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Sensor Network Overview

Sensor Network Overview. Taekyoung Kwon tk@mmlab.snu.ac.kr. For starters. The problems of engineering education Problem solving English Communication skills. For starters. What you can achieve by taking this course Problem solving Problem definition

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Sensor Network Overview

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  1. Sensor Network Overview Taekyoung Kwon tk@mmlab.snu.ac.kr

  2. For starters • The problems of engineering education • Problem solving • English • Communication skills

  3. For starters • What you can achieve by taking this course • Problem solving • Problem definition • Topics in the wireless/sensor network • Idea • Verify/evaluate • sensor network • Ubiquitous computing • standardization

  4. Evolution (size and number)

  5. Confluence of technologies

  6. Ubiquitous computing • 21st century computers • Embedded in our world (ubiquitous, pervasive) • They weave themselves into the fabric of everyday life until they are indistinguishable from it [Mark Weiser, 1991] • The anti-thesis of “virtual reality” • Like motor technology, embedding computers everywhere and having them “disappear in the background” is easy

  7. Wired vs. wireless • Bandwidth • Reliability • CSMA/CD vs CSMA/CA

  8. Wireless networks • Wireless network  ad hoc network • Ad hoc network  sensor network? • Wireless WAN: Cellular • Wireless MAN: IEEE 802.16 • Wireless LAN: IEEE 802.11 series • Wireless PAN: IEEE 802.15 family

  9. What is sensor? • Sensor: a transducer that converts a physical, chemical, or biological parameter into an electrical signal • Actuator: a transducer that accepts an electrical signal and converts it into a physical, chemical, or biological action • Transducer: a device converting energy from one domain into another. The device may either be a sensor or an actuator

  10. Sensor network • Tens of thousand nodes • Densely deployed Sink Internet, Satellite, etc Sink Task Manager

  11. Sensor node hardware • Small • Low power • Low bit rate • High density • Low cost (dispensable) • Autonomous • Adaptive Mobilizer Location Finding System Transceiver Sensor ADC Processor Memory Power Unit

  12. Sensor network • Power constraint • Battery powered  mains powered • Energy harvest • Light(solar), vibration, temperature • Tradeoff between energy and QoS • Prolong network lifetime by sacrificing application requirements • Delay, throughput, reliability, data fidelity,… • Still QoS is attractive • Deterministic or probabilistic bound

  13. Application Layer Transport Layer Task Management Plane Mobility Management Plane Network Layer Power Management Plane Data Link Layer Physical Layer Sensor network • Traffic type: streaming, periodic, event • Low cost, Low bit rate, low duty cycle • IEEE 802.15.4: 250Kbps

  14. Ad hoc vs. sensor • Number of sensor nodes can be several orders of magnitude higher • Sensor nodes are densely deployed and are prone to failures • The topology of a sensor network changes very frequently due to node mobility and node failure • May leverage broadcasting than point-to-point communications • May operate in aggregate fashion • In-network processing • Sensor nodes are limited in power, computational capacities, and memory • May not have global ID like IP address • Need tight integration with sensing tasks

  15. Design issues • Fault tolerance • Battlefield application • Scalability • Node density: (NR^2)/A (transmission) • Production costs • Hardware constraints • Topology • Deployment phase • Post-deployment phase • Environment • Transmission media: ISM, IR • Power consumption: sensing, processing, communication

  16. PHY layer • Sync • Self-organization • Beacon scheduling (periodic) • Directional/smart antenna • Ultra-wideband (UWB) • Transmit-only device • pros: cost, energy • Cons: uncontrollable, communications/networking overhead

  17. MAC layer • TDMA vs. CSMA • TDMA: inter-cluster, scalability • CSMA: idle listening, overhearing • Sleep cycle • Coordination • Spatial correlation • Clustering (MAC vs NWK) • Additional control channel • FDMA or TDMA • Location awareness • Exposed terminal problem

  18. network layer • Attribute-based addressing • Information-centric delivery • Routing • Route discovery • Data aggregation/coordination • Location awareness • Directional antenna (AOA) • UWB (distance measure via signal flight time) • GPS

  19. routing • Route discovery (AODV, DSR,…) • Route selection metric: hop count • Metric can be generalized to cost • Hierarchical tree routing • Gradient routing: data broadcasting

  20. Transport layer • Goodput decreases drastically as the offered traffic exceeds the network capacity • Flow control vs. Congestion control • open loop vs closed loop • Proactive vs. reactive

  21. Transport layer • Reliability concept should be relaxed • Event-to-sink reliability • Not all event-sensing nodes need to report • N reception among M transmission might be OK (M > N) • Hop-by-hop approaches

  22. Middleware/Language/Appl. • query/advertisement • Publish/subscribe • nesC, Mate, SQTL • Declarative rather than procedural • TEDS (IEEE 1451)

  23. Some of the commercial applications • Industrial automation (process control) • Defense (unattended sensors, real-time monitoring) • Utilities (automated meter reading), • Weather prediction • Security (environment, building etc.) • Building automation (HVAC controllers). • Disaster relief operations • Medical and health monitoring and instrumentation

  24. What to consider: application requirements • Energy-saving • QoS • Throughput/Goodput • Reliability • timeliness • Traffic/application scenario • Amdahl’s law • Every possible case • Self-organization

  25. What to consider: enabling technologies • Directional (smart, MIMO) antenna • Multi-hop reachability • AoA • Hidden node problem • Heterogeneous node type • E.g., Transmit-only device • GPS: too costly • UWB (distance measurement) • Location aware • Energy harvesting device • Additional (separate) control channel

  26. Possible approaches • Conservative vs. aggressive • Pessimistic vs. opportunistic vs. optimistic • Proactive (a priori) vs reactive (on demand) • Information amount vs. performance (better control/decision) • History • Neighbors within some hops • Deterministic (e.g. threshold) vs. probabilistic • N * p = 1? • Reservation vs. random access • Heterogeneous functionalities • E.g, cluster head, member

  27. Possible enhancements: • Flexibility vs. efficient • adaptivity • Stability vs. throughput (utilization) • Goodput • Reliable vs. fault-tolerant vs. error-resilient vs. robust • fairness • Legacy-system support, standard-compliant, backward compatibility

  28. Final goal • Tradeoff • Quantitative trend • Qualitative feature • How to verify? • Analysis • Simulation • Implementation

  29. analysis • assumptions • Whole system vs key element • Steady state probability • Upper/lower bound • Worst/average case • Complexity: O() • Temporal vs. spatial

  30. Simulation • Arbitrary level of detail • Still too many ambiguities • Follow the norm, other reference • How to emphasize the strength? • Also show the weakness

  31. Implementation • Most time and energy consuming • Good luck!

  32. Leverage other techniques • Algorithm • Combination theory • AI • e.g., self-learning • Operations Research • optimization • Network Flow, scheduling theory • Probability • Queuing theory

  33. Let’s make team!

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