Mobile Computing and Wireless Networking

Lec 01

01/03/2010

ECOM 6320

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Outline

Introduction to wireless networks and mobile computing

Challenges facing wireless networks and mobile computing

Introduction to wireless physical layer

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Goal of Wireless Networking and Mobile Computing

“People and their machines should be able to access information and communicate with each other easily and securely, in any medium or combination of media – voice, data, image, video, or multimedia – any time, anywhere, in a timely, cost-effective way.”

Dr. G. H. Heilmeier, Oct 1992

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Enabling Technologies Development and deployment of

wireless/mobile technology and infrastructure in-room, in-building, on-campus, in-the-field,

MAN, WAN Miniaturization of computing machinery . . . -> PCs -> laptop -> PDAs/smart

phones -> embedded computers/sensors Improving device capabilities/software

development environments, e.g., andriod: http://code.google.com/android/ iphone: http://developer.apple.com/iphone/ windows mobile

Pervasive Use of Mobile Wireless Devices There are ~4 billion mobile phones

Over 50 countries have mobile phone subscription penetration rates higher than that of the population (Infoma 2007)

http://en.wikipedia.org/wiki/Mobile_phone_penetration_rate

The mobile device will be the primary connection tool to the Internet for most people in the world in 2020. PEW Internet and American Life Project, Dec. 2008

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At Home

WiFi

WiFi

WiFi

cellular

bluetooth

UWB

satellite

WiFi 802.11g/n

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At Home

Source: http://teacher.scholastic.com/activities/science/wireless_interactives.htm

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At Home: Last-Mile Many users still don’t

have broadband reasons: out of service

area; some consider expensive

Broadband speed is still limited DSL: 1-6 Mbps

download, and 100-768Kbps upload

Cable modem: depends on your neighbors

Insufficient for several applications (e.g., high-quality video streaming)

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On the Move

Source: http://www.ece.uah.edu/~jovanov/whrms/

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On the Move: Context-Aware

Source: http://www.cs.cmu.edu/~aura/docdir/sensay_iswc.pdf

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ad ho

cGSM/UMTS, cdmaOne/cdma2000,WLAN, GPSDAB, TETRA, ...

road condition, weather,location-based services,emergency

On the Road

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Example: IntelliDrive (Vehicle Infrastructure Integration) Traffic crashes resulted in

more than 41,000 lives lost in 2007

Establishing vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) and vehicle-to-hand-held-devices (V2D) communications safety: e.g., intersection

collision avoidance/violation warning/turn conflict warning, curve warning

mobility: e.g., crash data, weather/road surface data, construction zones, emergency vehicle signal pre-emptionMore info: http://www.its.dot.gov/intellidrive/index.htm

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Collision Avoidance : V2V Networks stalled vehicle

warning

http://www.gm.com/company/gmability/safety/news_issues/releases/sixthsense_102405.html

bland spots

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Collision Avoidance at Intersections Two million

accidents at intersections per year in US

Source: http://www.fhwa.dot.gov/tfhrc/safety/pubs/its/ruralitsandrd/tb-intercollision.pdf

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Wireless and Mobile Computing Driven by technology and vision

wireless communication technology global infrastructure device miniaturization mobile computing platforms

The field is moving fast

Why is the Field Challenging?Challenge 1: Unreliable and Unpredictable Wireless Coverage

• Wireless links are not reliable: they may vary over time and space

Challenge 2: Open Wireless Medium

• Wireless interference• Hidden terminals• Wireless security

• eavesdropping, denial of service, …

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Challenge 3: Mobility

Mobility causes poor-quality wireless links

Mobility causes intermittent connection under intermittent connected networks,

traditional routing, TCP, applications all break

Mobility changes context, e.g., location

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Challenge 4: Portability Limited battery power Limited processing, display and storage

Sensors,embeddedcontrollers

Mobile phones• voice, data• simple graphical displays• GSM/3G

PDA phone• data• simpler graphical displays• 802.11/3G

Laptop• fully functional• standard applications• battery; 802.11

Performance/Weight/Power Consumption

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Challenge 5: Changing Regulation and Multiple Communication Standards

cellular phones satellites wireless LAN

cordlessphones

1992:GSM

1994:DCS 1800

2001:IMT-2000

1987:

CT1+

1982:Inmarsat-

A

1992:Inmarsat-BInmarsat-M

1998:Iridium

1989:CT 21991:DECT 199x:

proprietary

1997:IEEE 802.11

1999:802.11b, Bluetooth

1988:Inmarsat-

C

analogue

digital

1991:D-AMPS

1991:CDMA

1981:NMT 450

1986:NMT 900

1980:

CT01984

:CT1

1983:AMPS

1993:PDC

2000:GPRS

2000:IEEE 802.11a

Fourth Generation

(Internet based)

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3G Networks

http://en.wikipedia.org/wiki/List_of_mobile_network_operators_of_the_Americas#United_States

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Application

Transport

Network

Data Link

Physical

Medium

Data Link

Physical

Application

Transport

Network

Data Link

Physical

Data Link

Physical

Network Network

Radio

Often we need to implement a function across multiple layers.

The Layered Reference Model

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Overview of Wireless Transmissions

source decoding

bitstream

channel decoding

receiver

demodulation

source coding

bitstream

channel coding

analogsignal

sender

modulation

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Signal Signal are generated as physical

representations of data A signal is a function of time and location

t

1

0t

a special type of signal, sine waves, also called harmonics: s(t) = At sin(2 ft t + t)

with frequency f, period T=1/f, amplitude A, phase shift

1

0

ideal digital signal

t

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Fundamental Question: Why Not Send Digital Signal in Wireless Communications?

1

0

ideal digital signal

t

25

)2cos()2sin(21)(

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nftbnftactgn

nn

n

1

0

1

0t t

ideal periodical digital signal decomposition

Fourier Transform: Every Signal Can be Decomposed as a Collection of Harmonics

The more harmonics used, the smaller the approximation error.

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Fundamental Question: Why Not Send Digital Signal in Wireless Communications? May cause interference

suppose digital frame length T, then signal decomposes into frequencies at 1/T, 2/T, 3/T, …

let T = 1 ms, generates radio waves at frequencies of 1 KHz, 2 KHz, 3 KHz, …

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Frequencies for Communications

VLF = Very Low Frequency UHF = Ultra High FrequencyLF = Low Frequency SHF = Super High FrequencyMF = Medium Frequency EHF = Extra High Frequency

HF = High Frequency UV = Ultraviolet LightVHF = Very High Frequency

Frequency and wave length: = c/f

wave length , speed of light c 3x108m/s, frequency f

1 Mm300 Hz

10 km30 kHz

100 m3 MHz

1 m300 MHz

10 mm30 GHz

100 m3 THz

1 m300 THz

visible lightVLF LF MF HF VHF UHF SHF EHF infrared UV

optical transmissioncoax cabletwisted pair

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ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences)

Frequencies and Regulations

Europe USA Japan

Cellular Phones

GSM 450 - 457, 479 -486/460 - 467,489 -496, 890 - 915/935 -960, 1710 - 1785/1805 -1880 UMTS (FDD) 1920 -1980, 2110 - 2190 UMTS (TDD) 1900 -1920, 2020 - 2025

AMPS , TDMA , CDMA 824 - 849, 869 -894 TDMA , CDMA , GSM 1850 - 1910, 1930 - 1990

PDC 810- 826, 940- 956, 1429 - 1465, 1477 - 1513

Cordless Phones

CT1+ 885 - 887, 930 -932 CT2 864-868 DECT 1880 - 1900

PACS 1850 - 1910, 1930 -1990 PACS -UB 1910 - 1930

PHS 1895 - 1918 JCT 254-380

Wireless LANs

IEEE 802.11 2400 - 2483 HIPERLAN 2 5150 - 5350, 5470 -5725

902 -928 I EEE 802.11 2400 - 2483 5150 - 5350, 5725 - 5825

IEEE 802.11 2471 - 2497 5150 - 5250

Others RF- Control 27, 128, 418, 433,

868

RF- Control 315, 915

RF- Control 426, 868

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Spectrum and Bandwidth: Shannon Channel Capacity The maximum number of bits that can be

transmitted per second by a physical channel is:

where W is the frequency range of the channel, and S/N is the signal noise ratio, assuming Gaussian noise

)1(log2 NSW

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Objective encode digital data into analog signals at the

right frequency range with limited usage of spectrum

Modulation

Basic schemes Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM)

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Modulation of digital signals known as Shift Keying Amplitude Shift Keying (ASK):

Frequency Shift Keying (FSK):

Phase Shift Keying (PSK):

1 0 1

t

1 0 1

t

1 0 1

t

Modulation