Mobile Computing and Wireless Networking Lec 01 01/03/2010 ECOM
6320
Slide 2
2 Outline r Introduction to wireless networks and mobile
computing r Challenges facing wireless networks and mobile
computing r Introduction to wireless physical layer
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3 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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4 Enabling Technologies r Development and deployment of
wireless/mobile technology and infrastructure m in-room,
in-building, on-campus, in-the-field, MAN, WAN r Miniaturization of
computing machinery... -> PCs -> laptop -> PDAs/smart
phones -> embedded computers/sensors r Improving device
capabilities/software development environments, e.g., m andriod:
http://code.google.com/android/ m iphone:
http://developer.apple.com/iphone/ m windows mobile
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Pervasive Use of Mobile Wireless Devices r There are ~4 billion
mobile phones m Over 50 countries have mobile phone subscription
penetration rates higher than that of the population (Infoma 2007)
m http://en.wikipedia.org/wiki/Mobile_phone_pen etration_rate r 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 5
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6 At Home WiFi cellular bluetooth UWB satellite WiFi
802.11g/n
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7 At Home Source:
http://teacher.scholastic.com/activities/science/wireless_interactives.htm
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8 At Home: Last-Mile r Many users still dont have broadband m
reasons: out of service area; some consider expensive r Broadband
speed is still limited m DSL: 1-6 Mbps download, and 100- 768Kbps
upload m Cable modem: depends on your neighbors m Insufficient for
several applications (e.g., high- quality video streaming)
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9 On the Move Source:
http://www.ece.uah.edu/~jovanov/whrms/
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10 On the Move: Context-Aware Source:
http://www.cs.cmu.edu/~aura/docdir/sensay_iswc.pdf
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11 ad hoc GSM/UMTS, cdmaOne/cdma2000, WLAN, GPS DAB, TETRA,...
road condition, weather, location-based services, emergency On the
Road
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12 Example: IntelliDrive (Vehicle Infrastructure Integration) r
Traffic crashes resulted in more than 41,000 lives lost in 2007 r
Establishing vehicle-to- vehicle (V2V), vehicle-to- infrastructure
(V2I) and vehicle-to-hand-held- devices (V2D) communications m
safety: e.g., intersection collision avoidance/violation
warning/turn conflict warning, curve warning m mobility: e.g.,
crash data, weather/road surface data, construction zones,
emergency vehicle signal pre-emption More info:
http://www.its.dot.gov/intellidrive/index.htm
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13 Collision Avoidance : V2V Networks r stalled vehicle warning
http://www.gm.com/company/gmability/safety/news_issues/releases/sixthsense_102405.html
r bland spots
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14 Collision Avoidance at Intersections r 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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15 Wireless and Mobile Computing r Driven by technology and
vision m wireless communication technology m global infrastructure
m device miniaturization m mobile computing platforms r 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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17 Challenge 3: Mobility r Mobility causes poor-quality
wireless links r Mobility causes intermittent connection m under
intermittent connected networks, traditional routing, TCP,
applications all break r Mobility changes context, e.g.,
location
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18 Challenge 4: Portability r Limited battery power r Limited
processing, display and storage Sensors, embedded controllers
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
21 Application Transport Network Data Link Physical Medium Data
Link Physical Application Transport Network Data Link Physical Data
Link Physical Network Radio Often we need to implement a function
across multiple layers. The Layered Reference Model
Slide 22
22 Overview of Wireless Transmissions source decoding bit
stream channel decoding receiver demodulation source coding bit
stream channel coding analog signal sender modulation
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23 Signal r Signal are generated as physical representations of
data r A signal is a function of time and location t 1 0 t a
special type of signal, sine waves, also called harmonics: s(t) = A
t sin(2 f t t + t ) with frequency f, period T=1/f, amplitude A,
phase shift 1 0 ideal digital signal t
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24 Fundamental Question: Why Not Send Digital Signal in
Wireless Communications? 1 0 ideal digital signal t
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25 1 0 1 0 tt 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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26 Fundamental Question: Why Not Send Digital Signal in
Wireless Communications? r May cause interference m suppose digital
frame length T, then signal decomposes into frequencies at 1/T,
2/T, 3/T, m let T = 1 ms, generates radio waves at frequencies of 1
KHz, 2 KHz, 3 KHz,
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27 Frequencies for Communications VLF = Very Low FrequencyUHF =
Ultra High Frequency LF = Low Frequency SHF = Super High Frequency
MF = Medium Frequency EHF = Extra High Frequency HF = High
Frequency UV = Ultraviolet Light VHF = Very High Frequency
Frequency and wave length: = c/f wave length, speed of light c 3x10
8 m/s, frequency f 1 Mm 300 Hz 10 km 30 kHz 100 m 3 MHz 1 m 300 MHz
10 mm 30 GHz 100 m 3 THz 1 m 300 THz visible light
VLFLFMFHFVHFUHFSHFEHFinfraredUV optical transmission coax
cabletwisted pair
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28 r ITU-R holds auctions for new frequencies, manages
frequency bands worldwide (WRC, World Radio Conferences)
Frequencies and Regulations
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29 Spectrum and Bandwidth: Shannon Channel Capacity r 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
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30 r Objective m encode digital data into analog signals at the
right frequency range with limited usage of spectrum Modulation r
Basic schemes m Amplitude Modulation (AM) m Frequency Modulation
(FM) m Phase Modulation (PM)
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31 r Modulation of digital signals known as Shift Keying r
Amplitude Shift Keying (ASK): r Frequency Shift Keying (FSK): r
Phase Shift Keying (PSK): 101 t 101 t 101 t Modulation