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Wireless Networks Spring 2005
Outline of the course: Basic topics
Transmission Fundamentalso Analog and digital transmissiono Channel capacityo Antennas, propagation modes, and fading o Signal encoding techniques
Spread spectrum technologyCoding and error controlCellular networksWireless LANs
o IEEE 802.11o Bluetooth
Wireless Networks Spring 2005
Outline: Advanced topicsMobile IP
TCP for wireless
Multihop ad hoc networkso MAC and routing protocols
o Power control and topology control
o Capacity of ad hoc networks
Sensor networkso Infrastructure, MAC, and routing protocols
o Algorithms for query processing
Wireless Networks Spring 2005
Wireless Comes of Age
Guglielmo Marconi invented the wireless telegraph in 1896o Communication by encoding alphanumeric characters in analog signal
o Sent telegraphic signals across the Atlantic Ocean
Communications satellites launched in 1960s
Advances in wireless technologyo Radio, television, mobile telephone, communication satellites
More recentlyo Satellite communications, wireless networking, cellular technology, ad
hoc networks, sensor networks
Wireless Networks Spring 2005
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 PCSo Number of subscribers:
• by 2001: over 700M mobile phones • by 2003: 1 billion wireless subscribers (source Ericsson)
o 300% growth in wireless data from 1995-1997
Large diversity of standards and products Confusing terminology
Wireless Networks Spring 2005
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 limitationso 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
Wireless Networks Spring 2005
ad hocIMT200, WLAN,
DAB, GSM, TETRA, ...
Personal Travel Assistant,PDA, laptop, GSM, cdmaOne, WLAN, Bluetooth, ...
Wireless Networks Spring 2005
Radio frequency spectrum
Wireless technologies have gradually migrated to higher frequencies
1 Mm300 Hz
10 km30 kHz
100 m3 MHz
1 m300 MHz
10 mm30 GHz
100 µm3 THz
1 µm300 THz
visible lightVLF LF MF HF VHF UHF SHF EHF infrared UV
optical transmissioncoax cabletwisted pair
Wireless Networks Spring 2005
Wireless & MobilityWireless:
o Limited bandwidtho Broadcast medium: requires multiple access schemeso Variable link quality (noise, interference)o High latency, higher jittero Heterogeneous air interfaceso Security: easier snooping
Mobility:o User location may change with timeo Speed of mobile impacts wireless bandwidtho Need mechanism for handoffo Security: easier spoofing
Portabilityo Limited battery, storage, computing, and UI
Wireless Networks Spring 2005
Classification of Wireless Systems Personal communication systems
o Focus on voice communicationo Limited bit-rate data transmissiono Large-scale mobility and coverageo Operate over licensed frequency bands
Wireless LANso Designed for high bit-rate transmissiono IP orientedo Low-scale coverageo Use unlicensed ISM frequency bands
Multihop ad hoc networkso Have little or no infrastructureo Low-scale coverageo Need new routing protocolso Emerging applications
Wireless Networks Spring 2005
Transmission fundamentals
Electromagnetic signalso Time domaino Frequency domain
Data rate and bandwidthAnalog and digital data transmissionChannel capacity
o Nyquist theoremo Shannon capacity theorem
Transmission media
Wireless Networks Spring 2005
Classification of transmission media
Transmission mediumo Physical path between transmitter and receiver
Guided mediao Waves are guided along a solid mediumo E.g., copper twisted pair, copper coaxial cable, optical fiber
Unguided mediao Provides means of transmission but does not guide
electromagnetic signalso Usually referred to as wireless transmissiono E.g., atmosphere, outer space
Wireless Networks Spring 2005
Unguided media
Transmission and reception are achieved by means of an antenna
Configurations for wireless transmissiono Directional
o Omnidirectional
Wireless Networks Spring 2005
General frequency ranges
Microwave frequency rangeo 1 GHz to 40 GHzo Directional beams possibleo Suitable for point-to-point transmissiono Used for satellite communications
Radio frequency rangeo 30 MHz to 1 GHz o Suitable for omnidirectional applications
Infrared frequency rangeo Roughly, 3x1011 to 2x1014 Hzo Useful in local point-to-point multipoint applications within confined
areas
Wireless Networks Spring 2005
Terrestrial microwave
Description of common microwave antennao 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
Applicationso Long haul telecommunications service
o Short point-to-point links between buildings
Wireless Networks Spring 2005
Satellite microwave
Description of communication satelliteo Microwave relay stationo Used to link two or more ground-based microwave
transmitter/receiverso Receives transmissions on one frequency band (uplink), amplifies
or repeats the signal, and transmits it on another frequency (downlink)
Applicationso Television distributiono Long-distance telephone transmissiono Private business networks
Wireless Networks Spring 2005
Broadcast radio
Description of broadcast radio antennaso Omnidirectional
o Antennas not required to be dish-shaped
o Antennas need not be rigidly mounted to a precise alignment
Applicationso 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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