User's Manual
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12. WhatisDSSS?WhatisFHSS?Andwhataretheirdifferences?
Frequency‐hoppingspread‐spectrum(FHSS)usesa
narrowbandcarrierthatchangesfrequencyinapatternthatis
knowntobothtransmitterandreceiver.Properlysynchronized,the
neteffectistomaintainasinglelogicalchannel.Toan
unintended
receiver,FHSSappearstobeshort‐durationimpulse
noise.Direct‐sequencespread‐spectrum(DSSS)generat e sa
redundantbitpatternforeachbittobetransmitted.Thisbitpattern
iscalledachip(orchippingcode).Thelongerthechipis,thegreater
theprobabilitythattheoriginaldatacanberecovered.
Evenifone
ormorebitsinthechiparedamagedduringtransmission,statistical
techniquesembeddedintheradiocanrecovertheoriginaldata
without‐theneedforretransmission.Toanunintendedreceiver,
DSSSappearsaslowpowerwidebandnoiseandisrejected(ignored)
bymostnarrowbandreceivers.
13. WhatisSpreadSpectrum?
SpreadSpectrumtechnologyisawidebandradiofrequency
techniquedevelopedbythemilitaryforuseinreliable,secure,
mission‐criticalcommunicationsystems.Itisdesignedtotradeoff
bandwidthefficiencyforreliability,integrity,andsecurity.Inother
words,morebandwidthisconsumedthaninthecase
of
narrowbandtransmission,butthetradeoffproducesasignalthatis,
ineffect,louderand thuseasiertodetect,providedthatthe
receiverknowstheparametersofthespread‐spectrumsignalbeing
broadcast.Ifareceiverisnottunedtotherightfrequency,a
spread–spectrumsignallookslike
backgroundnoise.Therearetwo
mainalternatives,DirectSequenceSpreadSpectrum(DSSS)
andFrequencyHoppingSpreadSpectrum(FHSS).
14. WhatisWPS?
WPSstandsforWi‐FiProtectedSetup.Itprovidesasimplewayto
establishunencryptedorencryptedconnectionsbetween
wirelessclientsandaccesspointautomatically.Usercanpress
a
softwareorhardwarebuttontoactivateWPSfunction,
andWPS‐compatiblewirelessclientsandaccesspointwill
establishconnectionbythemselves.TherearetwotypesofWPS:
PBC(Push‐ButtonConfiguration)andPINcode.