Wireless Networking Technology

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Wireless networking technology

By Abbas Izadpanah

January 2007


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ContentsThe components of Wires-WLAN

Wireless stations

Access points

Ad hoc mode

Infrastructures mode

RoamingHow wireless LANs work

ISM band

FHSS

DSSS

HR/DSSSCOFDM

Some other physical layers

MIMO


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Wireless Local Area Network

A local area network that usewireless technology toconnected computers in the

network is called a wirelesslocal area network(WLANs).


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The components of Wires-WLAN

WLAN Stations-It Takes TwoWireless networking requires at least

two radios. Each computer or devicecontaining a radio that transmits and/orreceives data over the wireless networkis called a station. And station can be

clientor aserver.


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The components of Wires-WLAN

Access points

Wireless access point(APs), also calledwireless stations, have become a crucial

component for any wireless network that goesbeyond simple ad hoc status.

There are two kinds of access points:

Software Access Points

hardware access points


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Software Access Points

Software Access Points which run on a computerequipped with a wireless network interface card as usedin an ad-hoc or peer-to-peer wireless network.


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Hardware Access Point

Dedicated hardware access points (HAP) such asLucent's WaveLAN, Apple's Airport Base Station orWebGear's AviatorPRO.


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Hardware Access Point cont

Access points come in many shapes, size, andconfiguration. However, no matter how else theymight differ, all APs share the followingcomponents:

Antenna Ethernet Port LED Indicators Reset Button

Power cord Note

Both wireless adapters and accesspoints must be the same brand.


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Extension point

Some manufacturers produceextension points, which act aswireless relays, extending the

range of a single access point.Multiple extension points can bestrung together to provide wireless

access to far away locations fromthe central access point.


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An ad-hoc, or peer-to-peer wireless network

An ad-hoc, or peer-to-peerwireless network consists ofa number of computers each

equipped with a wirelessnetworking interface card.Each computer can

communicate directly with allof the other wireless enabledcomputers.


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Wirelesspc

Wireles

spc

Wireles

spc

A

C

B

BSS 1

BSS 2


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Infrastructures Wireless Network

Infrastructures mode refer to awireless network controlledthrough their wireless network

access point that generate thesignal for individual devices to readthrough their wireless network

adapter.


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PC

PC

PC

PC

PC

LAN

AP

Portal

BSS 1

BSS 2

ESS

DS


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Roaming

A wireless computer can "roam" from oneaccess point to another, with the softwareand hardware maintaining a steady

network connection by monitoring thesignal strength from in range accesspoints and locking on to the one with the

best quality.


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A user can move from Area 1 to Area 2transparently. The Wireless networkinghardware automatically swaps to theAccess Point with the best signal.

USER


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How wireless LANs work

The IEEE 802.11 wireless networkingstandard define five ways that data can betransmitted between two wireless devices.

These transmission method are calledphysical layers. Each physical layer isindependent of other physical layers. Each

pair of 802.11 complain radios uses ofthese physical layers to communicate.


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The ISM Band

In 1985 the Federal Communicationcommission(FCC) made change radiosthe radio spectrum regulation andassigned three bands designated as theindustrial, scientific, and medical(ISM).These frequency bands are : 902 MHz-928 MHz, a 26 MHz bandwidth 2.4 GHz-2.4835 GHZ , a 83.5 MHz

bandwidth 5.725 GHz-5.850 GHz, a 125 MHz

bandwidth


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Frequency Hopping Spread Spectrum

The Frequency Hopping

Spread Spectrumphysical layer is one of

five available physical

layers in 802.11.


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Direct sequence Spread Spectrum

Direct-sequence spread-spectrum(DSSS) is anothertechnique include in the IEEE802.11 physical layer thatuses DSSS can also transmit

data at up to two Mbps.It operates in the 2.4 MHz ISMband.


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High Rate Direct Sequence Spectrum

The High Rate Direct SequenceSpectrumphysical layer is the mostwidely used 802.11 IEEE physical

layer (1999). This layer specified by IEEE 802.11b

supplement to the initial standard, usesan extension of IEEE 802.11 DSSS

standard.

It operates in the 2.4 MHz ISM band.


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Coded Orthogonal Frequency Division Multiplexing

Coded Orthogonal FrequencyDivision Multiplexing(COFDM) layer, specified in

802.11a supplement to the802.11 standard. It operatesin the 5 GHz ISM band.


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Some other physical layers

The IEEE 802.11 group isdefining a physical layer that

use OFDM in 2.4 GHz band.This allows 802.11a data rate(up to 54 Mbps) in the band

used by 802.11b.


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MIMO (Multiple Input Multiple Output) Pronounced

my-mo," it is the use of multiple transmittersand receivers (multiple antennas) on wirelessdevices for improved performance. When two

transmitters and two or more receivers areused, two simultaneous data streams can besent, which double the data rate. Multiplereceivers alone allow greater distances

between devices. The upcoming IEEE 802.11nwireless standard uses MIMO to, at a minimum,double the 54 Mbps speed of 802.11a and802.11g to 108 Mbps.


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Thank you

ThanksNivedita Gupta

Wireless Networking Technology

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