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COMP 635: WIRELESS NETWORKS

COURSE INTRODUCTION

Jasleen Kaur

Fall 2015

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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 Examples û û Stationary computer û ü Notebook on a hotel Ethernet ü û Wireless LANs in historic buildings ü ü Smart phone

Our focus: wireless (including non-mobile)

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THE IMPORTANCE OF WIRELESS NETWORKS Why Should We Care?

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Explosion of User Base

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

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 10.0    

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 90.0    

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

Mobile  cellular  telephone  subscripCons  

Fixed-­‐telephone  subscripCons  

AcCve  Mobile-­‐broadband  subscripCons  

Fixed  broadband  subscripCons  

Internet  Users  

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Benefits of Wireless

q  Unrestricted mobility Ø  Unplugged from power outlet

q  Significantly lower cost

Ø  No cable, low labor cost, low maintenance

q  Ease Ø  Minimum infrastructure - scatter and play

q  Ubiquity Ø  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 Environments

q  Personal communication

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

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Location-based Services: Opportunities q  Location aware services

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

q  Follow-me services Ø  Call-forwarding, mobile desktop

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

q  Privacy services Ø  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/UMTS Ø  News, road condition, weather, music via DAB/DVB-T Ø  Position via GPS Ø  Local ad-hoc network with vehicles close-by

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

q  Emergencies Ø  Early transmission of patient data to the hospital

§  Current status, first diagnosis Ø  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 Environments

q  Traveling salesmen Ø  Access to central (consistent) customer database Ø  Mobile office Ø  Location-aware services (call-forwarding, hotel printer)

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

dependent information Ø  Ad-hoc networks for multi user games

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Explosion of Mobile Devices

Prof.  Dr.-­‐Ing.  Jochen  H.  Schiller        www.jochenschiller.de          MC  -­‐  2009  

performance  

Pager  •   receive  only  •   Cny  displays  •   simple  text        messages  

Mobile  phones  •   voice,  data  •   simple  graphical  displays  

PDA  •   graphical  displays  •   character  recogniCon  •   simplified  WWW  

Smartphone  •   Cny  keyboard  •   simple  versions        of  standard  applicaCons  

Laptop/Notebook  •   fully  funcConal  •   standard  applicaCons  

Sensors,  embedded  controllers  

www.sca\erweb.net  

No  clear  separaCon  between  device  types  possible    (e.g.  smart  phones,  embedded  PCs,  …)  

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Explosion of Technologies

q  Wide-area communications (cellular, satellite-based): Ø  GSM, AMPS, UMTS, cdma2000, DAB, DVB-T

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

q  Short-range: Ø  Bluetooth Ø  Low bit-rates

ITU efforts for standardization/convergence

Mobile communications greatly influenced by merging of telecommunications and computer networks

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The Future

Courtesy:  Romit  Roy  Choudhary,  Duke  University  

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 Issues q  Power consumption

Ø  Low quality displays, small disks due to limited battery Ø  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 memory Ø  Limited usage of mass memories with moving parts Ø  Flash-memory as alternative

q  Limited user interfaces Ø  Compromise between size of fingers and portability Ø  Integration of voice recognition, abstract symbols

q  Loss of data Ø  E.g., errors, theft

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Wireless Networks: Unique Issues q  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 occupied Ø  Spatial reuse (facilitated by signal attenuation)

§  How to reuse frequency spectrum?

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Wireless Networks: Unique Issues q  Constraints on performance:

Ø  Low transmission rates (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.  Jochen  H.  Schiller        www.jochenschiller.de          MC  -­‐  2009  

Application layer Transport layer Network layer Data link layer Physical layer

service location new/adaptive applications multimedia congestion/flow control quality of service addressing, routing device location hand-over authentication media access/control multiplexing encryption modulation interference attenuation frequency

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Course Syllabus

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

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

efficient, provide seamless mobility, …

Focus: protocol mechanisms for optimal performance

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Course Structure

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

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

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

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

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 Types q  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 mechanism/application §  How best to use all sensors on a smartphone to best manage

(communication in) a dream app §  How best to use network, cloud, compute 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: 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