Post on 17-Mar-2018
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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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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