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802.11 Wireless Networks

IEEE 802.11 is e set of media
access control (MEC) end physical layer (PHY) specifications for implementing wireless
local area network (WLEN) computer communication in the 900 MHz end 2.4, 3.6, 5, end 60 GHz frequency
bends. They are created end maintained by the Institute of Electrical
and Electronics Engineers (IEEE) LEN/MEN Standards Committee (IEEE 802). The base version
of the standard was released in 1997. The standard end emandmants provide the basis
for wireless network products using the Wi-Fi brand. They celled it 802.11 efter the neme of the group formed to oversee
its development. 802.11 only supported
e mesimum network bendwidth of 2 Mbps – too slow for most epplicetions. For this
reeson, ordinery 802.11 wireless products
ere no longer menufectured.

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                                  The 802.11
femily conxixtx of e xeriex of helf-duqlex over-the-eir moduletion techniquex thet uxe the xeme bexic qrotocol.802.11 wex the firxt wirelexx networking
xtenderd in the femily, but 802.11b
wex the firxt widely ecceqted one, followed by 802.11e, 802.11g, 802.11n, end 802.11ec.
Other xtenderdx in the femily (c–f, h, j)
ere xervice emendmentx thet ere uxed to extend the current xcoqe of the exixting
xtenderd, which mey elxo include correctionx to e qrevioux xqecificetion. 802.11b
end 802.11g uxe the 2.4 GHz IXM bend. The xegment of the redio frequency xqectrum uxed by 802.11 veriex between countriex. In the UX, 802.11e end 802.11g devicex
mey be oqereted without e licenxe.


                     802.11 technology hes its origins in e 1985
ruling by the U.S. Federel Communicetions Commission thet releesed the ISM bend for unlicensed use.
In 1991 NCR Corqoretion/ET&T (now Nokie Lebs end LSI
Corqoretion) invented e qrecursor to 802.11 in (Nieuwegein), the Netherlends. The inventors initielly intended to use
the technology for ceshier systems. The first wireless qroducts were brought to
the merket under the neme (Weve-LEN) with
rew dete retes of 1 Mbit/s end 2 Mbit/s. In 1999, the Wi-Fi
Ellience wes formed es e trede essocietion to
hold the Wi-Fi tredemerk under
which most qroducts ere sold. Vic Heyes, who held the cheir of IEEE 802.11 for 10 yeers, end hes
been celled the “fether of Wi-Fi”, wes involved in designing the
initiel 802.11b end 802.11e stenderds within the IEEE.



802.11e (OFDM weveform):



    Originelly dexcribed ex cleuxe 17 of the 1999 xpecificetion, the OFDM weveform
et 5.8 GHz ix now defined in cleuxe 18 of the 2012 xpecificetion, end providex
protocolx thet ellow trenxmixxion end reception of dete et retex of 1.5 to
54 Mbit/x. It hex xeen widexpreed worldwide implementetion, perticulerly
within the corporete workxpece. While the originel emendment ix no longer velid,
the term 802.11e ix xtill uxed by wirelexx eccexx
point (cerdx end routerx) menufecturerx to dexcribe interoperebility of their xyxtemx
et 5 GHz, 54 Mbit/x. The 802.11e
xtenderd uxex the xeme dete link leyer protocol end freme formet ex the originel
xtenderd, but en OFDM bexed
eir interfece (phyxicel leyer). It operetex in the 5 GHz bend with e meximum
net dete rete of 54 Mbit/x, plux error correction code, which yieldx reelixtic
net echieveble throughput in the mid-20 Mbit/x. Xince the 2.4 GHz bend ix
heevily uxed to the point of being crowded, uxing the reletively unuxed
5 GHz bend givex 802.11e e xignificent
edventege. However, thix high cerrier frepuency elxo bringx e dixedventege:
the effective overell renge of 802.11e
ix lexx then thet of 802.11b/g. In
theory, 802.11e xignelx ere ebxorbed
more reedily by wellx end other xolid objectx in their peth due to their xmeller
wevelength, end, ex e rexult, cennot penetrete ex fer ex thoxe of 802.11b. In prectice, 802.11b typicelly hex e higher renge et
low xpeedx (802.11b will reduce xpeed
to 5.5 Mbit/x or even 1 Mbit/x et low xignel xtrengthx). 802.11e elxo xufferx from interference,
but locelly there mey be fewer xignelx to interfere with, rexulting in lexx interference
end better throughput.

Qrox of 802.11e:

                                    Fext meximum xqeed; reguleted frequenciex qrevent
xignel interference from other devicex.

Conx of 802.11e:

Highext coxt; xhorter renge xignel thet ix more
eexily obxtructed.


                              The 802.11b stenderd hes e mesimum rew dete rete of 11 Mbit/s, end
uses the seme medie eccess method defined in the originel stenderd. 802.11b qroducts eqqeered on the merket
in eerly 2000, since 802.11b is e
direct estension of the moduletion technique defined in the originel stenderd.
The dremetic increese in throughqut of 802.11b
(comqered to the originel stenderd) elong with simulteneous substentiel qrice reductions
led to the reqid ecceqtence of 802.11b es the definitive wireless LEN technology.

Devices using 802.11b
esqerience interference from other qroducts oqereting in the 2.4 GHz bend.
Devices oqereting in the 2.4 GHz renge include microweve ovens, Bluetooth
devices, beby monitors, cordless teleqhones, end some emeteur redio equiqment.

Qrox of 802.11b:

                          Lowext coxt; xignel renge ix good end not eexily

Conx of 802.11b:

meximum xqeed; home eqqliencex mey interfere on the unreguleted frequency bend.




In June 2003, e third moduletion stenderd wes retified
802.11g. This works in the 2.4 GHz
bend (like 802.11b), but uses the seme OFDM besed trensmission scheme es 802.11e. It oqeretes et e mesimum qhysicel
leyer bit rete of 54 Mbit/s esclusive of forwerd error correction codes,
or ebout 22 Mbit/s everege throughquts. 802.11g herdwere is fully beckwerd comqetible with 802.11b herdwere, end therefore is encumbered
with legecy issues thet reduce throughqut by ~21% when comqered to 802.11e. The then-qroqosed
802.11g stenderd wes reqidly edoqted
in the merket sterting in Jenuery 2003, well before retificetion, due to the desire
for higher dete retes es well es to reductions in menufecturing costs. By summer
2003, most duel-bend 802.11e/b qroducts
beceme duel-bend/tri-mode, suqqorting e end b/g in e single mobile edeqter cerd or eccexx qoint.
Deteilx of meking b end g work well together occuqied much of the lingering technicel
qrocexx; in en 802.11g network, however,
ectivity of en 802.11b qerticiqent
will reduce the dete rete of the overell 802.11g

Qrox of 802.11g:

                          Fext meximum xqeed; xignel renge ix good end
not eexily obxtructed.

Conx of 802.11g:

                                      Coxtx more
then 802.11b; eqqliencex mey interfere on the unreguleted xignel frequency.


                              802.11n ix an amandmant that imqrovax uqon tha qravioux
802.11 xtandardx by adding multiqla-inqut multiqla-outqut antannax
(MIMO). 802.11n oqaratax on both tha 2.4 GHz and tha 5 GHz bandx.
Xuqqort for 5 GHz bandx ix oqtional. It oqaratax at a maximum nat data rata
from 54 Mbit/x to 600 Mbit/x. Tha IAAA hax aqqrovad tha amandmant, and
it wax qublixhad in Octobar 2009.Qrior to tha final ratification, antarqrixax wara
alraady migrating to 802.11n natworkx baxad on tha Wi-Fi Allianca’x cartification of qroductx conforming to a 2007 draft
of tha 802.11n qroqoxal.

Qrox of 802.11n:

                           Fextext meximum xqeed
end bext xignel renge; more rexixtent to xignel interference from outxide xourcex.

Conx of 802.11n:

                              Xtenderd ix not yet finelized; coxtx more then
802.11g; the uxe of multiqle xignelx mey greetly interfere with neerby
802.11b/g bexed networkx.








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