第二章-通信电波传播特性

Chapter2Chapter2MobileRadioPropagationdChlMdliandChannelModelingHITCRC1Outline(目录)Outline(目录)21Propertiesofradiopropagation2.1Propertiesofradiopropagation2.2Freespacepropagation2.3Transmissionmechanismofelectromagneticwave2.4PathTransmissionLoss25ShadowingFading2.5ShadowingFading2.6Multi-pathfading27Channelmodelingformultipathchannel2.7Channelmodelingformulti-pathchannelHITCRC2HITCRC2HITCRC2Outline(目录)Outline(目录)21Propertiesofradiopropagation2.1Propertiesofradiopropagation2.2Freespacepropagation2.3Transmissionmechanismofelectromagneticwave2.4PathTransmissionLoss25ShadowingFading2.5ShadowingFading2.6Multi-pathfading27Channelmodelingformultipathchannel2.7Channelmodelingformulti-pathchannelHITCRC3HITCRC3HITCRC3PropertiesofradiopropagationPropertiesofradiopropagationMultipathfading多径衰落多径衰落约1mShadowing阴影衰落Pathloss约100m距离基站Pathloss路径传输损耗HITCRC4距离Distance基站BasestationHITCRC4Outline(目录)Outline(目录)21Propertiesofradiopropagation2.1Propertiesofradiopropagation2.2Freespacepropagation2.3Transmissionmechanismofelectromagneticwave2.4PathTransmissionLoss25ShadowingFading2.5ShadowingFading2.6Multi-pathfading27Channelmodelingformultipathchannel2.7Channelmodelingformulti-pathchannelHITCRC5HITCRC5HITCRC5FreespacepropagationFreespacepropagationFreespace，isauniformnon-lossinfinitespace.Inidealcondition,thespaceisisotropic,itselectricconductivityis0,andbothofitsrelativepermittivityandrelativemagneticconductivityareequalto1（所谓自由空间，严格来说应指真空。通常把均匀无损耗的1.（所谓自由空间，严格来说应指真空。通常把均匀无损耗的无限大空间视为自由空间。该空间具有各向同性、电导率为零、相对介电系数和相对磁导率均恒为1的特点，这是一种理想情况）情况。）实际无线电波传播路径是不可能获得这种条件的。现实的电波传播媒质是有损耗的且是不均匀的因而电波传播的过程中除传播媒质是有损耗的且是不均匀的，因而电波传播的过程中除有衰减外，还会出现折射、反射、散射和绕射现象。在研究移动通信电波传播问题时，为了能提供一个比较各种传播情况的标准，并简化场强和传输损耗的计算方法，才引入了自由空间电波传播这一概念。HITCRC6FreespacepropagationFreespacepropagationAnisotropicantennainfreespaceandradiatedpowerppp(辐射功率)P(W)，aspheresurface(球面面积)ofdistanced(m)fromradiatoris:42dThepowerfluxdensity(功率密度)(poyntingvector,坡印廷矢量)2/4TTSPGdHITCRC7FreespacepropagationFreespacepropagationAntennaeffectivearea(有效面积)AG(/)24ReceivedpowerAGeR(/)4222(/4)(/4)()4ReTTRTTRPSAPGdGPGGdSo,propagationloss(传输损耗)infreespace：So,propagationloss(传输损耗)infreespace：LPPdbsT10204lglg()Inlogarithmtype:PbsRgg()Lossincreased6dBwithadoublefrequencyor32.4520lg()20lg()bsLfMHzdkm例题ossceased6dwtadoubeequecyodistancedHITCRC8LineofsightcalculationABCLineofsightcalculationR1d2d1h2h222010011()2ABRhRRhhWegot0RCBRhRRhh()0220202222gO10122dABRhdCBRh2022dCBRhdddRhRh22357()()dhhkdddRhRhRhh0120102012222()so0123.57()()dhhkmHITCRC9HITCRC9HITCRC906370RkmLineofsightcalculationConsideringthemisproportionofatmosphere,directpathwillcurvealittle实际上当考虑空气的不均匀性对电波传播轨迹的影响时直射波传播Lineofsightcalculation（实际上当考虑空气的不均匀性对电波传播轨迹的影响时，直射波传播所能到达的视线距离的数值稍有变化。例如在标准大气折射的情况下，上述公式可以修正为下面的式子）dhhkm012412.()()亮区070dd亮区半阴影区07.0dd07121400.(.~.)ddd阴影区00dd(.~.)12140HITCRC10HITCRC10HITCRC10Outline(目录)Outline(目录)21Propertiesofradiopropagation2.1Propertiesofradiopropagation2.2Freespacepropagation2.3Transmissionmechanismofelectromagneticwave2.4PathTransmissionLoss25ShadowingFading2.5ShadowingFading2.6Multi-pathfading27Channelmodelingformultipathchannel2.7Channelmodelingformulti-pathchannelHITCRC11HITCRC11HITCRC112.3Transmissionmechanismofelectromagneticwave2.3TransmissionmechanismofelectromagneticwaveReflectionoccurswhenapropagatingelectromagneticwaveimpingesuponanobjectwhichhasverylargedimensionswhencomparedtothewavelengthofthepropagationwave.（当电磁波遇到比自身波长大得多的物体时就会发生发射。）遇到比自身波长大得多的物体时就会发生发射。）Diffractionoccurswhentheradiopathbetweenthetransmitterandreceiverisobstructedbyasurfacethathassharpirregularities(edges).（当接收机和发射机之间的无线传播路径被尖锐的边缘阻挡时，电磁波将发生绕射。）SttihthdithhhihthtlScatteringoccurswhenthemediumthroughwhichthewavetravelsconsistsofobjectswithdimensionsthataresmallcomparedtothewavelength,andwherethenumberofobstaclesperunitvolumeisg,plarge.（当电磁波穿行的介质中存在小于自身波长的物体，并且单位体积内阻挡体的数目非常巨大时，将发生散射。）HITCRC122.3.1Reflection2.3.1Reflection电磁波平滑表面的反射HITCRC132.3.1Reflection2.3.1Reflection200V200sincossincosR20H20sincossincosRThereflectioncoefficientsforthetwocasesofparallelandperpendicularEfieldpolarizationattheboundaryofandperpendicularE-fieldpolarizationattheboundaryoftwodielectrics.（在介质边界处，垂直和水平两种极化场的反射系数）HITCRC14化场的反射系数）2.3.2Diffraction2.3.2DiffractionTheexcesspathlength（附加路径长度）2222c1212()ddhdhdd（附加路径长度）c12122222221122()hhdhddhd刃形绕射接收机和发射机112221212()2ddhdd2c12122π()πdddhddThecorrespondingphasedifference（响应的相位差）hdiillihffThedimensionlessFresnel-Kirchoffdiffractionparameter（无量纲的菲涅尔绕射参数）F2/πvHITCRC15HITCRC15HITCRC15涅尔绕射参数）2.3.2DiffractionFresnelzoneandminimumfresnelradius2.3.2Diffraction)()()()()(6.31)()()()()())((21212121kmdkmdkmdkmdmnmdmdmdmdmnmrFnn)()()()(212110577.0FFSRRr2N2N3N4S1022()RrRrRRr1RRr0PAN12202()2RrRr(a)(b)0()2nRrRrnHITCRC16HITCRC16当r0λ时，各带的面积大致相等HITCRC162.3.3ScatteringTheactualreceivedsignalinamobileradioenvironmentis2.3.3Scatteringoftenstrongerthanwhatispredictedbyreflectionan