Introduction of wireless communication system

Wireless Networks
CS 6710
Spring 2010
Rajmohan Rajaraman

Outline of the course: Basic topics
Transmission Fundamentals
o Analog and digital transmission
o Channel capacity
o Antennas, propagation modes, and fading
o Signal encoding techniques
Spread spectrum technology
Coding and error control
Cellular networks
Wireless LANs
o IEEE 802.11
o Bluetooth

Outline: Advanced topics
WiMAX, Zigbee, UWB, 3G and 4G
Mobile Application platforms
Mobile IP, TCP for wireless
Multihop ad hoc networks
o MAC and routing protocols
o Power control and topology control
o Capacity of ad hoc networks
Sensor networks
o Infrastructure, MAC, and routing protocols
o Algorithms for query processing

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

Wireless communication systems
 Target information systems: “Anytime, Anywhere,
Any form”
 Applications: Ubiquitous computing and
information access
 Market in continuous growth:
o 35-60% annual growth of PCS
o Number of subscribers:
• By 2001: over 700M mobile phones
• By 2003: 1 billion subscribers
• By 2005: 2 billion
• By 2009: 4.6 billion
 Large diversity of standards and products
 Confusing terminology

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
o E.g., small LCD on a mobile telephone can only
displaying a few lines of text
o E.g., browsers of most mobile wireless devices
use wireless markup language (WML) instead of
HTML
o Switching speed of the material (e.g., silicon)

ad
hoc
IMT200, WLAN,
GSM, TETRA, ...
Personal Travel Assistant,
PDA, laptop, GSM, cdmaOne,
WLAN, Bluetooth, ...

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

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

Transmission fundamentals
Electromagnetic signals
o Time domain
o Frequency domain
Data rate and bandwidth
Channel capacity
o Nyquist theorem
o Shannon capacity theorem
Analog and digital data transmission
Transmission media

Introduction of wireless communication system

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

Unguided media
Transmission and reception are achieved
by means of an antenna
Configurations for wireless transmission
o Directional
o Omnidirectional

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

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

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

Broadcast radio
 Description of broadcast radio antennas
o Omnidirectional
o Antennas not required to be dish-shaped
o Antennas need not be rigidly mounted to a precise
alignment
 Applications
o 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
o 1012
to 1014
Hz
Transceivers must be within line of sight or
reachable via reflection
o Does not penetrate walls

Introduction of wireless communication system

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