Wireless networks - Lecture 34: Wireless sensor networks

Wireless networks - Lecture 34: Wireless sensor networks. The main topics covered in this chapter include: introduction to WSN; applications of WSN; factors influencing performance of WSN; architecture and communication protocols; challenges in WSNs;...

Wireless Networks

Lecture 34 Wireless Sensor Networks Part I

Dr Ghalib A Shah

 Introduction to WSN

 Applications of WSN

 Factors Influencing Performance of WSN

► Power consumption, fault tolerance, scalability, topology,

cost

 Architecture and Communication Protocols

 Challenges in WSNs.

Last Lecture Review

 Motivation

► Fixed-end systems, fixed wired network, window-based, slow-start,

loss-based congestion control

 TCP Variants

► Slow start

► Fast Retransmit/Recovery (TCP Reno)

 Issues in Heterogeneous Wireless Networks

► BER, Bandwidth, variable RTT, Mobility, Power

 TCP Schemes for Wireless

► Revolve around distinguishing congestion loss, error loss, delay

bounds, dup Acks

► Pure Link-level Approaches (FEC/ARQ)

► Soft-state Transport Layer Caching Approaches (SNOOP)

► Soft-state Cross Layer Signalling Approaches (ECN, EBSN, ELN,

ATCP)

► Hard-state Transport Layer Approaches (I-TCP, Mobile TCP)

Introduction to WSNs

 A sensor network is composed of a large number of

sensor nodes, which are densely deployed either inside the phenomenon or very close to it.

What is a Sensor ?

 Sensor is a small sized,

low power, low cost,

Radio Frequency 916 MHz/ 2.4 GHz (ISM)

Data Rate 40 Kbits/Sec (Max)

Radio Range 100 feet

Services

Dot 9/01

Demonstrate scale

Telos 4/04 Robust Low Power 250kbps Easy to use

Mica2 12/02 38.4kbps radio FSK

Sensor networks VS ad hoc networks:

 Scalability

► The number of nodes in a sensor network can be several orders of

magnitude higher than the nodes in an ad hoc network.

 Deployment

► Sensor nodes are densely deployed.

 Failure Rate

► Sensor nodes are prone to failures.

 Highly Dynamic topology

► The topology of a sensor network changes very frequently?

Applications of sensor networks

Applications of sensor networks (Cntd.)

 Military applications

► Monitoring friendly forces, equipment and ammunition

► Battlefield surveillance

► Reconnaissance of opposing forces and terrain

► Battle damage assessment

► Nuclear, biological and chemical attack detection and

reconnaissance

 Environmental applications

► Forest fire detection

► Biocomplexity mapping of the environment

► Flood detection

► Precision agriculture

Applications of sensor networks (Cntd.)

 Health applications

► Telemonitoring of human physiological data

► Tracking and monitoring patients and doctors inside

Applications of sensor networks

Other commercial applications

 Environmental control in office buildings

 Interactive museums

 Managing inventory control

 Vehicle tracking and detection

 Detecting and monitoring car thefts

Factors influencing sensor network design

 Fault tolerance

► Fault tolerance is the ability to sustain sensor network

functionalities without any interruption due to sensor node failures

► The fault tolerance level depends on the application of the

► The cost of a single node is very important to justify the overall

cost of the networks

Factors influencing sensor network design

Hardware constraints

Factors influencing sensor network design

 Sensor network topology

► Pre-deployment and deployment phase

Energy Consumption

bit 100m by radio.

Power consumption of a typical senor node

0 5 10 15 20

Factors influencing sensor network design

 Biologically or chemically contaminated field

 Battlefield beyond the enemy lines

 Home or a large building

 Large warehouse

 Fast moving vehicles

Communication architecture of sensor

networks

Communication architecture of sensor

networks

Protocol Stack

 Power Management Plan

► Turning off the receiver after a msg is received from neighbor in order

to avoid getting duplicate msg and conserving energy.

► Informing neighbor nodes during low battery power.

 Mobility Management Plan

► The mobility management plane detects and registers the movement

of sensor nodes, so a route back to the user is always maintained, and the sensor nodes can keep track of who are their neighbor sensor

nodes.

 Task Management Plan

► The task management plane balances and schedules the sensing

tasks given to a specific region Not all sensor nodes in that region are required to perform the sensing task at the same time As a result, some sensor nodes perform the task more than the others depending

on their power level.

Communication architecture of sensor

networks

 Application layer

► An application layer management protocol makes the hardware

and software of the lower layers transparent to the sensor network management applications

► Sensor management protocol (SMP)

► Task assignment and data advertisement protocol (TADAP)

► Sensor query and data dissemination protocol (SQDDP)

 Transport layer

► This layer is especially needed when the system is planned to

be accessed through Internet or other external networks

► No attempt thus far to propose a scheme or to discuss the

issues related to the transport layer of a sensor network in literature

Communication architecture of sensor

networks

Network layer

 Power efficiency is always an important consideration.

 Sensor networks are mostly data centric.

 Data aggregation is useful only when it does not hinder

the collaborative effort of the sensor nodes.

 An ideal sensor network has attribute-based addressing

and location awareness.

Communication architecture of sensor

networks

•Maximum available power (PA) route: Route 2

•Minimum energy (ME) route: Route 1

Communication architecture of sensor

networks

Data aggregation

Communication architecture of sensor

networks

 Data link layer

► The data link layer is responsible for the medium access and

error control It ensures reliable point and multipoint connections in a communication network

► Creation of the network infrastructure

► Fairly and efficiently share communication resources between

sensor nodes

► Operation in a power saving mode is energy efficient only if the

Communication architecture of sensor

networks

Error control

 Forward Error Correction (FEC)

 Automatic Repeat Request (ARQ).

Simple error control codes with low-complexity

encoding and decoding might present the best solutions for sensor networks

Challenges in WSN

 Cross-layer approach: A Grand Challenge

► Traditional layered approach is  not s uitable for 

WSNs

► Good for des ign, abs traction & debugging

► Bad for energy efficiency, overhead & 

performance

 How to realize mapping?

 User/Applications Requirements 

► Arch & Topology or Communication Protocols

► E.g reliability ?

Simulation for Sensor Networks

Simulation provides :

 Controlled , Reproducible testing environment

 Cost – effective alternative

 Means to explore and improve design space

 The role of any operating system (OS) is to promote

development of reliable application software by

providing a convenient and safe abstraction of

hardware resources

 Wireless sensor networks (WSNs) are embedded but

general-purpose, supporting a variety of applications, incorporating heterogeneous components, and capable

of rapid deployment in new environments

 An open-source development environment

 Introduction to WSN

 Applications of WSN

 Factors Influencing Performance of WSN

 Architecture and Communication Protocols

 Challenges in WSNs.