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COMP 635: WIRELESS & MOBILE COMMUNICATIONS

COURSE INTRODUCTION

http://wireless.web.unc.edu

Jasleen Kaur

Fall 2017

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Introductions

q Namesq BS/MS, First-year Grad, Senior Grad?q If you’re new, where have you come from?q Your CS interests?q Why this course?q What are you expecting to learn from this course?

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“Wireless” vs. “Mobile”

q Two aspects of mobility:Ø User mobility:

§ Users can communicate “anytime, anywhere, with anyone”Ø Device portability:

§ Devices can connect anytime, anywhere to the “network”

q Wireless vs. mobile Examplesû û Stationary computerû ü Notebook on a hotel Ethernetü û Wireless LANs in historic buildingsü ü Personal Digital Assistant (PDA)

Our focus: wireless (including non-mobile)

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THE IMPORTANCE OF WIRELESS COMMUNICATIONWhy Should We Care?

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Explosion of User Base

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2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015*

Mobilecellular telephonesubscriptions

Fixed-telephonesubscriptions

ActiveMobile-broadbandsubscriptions

Fixed broadbandsubscriptions

InternetUsers

Explosive growth in developing countries

~ 7 billion current mobile phone service subscriptionsè more than 96% of world population !

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Benefits of Wirelessq Unrestricted mobility

Ø Unplugged from power outlet

q Significantly lower costØ No cable, low labor cost, low maintenance

q EaseØ Minimum infrastructure - scatter and play

q UbiquityØ Available everywhere like water/air - holy grail

90% of world’s populated areas (in 2011) covered by a mobile cellular network !

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Example Application Environmentsq Personal communication

q Replacement of fixed networksØ Access to remote areasØ Sensors in difficult terrains (weather, earth activities)Ø Flexibility for trade showsØ LANs in historic buildings

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Location-based Services: Opportunitiesq Location aware services

Ø Resource-discovery, e.g., printer, fax, phone, server etc.

q Follow-me servicesØ Call-forwarding, mobile desktop

q Information servicesØ “push”: e.g., current special offers in the supermarketØ “pull”: e.g., where is the Black Forrest Cheese Cake?

q Privacy servicesØ Who should gain knowledge about the location?Ø What information should environment gain about you?

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Example Application Environments

q Vehicular Traffic:Ø Personal communication using GSM/UMTSØ News, road condition, weather, music via DAB/DVB-TØ Position via GPSØ Local ad-hoc network with vehicles close-by

§ To prevent accidents, guidance system, redundancy Ø Transport networks (buses, trains)

q EmergenciesØ Early transmission of patient data to the hospital

§ Current status, first diagnosisØ Quick replacement of a fixed infrastructure in case of

earthquakes, hurricanes, fire etc.Ø Crisis, war, ...

§ Only wireless ad-hoc networks survive

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Example Application Environmentsq Traveling salesmen/employee

Ø Access to central (consistent) customer databaseØ Mobile officeØ Location-aware services (call-forwarding, hotel printer)

q Entertainment, education, ...Ø Outdoor Internet access Ø Intelligent travel guide with up-to-date location-

dependent informationØ Ad-hoc networks for multi user games

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Example Application Environmentsq Wireless sensing

Ø Using RF signals for geolocationØ Using RF signals to sense physical objects

§ Even behind wallsØ “Piggy-back” RF signals for no-power communicationØ …

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Explosion of Mobile Devices

Prof.Dr.-Ing.JochenH.Schillerwww.jochenschiller.de MC- 2009

performance

Pager• receiveonly• tinydisplays• simpletextmessages

Mobilephones• voice,data• simplegraphicaldisplays

PDA• graphicaldisplays• characterrecognition• simplifiedWWW

Smartphone• tinykeyboard• simpleversionsofstandardapplications

Laptop/Notebook• fullyfunctional• standardapplications

Sensors,embeddedcontrollers

www.scatterweb.net

Noclear separationbetweendevicetypespossible(e.g. smartphones,embeddedPCs,…)

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Explosion of Technologiesq Wide-area communications (cellular, satellite-based):

Ø GSM, AMPS, UMTS, cdma2000, DAB, DVB-T

q Wireless LANs:Ø 802.11x seriesØ Small-to-medium range, higher bit-rates

q Short-range:Ø BluetoothØ Low bit-rates

ITU efforts for standardization/convergence

Mobile communications greatly influenced bymerging of telecommunications and computer networks

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The Future

Courtesy:Romit RoyChoudhary,DukeUniversity

QuickTime™ and a decompressor

are needed to see this picture.

Internet

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WHAT’S DIFFERENT ABOUT WIRELESS SYSTEMS?What Issues are Unique to These?

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Mobile Devices: Unique Issuesq Power consumption

Ø Low quality displays, small disks due to limited batteryØ Limited compute power: CPU power consumption ~ CV2f

§ C: internal capacity, reduced by integration§ V: supply voltage, can be reduced to a certain limit§ f: clock frequency, can be reduced temporally

q Limited memoryØ Limited usage of mass memories with moving partsØ Flash-memory as alternative

q Limited user interfacesØ Compromise between size of fingers and portabilityØ Integration of voice recognition, abstract symbols

q Loss of dataØ E.g., errors, theft

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Wireless Networks: Unique Issuesq Providing seamless support for mobility

Ø Without disrupting users or applications

q Signal propagation:Ø Signal attenuation (as signal propagates)

§ How long should the “wireless link” be?Ø Higher loss-rates due to interference

§ Emissions of engines, lightning§ How to ensure reliability of “wireless link”?

q Frequency-usage:Ø Restrictive regulations of frequencies

§ Useful frequencies are almost all occupiedØ Spatial reuse (facilitated by signal attenuation)

§ How to reuse frequency spectrum?

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Wireless Networks: Unique Issuesq Constraints on performance:

Ø Low transmission rates (few Mbps)Ø Higher delays, higher jitter

§ Connection setup time: GSM (seconds), others (ms)

q Exploiting/dealing with diversity / dynamism:Ø Antenna selection, Time diversity, Frequency selection

q Energy conservation:Ø Wireless devices often battery-powered

q Security-related issues:Ø Lower security, simpler active attacking

§ Radio interface accessible for everyone§ Base station can be simulated (attracting mobile calls)

Ø Broadcast medium è easier to snoop or tamper with§ How to provide integrity and privacy?

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WHAT IS THIS COURSE ABOUT?Syllabus and Structure

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Impact of Wireless on the Layer Model

Prof.Dr.-Ing.JochenH.Schillerwww.jochenschiller.de MC- 2009

Application layer

Transport layer

Network layer

Data link layer

Physical layer

service location new/adaptive applicationsmultimediacongestion/flow controlquality of serviceaddressing, routingdevice locationhand-overauthenticationmedia access/controlmultiplexingencryptionmodulationinterferenceattenuationfrequency

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Course Syllabus

q Background: Ø Physical Layer (modulation, interference, attenuation)Ø MAC Protocols (coordinated access, random access)Ø Mobile IPØ Ad-hoc Routing ProtocolsØ TCP in Wireless

q Recent proposals:Ø Enhance physical performance, make MAC more

efficient, provide seamless mobility, …

Focus: protocol and physical mechanisms for optimal performance

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Course Structure

q Initial set of lectures (by me):Ø Will cover all background material

q Review of recent publicationsØ Paper presentations (by you)Ø Critical reviews (by you)

q Semester-long projects (groups of 2 welcome)Ø Topics: investigating, designing something new

§ Experimental study§ Formal analysis§ Design and evaluation of new mechanism

Ø Preferably on one of the focus topics for this course§ Unless motivated by strong interest in other topics

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Example Project Typesq Project topics: investigating or designing something

Ø Experimental study§ Characterization of traffic generated by a popular app§ Simulator-based comparison of two protocols§ Measurement of a WiFi deployment§ Wireless trace analysis

Ø Formal analysis§ Expanding on the analysis of a paper you’ve read

Ø Design and evaluation of new mechanisms/application§ How best to use all sensors in a smartphone to best manage

(communication in) a dream app§ How best to use network & cloud to support a dream app§ Bandwidth estimation on wireless “links”§ Localization using signal strengths

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Course Grading

q Paper Presentations: 25%

q Critical Reviews: 20%

q Projects (groups of 2 are welcome): Ø Progress: 30%Ø Presentation + report: 10%

q Final Exam (oral): 15%

q Class Participation: Ø Will be used to potentially bump up (or down) half a

grade

q All percentage points above are flexible by 5-10%

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References For Background Material

q Several reputable texts for background material:Ø Jochen Schiller, “Mobile Communications”.Ø William Stallings, “Wireless Communications &

Networks”.Ø Theodore S. Rappaport, “Wireless Communications”.Ø Pahlavan & Krishnamurthy, “Principles of Wireless

Networks”.

q Unfortunately, none is sufficient by itself for this course

q Nearly half the course will cover recent research papers

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QUESTIONS ?

http://wireless.web.unc.edu

jasleen@cs.unc.edu