Channel Modeling for AirtoGround Wireless Communication.docx
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Channel Modeling for AirtoGround Wireless Communication.docx
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ChannelModelingforAirtoGroundWirelessCommunication
ChannelModelingforAirtoGroundWirelessCommunication
Abstract
Inthispaper,wediscussseverallarge?
scalefadingmodelsfordifferentenvironments.TheCOST231?
Hatamodelisadaptedforair?
to?
groundmodeling.Weproposetwocriteriaforair?
to?
groundchannelmodellingbasedontestdataderivedfromfieldtestinginBeijing.Wedevelopanewpropagationmodelthatismoresuitableforair?
to?
groundcommunicationthatpreviousmodels.Wefocusonimprovingthispropagationmodelusingthefieldtestdata.
Keywords
air?
to?
groundcommunication;large?
scalefadingmodel
R1Introduction
esearchonlarge?
scalefadingmodelshasahistoryofabout40years[1]-[4].Inthe1960s,P.L.RiceandA.G.Longleyetal.proposedtheRice?
Longleymodel,alsocalledtheIrregularTerrainModel(ITM),forforecastingthemediantransmissionfadingcausedbyirregularterraininfreespace.Withthismodel,transmissionlosscouldbecomputedwithrespecttoparameterssuchasfrequency,antennaheight,andtransmissiondistance.However,onlytheeffectofirregularterrainwastakenintoaccount.
TheDurkin?
Edwardsmodelpromotedthedevelopmentoflarge?
scalemodeling.Withthismodel,lossduringtransmissioncouldbecalculatedandlossofbarrierduetoirregularitiescouldalsobepredicted.Themodelcouldaccuratelypredictthefieldstrengthofthesignalbutnottheeffectofobstacles,suchasbuildingsandtrees,onthesignal.
TheOkumuramodelwasamilestoneinlarge?
scalefadingmodeling.Itistheclassicmodelforlarge?
scalefadingandthefoundationofresearchonlarge?
scalefading.Duringtesting,theparametersofOkumuramodelwerecontinuallycorrectedsothatthemodelhadstrongapplicability.However,ifthespreadofthesignalchangedfasterthanthatpredictedbythemodel,therewouldbelargeerrors.Althoughthemodelstillhassomeflaws,itworksreasonablywell.TheOkumara?
Hatamodelisnowthemostwidelyusedmodelforlarge?
scalefading.
Therearetwotypesoffadingmodelfordifferentfrequencyranges:
Okumura?
HataandCOST231?
Hatamodel.TheformerisbasedontheOkumuramodelandmainlyusedinmacrocellsystemswherethecellradiusisgreaterthan1km.Itisparticularlyapplicabletocities.However,asurbanconstructionbecomesdenser,thecellradiusisnolongergreaterthan1km,andasecondmodel,?
?
COST231?
Hata,isused.
Inourresearch,wefocusonair?
to?
groundcommunication,wherethefrequencyis2.36GHzandthemaximumheightofanaircraftisabout3km.Tothebestofourknowledge,noonehasproposedair?
to?
groundchannelmodelingbefore.However,withtherapiddevelopmentof4Gandthederegulationoflow?
altitudeairspace,suchmodelinghasbecomeincreasinglyimportant.Ourresearchinthisareaisbasedontestdata. 2LargeScaleFadingMechanism
Whenasignalwaveencountersruggedterrain,buildings,vegetationorotherobstaclesalongthepropagationpath,itcastsashadowontheelectromagneticfields[5],[6].Ifamobilestationinmotionfallsundertheshadowofanobstacle,shadowfadingoccurs.Shadowfadingismeasuredinlargespatialscalesandmainlydependsonthepropagationenvironment.Factorssuchasrollinghills,heightdistributionofbuildings,streetdirectionandposition,heightofbasestationantennas,andspeedofthemobilestationallneedtobetakenintoaccountwhendeterminingtheextentofshadowfading.
Therelationshipbetweenshadowfadingandpropagationdistanceis:
where[Xσ]isthezeromeanstandarddeviationforaGaussianrandomvariable[σ]dBwithitspdfgivenby:
where[σ]iscalculatedusingthelinearrecursivemethodtominimizethemeansquarederrorofthemeasuredvalueandestimatedvalue.
2.1OkumuraModel
TheOkumuramodelisthemostwidelyusedmodelforpredictingcitysignalsinJapanandhasbecomethestandardsystemmodel.InTokyo,itiscommontousedifferentfrequencies,antennaheight,anddistancetoselectadifferentseriesoftests[7].Theexperiencecurveconstructsthemodelandisapplicableforafrequencyof150MHzto3GHz,adistanceof1km-100km,andanantennaheightof30-1000m.
Acityisassumedtobeaquasi?
smoothterrainintheOkumuramodel,soafixedfieldstrengthvalueisset.Foranirregularterrain,thereareseveralcorrectionfactors.Byobtainingdetailsofthetopographyandsurfaceofthesituation,amoreaccuratepredictioncanbemade.
Inaquasi?
smoothterrain,thepropagationattenuationvalues?
arealsocalledthebasicattenuationvalues.Themodelgivesaquasi?
smoothterrainaswellasthefamilyofcurvesofpropagationattenuationvaluesintheurbanarea.
Withinacity,wavepropagationattenuationdependsonthepropagationdistance,frequency,basestationantennaeffectiveheight,mobileantennaheightandstreetwidth,antennadirection,andmore.Theattenuationcanbeexpressedas:
where[LF]isthefreespaceloss,[Amuf,d]istherelativespatialattenuationvalue,[Ghb,d]isthebasestationantennaheightgain,[Ghm,f]istheterminalantennaheightgain,and[GAREA]istheenvironmentalgain.
Themodelisderivedfromtestdataanddoesnotprovideanyanalysisorinterpretation.Itmakesthemostreliablepath?
losspredictionandisthemostaccuratesolutionforcellularsystemsandterrestrialwirelesssystems.Thedeviationinpathlossbetweenthepredictionandtesteddataisabout10-14dB. 2.2OkumuraHataModel
ThefrequencyrangeapplicabletotheOkumura?
Hatamodelis150-1500MHz.Theformulaforurbanpathlossis:
where[fc]isthefrequency,[hte]istheheightoftransmittingantenna,and[hre]istheheightofthereceivingantenna.Theantennaheightcorrectionfactoris[αhre].
TheOkumura?
Hatamodelmakesanaccuratepredictioninamacrocellularsystemandalsoinattenuation.
2.3Cost231HataModel
TheCOST231?
Hatamodelisusedontheconditionthatthecarrierfrequencyislessthan2.5GHz.ThismodelisamodifiedHatamodelthatcanbeappliedinurbanmacrocell,suburbanmacrocell,ormicrocellcitysituation[8].
Fortheurbanmacrocell,thepathlossmodelis:
Forsuburbs,themacrocellenvironmentpathlossmodelis:
where[f]isthefrequencyoftransmittingantenna,and[d]isthedistancebetweentransmittingantennaandreceivingantenna.Alltheabovemodelsarenotcompletelyaccordswiththespecificenvironmentofair?
to?
groundcommunication.
3ImprovedModelBasedonMeasuredData
OnFebruary27,2014,low?
altitudeair?
to?
groundtestingofTD?
LTEwascarriedoutinPingguDistrict,Beijing.Therewasoneaircraftatanaltitudeof300m-600m.Thetestingwascarriedoutinabasinsurroundedbymountainsonthreesides.Theheightofmountainwasabout200m-300m.ThetestingenvironmentisshowninFig.1.
Thefrequencywas2.36GHz,thereweretwotransmittingandreceivingantennas,themaximumaltitudeoftheaircraftwas600m,andthespeedofaircraftwasabout150km/h.Fig.2showsthefightpathoftheaircraft.
Anair?
groundchannelmodelhasneverbeenbuiltorappearedinanyoftheliteraturebefore.Buildinganair?
to?
groundchannelmodelbasedonthetestdataandoptimizationmethodsisacreativejob.
3.1ImprovedCOST231HataModelBasedonMMSE
Criterion
ThereasonwechoosetheCOST231?
Hatamodeltooptimizetheair?
to?
groundchannelmodelisthatCOST231?
Hatamodelissuitableformacrocellsinruralareas,whichissimilartotheconditionofair?
to?
groundcommunication.
Intheurbanmacrocellenvironment,thegeneralCOST231?
HATAurbanpath?
lossmodelis[9]:
where[L]isthepathlossand[a1,b1,c1,d1,e1,f1,g1]arethecorrespondingcoefficients.AssumingthatthetotalnumberofreceivedsignalsisNandthepathlosscorrespondingtothesamplingpointnis[L(n)],theinstantaneousfrequencyis[f(n)]. Theminimummean?
squareerror(MMSE)criterion?
basedapproachisusedtooptimizetheformulacoefficients.Theobjectivefunctioncanbeexpressedas:
Thepartialderivativesoftheobjectivefunctionareexpressedas:
[?
F/?
b1,?
F/?
c1,?
F/?
d1,?
F/?
e1,?
F/?
f1,and?
F/?
g1]takethesameprocessas[?
F/?
a1].
Thiscanbeexpressedinsimplifiedmatrixformat:
where[M]isa7×7dimensionalmatrix,and[miji,j=1,2,...,7]are:
Tosolve(10),weobtaintheoptimalsolutionbasedontheMMSEcriterion:
where[a1opt],[b1opt],[c1opt],[d1opt],[e1opt],[f1opt],[g1opt]aretheoptimalvaluesof[a1opt],[b1opt],[c1opt],[d1opt],[e1opt],[f1opt],[g1opt],respectively.Accordingtotheair?
to?
groundchanneltesting,parameterssuchas[f]and[hte]aredecided;wereducethecomputationalcomplexity;and(7)canbesimplifiedas:
Theobjectivefunction(7)hasonlythreevariables[a1,b1]:
Weobtaintheoptimalcoefficientvector:
where
Accordingtotheanalysisabove,weobtaintheresult[[a1b1]*opt]usingthetestingdata[L(n),d(n),hte,f],and(13)canbeexpressedwith[[a1b1]*opt].
4OptimizationResult
Accordingtotheanalysisandcalculationinthelastsection,weobtainthecoefficientsa1,b1,andc1.Intesting,[f]and[hte]aredecided,andwerecordthelocationinformationofeachsamplingpoint.TheresultofoptimizationinaMatlabsimulationisshowninFig.3.
Theformulaofair?
groundchannelfadingmodelcorrespondingtoFig.3is:
Usingthedistancebetweentransmittingantennaandreceivingantenna,wedividethelarge?
scalefadingintothreedifferentsituations(Table1).
Accordingtotheanalysis,wegivetheair?
to?
groundlarge?
scalefadingmodelformulaandthemodelformulaindifferentsituations(Table2).
Theformulafortheparkedsituation(Fig.4)is:
The
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