Wireless Networks

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Wireless Networks

• Asstt. Professor
• Adeel Akram

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Introduction to Wireless Communication
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Course Outline Basic topics

• Transmission Fundamentals
• Analog and digital transmission
• Channel capacity
• Antennas, propagation modes, and fading
• Signal encoding techniques
• Spread spectrum technology
• Coding and error control
• Cellular networks
• Wireless LANs
• IEEE 802.11
• Bluetooth

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Course Outline Advanced topics

• Mobile IP
• Multihop ad hoc networks
• MAC and routing protocols
• Power control and topology control
• Capacity of ad hoc networks
• Sensor networks
• Infrastructure, MAC, and routing protocols
• Synchronization Protocols
• Algorithms for query processing

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Tentative Course Schedule
Topics Lecture Slide
Administrivia Transmission Fundamentals Analog digital transmission channel capacity WirelessNetworks1.ppt
Transmission Fundamentals Antennas and propagation modes, fading WirelessNetworks2.ppt
Signal encoding techniques WirelessNetworks3.ppt
Spread spectrum Frequency hopping, Direct sequence, and CDMA WirelessNetworks4.ppt
Coding and error control Error detection, error correction codes, convolution codes, and ARQ WirelessNetworks5.ppt
Cellular wireless networks WirelessNetworks6.ppt
Medium access control and Wireless LANs IEEE 802.11 protocol WirelessNetworks7.ppt
Wireless LANs Bluetooth Mobile IP WirelessNetworks8.ppt
Multihop ad hoc networks Routing protocols WirelessNetworks9.ppt
Multihop ad hoc networks Topology and power control WirelessNetworks10.ppt
Sensor networks MAC and routing protocols WirelessNetworks11.ppt
Sensor networks synchronization protocols algorithms for query processingMultihop ad hoc networks Fundamental limits on capacity WirelessNetworks12.ppt
Student presentations / Project
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Text Books

• Wireless Communications and Networks, by William
  Stallings, Prentice Hall, 2nd Edition, 2005
• This textbook will be followed for most of the
  course. 
• The material on multihop and sensor networks will
  be taken from research papers,
• and other collections. 

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Wireless Comes of Age

• Guglielmo Marconi invented the wireless telegraph
  in 1896
• Communication by encoding alphanumeric characters
  in analog signal
• Sent telegraphic signals across the Atlantic
  Ocean
• Communications satellites launched in 1960s
• Advances in wireless technology
• Radio, television, mobile telephone,
  communication satellites
• More recently
• Satellite communications, wireless networking,
  cellular technology, adhoc networks, sensor
  networks

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Layered Architecture
Application
Application
Transport
Transport
Network
Network
Data Link
Data Link
Data Link
Data Link
Physical
Physical
Physical
Physical
Medium
Radio
Scope of this course Anything above and
related protocols
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Wireless communication systems

• Target information systems Anytime, Anywhere,
  Anyform
• Applications Ubiquitous computing and
  information access
• Market in continuous growth
• 35-60 annual growth of PCS (Personal
  Communications Services)
• Number of subscribers
• by 2001 over 700M mobile phones
• by 2003 1 billion wireless subscribers (source
  Ericsson)
• 300 growth in wireless data from 1995-1997
• Large diversity of standards and products
• Confusing terminology

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Number of Subscribers in Hong Kong
Fixed Telephone
Mobile Phone
Broadband Internet
Will wireless Internet take off?
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Mobile Subscribers in Pakistan
       Customers of Mobile Service Providers in Pakistan        Customers of Mobile Service Providers in Pakistan        Customers of Mobile Service Providers in Pakistan        Customers of Mobile Service Providers in Pakistan        Customers of Mobile Service Providers in Pakistan        Customers of Mobile Service Providers in Pakistan        Customers of Mobile Service Providers in Pakistan        Customers of Mobile Service Providers in Pakistan        Customers of Mobile Service Providers in Pakistan
 Year Mobilink Ufone Paktel Instaphone Telenor Warid Total Growth Rate
2000 114,272   80,221 112,000     306,493 15.39
2001 309,272 116,711 96,623 220,000     742,606 142.29
2002 800,000 350,000 218,536 330,000     1,698,536 128.73
2003 1,115,000 550,000 319,400 420,000     2,404,400 41.56
2004 3,215,989 801,160 470,021 535,738     5,022,908 108.90
2005 7,469,085 2,579,103 924,486 454,147 835,727 508,655 12,771,203 154.26
Jul-05 Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis 14,119,257 10.56
Aug -05 Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis Company wise Data is updated on Quarterly Basis 15,511,045 9.7

More than 15,511,045 subscribers of Cellular
Networks From Telecom Indicators section of PTA
Website
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Limitations and difficulties

• Wireless is convenient and less expensive
• Limitations and political and technical
  difficulties inhibit wireless technologies
• Lack of an industry-wide standard
• Device limitations
• E.g., small LCD on a mobile telephone can only
  displaying a few lines of text
• E.g., browsers of most mobile wireless devices
  use wireless markup language (WML) instead of
  HTML

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Wireless around us
WLAN, DAB, GSM, etc
Personal Travel Assistant, PDA, Laptop, GSM,
cdmaOne, WLAN, Bluetooth, ...
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Portable Devices
performance
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Radio frequency spectrum

• Wireless technologies have gradually migrated to
  higher frequencies

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Wireless Mobility

• Wireless
• Limited bandwidth
• Broadcast medium requires multiple access
  schemes
• Variable link quality (noise, interference)
• High latency, higher jitter
• Heterogeneous air interfaces
• Security easier snooping
• Mobility
• User location may change with time
• Speed of mobile impacts wireless bandwidth
• Need mechanism for handoff
• Security easier spoofing
• Portability
• Limited battery, storage, computing, and UI

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Challenges in Mobile Computing

• Three major challenges
• Wireless Channel
• Mobility
• Device Limitation

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Wireless Channel

• The 1st challenge

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Communication Channel
Transmitter
Receiver
Channel
The medium used to transmit the signal from the
transmitter to the receiver Wireline / Wireless
channel
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Wireline Channel
Transmitter
Receiver
Wireline Channel, e.g. copper wire
Shielded against electromagnetic noise
Too many noises?
Large signal attenuation?
Use repeaters
Upgrade to coaxial cable
Data speed too low?
Data speed still too low?
Upgrade to optical fiber
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Fading Effect

• Typical Indoor Wireless Environment
• Signal strength fluctuates significantly
• Wireless channel cannot be engineered.
• You can only improve your transmission and
  reception techniques.

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Bit Error Rate

• Optical fiber 10-11 or 10-12
• Mobile channel
• Good quality 10-6
• Actual condition 10-2 or worse

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Implication

• For wireline systems, it is assumed that the
  channel is error free
• Many protocols are designed with this assumption
• These protocols do not work well in a wireless
  environment
• e.g. TCP (why?)

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What if more than 1 transmitter?
Every user accesses the network by means of a
dedicated channel
Switching Center or Network Access Point
Dedicated Channel
New user is served by a new wire-line circuit
Access capacity is unlimited.
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How about wireless networks?
Wireless users access the network by means of a
shared channel
Shared Channel
Access capacity is inherently limited.
Base Station
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Implication

• For wire-line systems, we can simply install new
  cables to increase capacity.
• For wireless systems, the channel can only be
  shared by the users.
• Capacity does not increase.

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Interference

• Multiuser Interference
• Radio signals of different users interfere with
  each other
• Self-Interference
• Multipath effect
• Phase-shifted images of the signal at the
  receiver interact and may cancel the entire
  signal, (i.e. destructive interference).

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Interference Management

• How to manage multiuser interference?
• i.e. how to share the channel?
• Multiple Access Problem
• FDMA, TDMA, CDMA, etc.
• Media Access Control
• Aloha, CSMA, etc.
• How to manage self-interference?
• Physical layer issue
• Equalization, coding, diversity, etc.
• These issues will NOT be considered in this course

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Mobility

• The 2nd challenge

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User Mobility

• Location Management Problem
• How does the network know where the intended
  recipient of a message is currently located?

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Cellular Scenario
Where is 5008011?
Send broadcast messages from every base station?
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Internet Scenario
Forwarding table in router
Suppose A sends a datagram to E
misc fields
data
223.1.1.1
223.1.2.2
The router sends the datagram to 223.1.2.2 via
interface 223.1.2.9
What happens if E moves to elsewhere?
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Ad hoc Network Scenario
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N
How to find a suitable path from source S to
destination D?
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Device Limitation

• The 3rd challenge

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Device Limitation

• Resource Limitation
• Limited memory
• Limited computational power
• Small display
• Limited battery life
• This issue will NOT be considered at the moment
  but may be extended later

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Classification of Wireless Systems

• Personal communication systems
• Focus on voice communication
• Limited bit-rate data transmission
• Large-scale mobility and coverage
• Operate over licensed frequency bands
• Wireless LANs
• Designed for high bit-rate transmission
• IP oriented
• Low-scale coverage
• Use unlicensed ISM frequency bands
• Multihop ad hoc networks
• Have little or no infrastructure
• Low-scale coverage
• Need new routing protocols
• Emerging applications

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Transmission fundamentals

• Electromagnetic signals
• Time domain
• Frequency domain
• Data rate and bandwidth
• Analog and digital data transmission
• Channel capacity
• Nyquist theorem Sampling Rate gt2fmax
• Shannon capacity theorem CWlog2(1S/N)
• Transmission media

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Analog signaling
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Digital signaling
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Classification of transmission media

• Transmission medium
• Physical path between transmitter and receiver
• Guided media
• Waves are guided along a solid medium
• E.g., copper twisted pair, copper coaxial cable,
  optical fiber
• Unguided media
• Provides means of transmission but does not guide
  electromagnetic signals
• Usually referred to as wireless transmission
• E.g., atmosphere, outer space

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Unguided media

• Transmission and reception are achieved by means
  of an antenna
• Configurations for wireless transmission
• Directional
• Omnidirectional

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General frequency ranges

• Microwave frequency range
• 1 GHz to 40 GHz
• Directional beams possible
• Suitable for point-to-point transmission
• Used for satellite communications
• Radio frequency range
• 30 MHz to 1 GHz
• Suitable for omnidirectional applications
• Infrared frequency range
• Roughly, 3x1011 to 2x1014 Hz
• Useful in local point-to-point multipoint
  applications within confined areas

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Terrestrial microwave

• Description of common microwave antenna
• Parabolic "dish", 3 m in diameter
• Fixed rigidly and focuses a narrow beam
• Achieves line-of-sight transmission to receiving
  antenna
• Located at substantial heights above ground level
• Applications
• Long haul telecommunications service
• Short point-to-point links between buildings

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Microwave antenna
Parabolic Dish
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Satellite microwave

• Description of communication satellite
• Microwave relay station
• Used to link two or more ground-based microwave
  transmitter/receivers
• Receives transmissions on one frequency band
  (uplink), amplifies or repeats the signal, and
  transmits it on another frequency (downlink)
• Applications
• Television distribution
• Long-distance telephone transmission
• Private business networks

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Broadcast radio

• Description of broadcast radio antennas
• Omni directional
• Antennas not required to be dish-shaped
• Antennas need not be rigidly mounted to a precise
  alignment
• Applications
• Broadcast radio
• VHF and part of the UHF band 30 MHZ to 1GHz
• Covers FM radio and UHF and VHF television

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Infrared

• Beyond the EHF spectrum
• 1012 to 1014 Hz
• Transceivers must be within line of sight or
  reachable via reflection
• Does not penetrate walls

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Next Lecture

• Antennas PropagationSignal Encoding

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Questions

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