Mobile Computing and Wireless Networking Lec 01
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Transcript of Mobile Computing and Wireless Networking Lec 01
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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
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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
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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
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)2cos()2sin(21)(
11
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