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Wireless Networks Spring 2007
Wireless Networks
CSG 250Spring 2007
Rajmohan Rajaraman
Wireless Networks Spring 2007
Outline of the course: Basic topics
Transmission Fundamentalso Analog and digital transmissiono Channel capacityo Antennas, propagation modes, and fadingo Signal encoding techniques
Spread spectrum technologyCoding and error controlCellular networksWireless LANs
o IEEE 802.11o Bluetooth
Wireless Networks Spring 2007
Outline: Advanced topicsMobile IPTCP for wirelessMultihop ad hoc networks
o MAC and routing protocolso Power control and topology controlo Capacity of ad hoc networks
Sensor networkso Infrastructure, MAC, and routing protocolso Algorithms for query processing
Wireless Networks Spring 2007
Wireless Comes of Age Guglielmo Marconi invented the wireless telegraph in 1896
o Communication by encoding alphanumeric characters in analogsignal
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 recentlyo Satellite communications, wireless networking, cellular
technology, ad hoc networks, sensor networks
Wireless Networks Spring 2007
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 subscribers• By 2005: 2 billion, and by 2010 3.3 billion
Large diversity of standards and products Confusing terminology
Wireless Networks Spring 2007
Limitations and difficulties
Wireless is convenient and less expensiveLimitations and political and technical
difficulties inhibit wireless technologiesLack of an industry-wide standardDevice limitations
o E.g., small LCD on a mobile telephone can onlydisplaying a few lines of text
o E.g., browsers of most mobile wireless devicesuse wireless markup language (WML) insteadof HTML
Wireless Networks Spring 2007
ad ho
cIMT200, WLAN,GSM, TETRA, ...
Personal Travel Assistant,PDA, laptop, GSM, cdmaOne, WLAN, Bluetooth, ...
Wireless Networks Spring 2007
Wireless & Mobility Wireless:
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 2007
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 2007
Transmission fundamentals
Electromagnetic signalso Time domaino Frequency domain
Data rate and bandwidthChannel capacity
o Nyquist theoremo Shannon capacity theorem
Analog and digital data transmissionTransmission media
Wireless Networks Spring 2007
Wireless Networks Spring 2007
Wireless Networks Spring 2007
Analog signaling
Wireless Networks Spring 2007
Digital signaling
Wireless Networks Spring 2007
Wireless Networks Spring 2007
Classification of transmission media Transmission medium
o 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 2007
Unguided media
Transmission and reception are achievedby means of an antenna
Configurations for wireless transmissiono Directionalo Omnidirectional
Wireless Networks Spring 2007
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 GHzo 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 2007
Terrestrial microwave
Description of common microwave antennao Parabolic "dish", 3 m in diametero Fixed rigidly and focuses a narrow beamo Achieves line-of-sight transmission to receiving antennao Located at substantial heights above ground level
Applicationso Long haul telecommunications serviceo Short point-to-point links between buildings
Wireless Networks Spring 2007
Satellite microwave Description of communication satellite
o 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 onanother frequency (downlink)
Applicationso Television distributiono Long-distance telephone transmissiono Private business networks
Wireless Networks Spring 2007
Broadcast radio
Description of broadcast radio antennaso Omnidirectionalo Antennas not required to be dish-shapedo 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
Wireless Networks Spring 2007
Infrared
Beyond the EHF spectrumo 1012 to 1014 Hz
Transceivers must be within line of sight orreachable via reflectiono Does not penetrate walls