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Introduction to
Wireless Networking
People
Examiner, lecturer, and lab assistant
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TDDD36 – mobile systems
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Lab assistants
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Director of studies
Linkoping, Sweden, fall 2011
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Niklas Carlsson
Email: niklas.carlsson@liu.se
Office: 2B:478
Niklas Carlsson
Research area: Design, modeling, and
performance evaluation of distributed systems
and networks
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Farrokh Ghani Zadegan, PhD student
Lena Strömbäck
Slides in this course are adapted or based on various on-line resources (including lectures
notes by Juha Takkinen, Anirban Mahanti, Carey Williamson, Jim Kurose, and Keith Ross)
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Course Overview
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My expectations
Written exam
n Grads: ‘fail’, 3, 4, 5.
One (1) optional assignment
n Wireshark + (short) mobile Web trace
n 2 x 2hours (Sept 20 & 30, I think)
Five (5) lectures
See website for more information ...
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Read textbook
n 2.5 textbooks (one main book)
n Lots of content
n Not time to cover everything during lectures
Work hard
n Pay attention during lectures
n Read after class
n Make sure you understand all the material
Follow deadlines and office hours
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What is Wireless Networking?
What to expect? (What will be covered?)
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Design principles for mobile systems
n Conceptual view
Design, resource, and performance tradeoffs in the
mobile systems
n General working knowledge of protocols and
applications
n Detailed knowledge of selected protocols and
applications
n Some practical hands on experience
Glimpse into the future of the Internet
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1-4
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The use of infra-red (IR) or radio frequency (RF)
signals to share information and resources
between devices
Promises anytime, anywhere connectivity
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Laptops, palmtops, PDAs, Internet-enabled phone
promise anytime untethered Internet access
No wires!
Emerging trends and technologies
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What is Wireless Networking?
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What is Wireless Networking?
The use of infra-red (IR) or radio frequency (RF)
signals to share information and resources
between devices
Promises anytime, anywhere connectivity
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Laptops, palmtops, PDAs, Internet-enabled phone
promise anytime untethered Internet access
The use of infra-red (IR) or radio frequency (RF)
signals to share information and resources
between devices
Promises anytime, anywhere connectivity
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No wires!
Laptops, palmtops, PDAs, Internet-enabled phone
promise anytime untethered Internet access
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No wires!
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Lots of media buzzwords!
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Mobile Internet, Pervasive Computing, Nomadic
Computing, M-Commerce, Ubiquitous Computing …
… and acronyms; e.g., CSMA, WiFi, 802.11, …
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Wireless Networking Technologies
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Two important (but different!) challenges
Mobile devices – laptop, PDA, cellular
phone, wearable computer, sensors, …
Operating modes
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Infrastructure mode (Access Point (AP))
Ad hoc mode
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Communication over wireless link
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Handling mobile user who changes point of
attachment to network
Access technology
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Bluetooth (1 Mbps, up to 3m)
IEEE 802.11 (up to 54 Mbps, 20 – 100m)
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Two important (but different!) challenges
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Two important (but different!) challenges
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Communication over wireless link
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Communication over wireless link
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Handling mobile user who changes point of
attachment to network
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Handling mobile user who changes point of
attachment to network
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Wireless Link Characteristics
Two important (but different!) challenges
Differences from wired link ….
Communication over wireless link
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Decreasing signal strength: radio signal attenuates as it
propagates through matter (path loss)
Interference from other sources: standardized wireless
network frequencies (e.g., 2.4 GHz) shared by other devices
(e.g., phone); devices (motors) interfere as well
Multi-path propagation: radio signal reflects off objects
ground, arriving at destination at slightly different times
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Handling mobile user who changes point of
attachment to network
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** In this course we will look at unique
challenges and opportunities in wireless
communication, including the two above.
…. make communication across (even a point to point) wireless link
much more “difficult”
n Higher error rates; lower bandwidths; non-uniform
transmission characteristics; increased usage costs; and
increased susceptibility to interference and eavesdropping
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Wireless Network Characteristics
Wireless Link Characteristics
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SNR: signal-to-noise ratio
n larger SNR – easier to extract
signal from noise (a “good
thing”)
SNR versus BER tradeoffs
n given physical layer: increase
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power -> increase SNR
->decrease BER
given SNR: choose physical
layer that meets BER
requirement, giving highest
throughput
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Multiple wireless senders and receivers create additional
problems (beyond multiple access):
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10-2
C
10-4
10-5
A
10-6
10-7
SNR may change with
mobility: dynamically adapt
physical layer (modulation
technique, rate)
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30
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SNR(dB)
B
Hidden terminal problem
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C’s signal
strength
A’s signal
strength
space
❒ A and B can hear each other
Signal fading:
❒ B and C can hear each other
QAM256 (8 Mbps)
❒ A and B hear each other
❒ A and C can’t hear each other
❒ B and C hear each other
QAM16 (4 Mbps)
❒ thus A and C are unaware of
❒ A and C can’t hear each other
their interference at B
BPSK (1 Mbps)
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Infrastructure Mode
network
infrastructure
B
A
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BER
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interfering at B
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Ad hoc Mode
Infrastructure mode
❒ base station connects
mobiles into wired
network
❒ handoff: mobile
changes base station
providing connection
into wired network
Ad hoc mode
❒ no base stations
❒ nodes can only
transmit to other
nodes within link
coverage
❒ nodes organize
themselves into a
network: route among
themselves
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