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Wireless sensor network

Wireless sensor network: a surveyLF.Akyildiz, W. Su, Y. Sankarasubramanisam, E. Cayirci

Computer Network 38 (2002) 393-422Speaker: 高新傑

Member: 孫明煌 林承毅 陳立明 趙偉成 吳展奇

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Outline

Introduction Factors influencing sensor network

design Sensor networks communication

architecture Conclusion

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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

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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

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Sensor network applications

Military applications Environmental applications Health applications Home applications Other commercial applications

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

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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

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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

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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$

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Hardware constraint

Four basic hardware components: Sensing unit Processing unit Transceiver unit Power unit

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The components of a sensor node

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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

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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

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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

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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

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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

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Power consumption

Sensor node lifetime shows a strong dependence on battery lifetime

Power consumption can be divided into: Sensing Communication Processing

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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

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The architecture

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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.

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Protocol stack - continue

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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

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Application layer

Sensor management protocol (SMP)

Task assignment and data advertisement protocol (TADAP)

Sensor query and data dissemination protocol (SQDDP)

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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

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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

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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

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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

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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 nami

ng

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Energy efficient route

Maximum available power (PA) route

Minimum energy (ME) route Minimum hop (MH) route Maximum minimum PA node route

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Energy efficient route - continue

PA: Available Powerα: Energy required to transmit a data packet through the related link

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Data centric routing

Two approach Sinks broadcast the interest Sensor nodes broadcast an

advertisement for available data Attribute-based naming required

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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

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Data aggregation - continue

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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

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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

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SPIN

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Data link layer

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

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Medium access control

Two goals: Creation of the network infrastructure Fairly and efficiently share communicatio

n resources between sensor nodes Why existing MAC protocol can’t be

used? The primary goal of the existing MAC prot

ocol is the provision of high QoS and bandwidth efficiency

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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

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Some MAC protocols proposed for sensor network

SMACS and EAR algorithm CSMA based medium access Hybrid TDMA/FDMA based

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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

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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

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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

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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