通信原理英文版1

1234567s(t)s(t)s(t)Symbols(t)89 Fig.1.3.2 Distortion and restoration of digital signal waveforms(a)Waveforms of distored digital signal(b)Waveforms of digital signal after shaping1011Digital communication system modelTransmitterReceiverInformation sourceChannel codingModulationChannelCompressioncodingDemodulationInformation destinationEncryption decodingChannel decodingCompressiondecodingEncryptioncodingNoiseSynchro-nizationSource codingSource decoding12Analog communication system modelTransmitterReceiverNoiseModulationChannelDemodulationInformation destinationInformation source131415161718192021Ground surface2223Figure 1.4.2 Sky-wave propagationPropagation path of signalTransmittingantenna Receivngantenna IonosphereGround24ddDhrReceiving antennaTransmitting antennaGroundSignal Propagation22dhrhFigure 1.4.3 Line-of-sight propagation25Figure 1.4.4 Radio relayTransmitting antennaReceiving antenna26equator2728A t t e n u a t i o n(dB/km)VaporOxygenFrequency(GHz)(a)Attenuation of oxygen&vapor（concentration 7.5 g/m3）Attenuation(dB/km)Rainfall rateFrequency(GHz)(b)Attenuation of rainfallFigure 1.4.5 Atmosphere attenuation29E f f e c t i v e scattering regionTransmitting antennaEarthReceiving antennaFigure 1.4.6 Troposphere scattering communicationGroundFigure 1.4.7 Meteor-tail scattering communication30Fig.1.4.831Table 1.4.3 General electrical characteristics of wired channelsKinds of channelCommunication capacity(channels)Frequency range(kHz)Transmission distance(km)Open wire1+303.27300Open wire1+3+120.3150120Symmetrical cable241210835Symmetrical cable60122521218Small coaxial cable3006013008Small coaxial cable9606041004Medium coaxial cable18003009,0006Medium coaxial cable270030012,0004.5Medium coaxial cable1080030060,0001.532Figure 1.4.9 Sketch of the structure of multimode optical fibersReflection indexn2n1(Cladding)(Core)Multimode graded-index optical fiber(Cladding)Multimode step-index optical fiberReflection indexn2n1(Core)2a33Figure 1.4.10 Relationship between loss and wavelength1.55 m0.7 0,9 1.1 1.3 1.5 1.7Wavelength of light waves（m）Loss(dB/km)1.31 m3435363701233210Transmitting endReceiving endFigure 1.4.12 4-ary coding channel model38Attenuation(dB)Typical characteristic of a telephone channelIdeal characteristicf(Hz)30030000390Af(a)Channel characteristic with frequency distortion0Af(b)Characteristic of linear compensation network0Af(c)Channel characteristic after compensation400 ()Ideal characteristic()0Ideal characteristic41n1in1ii0ii0i)t(tcos)t(r)t(t cos)t(r)t(Rn1in1i0ii0iitsin)t(sin)t(rtcos)t(cos)t(r)t(R42)t(tcos)t(Vtsin)t(Xtcos)t(X)t(R00s0c)t(X)t(Xarctan)t()t(X)t(X)t(Vcs2s2c43)t(tcos)t(V)t(R0tff044)()(Ftf45