Post on 13-Jan-2015
description
ECE, UMD
Peng Li
Introduction to Wireless Network
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Motivation
Why we use Wireless Network
Mobility Ease of use Installation Simplicity and Flexibility Cost
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Outline
The elements in Wireless Network1
Spread Spectrum2
OFDM3
Wireless Data Services4
Summary5
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The elements in Wireless Network
WirelessNetwork
DataFormat
NetworkStructure
RadioSignals
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The elements in Wireless Network
In terms of the OSI reference model Data format controls several of high layers.
Network Structure includes the wireless network interface adapters and base stations that send and receive the radio signals.
Radio signal operates at physical layers.
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Spread Spectrum
What’s the modulation method for Radio signal in Wireless Network ?
AM ? FM ? PCM ? Something else ?
Spread Spectrum !
Spread Spectrum
What’s Spread Spectrum ? Spread spectrum is a family of
methods for transmitting a single radio signal using a relatively wide segment of the radio spectrum.
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Spread Spectrum
FHSSFrequency-Hopping Spread Spectrum
DSSSDirect-Sequence Spread Spectrum
OFDMOrthogonal Frequency Division Multiplexing
OFDM
What’s OFDM ? OFDM is a combination of modulation
and multiplexing. OFDM is a special case of FDM
(Frequency Division Multiplex). The main concept in OFDM is
orthogonality of the sub-carriers.
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OFDM
OFDM System Diagram
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OFDM
Benefits of OFDM Very easy and efficient in dealing with
multi-path
Robust again narrow-band interference
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www.d.umn.edu/~lixxx988
Wireless Data Services
Wi-Fi
Cellular Mobile Wireless Services
WiMAX
Bluetooth
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Wireless Data Services
Wi-Fi It covers the various IEEE 802.11
technologies (including 802.11n, 802.11b, 802.11g, and 802.11a).
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Wireless Data Services
Wi-Fi Characteristics
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Wireless Data Services
Wi-Fi Type Frequency Modulation
802.11a 5 GHz OFDM
802.11b 2.4 GHz DSSS
802.11g 2.4 GHz OFDM
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Wireless Data Services
Cellular Mobile Wireless Services
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Wireless Data Services
WiMAX
Worldwide Interoperability for Microwave Access, The technology is based on the IEEE 802.16 standard (also called WirelessMAN).
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Wireless Data Services
Bluetooth Bluetooth is an FHSS system that splits the radio
signal into tiny pieces. It moves among 79 different frequencies 1,600 times per second in the same unlicensed 2.4 GHz range as 802.11b and 802.11g Wi-Fi services.
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Summary
Connecting your computer to the Internet (or a local network) by radio offers several advantages over connecting the same computer through a wired connection.
First, wireless provides convenient access for portable computers; it’s not necessary to find a cable or network data outlet.
Second, it allows a user to make a connection from more than one location and to maintain a connection as the user moves from place to place.
ECE, UMD
Q & A