无线通信基础知识讨论Discussion on basic knowledge of wireless communication文档格式.docx

无线通信基础知识讨论Discussion on basic knowledge of wireless communication文档格式.docx

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Thesetwotypesofdeclinearecontradictoryandshouldbeconsideredwhendesigningasystem.

6,wirelesscommunicationbooksareonthetop

7,multipathchannelmodelingrequiresthatmultipathshouldbeindependent.Howshouldindependencebereflectedinchannelmodeling?

ThisshouldalsobethecaseforMIMOchannelsandmultiuserchannels.

Thecorrelationcoefficientsofthetwopathsareassmallaspossible,ormodeledseparatelyaccordingtowhatissaidabove.

8,MIMOchannelmodeling,sometimesrequiredtoconsiderthecorrelationbetweenantennas,andhowthiscorrelationshouldbemodeled?

Firstly,thecorrelationcoefficientmatrixisconstructed,andthentheCholisdecomposed.Thematrixobtainedbythedecompositionismultipliedbythesignalofeachantenna.

Biezswaspublishedat20:

532006-10-25

[quote]or2006-10-2520:

42publishedby[i]lucatt0415[/i]in

（butit'

sgoodagainstfrequencyselectivefading）.

[/quote]

Canyouexplainwhythesetwotypesofdeclinearecontradictory?

562006-10-25

Thecorrelationcoefficientsofthetwopathsareassmallaspossible,ormodeledseparatelyaccordingtowhatissaidabove.[/quote]

Therelativecoefficientofthetwopathsassmallaspossibleisourgoal,butI'

mnotsurewhattheso-called"

individualmodeling"

means.Forexample,whatdoesthissinglemodelingmeanforthetraditionalJakesmodel?

Lucatt0415waspublishedat23:

392006-10-25

Thereasonsareasfollows:

thecoherencebandwidthrequirementsofsignalbandwidthlessthanthechannelagainstfrequencyselectivefading,whichrequiresbandwidthassmallaspossible,fromthetimeitissymbolictimeorchiptimeaslargeaspossible,butwiththeincreaseofsymbolorofthechipcycle,andwhenthechannelphasedowhenalongtime,itisdifficulttofightagainstfastfadingso,thedesignofthesystemshouldfullyconsidertheapplicationobjectsystem,reasonabledesignparameters.

442006-10-25

OrinaccordancewiththeMIMOmodelingmethodisbetter,thatis,theuseofcoefficientcorrelationmatrixforCholdecomposition,andthenusethedecomposedmatrixmultipliedbytwosignals,

Individualmodelingdoesnotnecessarilyguaranteethatthetwopathsareuncorrelated.

SWAswaspublishedin2006-10-2608:

46

Largescalefadingismainlypathloss,whichcanbeapproximatedbyfreespacepropagationmodel,butsomecharacteristicsaredifferent,suchasfadingindex,andsoon

Whatarethefactorsassociatedwiththelognormalvarianceofshadowfading?

Howmuchisthetypicalvalue?

OFDMsystemisusedtodiscusstheguidingroleofcoherenttimeandcoherentbandwidthinpracticalsystemdesign.

Inadditiontothefadingcharacteristicsofwirelesschannel,whichisdifferentfromwiredchannel,wemustconsider,suchasmultiusersharedchannel,multipleaccessmethodsarediscussed,thediscussiononthebasisoftheunderstandingofgreathelp.Agoodsubject.Ihopeyouwillhaveaheateddiscussion.

Lucatt0415waspublishedin2006-10-2608:

54

Thethreeeffectsofthewirelesschannelaremissing:

Threeeffectsofwirelesschannel

Shadoweffect,nearfareffectandDopplereffect

（1）shadoweffect:

whentheelectricwaveisdisturbedbyundulatingterrain,buildings,vegetationandotherobstaclesonthepropagationpath,thehalfblindzoneofelectromagneticfieldwillbeproduced

（2）:

Nearfareffectduetorandommobilityreceivingusers,mobileusersandthedistancebetweenthebasestationandthenlowchange,ifthemobileuserstransmitpower,thenarriveatthebasestationsignalisstrongifdifferentfromthebasestationnearstrongsignal,farfromthebasestationsignalisweak.Inwhichthebasestationreceiverappearsstrongstrongerandtheweakweakerandstrongweakphenomenon.Thisisthereasonforpowercontrol

（3）Dopplereffect:

becauseofthehighspeedmotionofthemobileuserinthereceivingstate,thepropagationfrequencyisdiffused,andthediffusiondegreeisdirectlyproportionaltotheuser'

smovingspeed.

Lcj2212916waspublishedat18:

232006-10-26

Whatarethecharacteristicsofwireless（mobile）channels?

Turnfrom:

[url]

Radiowavesindifferentfrequencybandshavedifferentpropagationmodesandcharacteristics.

ThemobilecommunicationsystemtoworkintheVHFandUHFbands,radiowavepropagationisthemainwayofspace,namelydirectwave,refractionwave,wavescatteringandtheirsynthesiswave.

Inthelandmobilesystem,themobilestationisinthecityorinthebuildingsinthecomplexterrainarea,theantennawillreceivesignalsfrommultiplepathscame,coupledwiththemobilestationitself,thewirelesschannelbetweenthemobilestationandthebasestationischangeableanddifficulttocontrol.

Inanalogwiredchannels,thetypicalsignal-to-noiseratioisabout46dB,thatis,thesignallevelis40000timeshigherthanthenoiselevel,andforthewiredchannel,thequalityoftransmissioniscontrollable.Byselectingtherightmaterialsandcarefulprocessing,youcanensurethatthereisarelativelystableelectricalenvironmentinthewiredtransmissionsystem.Asaresult,thesignal-to-noiseratiousuallydoesnotexceed1~2dBinawiredtransmissionline.Onlywhenalinehasbeenrunningforalongperiodoftime,willthelossofthelinegraduallyreach10~15dB,sointhiscase,thelinewillneedtobeupdated.

Interrestrialmobileradiochannels,asuddendropinsignalintensity,knownasfading,isfrequent,withadepthofabout30dB.

Inurbanenvironments,thenumberofsignalsreceivedbyamobilestationonafastmovingvehiclecandeclinesignificantlywithinasecond.Thiskindoffadingseriouslydeterioratesthequalityofreceivedsignalsandaffectsthereliabilityofcommunications.

Inthecellularmobileenvironment,thesamefrequencyinterferenceisaproblemthatmustbepaidattentionto.Whenfadingoccurs,thesignaltobereceivedmaybeweakerthantheinterferencesignalfromthesamefrequencycellbasestation,sothereceiverwilleasilylockonthewrongsignal.

TheanalogmobilecommunicationadoptsFMsignal,andthecaptureeffectofFMmodehasacertaininhibitoryeffectonthesamefrequencyinterference.ThefadingphenomenonwillsignificantlychangethecharacteristicsofFMsignalandweakenitscaptureeffect.Fordigitaltransmission,fadingwillgreatlyincreasebiterrorrate（BER）.

Thefadingcharacteristicsofmobilechannelsdependonthepropagationenvironmentofradiowaves.Differentenvironments,theirpropagationcharacteristicsarenotthesame.

Alargecitywithmanytallbuildings,forexample,hasaverydifferentspreadenvironmentcomparedtoaflatopencountry,andthemobilechannelcharacteristicsvarygreatly.Thecommunicationenvironmentitselfisquitecomplex,whichmakesthemobilechannelcharacteristicsisverycomplex.

Itisspreadindifferentenvironment,leddirectlytothemultipathdelaysizehaveobviousdifference,ifwewanttotransmithigh-speeddata,Tsymbolperiodshouldbeassmallaspossible,butthesmallertheT,theabilitytoresistmultipathdelayisweak,resultinginaOFDM,itisbecausethesymbolperiodinOFDMsystembecauseoftheparalleltransmissionofvariablelength,whichcaneffectivelyresistthemultipathdelay.

Complexandharshpropagationconditionsarethecharacteristicsofmobilechannels.Inordertomaintainacceptabletransmissionqualityundersuchpropagationconditions,avarietyoftechnicalmeasuresmustbeadoptedtocounteracttheadverseeffectsoffading.Therefore,avarietyofantifadingtechnologieshavebeendeveloped,includingdiversity,spreadspectrum/frequencyhopping,equalization,interleavinganderrorcorrectioncoding.Inaddition,thesignaltransmissionmode,suchasmodulationmode,willalsohaveacertainadaptabilitytofadinginthechannel.

[[i]thispostwasfinallyeditedbysreightat19:

142006-10-26on[/i]]

Lcj2212916waspublishedat20:

292006-10-26

Providetworeferencematerials,thebasicknowledgewritteninmoredetail,theXi'

anelectronicsdivisionofthebiglessonplans!

!

Wemainlydiscusslargescaleandsmallscalefadingandgeneralmodelingofchannel