Asstt. Professor
Adeel Akram
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
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
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 processing
Multihop ad hoc networks: Fundamental limits on capacity
WirelessNetworks12.ppt
Student presentations / Project
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.
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
Layered Architecture
Application
Application
Transport
Transport
Network
Network
Network
Network
Data Link
Data Link
Data Link
Data Link
Physical
Physical
Physical
Physical
Radio
Medium
Scope of this course:
Anything above and related protocols
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
Number of Subscribers in Hong Kong
Fixed Telephone
Mobile Phone
Broadband Internet
Will wireless Internet take off?
Mobile Subscribers in Pakistan
Customers of Mobile Service Providers in Pakistan*
Year
Mobilink
2000
114,272
2001
309,272
2002
Ufone
Paktel
Instaphone
80,221
116,711
800,000
2003
Telenor
Total
Growth Rate
112,000
306,493
15.39
96,623
220,000
742,606
142.29
350,000
218,536
330,000
1,698,536
128.73
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
12,771,203
154.26
14,119,257
10.56
15,511,045
9.7
835,727
Jul-05
Warid
508,655
Company wise Data is updated on Quarterly Basis
Aug -05
More than 15,511,045 subscribers of Cellular Networks
*From
Telecom Indicators section of PTA Website
Mobile Subscribers in Pakistan
Warid
2005
2004
Telenor
2003
Instaphone
2002
2001
Paktel
2000
Ufone
Mobilink
0
2,000,000
4,000,000
6,000,000
8,000,000
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
Wireless around us…
WLAN, DAB, GSM,
etc…
Personal Travel Assistant,
PDA, Laptop, GSM, cdmaOne,
WLAN, Bluetooth, ...
Portable Devices
PDA
• simple graphical displays
• character recognition
• simplified WWW
Mobile phones
• voice, data
• simple text displays
Laptop
• fully functional
• standard applications
Palmtop
• tiny keyboard
• simple versions
of standard applications
performance
Radio frequency spectrum
 Wireless technologies have gradually migrated to
higher frequencies
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
Challenges in Mobile Computing
 Three major challenges:
 Wireless Channel
 Mobility
 Device Limitation
The 1st challenge
Communication Channel
Transmitter
Channel
The medium used to
transmit the signal
from the transmitter
to the receiver
Wireline / Wireless
channel
Receiver
Wireline Channel
Transmitter
Wireline Channel,
e.g. copper wire
Too many noises?
Large signal attenuation?
Data speed too low?
Data speed still too low?
Receiver
Shielded against
electromagnetic noise
Use repeaters
Upgrade to coaxial cable
Upgrade to optical fiber
Fading Effect
 Typical Indoor
Wireless
Environment
 Signal strength
fluctuates
significantly
 Wireless channel
cannot be
engineered.
 You can only
improve your
transmission and
reception
techniques.
Bit Error Rate
 Optical fiber: 10-11 or 10-12
 Mobile channel:
 Good quality: 10-6
 Actual condition: 10-2 or worse
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?)
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”.
How about wireless networks?
Wireless users access
the network by means
of a shared channel
Base
Station
Access capacity is
inherently limited.
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.
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).
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
The 2nd challenge
User Mobility
 Location Management Problem
 How does the network know where the intended
recipient of a message is currently located?
Cellular Scenario
Where is 5008011?
Send broadcast
messages from
every base station?
Internet Scenario
Forwarding table in router
Dest. Net router Nhops interface
223.1.1
223.1.2
223.1.3
-
1
1
1
A
223.1.1.4
223.1.2.9
223.1.3.27
223.1.1.1
223.1.2.1
B
223.1.1.2
223.1.1.4
223.1.2.2
223.1.1.3
Suppose A sends a datagram to E
223.1.2.9
223.1.3.27
223.1.3.1
E
223.1.3.2
misc
data
fields 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?
Ad hoc Network Scenario
S
E
F
B
C
M
J
A
L
G
H
K
D
I
How to find a suitable path from source S to
destination D?
N
The 3rd challenge
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
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
Transmission fundamentals
 Electromagnetic signals
 Time domain
 Frequency domain
 Data rate and bandwidth
 Analog and digital data transmission
 Channel capacity
 Nyquist theorem [Sampling Rate >2fmax ]
 Shannon capacity theorem [C≤Wlog2(1+S/N)]
 Transmission media
Analog signaling
Digital signaling
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
Unguided media
 Transmission and reception are achieved by means of
an antenna
 Configurations for wireless transmission
 Directional
 Omnidirectional
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
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
Microwave antenna
Parabolic “Dish”
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
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
Infrared
 Beyond the EHF spectrum
 1012 to 1014 Hz
 Transceivers must be within line of sight or reachable
via reflection
 Does not penetrate walls
Next Lecture
 Antennas & Propagation
Signal Encoding
Questions
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