Asstt. ProfessorAdeel Akram

Course Outline: Basic topicsTransmission Fundamentals

Analog and digital transmissionChannel capacityAntennas, propagation modes, and fadingSignal encoding techniques

Spread spectrum technologyCoding and error controlCellular networksWireless LANs

IEEE 802.11Bluetooth

Course Outline: Advanced topicsMobile IPMultihop ad hoc networks

MAC and routing protocolsPower control and topology controlCapacity of ad hoc networks

Sensor networksInfrastructure, MAC, and routing protocolsSynchronization ProtocolsAlgorithms for query processing

Tentative Course Schedule Topics Lecture Slide

Administrivia; Transmission Fundamentals: Analog & digital transmission channel capacity WirelessNetworks1.ppt

Transmission Fundamentals: Antennas and propagation modes, fading WirelessNetworks2.ppt

Signal encoding techniques WirelessNetworks3.ppt

Spread spectrum: Frequency hopping, Direct sequence, and CDMA WirelessNetworks4.ppt

Coding and error control: Error detection, error correction codes, convolution codes, and ARQ WirelessNetworks5.ppt

Cellular wireless networks WirelessNetworks6.ppt

Medium access control and Wireless LANs: IEEE 802.11 protocol WirelessNetworks7.ppt

Wireless LANs: Bluetooth; Mobile IP WirelessNetworks8.ppt

Multihop ad hoc networks: Routing protocols WirelessNetworks9.ppt

Multihop ad hoc networks: Topology and power control WirelessNetworks10.ppt

Sensor networks: MAC and routing protocols WirelessNetworks11.ppt

Sensor networks: synchronization protocols; algorithms for query processingMultihop ad hoc networks: Fundamental limits on capacity

WirelessNetworks12.ppt

Student presentations / Project

Text BooksWireless Communications

and Networks, by William Stallings, Prentice Hall, 2nd Edition, 2005

This textbook will be followed for most of the course. 

The material on multihop and sensor networks will be taken from research papers,

and other collections. 

Wireless Comes of AgeGuglielmo Marconi invented the wireless

telegraph in 1896Communication by encoding alphanumeric characters in

analog signalSent telegraphic signals across the Atlantic Ocean

Communications satellites launched in 1960sAdvances in wireless technology

Radio, television, mobile telephone, communication satellites

More recentlySatellite communications, wireless networking, cellular

technology, adhoc networks, sensor networks

Application

Transport

Network

Data Link

Physical

Medium

Data Link

Physical

Application

Transport

Network

Data Link

Physical

Data Link

Physical

Network Network

Radio

Scope of this course:

Anything above and related protocols

Wireless communication systemsTarget information systems: “Anytime, Anywhere,

Anyform”Applications: Ubiquitous computing and

information accessMarket in continuous growth:

35-60% annual growth of PCS (Personal Communications Services)Number of subscribers:

by 2001: over 700M mobile phones by 2003: 1 billion wireless subscribers (source Ericsson)

300% growth in wireless data from 1995-1997Large diversity of standards and productsConfusing terminology

Number of Subscribers in Hong Kong

Mobile Phone

Fixed Telephone

Broadband Internet

Will wireless Internet take off?

Mobile Subscribers in Pakistan       Customers of Mobile Service Providers in Pakistan*

 Year Mobilink Ufone Paktel Instaphone Telenor Warid Total Growth Rate

2000 114,272   80,221 112,000     306,493 15.39

2001 309,272 116,711 96,623 220,000     742,606 142.29

2002 800,000 350,000 218,536 330,000     1,698,536 128.73

2003 1,115,000 550,000 319,400 420,000     2,404,400 41.56

2004 3,215,989 801,160 470,021 535,738     5,022,908 108.90

2005 7,469,085 2,579,103 924,486 454,147 835,727 508,655 12,771,203 154.26

Jul-05Company wise Data is updated on Quarterly Basis

14,119,257 10.56

Aug -05 15,511,045 9.7

More than 15,511,045 subscribers of Cellular Networks

*From Telecom Indicators section of PTA Website

Mobile Subscribers in Pakistan

0 2,000,000 4,000,000 6,000,000 8,000,000

Mobilink

Ufone

Paktel

Instaphone

Telenor

Warid2005

2004

2003

2002

2001

2000

Limitations and difficultiesWireless is convenient and less expensiveLimitations and political and technical

difficulties inhibit wireless technologiesLack of an industry-wide standardDevice limitations

E.g., small LCD on a mobile telephone can only displaying a few lines of text

E.g., browsers of most mobile wireless devices use wireless markup language (WML) instead of HTML

Wireless around us…

WLAN, DAB, GSM, etc…

Personal Travel Assistant,PDA, Laptop, GSM, cdmaOne,WLAN, Bluetooth, ...

performanceperformance

Mobile phones• voice, data• simple text displays

PDA• simple graphical displays• character recognition• simplified WWW

Palmtop• tiny keyboard• simple versions of standard applications

Laptop• fully functional• standard applications

Radio frequency spectrumWireless technologies have gradually

migrated to higher frequencies

Wireless & MobilityWireless:

Limited bandwidthBroadcast medium: requires multiple access schemesVariable link quality (noise, interference)High latency, higher jitterHeterogeneous air interfacesSecurity: easier snooping

Mobility:User location may change with timeSpeed of mobile impacts wireless bandwidthNeed mechanism for handoffSecurity: easier spoofing

PortabilityLimited battery, storage, computing, and UI

Challenges in Mobile ComputingThree major challenges:

Wireless ChannelMobilityDevice Limitation

The 1st challenge

Communication Channel

Transmitter Receiver

The medium used to transmit the signal from the transmitter to the receiver

Wireline / Wireless channel

Channel

Wireline Channel

Transmitter Receiver

Wireline Channel, e.g. copper wire

Too many noises?

Shielded against electromagnetic noise

Large signal attenuation?

Use repeaters

Data speed too low? Upgrade to coaxial cable

Data speed still too low?

Upgrade to optical fiber

Fading Effect

Typical Indoor Wireless EnvironmentSignal strength

fluctuates significantly

Wireless channel cannot be engineered.You can only

improve your transmission and reception techniques.

Bit Error RateOptical fiber: 10-11 or 10-12

Mobile channel: Good quality: 10-6

Actual condition: 10-2 or worse

ImplicationFor wireline systems, it is assumed that the

channel is error freeMany protocols are designed with this

assumptionThese protocols do not work well in a

wireless environment e.g. TCP (why?)

What if more than 1 transmitter?

Switching Center

or

Network Access Point

Every user accesses the network by means of a dedicated channel

New user is served by a new wire-line circuit

Access capacity is “unlimited”.

Dedicated Channel

How about wireless networks?

Base Station

Shared Channel

Wireless users access the network by means of a shared channel

Access capacity is inherently limited.

ImplicationFor wire-line systems, we can simply install

new cables to increase capacity.

For wireless systems, the channel can only be shared by the users.Capacity does not increase.

InterferenceMultiuser Interference

Radio signals of different users interfere with each other

Self-InterferenceMultipath effectPhase-shifted images of the signal at the

receiver interact and may cancel the entire signal, (i.e. destructive interference).

Interference ManagementHow to manage multiuser interference?

i.e. how to share the channel?Multiple Access Problem

FDMA, TDMA, CDMA, etc.Media Access Control

Aloha, CSMA, etc.

How to manage self-interference?Physical layer issue

Equalization, coding, diversity, etc.These issues will NOT be considered in this course

The 2nd challenge

User Mobility Location Management Problem

How does the network know where the intended recipient of a message is currently located?

Cellular ScenarioWhere is 5008011?

Send broadcast messages from every base station?

Internet Scenario Dest. Net router Nhops interface

223.1.1 - 1 223.1.1.4 223.1.2 - 1 223.1.2.9

223.1.3 - 1 223.1.3.27

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

A

BE

Forwarding table in routerForwarding table in router

Suppose A sends a datagram to E

miscfields223.1.1.1223.1.2.2 data

The router sends the datagram to 223.1.2.2 via interface 223.1.2.9

What happens if E moves to elsewhere?

B

A

S E

F

H

J

D

C

G

IK

M

N

L

How to find a suitable path from source S to destination D?

The 3rd challenge

Device LimitationResource Limitation

Limited memoryLimited computational powerSmall displayLimited battery life

This issue will NOT be considered at the moment but may be extended later

Classification of Wireless SystemsPersonal communication systems

Focus on voice communication Limited bit-rate data transmission Large-scale mobility and coverage Operate over licensed frequency bands

Wireless LANs Designed for high bit-rate transmission IP oriented Low-scale coverage Use unlicensed ISM frequency bands

Multihop ad hoc networks Have little or no infrastructure Low-scale coverage Need new routing protocols Emerging applications

Transmission fundamentalsElectromagnetic signals

Time domainFrequency domain

Data rate and bandwidthAnalog and digital data transmissionChannel capacity

Nyquist theorem [Sampling Rate >2fmax ]

Shannon capacity theorem [C≤Wlog2(1+S/N)]

Transmission media

Analog signaling

Digital signaling

Classification of transmission media

Transmission mediumPhysical path between transmitter and receiver

Guided mediaWaves are guided along a solid mediumE.g., copper twisted pair, copper coaxial cable,

optical fiberUnguided media

Provides means of transmission but does not guide electromagnetic signals

Usually referred to as wireless transmissionE.g., atmosphere, outer space

Unguided mediaTransmission and reception are achieved by

means of an antennaConfigurations for wireless transmission

DirectionalOmnidirectional

General frequency rangesMicrowave frequency range

1 GHz to 40 GHzDirectional beams possibleSuitable for point-to-point transmissionUsed for satellite communications

Radio frequency range30 MHz to 1 GHzSuitable for omnidirectional applications

Infrared frequency rangeRoughly, 3x1011 to 2x1014 HzUseful in local point-to-point multipoint

applications within confined areas

Terrestrial microwaveDescription of common microwave

antennaParabolic "dish", 3 m in diameterFixed rigidly and focuses a narrow beamAchieves line-of-sight transmission to receiving

antennaLocated at substantial heights above ground

levelApplications

Long haul telecommunications serviceShort point-to-point links between buildings

Microwave antenna

Parabolic “Dish”

Satellite microwaveDescription of communication satellite

Microwave relay stationUsed to link two or more ground-based

microwave transmitter/receiversReceives transmissions on one frequency band

(uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink)

ApplicationsTelevision distributionLong-distance telephone transmissionPrivate business networks

Broadcast radioDescription of broadcast radio antennas

Omni directionalAntennas not required to be dish-shapedAntennas need not be rigidly mounted to a

precise alignment

ApplicationsBroadcast radio

VHF and part of the UHF band; 30 MHZ to 1GHz Covers FM radio and UHF and VHF television

InfraredBeyond the EHF spectrum

1012 to 1014 HzTransceivers must be within line of sight or

reachable via reflectionDoes not penetrate walls

Next LectureAntennas & Propagation

Signal Encoding

Questions

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