Chapter9 wirelessnetwork

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Wireless Network
Chapter 9
Wireless Network
Korea-Vietnam Friendship IT College
Wireless Network
Overview
• Introduction
• Wireless network technologies and
Standards
• Wireless network protocols
• Wireless network security
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Korea-Vietnam Friendship IT College
Wireless Network
Introduction
• Provide links to Web resources and narrowband and
broadband network applications via RF (Radio
Frequency) waves in free space, thus eliminating
requirements for fixed wireline connections.
– e-mail, E-banking transactions, distance education, and
telehealthcare treatment
• Operate at various rates and levels of complexity; feature
a multiplicity of architectures, protocols, and topologies;
and vary in size and capacity.
– WPANs, WLANs, WMANs, and WWANs
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Korea-Vietnam Friendship IT College
Wireless Network
Introduction
Personal Area Network Local Area Network Wide Area Network
1-20 Mbps 11-54 Mbps 9-144 Kbps
Three wireless Internet
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Wireless Network
Wireless Network Technology
• Infrared technology
• Laser technology
• Spread spectrum technology
• Microwave technology
• Satellite technology
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Wireless Network
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Korea-Vietnam Friendship IT College
Wireless Network
Infrared Technology
• Based on the use of light emissions from a Light Emitting
Diode (LED).
– half-duplex or one-way
– full-duplex or bi-directional
– data exchange at distances ranging from zero meters to
one meter and higher.
• Integrated into wireless terminals and devices
– PDAs (Personal Digital Assistants), laptops, printers, digital
cameras, overhead, projectors, cellular telephones, portable
scanners, credit card readers, headsets, game controls, fax
(facsimile) equipment, and bank automated teller machines.
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Wireless Network
Infrared types
• Serial Infrared (SIR)
– 115KBps
• Fast Infrared (FIR)
– 4 Mbps, supporting WLAN
• Advanced Infrared (AIR)
– collaborative workgroup applications via infrared LAN
configurations.
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Wireless Network
Direct Infrared
point-to-point links
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Wireless Network
Diffuse Infrared
multipoint-to-multipoint connections
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Omnidirectional IR
• Single base station in LOS of all stations
• The base station acts as a repeater
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Korea-Vietnam Friendship IT College
Wireless Network
Standards
• IrDA (Infrared Data Association)
– 1993
– standards for infrared networking solutions that
facilitate point-to-point, point-to-multipoint, and
multipoint-to-multipoint connections.
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Wireless Network
Laser Technology
• Laser (Light Amplification by Stimulated Emission of
Radiation)
– Lasers emit narrow light beams at precise wavelengths for
enabling point-to-point connections to enable voice, video, and
data transport.
– A laser network requires the use of laser transceivers (laser
transmitters and laser receivers) for enabling direct line-of-sight,
point-to-point transmissions and a tower to which this
equipment is affixed.
• Supports fast implementation of high-performance
communications systems that operate in diverse
environments.
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Wireless Network
FSO
• FSO (Free Space Optics)
• Using laser light sources it is possible to achieve very
high speeds (typically OC-3 (155Mbps), OC-12
(622Mbps), or 1.25Gbps; but some systems operate at
2Gbps and 10GBps) for point-to-point links
• Uses Terahertz (THz) spectrum range
• Short ranges - typically below 2km
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Wireless Network
Spread Spectrum Technology
• Spread spectrum modulation spreads out the modulated
signal bandwidth so it is much greater than the message
bandwidth
• Independent code spreads signal at transmitter and
despreads signal at receiver
interference
spread power signal
power signal spread
interference
detection at
receiver
f f
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Wireless Network
Spread Spectrum Technology
• DS/SS (Direct Sequence Spread Spectrum):
– XOR the signal with pseudonoise (PN) sequence
(chipping sequence)
• FH/SS (Frequency Hopping Spread Spectrum):
– Discrete changes of carrier frequency
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Spread Spectrum Allocation
• FCC (U.S. Federal Communications Commission)
– Monitors spread spectrum licensing and allocates spectrum:
902 - 928 MHz, 2.400 - 2.483 GHz for spread spectrum
operations.
• UK Radio Communications Agency
– manages nonmilitary spread spectrum allocations and monitors
spread spectrum use to prevent signal interference
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Microwave Technology
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Microwave Technology
• A microwave communication tower acts as a signal
repeater. It receives signals from one “dish” and repeats
them onto another.
• It requires Line-Of-Sight (LOS).
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Korea-Vietnam Friendship IT College
Wireless Network
Microwave Technology
• Parabolic dish antenna (typical size of 3 m in diameter).
• Focused beam to achieve line of sight transmission.
• Located at substantial heights above ground level.
• Microwave relay towers used to achieve long distance.
• Applications:
– Long haul telecommunications service.
– Short point-to-point links between buildings.
• Higher frequencies give higher data rates and require smaller
antennas.
• Attenuation and interference.
– Attenuation is increased with rainfall (especially above 10
GHz).
– With growing applications, transmission areas overlap and
resulting in interference.
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