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Wireless sensor network

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  1. Wireless sensor network Wireless sensor network: a survey LF.Akyildiz, W. Su, Y. Sankarasubramanisam, E. Cayirci Computer Network 38 (2002) 393-422 Speaker: 高新傑 Member: 孫明煌 林承毅 陳立明 趙偉成 吳展奇

  2. Outline • Introduction • Factors influencing sensor network design • Sensor networks communication architecture • Conclusion

  3. Introduction • A large number of low-cost, low-power, multifunctional, and small sensor nodes • Sensor node consists of sensing, data processing, and communicating components • Collaborative effort of a large number of nodes • Primarily focus on power consumption

  4. The difference between sensor network and ad hoc network • Sensor nodes: • Number of sensor nodes is larger • Densely deployed, prone to failures • The topology of a sensor network changes very frequently • Mainly use broadcast • Limited in power • No global identification

  5. Sensor network applications • Military applications • Environmental applications • Health applications • Home applications • Other commercial applications

  6. Factors influencing sensor network design • Fault tolerance • Scalability • Production costs • Hardware constraints • Sensor network topology • Environment • Transmission media • Power consumption

  7. Fault tolerance • Fault tolerance is the ability to sustain sensor network functionalities without any interruption due to sensor node failures • The protocols may be designed to address the level of fault tolerance

  8. Scalability • The number of sensor nodes may be in the order of hundreds or thousands • The node density depends on the application in which the sensor nodes are deployed

  9. Production costs • Since the sensor networks consist of a large number of sensor nodes, the cost of a single node is very important • The cost of a sensor node should be much less than 1$

  10. Hardware constraint • Four basic hardware components: • Sensing unit • Processing unit • Transceiver unit • Power unit

  11. The components of a sensor node

  12. Sensor network topology • Sheer numbers of inaccessible and unattended sensor nodes make topology maintenance a challenge • Topology maintenance: • Pre-deployment • Post-deployment • Mobility • Energy depletion or destruction

  13. Environment • The sensor nodes usually work unattended in remote geographic areas • They may work in interior of a large machinery, at the bottom of an ocean, inside a twister, in a battlefield, in a home, in a large building, or be attached to animals

  14. Transmission media • Radio • One option is ISM band • The advantages of ISM band are free, huge spectrum allocation and globally available • The constraints are power limitation and harmful interferencefrom existing applications

  15. Transmission media - continue • Infrared • The advantages are license-free and robust to interference from electrical device • The drawback is the requirement of a line of sight between sender and receiver

  16. Transmission media - continue • Optical media • Smart dust mote • Two transmission schemes: • Passive transmission using a corner-cube retroreflector (CCR) • Active communication using a laser diode and steerable mirror

  17. Power consumption • Sensor node lifetime shows a strong dependence on battery lifetime • Power consumption can be divided into: • Sensing • Communication • Processing

  18. Sensor network communication architecture • The sensor nodes are usually scattered in a sensor field • Sensor nodes can collect data and route data back to sink • The sink maycommunicate with the task manager node via Internet or Satellite

  19. The architecture

  20. Protocol stack • Application layer • Transport layer • Maintain flow of data • Network layer • Take care of routing the data supplied by the transport layer • Data link layer • Power aware • Minimize collision with neighbor’s broadcast • Physical layer • Simple but robust modulation, transmission, and receiving techniques.

  21. Protocol stack - continue

  22. Management Planes • These planes helps the sensor node coordinate the sensing task and lower the overall power consumption • Power management plane • Mobility Management Plane • Task Management Plane

  23. Application layer • Sensor management protocol (SMP) • Task assignment and data advertisement protocol (TADAP) • Sensor query and data dissemination protocol (SQDDP)

  24. Sensor management protocol • It makes the hardware and software of the lower layers transparent to the sensor network management application • SMP needs to access the node by using attribute-based naming and location-based addressing

  25. Task assignment and data advertisement management protocol • Task assignment • Users send their interest to a sensor node • Data advertisement • Sensor nodes advertise the available data to user

  26. Sensor query and data dissemination protocol • An interface to issue queries, respond to queries and collect incoming replies • Attributed-based or location-based naming is preferred • Example: The location of the nodes that sense temperature higher than 70°F • Sensor query and tasking language (SQTL) is proposed

  27. Transport layer • The layer is especially needed when the system is planned to be accessed through Internet or other external networks • The communication between the sink and user is by UDP or TCP • The communication between the sink and sensor is by UDP type protocols

  28. Network layer • Special multihop wireless routing protocols between the sensor nodes and sink node are needed • Design principles • Power efficiency • Sensor networks are data centric • Data aggregation • Attribute-based and location-based naming

  29. Energy efficient route • Maximum available power (PA) route • Minimum energy (ME) route • Minimum hop (MH) route • Maximum minimum PA node route

  30. Energy efficient route - continue PA: Available Power α: Energy required to transmit a data packet through the related link

  31. Data centric routing • Two approach • Sinks broadcast the interest • Sensor nodes broadcast an advertisement for available data • Attribute-based naming required

  32. Data aggregation • A technique used to solve the implosion and overlap problems in data-centric routing • Data coming from multiple sensor nodes with the same attribute of phenomenon are aggregated

  33. Data aggregation - continue

  34. Internetworking • Sink nodes can be used as a gateway to other network • Create a backbone by connecting sink nodes together and make it access other network via a gateway

  35. Some schemes proposed for the sensor network • Small minimum energy communication network (SMECN) • Flooding • Gossiping • Sensor protocols for information via negotiation (SPIN) • Sequential assignment routing (SAR) • Low-level adaptive clustering hierarchy (LEACH) • Directed diffusion

  36. SPIN

  37. Data link layer • The data link layer is responsible for the multiplexing of data stream, data frame detection, medium access and error control

  38. Medium access control • Two goals: • Creation of the network infrastructure • Fairly and efficiently share communication resources between sensor nodes • Why existing MAC protocol can’t be used? • The primary goal of the existing MAC protocol is the provision of high QoS and bandwidth efficiency

  39. MAC for sensor networks • MAC protocol for sensor network must have built-in power conservation, mobility management and failure recovery strategies • A variant of TDMA, random medium access, constant listening times and adaptive rate control schemes can help achieve energy efficiency

  40. Some MAC protocols proposed for sensor network • SMACS and EAR algorithm • CSMA based medium access • Hybrid TDMA/FDMA based

  41. Power saving modes of operation • The most obvious means of power conservation is to turn the receiver off • Operation in a power saving mode is energy efficient only if the time spent in that mode is greater than a certain threshold because of the short data packets

  42. Error Control • Forward error correction (FEC) • Encode data before sending decreases the bit error rate (BER) • Additional processing power goes into encoding and decoding • Automatic repeat request (ARQ) • Limited by the additional retransmission cost and overhead

  43. Physical layer • The physical layer is responsible for frequency selection, carrier frequency generation, signal detection, modulation and data encryption • The choice of a good modulation scheme is critical for reliable communication in a sensor network

  44. Conclusion • The sensor network needs to satisfy the constraint: • fault tolerance, scalability, cost, hardware, topology chance, environment and power consumption • New networking technique for the layers of the sensor networks protocol stack is required