Sensor Networks

31. Principles and properties Self-organizing networks Conventional networks Local state Networking functions for global connectivity and efficient resource usage Global state (globally optimized system behavior) Neighbor information Probabilistic methods Implicit coordination Explicit coordination

32. 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

33. 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 - table-driven routing- medium access control - data centric routing- task allocation • gossiping • collision avoidance - topology control- clustering probabilisticalgorithms locationinformation localstate neighborhoodinformation

34. 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) Control plane (e.g. mobilitymanagement) Application layer Transport layer Cross-layer optimization(e.g. energy control) Network layer MAC layer Physical layer

35. Mapping of Primary Self-Organization Techniques

36. 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)

37. 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

38. 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.