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CS647 - Advanced Topics in Wireless Networks

Introduction – Part II

Drs. Baruch Awerbuch & Amitabh MishraComputer Science Department

Johns Hopkins University

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A case for mobility – many aspectsHistory of mobile communicationMarketWireless Networks

Cellular NetworksAd hoc NetworksSensor Networks

Areas of research

Outline

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Classical Mail Forwarding Technique?

Baltimore Main Post Office

JH Univ Post Office

Mail from the world

Baltimore JH Univ

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Ideal cell area (2-10 km radius)

Fundamentals of Cellular Systems

Illustration of a cell with a mobile station and a base station

BS

MS

CellMS

Alternative shape of a cell Hexagonal cell area

used in most models

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Control and Traffic Channels

Base Station (BS)

Forward (downlink)

control ch

annel

Mobile Host (MH)

Reverse (u

plink) contro

l channel

Forward (downlink) tr

affic ch

annel

Reverse (u

plink) traffic

channel

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PSTNMS

HomeMobile

Switching Center

HLR Home network

Visitingarea

Caller

VisitingMobile

Switching Center

VLR

MS

1

Location update request Using Bacon Signals

Update location Info. sent to HLR

2

Automatic Location Update

Baltimore

JHU

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PSTN

MS

homeMobile

Switching Center

HLR Home Network

VisitingArea

Caller

Mobile Switching

Center

VLR

Automatic Call Forwarding using HLR-VLR

1 Call sent to home location

2Home MSC checksHLR; gets current location of MSin visiting area

3

Home MSC forwardscall to visiting MSC

4

MSC in visiting area sendscall to BS and connects MS

Baltimore

JHU

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Call Setup from MH (Cell Phone) to BS?

BS MS

1. Need to establish path

2. Frequency/time slot/code assigned(FDMA/TDMA/CDMA)

3. Control Information Acknowledgement4. Start communication

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Mobility and Handoff

BSi

Signal strength due to BSi

X2MS

X4

Pmin

Pi(x)

E

Signal strength due to BSj

X1 X3 X5 XthBSj

Pj(x)

By looking at the variation of signal strength from either base station it is possible to decide on the optimum area where handoff can take place

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Handoff Scenarios with Different Mobility Locations

PSTN

Paging Area 1

MSC2

c

MSC3

d

MSC4

Paging Area 2

e

MS

MSC1

a b

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A case for mobility – many aspectsHistory of mobile communicationMarketWireless Networks

Cellular NetworksAd hoc NetworksSensor Networks

Areas of research

Outline

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MANETs: Mobile Ad hoc Networks

Applications: Military applications (battlefield), disaster situations, etc.

Collection of wireless mobile nodes dynamically forming a distributed network without any pre-existing infrastructure

From DARPA Website

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An autonomous system of nodes (MHs) connected by wireless links

Lack of fixed infrastructure relays

Absence of centralized authority

Peer-to-peer connectivity Multi-hop forwarding to ensure network connectivity

Topology may change dynamically

Random Multi-hop Graph

Energy-constrained

Bandwidth-constrained, variable capacity links

Mobile Ad Hoc Networks - Characteristics:

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Mobile Ad Hoc Network (MANET)

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Applications of MANETsDefense applications: On-the-fly communication set up for soldiers on the ground, fighter planes in the air, etc.

Crisis-management applications: Natural disasters, where the entire communication infrastructure is in disarray

Tele-medicine: Paramedic assisting a victim at a remote location can access medical records, can get video conference assistance from a surgeon for an emergency intervention

Tele-Geoprocessing applications: Combines geographical information system, GPS and high capacity MS, Queries dependent of locationinformation of the users, and environmental monitoring using sensors

Virtual navigation: A remote database contains geographical representation of streets, buildings, and characteristics of large metropolis and blocks of this data is transmitted in rapid sequence to a vehicle to visualize needed environment ahead of time

Education via the internet: Educational opportunities on Internet to K-12 students and other interested individuals and it is possible to have last-mile wireless Internet access

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A case for mobility – many aspectsHistory of mobile communicationMarketWireless Networks

Cellular NetworksAd hoc NetworksSensor Networks

Areas of research

Outline

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Embedded Networked Sensing

Micro-sensors, on-board processing, and wireless interfaces all feasible at very small scale

can monitor phenomena “up close”

Will enable spatially and temporally denseenvironmental monitoringEmbedded Networked Sensing will reveal previously unobservable phenomena

Seismic Structure response

Contaminant Transport

Marine Microorganisms

Ecosystems, Biocomplexity

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Example use of a Sensor Network

Measuring pollutant concentration

Pass on information to monitoring station

Predict current location of pollutant contour based on various parameters

Take corrective action

Pollutants monitored by sensors in the river

Sensors report to the base monitoring station

ST

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Wireless Sensor Networks – Architecture

Sensor Field

Internet & Satellite

Sensor Node

C

Task ManagerNode

SINK

A

D

B

User

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Portable and self-sustained (power, communication, intelligence)Capable of embedded complex data processingNote: Power consumed in transmitting 1Kb data over 100m is equivalent to executing 30M Instructions on 10MIPS processorTechnology trends predict small memory footprint may not be a limitation in future sensor nodesEquipped with multiple sensing, programmable computing and communication capability

What is a Sensor and a Sensor Network?

Transceiver

Embedded Processor

Sensor

Battery

Memory

Transceiver

Embedded Processor

Sensor

Battery

Memory

1Kbps- 1Mbps3m - 300m

Lossy Transmission

8 bit, 10 MHzSlow Computation

Limited LifetimeRequires

SupervisionMultiple sensors

128Kb - 1MbLimited Storage

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Sensors and Wireless Radio

Types of sensors: -Pressure,-Temperature-Light-Biological-Chemical-Strain, fatigue-Tilt

• Capable of surviving harsh environments (heat, humidity, corrosion, pollution, radiation, etc)

• Could be deployed in large numbers

Wireless Wireless RadioRadio

SensorsSensors

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Wireless Sensor NetworksWireless sensor networks are a collection of tiny disposable and low power devices

A sensor node is a device that converts a sensed attribute (e.g. temperature, vibration) into a form understandable by users

Wireless sensor networks have been used for years for a number of applications

The number of sensors can be large to cover as much area as desirable

Sensor networks are usually unattended and some degree of fault-tolerance needed

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Characteristics of Wireless Sensor Networks

Advantages:Ease of deploymentExtended rangeFault toleranceMobility (some)

Limitations:Low-bandwidthError-prone transmissionsNeed for collision-free channel accessLimited amount of energy availableUsually sensors placed where it is difficult to replace their batteries

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Areas of research in mobile communication

Wireless Communicationtransmission quality (bandwidth, error rate, delay)modulation, coding, interferencemedia access, regulations...

Mobilitylocation dependent serviceslocation transparencyquality of service support (delay, jitter, security)Routing...

Portabilitypower consumptionlimited computing power, sizes of display, ...

Security..