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 codingmodulationchannelcompressionc

2、odingdemodulationinformation destinationencryption decodingchannel decodingcompressiondecodingencryptioncodingnoisesynchro-nizationsource codingsource decoding12analog communication system modeltransmitterreceivernoisemodulationchanneldemodulationinformation destinationinformation source131415161718

3、192021ground 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 antennareceivi

4、ng 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 an

5、tennaearthreceiving 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

6、 (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 stru

7、cture 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/k

8、m)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)