fall 2006 introduction to wireless sensor network part 2 choong seon hong kyung hee university...

Fall 2006

Introduction to Introduction to Wireless Sensor NetworkWireless Sensor Network

Part 2Part 2

Choong Seon HongChoong Seon Hong

Kyung Hee UniversityKyung Hee University [email protected]@khu.ac.kr

2Fall 2006

Sensor Networks ArchitectureSensor Networks Architecture

Sensor node Made up of four basic components

• Sensing unit, Processing unit, Transceiver unit, and Power unit

Additional application-dependent components• Location finding system, power generator, and mobilizer

Scattered in a sensor field Collect data and route data back to the sink

Sink Communicate with the task manager node (user) v

ia Internet or satellite

3Fall 2006

Hardware ConstraintsHardware Constraints

Location finding system Mobilizer

Power Unit

Sensor ADCProcessorStorage

Transceiver

Sensing Unit

Processing Unit

Power generator

Optional part

Components of a Sensor Node

4Fall 2006

Energy Consumption in Each Sensor NodeEnergy Consumption in Each Sensor Node

Each sensor node has limited energy supplyNodes may not be rechargeableEnergy consumption in

Sensing Data processing Communication (most energy intensive)

5Fall 2006

Sensor Network Protocol StackSensor Network Protocol Stack

Transport

Data Link

Physical

Network

Pow

er

Managem

ent

Application

Mobility

Managem

ent

Task M

anagem

ent

Power Management – How the sensor uses its power, e.g. turns off its circuitry after receiving a message.

Mobility Management – Detects and register the movements of the sensor nodes

Task Management – Balances and schedules the sensing tasks given to a specific region

6Fall 2006

Physical LayerPhysical Layer

Physical

Data Link

Network

Transport

Application

Frequency selection – The use of the industrial, scientific, and medical (ISM) bands has been often proposed

Carrier frequency generation and Signal detection – Depend on the transceiver and hardware design constraints which aim for simplicity, low power consumption, and low cost per unit

Modulation Binary and M-ary modulation schemes can transmit multiple bits per

symbol at the expense of complex circuitry Binary modulation schemes are simpler to implement and thus deemed

to be more energy-efficient for WSN applications

Low transmission power and simple transceiver circuitry make Ultra Wideband (UWB) an attractive candidate Baseband transmission, i.e. no intermediate or carrier frequencies Generally uses pulse position modulation Resilient to multipath Low transmission power and simple transceiver circuitry

7Fall 2006


Radio Model – Energy Consumption

Energy consumption minimization is of paramount importance when designing the physical layer for WSN in addition to the usual effects such as scattering, shadowing, reflection, diffraction, multipath, and fading.

)(),(),( mEdmEdmE RTL

),()(),( dmEmEdmE TATCT ETC = energy used by the transmitter circuitryETA = energy required by the transmitter amplifier to achieve an acceptable

signal to noise ratio or at the receiver

8Fall 2006


Assuming a linear relationship for the energy spent per bit by the transmitter

and receiver circuitry

deemdmE TATCT ),( RCR memE )(

eTC, eTA, and eRC are hardware dependent parameters

An explicit expression for energy consumption in the AMP can be derived as,

))()((

4))()(( 0

bitampant

Rxr

TA RG

BWNNFN

S

e

9Fall 2006


(S/N)r = minimum required signal to noise ratio at the receiver’s demodulator for an acceptable Eb/N0

NFrx = receiver noise figureN0 = thermal noise floor in a 1 Hertz bandwidth (Watts/Hz)BW = channel noise bandwidthλ = wavelength in metersα = path loss exponent whose value varies from 2 (for free space)

to 4 (for multipath channel models)Gant = antenna gainηamp = transmitter power efficiencyRbit = raw bit rate in bits per second

rTA N

Se

))()((

4))()(( 0

bitampant

Rx

RG

BWNNF

10Fall 2006

Data Link LayerData Link Layer

Medium Access Control (MAC) – Let multiple radios share the same communication media

Functions: Local Topology Discovery and Management Media Partition by Allocation or Contention Provide Logical Channels to Upper Layers

Physical

Data Link

Network

Transport

ApplicationThe data link layer is responsible for

•Multiplexing of data stream•Data frame detection•Medium access and error control•Ensures reliable point-to-point and point-to-multipoint connections in a communication network

MAC protocol for sensor network must have built-in power conservation mechanisms, and strategies for the proper management of node mobility or failure

11Fall 2006

Wireless MAC ProtocolsWireless MAC ProtocolsWireless MAC protocols can be classified into two categories, distributed and centralized, according of the type of network architecture for which they have been designed. Protocols can be further classified, based on the mode of operation, into random access protocols, guaranteed access protocols, and hybrid access protocols

Wireless MAC protocols

DistributedMAC protocols

CentralizedMAC protocols

Randomaccess

Randomaccess

Guaranteedaccess

Hybridaccess

Since it is desirable to turn off the radio as much as possible in order to conserve energy some type of TDMA mechanism is often suggested for WSN applications. Constant listening times and adaptive rate control schemes have also been proposed.

12Fall 2006

Network LayerNetwork Layer

Physical

Data Link

Network

Transport

ApplicationBasic issues to take into account when designing the network layer for a WSN are:

Power efficiency Data centric – The nature of the data (interest requests

and advertisement of sensed data) determines the traffic flow

Data aggregation is useful to manage the potential implosion of traffic because of the data centric routing

Rather than conventional node addresses an ideal sensor network uses attribute-based addressing, e.g. “region where humidity is below 5%”

Locationing systems, i.e. ability for the nodes to establish position information

Internetworking with external networks via gateway or proxy nodes

13Fall 2006

RoutingRouting

Multihop routing common due to limited transmission range

Phenomenonbeing sensed

Sink

Low node mobility Power aware Irregular topology MAC aware Limited buffer space

Some routing issues in WSNs

Data aggregationtakes place here

14Fall 2006

Data AggregationData Aggregation

It is a technique used to solve the problem of implosion in WSNs.

This problem arises when packets carrying the same information arrive a node.

This situation can happen when more than one node sense the same phenomenon.

This is different than the problem of “duplicate packets” in conventional ad hoc networks.

Here it is the high level interpretation of the data in the packets is what determines if the packets are the “same.”

Even for the case when the packets are deemed to be different they could still be aggregated into a single packet before the relaying process continues.

Data coming from multiple sensor nodes are aggregated, if they have about the same attributes of the phenomenon being sensed, when they reach a common routing or relaying node on their way to the sink. In this view the routing mechanism in a sensor network can be considered as a form of reverse multicast tree.

Phenomenon being sensed

15Fall 2006

Data CentralityData Centrality

In data-centric routing, an “interest ” dissemination is performed in order to assign the sensing tasks to the sensor nodes. This dissemination can take different forms such as:

The sink or controlling nodes broadcast the nature of the interest, e.g. “four legged animals of at least 50 Kg in weight”

Sink

Four-legged animal of at least 50 Kg

Flow of the request

16Fall 2006

Data CentralityData Centrality Sensor nodes broadcast an advertisement of available sensed data and wait for a

request from the interested sinks

Sink

Flow of the advertisement

Tiger, tiger, burning bright,In the forest of the night,

What immortal hand or eyeCould frame thy fearful symmetry?

17Fall 2006

Transport LayerTransport Layer

Physical

Data Link

Network

Transport

ApplicationTCP variants developed for the traditional wireless networks are not suitable for WSNs where the notion of end-to-end reliability has to be reinterpreted due to the “sensor” nature of the network which comes with features such as:

Multiple senders, the sensors, and one destination, the sink, which creates a reverse multicast type of data flow

For the same event there is high level of the redundancy or correlation in the data collected by the sensors and thus there is no need for end-to-end reliability between individual sensors and the sink but instead between the event and the sinkOn the other hand there is need of end-to-end reliability between the sink and individual nodes for situations such as re-tasking or reprogrammingThe protocols developed should be energy aware and simple enough to be implemented in the low-end type of hardware and software of many WSN applications

18Fall 2006

Application LayerApplication Layer

Physical

Data Link

Network

Transport

ApplicationThere has not been a lot of development on this layer for WSNs. Some potential applications have been suggested as listed below but little work of substance has been reported on any particular area.

Authentication, key distribution, and other security tasks Sensor movement management

Sensor Management Protocol (SMP) – Carries out tasks such as: Turning sensors on and off Exchanging data related to the location finding algorithms

Interest Dissemination – Interest is send to a sensor or a group of sensors. The interest is expressed in terms of an attribute or a triggering event.

Advertisement of Sensed Data – Sensor nodes advertise sensed data in a concise and descriptive way and users reply with requests of data they are interested in receiving

19Fall 2006

Technical ChallengesTechnical Challenges

Performance metrics Energy efficiency/system lifetime: The sensors are battery

operated, sensor energy must be wisely managed in order to extend the lifetime of the network

Latency: Many sensor applications require delay-guaranteed service. Protocols must ensure that sensed data will be delivered to the users within a certain delay.

Accuracy: Obtaining accurate information is the primary objectives; accuracy can be improved though joint detection and estimation

Fault tolerance: Robustness to sensor and link failures must be achieved through redundancy and collaborative processing and communication

20Fall 2006

Technical Challenges (cont’d)Technical Challenges (cont’d)

Scalability: Because a sensor network may contain thousand of nodes, scalability is a critical factor that guarantees that the network performance does not significantly degrade as the network size (or node density) increases

Transport capacity/throughput: Because most sensor data must be delivered to a single base station or fusion center, a critical area in the sensor network exists, whose sensor nodes must relay the data generated by virtually all nodes in the network

BSBSCritical RegionCritical Region

21Fall 2006

Technical Challenges (Cont’d)Technical Challenges (Cont’d)

Power Supply The most difficult constraints in the design of WSN When miniaturizing the node, the energy density of the

power supply is the primary issue Current technology yields batteries with approximately 1

J/mm3, while capacitors can achieve 1mJ/mm3

Sensor acquisition can be achieved at 1nJ/sample and modern processors can perform computations as low as 1nJ/instruction

In WSN, where sensor sampling, processing, data transmission and possibly actuation are involved, the trade-off between these tasks plays important role in power usage. Balancing these parameters will be the focus of the design process of WSN

22Fall 2006


Design of energy-efficient protocols: Clustering is an efficient way to save energy for

static sensor networks• Data compression can be applied to reduce the number

of packet• Data-centric property makes and identity• Randomize rotation of cluster heads helps ensure a

balanced energy consumption Broadcast and multicast trees can be used to

increase energy efficiency• Communication pattern many to one (when data from

sources to sink) and one to many (when query from sink to sources). So, multicast advantages offers less benefit

The exploration of sleep modes

23Fall 2006


Capacity/Throughput Throughput is a traditional measure of how much

traffic can be delivered by the network In packet network, the throughput is defined as the

expected number of successful packet transmissions of a given node per time slot

Throughput is related to transmission rate of each transmitter, which in turn, is upper bounded by the channel capacity

Considering node density, congestion, channel condition achieving good throughput is necessary for energy constrained sensor network

24Fall 2006


Channel Accessing and Scheduling Scheduling is studied at two levels

• System level: At system level, a scheme determines which nodes will be transmitting.

– System level scheduling essentially a medium access (MAC) problem, with the goal of minimum collisions and maximum spatial reuse

• Node level: At the node level, a scheduler determines which flow among all multiplexing flows will be eligible to transmit next

Current scheduling algorithms aim at improved fairness, delay, robustness (with respect to network topology changes) and energy efficiency

The scheduling algorithm and routing protocols must aim at energy and delay balancing, ensuring

• Packets originating close and far away from the base station experience a comparable delay and

• Critical nodes do not die prematurely due to the heavy traffic

25Fall 2006


Energy Consumption Considering energy consumption, four basic states

can be defined: Transmission, reception, listening and sleeping. They consists of the following tasks:

• Acquisition: A/D conversion and preprocessing • Transmission: Address determination, packetization,

encoding, framing and queuing• Reception: similar activities like transmission• Listening: same as reception except that the signal

processing chain stops at the detection• Sleeping: power supply to stay alive

26Fall 2006


Connectivity: Network connectivity is an important issue

because it is crucial for most applications that the network is not partitioned into disjoint parts

Node redundancy should be in such a rate that frequent node failure must keep the network connected

Protocols practicing periodic sleep must ensure connectivity among active node for reliable data transfer from sources to sink

27Fall 2006


Node Distribution and MobilitySecurityDistributed Signal ProcessingSynchronization and LocalizationWireless ProgrammingWireless Link Modeling

28Fall 2006

Cross Layer DesignCross Layer Design

Avoid Conflicting Behavior – For example a routing protocol that favors smaller hops to save transmission energy consumption does require a proper MAC protocol to coordinate the transmissions along the data flow that minimizes contention and keeps the transceivers off as much as possible

Remove Unnecessary Layers – Some applications do not require all layers

New Paradigm – WSNs does not have many of the feature of the conventional networks for which the OSI protocol layer stack model has proven to be successful. Therefore it is quite possible that a different mix of layers might prove to be more efficient for many WSN applications

Motivations:

29Fall 2006

Sensor Network Management IssuesSensor Network Management Issues

WSN is a tool for distributed sensing of one or more phenomenon that reports the sensed data to one or more observers

Wireless network services for observers as well as for itself Sensor nodes execute a common goal in a collaborative way A managed WSN is responsible for configuring and

reconfiguring under varying conditions Energy is a critical resource in WSNs. Thus all operations

performed in the network should be energy efficient Topology is dynamic because sensor nodes become out of

service temporarily or permanently. In this scenario failure in sensor network is a common fact and needed to be managed efficiently

WSN must detect, identify and protect itself against various types of attacks to maintain overall systems security and integrity

30Fall 2006

Sensor Network Management Issues (cont’d)Sensor Network Management Issues (cont’d)

An well managed sensor network must know its environment and the context surrounding its activities and act accordingly

WSN must be autonomic, i.e., self managed and robust to changes in network states while maintaining the quality of service

It must be capable of self-configuration, self-organization, self-healing and self-optimized

Finally management of WSN is concerned with how the management can promote plant and resource productivity, and

How it integrates functions of configuration, operation, administration and maintenance of all elements and services in an efficient way

31Fall 2006

Dimensions for WSN ManagementDimensions for WSN Management WSN Functionalities

Configuration Maintenance Sensing Processing Communication

Functional Areas Configuration

Management Fault Management Performance

Management Security

Management Accounting

Management

Management Levels Business

Management Service Management Network Management Network Element

Management Network Element

32Fall 2006

Management LevelsManagement Levels

Business Management Development and determination of cost functions Cost function is associated with network setup,

sensing, processing, communication and maintenance

WSN applications have enormous potential benefits for society as a whole and represent new business opportunities

In the future, it is expected to have Internet end-points equipped with a variety of sensors to monitor the network and their own state

33Fall 2006

Management Levels (cont’d)Management Levels (cont’d)

Service Management Quality of service: QoS support to WSN includes

• QoS model: It specifies the architecture in which some of the services can be provided in WSN

• QoS sensing: QoS sensing considers the sensor device calibration, environment interference monitoring and exposure (time, distance, and angle between sensor device and phenomenon)

• QoS dissemination: Handled in two layers– QoS routing

– QoS medium access control

• QoS processing: Processing quality depends on the robustness and complexity of the algorithms used, as well as processor and memory capacities

34Fall 2006

Management Levels (Cont’d)Management Levels (Cont’d)

Network Management Network Element Management

• Power Management• Mobility Management (in case of mobile sink)• State Management (States: operational, administrative and

usage)• Task Management (Schedules the sensing, processing and

dissemination) Network Element

• Power Supply– Linear Model– Dependent Model– Relaxation Model

• Computational Model• Sensor Element• Transceiver• Software

35Fall 2006

WSN FunctionalitiesWSN Functionalities

Configuration: The configuration functionality is related to the following: Definition of WSN application requirements Determination of the monitoring area (shape and

dimension) Characteristics of environment Choice of nodes Definition of the WSN type Service provided

36Fall 2006

WSN Functionalities (Cont’d)WSN Functionalities (Cont’d)

Sensing: Lowest level of sensing application is provided by the

autonomous sensor nodes Sensing functionality depends on the type of the

phenomenon Sensing can be classified into

• Continuous (when sensors collect data continuously along the time)

• Reactive (when they answer to an observer’s query)

• Periodic (when nodes collects data according to conditions defined by the application)

Redundancy (overlapping sensing coverage) should be utilized in such a way that fault tolerance in the communication network is avoided and better accuracy can be found

37Fall 2006


Processing Memory and processor of a sensor node form the

computational module It is a programmable unit that provides

computation and storage for other nodes in the system

The computational module performs • Basic signal processing• Dispatches the data according to the application

Processing also involves data aggregation Other tasks are security processing and data

compression

38Fall 2006


Communication Two types of communication cost

• Infrastructure: refers to the communication needed to configure, maintain and optimize operation

• Application: relates to the transfer of sensed data

The communication approach can be classified as:• Flooding • Gossiping• Bargaining• Unicast• Multicast

39Fall 2006

MANNA – An Integrating ArchitectureMANNA – An Integrating Architecture

MANNA architecture was proposed to provide a management solution to different WSN application

It provides a separation between both sets of functionalities, i.e. Application and management Making integration of organizational, administrative and

maintenance activities possible for this kind of network

The architecture also provides some automatic services, which feature Self-managing self-sustaining self-diagnostic, with a minimum of human interference

40Fall 2006

MANNA (Cont’d)MANNA (Cont’d)

Figure represents scheme to construct management

To determine management service the scheme uses different WSN model

A management service can use one or more management functions

Different services can use common functions that use models to retrieve a network state concerning a given aspect

WSN model WSN model

Function 1 Function 2

Service Y

Function 3

Uses UsesUses

Service X

Uses Uses Uses Uses

41Fall 2006


Partial List of Management Functions Environmental monitoring functions Monitored area definition function Coverage area supervision function Node deployment definition function Environmental requirement acquisition function Network operating parameters configuration function Topology map discovery function Network connectivity discovery function Aggregation function Data fusion function Node density control function Management operation schedule function Energy map generation function Energy level discovery function Node localization discovery function Node mobile function

42Fall 2006


Functional architecture WSN manager

• Depends on type or network• In centrally managed network, a single manager collects

information from all agents and control the entire network• Distributed managed network has several managers,

each responsible for a sub-network and communicating with other managers

• In hierarchically managed network, intermediate managers distribute the management tasks

WSN Agent

43Fall 2006


Manager and agent location in flat WSN Agents inside the

network and external manager

Agent in the sink node Agents and manager

in the network• Hierarchical

organization

• Distributed organization

Manager Sink

Sensor report responses notifications

Manager Sink


Manager Sink

Manager Sink Agent Ordinary node


Manager Sink


44Fall 2006


Manager and agent location in hierarchical WSN Agents in the cluster head and external manager Agent in the base station

ManagerBase

Station


ManagerBase

Station


ManagerAgent Cluster HeadBase

StationOrdinary node

45Fall 2006


Manager and agent location in hierarchical WSN Agents in the network and intermediate manager Agents and distributed managers in the network

ManagerBase

Station


ManagerAgent Cluster HeadBase

StationOrdinary node

ManagerBase

Station


46Fall 2006

Concluding WordsConcluding Words

Wireless Sensor Networks provide a fundamentally new set of research and application challenges

WSNs are a rich source of problems in communication protocols, sensor tasking and control, sensor fusion, distributed data bases, probabilistic reasoning, and algorithmic design

Few more issues in sensor network are: Deployment strategies Node localization Network capacity Fault tolerance Security

47Fall 2006

Example of Some Sensor NodesExample of Some Sensor Nodes

48Fall 2006

ReferencesReferences

“Handbook of Sensor Networks: Compact Wireless and Wired Sensing Systems, CRC PRESS, 2005

“I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, “A survey on sensor networks,” IEEE Communications Magazine, 2002.

Tilak, S., Abu-Ghazaleh, N.B., Heinzelman, W.: A taxonomy of wireless micro-sensor network models. ACM Mobile Computing and Communications Review (MC2R) 6 (2002) 28–36

L.B. Ruiz, J.M.S. Nogueria and A.A.F Loureiro, “MANNA: a management architecture for wireless sensor network”, IEEE communications magazine, 41(2) 116-125, February 2003

www.google.com

49Fall 2006

Thanks !Thanks !

fall 2006 introduction to wireless sensor network part 2 choong seon hong kyung hee university...

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