1 Wireless sensor network Wireless sensor network: a survey LF.Akyildiz, W. Su, Y. Sankarasubramanisam, E. Cayirci Computer Network 38 (2002) 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 interference from 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 may communicate 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