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Ch2:1WirelessNet
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Fundamental of Wireless LANFundamental of Wireless LAN
� Radio Waves� IEEE 802 Families� Appenidx (Infrared and Carrier Currents LANs)
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Wireless LAN Configuration
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Radio-Based Wireless LANs
� Most widely used method� Adv: penetrating walls and other obstacles with little
attenuation.� Disadv: security, interference, etc.
� 2 approaches: � Narrow band� ISM band and Spread spectrum
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Narrow Band Modulation
� Concentrate all transmission power in a narrow range of frequency.
� Efficient use of radio spectrum; save bandwidth.� ex: television, AM, FM� Adv: for long distance transmission (e.g. metropolitan
area)� Disadv: noise can easily corrupt the signals� Need to obtain FCC licenses to coordinate the use.
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ISM Bands� In 1985, FCC modified part 15 to stimulate the use of
wireless networks.� ISM=Industrial, Scientific, and Medical� Unlicensed, you can freelyinstall and move.
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ISM Spectrum Availability
� Only 2.4 GHz is the world-accepted ISM band.� 902 MHz is easier in manufacturing.
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Spread Spectrum Modulation
� Definition: spread a signals power over a wider band of frequency.
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Spread Spectrum
� Disadv: This contradicts with the goal of conserving bandwidth.
� Adv: less susceptible to electrical noise (especially from narrow band sources)� In World War II, US Army uses spread spectrum to avoid
hostile jamming. (invented by Hedy Lamarr, an actress)
� To spread a signal, there are two ways:� direct sequence (DSSS)� frequency hopping (FHSS)
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Direct Sequence Spread Spectrum (DSSS)
� Use bit sequence to represent zero and one (Fig. 2-5)
� Also referred to as chipping code.
� Longer chipping codes are more resilient to noise.
� Minimum length = 10 (by FCC)� IEEE 802.11 uses 11 chips per
data bit.
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Frequency Hopping Spread Spectrum (FHSS)
� Data is modulated by carrier signals that hop from frequency to frequencyas a function of time, over a wide band of frequencies.
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FHSS (cont.)
� Hopping Code: to determine the order of hopping frequencies
� The receiver must listen to incoming signals at the right time at the right frequency.
� FCC regulation: at least 75 frequencies, with max. dwell time 400ms.
� Adv.: very resilient to noise.� Orthogonal hopping codes: a set of hopping codes that
never use the same frequencies at the same time (can be on-line adjusted by software).
� Allow multiple wireless LANs to co-exist.
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Forms of Radio-based Wireless LAN
� Wireless Local Bridge� Infrastructure� Ad Hoc
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IEEE 802 FamiliesIEEE 802 Families
� IEEE? � a non-profit professional org. founded in 1884; now has
320,000 members in 150 countries;
� Most notable standards: � IEEE 802 family (802.2 LLC, 802.3 Ethernet, 802.5 Token
Ring, etc.)
� IEEE membership info:� Open to anyone. Its FREE!! Must pay meeting fees.� Membership Category: voting member, nearly member,
aspirant member, sleeping member.
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� 802.11a: Specification enabling up to 54 Mb/s to be achieved in the 5 GHz unlicensed radio band by utilizing OFDM
� 802.11b: Specification enabling up to 22 Mb/s to be achieved in the 2.4 GHz unlicensed radio band by utilizing DSSS
� 802.11c: Provides required information to ensure proper bridge operations, which is required when developing access points
� 802.11d: Covers additional regulatory domains, which is especially important for operation in the 5 GHz bands because the use of these frequencies differ widely from one country to another
Task groups of 802.11
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� 802.11e: Covers issues of MAC enhancements for QoS, such as EDCF service differentiation and HCF
� 802.11f: Provides interoperability for users roaming from one access point to another of different vendor
� 802.11g: Specification enabling up to 54 Mb/s to be achieved in the 2.4 GHz unlicensed radio band
� 802.11h: Dynamic channel selection and transmission power control� 802.11i: Specification for WLAN security to replace the weak Wired
Equivalent Privacy (WEP)� 802.11k: Radio resource measurement for 802.11 specifications so that a
wireless network can be used more efficiently
� 802.11p:�� WAVE � Wireless Access in the Vehicular Environment����� IEEE 802.11 �� ���������������� ��������������� ���������������� �������� IEEE 802.11��� ! "�#$ %&’()*+ , Intelligent Transportation Systems" ITS�-./� �
Task groups of 802.11
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Appendix:(for your reference)
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Infrared Light-based Wireless LAN
� Wavelength range: 0.75 ~ 1000 u� ultraviolet < visible lights < infrared < radio� typically operating at 0.82u
� Adv: � higher security:does not propagate through opaque objects,
keeping signals within rooms and building� no interference from microwave ovens and radio transmitters
� Disadv: � directional, not suitable for mobile applications
� Two types of infrared light LANs:� Diffused� Point-to-point
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Diffused Infrared-based LANDiffused Infrared-based LAN
� Example: TV remote controller
� Example: three stations using a ceiling� Just like using a flashlight,
and talking to people using Morse Code.
� A person wants to send must look at the ceiling to make sure that no other people are sending.
� The receiver looks at the packet header to check for incoming packets.
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� Point-to-Point Infrared LAN System� Each link has a pair of transducers (uni-directional):
� up to 75 ft.
� connect as a token ring(what is token ring??)� Each transducer can talk with a IEEE 802.5 token ring board.
� data rate: 4 and 16 Mbps); � Good security:
� Resilient to electrical noise.
� No mobility, little fault-tolerant capability
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Carrier Current LANsCarrier Current LANs
� Use power line as a medium to transmit data.� Fig. 2.15
� The electrical power companies provide 110V, 60Hz alternating current; the signal can support 1~2 Mbps data signals.
� Adv: adopt already-existing cables� Products are being seen/proposed in the market.
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Power Line CommunicationPower Line Communication
� Power line communicationor power line carrier (PLC)is a system for carrying data on a conductor also used for electric power transmission � Different types of power line communications use different frequency
bands, depending on the signal transmission characteristics of the power wiring used
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� Ultra-High-frequency communication (� 100 MHz)� High-frequency communication (� 1 MHz)
� Home networking (broadband)� Used to interconnect home computers, peripherals or other
networked consumer peripherals
� Internet access (broadband over power lines)� The use of PLC technology to provide broadband Internet
access through ordinary power lines
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broadband over power lines(BLP)
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� Medium frequency (� 1 kHz)� Home control (narrowband)
� Use the household electrical power wiring as a transmission medium
� Low-speed narrow-band communication� Control and telemetry of electrical equipment such as meters,
switches, heaters and domestic appliances
� Transmitting radio programs� Low frequency (< 1 kHz)
� PLC is one of the technologies used in the automatic meter reading industry
Remote control of lighting and appliances without installation of
additional control wiring
Automatic meter reading X10
ZigBee