通信原理第5章模擬調(diào)制系統(tǒng)

1、本章研究各種模擬調(diào)制、解調(diào)方式、系統(tǒng)的可靠性本章研究各種模擬調(diào)制、解調(diào)方式、系統(tǒng)的可靠性和有效性。和有效性。基帶信號m(t)調(diào)制器Sm(t)C(t)載波0( )coscc tAt( )( )cosmcstAm tt( )()2mccASMM00( )( )coscos( )cosAMcccstAm ttAtm tt01( ) ()()()()2AMccccSAMM 載頻分量載頻分量載頻分量載頻分量上邊帶上邊帶上邊帶上邊帶下邊帶下邊帶下邊帶下邊帶HAMfB222202222200( )( ) coscos( )cos2( )cosAMAMccccPstAm ttAtm ttA m tt0)(tm

2、ScAMPPtmAP2)(22202/ )(2tmPs 2220SAMAMmtPPAmt22( )/2mmtA 222222002mAMmmtAAAAmtttmtscDSBcos)()()()(21)(ccDSBMMS1,( )( )0,cUSBcHH1,( )( )0,cLSBcHH ( )( )SSBDSBSSHtAtmmmcos)(ttcccos)(tAtAttAtsmcmmcmcmmDSB)cos(21)cos(21coscos)(1( )cos()2USBmCmstAt11coscossinsin22mmcmmcAtAt1( )cos()2LSBmCmstAt11coscossins

3、in22mmcmmcAttAtt兩式僅正負(fù)號不同ttAttAtscmmcmmSSBsinsin21coscos21)(tAtAmmmmsinso c11( )coscoscossin22SSBmmcmmcstAttAtt11( )coscoscossin22SSBmmcmmcstAttAttttmttmtsccSSBsin)(21cos)(21)(的希爾伯特變換是)()(tmtm ( )VSBDSBSSH1()( )2ccMMH VSB2( )cospcststt ( )VSBVSBstScccosct ()()pVSBcVSBcSSS ()()pVSBcVSBcSSS ( )VSBDSBSS

4、H1()( )2ccMMH 1(2)()2pccSMMH1( )(2)()2ccMMH1( )( )()()2dccSMHH1( )( )()()2dccSMHH()()ccHHH 常數(shù)，)(cos)()(thttmtscm)()(21)(HMMSccm)()(thH)(cos)()(thttmtscm( )( )cos( ) inmIcQcsts ttst st( )( )( )IIs th tm t( )( )cosIch th tt( )( )( )QQsthtm t( )( )sinQchth tt( )( )cos( ) inmIcQcsts ttst stttmAtscAMcos)

5、()(0cHfRCf /1 0( )dstAm tisciNtntntn)()()(222BnNi0( )( )cos( )siniicscn tn ttn tt2oo2oo( )( )Sm tNn t解調(diào)器輸出有用信號的平均功率解調(diào)器輸出噪聲的平均功率iiNSNSG/00)()(22tntsNSimii功率解調(diào)器輸入噪聲的平均平均功率解調(diào)器輸入已調(diào)信號的類別BGAM2fH2/3DSB2fH2SSBfH1VSBfH2fH/OONSm0ifnS31H0ifnSH0ifnS 性能比較性能比較: 可靠性可靠性 優(yōu)優(yōu)劣劣:SSB（DSB），），AM 有效性有效性 優(yōu)優(yōu)劣劣:SSB，VSB，AM（DSB

6、） VSB的可靠性，無分析結(jié)論。的可靠性，無分析結(jié)論。 ( )mst BPF )(tn ( )mst )(tni )(tno o( )m t 包絡(luò)檢波 ttmAtscmcos)()(0ttnttntncsccisin)(cos)()(2)(2)(2202tmAtsSmiBntnNii02)(BntmANSii02202)(0( )( )( )( )cos( )sin( )cos( )miccsccstn tAm tn ttn ttE ttt220( )( )( )( )csE tAm tn tn t)()()()(0tntmAtnarctgtcs)()()(220tntntmAsc220( )

7、( )( )( )csE tAm tn tn t)()()()( 2)()(22020tntntntmAtmAtEscc200120000( )2( )( )2( )( ) 1( )( )( ) 1( )cccAm tAm t n tn tAm tAm tn tAm tAm t0( )( )cAm tn t12(1)1,12xxx 當(dāng)時(shí)2o( )Sm t22o0( )( )ciNn tn tn B2oo0( )Sm tNn B2oo220/2( )/( )AMiiSNm tGSNAm t2oo220/2( )/( )AMiiSNm tGSNAm t32AMG220( )( )( )csAm t

8、n tn t220( )( )( )( )csE tAm tn tn t)()(2)()()()(02220tmAtntntntmAtEcsc)()(2)()(022tmAtntntncsc)()()()(21)()(22022tntntmAtntntnsccsc)(cos)()( 21)(0ttRtmAtR)()()(22tntntRsc)()()(tntnarctgtcs)()(0tmAtR)(cos)()(1)(ttRtmAtR)(cos)()( 21)()(0ttRtmAtRtE）時(shí)1(21)1 (21xxx)(cos)()(ttmAtR)(cos)(ttAtscm)()(tmKtp)

9、(cos)(tmKtAtspcPM)(cos)(ttAtscm)()(tmKdttdf( )( )ftKmd( )cos( )FMcfstAtKmd)(cos)(ttAtscm)(cos)(tmKtAtspcPM( )cos( )FMcfstAtKmd( )coscos2mmmmm tAtAf t)(cos)(tmKtAtspcPMPM( )coscoscpmmstAtK AtcosscpmAtm cot( )coscos2mmmmm tAtAf tFM( )coscoscfmmstAtK Ad ( )cos( )FMcfstAtKmdcosncfmAtm sitfmfmmmK AfmffmK

10、 Afmfmf )(cos)(tmKtAtspcPM( )cos( )FMcfstAtKmd （a a）直接調(diào)頻）直接調(diào)頻 （b b）間接調(diào)頻）間接調(diào)頻(c) (c) 直接調(diào)相直接調(diào)相 (d) (d) 間接調(diào)相間接調(diào)相）（或 5 . 06)(tfdmK( )cos( )tFMcfstAtKmdcoscos( )sinsin( )ttcfcfAtKmdAtKmd1( )tfKmdcos( )1sin( )( )tfttffKmdKmdKmd( )os( )sintNBFMcfcstActAKmdt)()(sin)()(cos)()(ccccccjttMtmjMdttm)()(（設(shè)（設(shè)m(t)的均

11、值為的均值為0） ()()1( )sin2cccccMMm t dttNBFM( ) ()()ccsA ()()2fccccAKMM1( ) ()()()()2AMccccSAMM NBFM( ) ()()ccsA ()()2fccccAKMMtAtmmmcos)( )cos( )sintNBFMcfcstAtAKmdt1cossinsincmfmcmAtAA Kttcoscos()cos()2mFccmcmmAA KAttt(cos)cosAMmmcsAAttscoscoscmmcAcotAtcoscos()cos()2mccmcmAAttttfAtAtmmmmm2coscos)(sinco

12、s)(tmtAtsmfcFM( )coscos(sin)sinsin(sin)FMcfmcfmstAtmtAtmttnmJmJtmmfnnfmf2cos)(2)()sincos(120tnmJtmmfnnmf) 12sin()(2)sinsin(112tnmJmJtmmfnnfmf2cos)(2)()sincos(120tnmJtmmfnnmf) 12sin()(2)sinsin(112( )coscos(sin)sinsin(sin)FMcfmcfmstAtmtAtmt)cos(21)cos(21sinsin)cos(21)cos(21coscosBABABABABABA為奇數(shù)時(shí)當(dāng)nmJmJ

13、fnfn)()(為偶數(shù)時(shí)當(dāng)nmJmJfnfn)()( )()()()FMnfcmcmSAJ mnn )(2) 1(2mmfFMfffmBmFMfB2)( 2) 1( 2mmfFMfffmBfBFM2 2FMFMPst22FMcAPP0( )( )iftK m t NBFM( )st LPF BPF )(tSi o( )m t ( )c t 微分 )(tSp ( )dst ( )cos( ) sintNBFMcfcstAtA Kmdtttccsin)( )sin2( ) (1 cos2)22tpcfcAAsttKmdt tFddmKAts)(2)()(2)(0tmAKtmF NBFM( )st

14、LPF BPF )(tSi o( )m t ( )c t 微分 )(tSp ( )dst ( )cos( )tFMcfstAtKmdo( )( )fm tK m to( )( )dfm tK K m tFMAMdt) t (mKtsin) t (mKAdt) t (dSdt) t (mKtcosA) t (SFcFcFMFcFM FM( )st BPF )(tn )(tSi )(tni LPF )(tno o( )m t 限幅 鑒頻 FM( )cos( )tcFstAtKmd2/2ASiFMiBnN0FMiiBnANS022o( )( )dfmtK K m t222oo( )( )dfSmtK

15、 Kmt 2220o222302483mmmmffddffdmK nNPf dff dfAK n fA222o23o03( )8fmA K m tSNn fttmmcos)(sincos)(tmtAtsmfcFMffmmmKfmf22oo03/22fmSAmNn f2ooFMFM/3/2fiimSNBGmSNf)(2) 1(2mmfFMfffmB23(1)FMffGmm33FMfGm2oo0( )Sm tNn B22( )2Am t 2oo0/2SANn B2oo0/2()2AMmSANn foo2FMooAM/3/fSNmSN22oo03/2()2FMfmSAmNn foo2FMooAM/3

16、/fSNmSNFMAM2(1)(1)fmfBmfmBFMAM2(1)(1)fmfBmfmBFMAMfBm BFMAMfBmB2ooFMFMooAMAM/3/SNBSNBoo2FMooAM/3/fSNmSN 1( )( )pdHfHf 去加重網(wǎng)絡(luò)與網(wǎng)絡(luò)特性調(diào)制調(diào)制方式方式傳輸帶寬傳輸帶寬設(shè)備復(fù)雜設(shè)備復(fù)雜程度程度主要應(yīng)用主要應(yīng)用AM2fm簡單簡單中短波無線電廣播中短波無線電廣播DSBDSB2fm中等中等應(yīng)用較少應(yīng)用較少SSBSSBfm復(fù)雜復(fù)雜短波無線電廣播、話音短波無線電廣播、話音頻分復(fù)用、載波通信、頻分復(fù)用、載波通信、數(shù)據(jù)傳輸數(shù)據(jù)傳輸VSBVSB略大于略大于fm 近似近似SSBSSB復(fù)雜復(fù)雜電視廣播、數(shù)據(jù)傳輸電視廣播、數(shù)據(jù)傳輸FM中等中等超短波小功率電臺（窄超短波小功率電臺（窄帶帶FMFM）；調(diào)頻立體聲廣）；調(diào)頻立體聲廣播等高質(zhì)量通信（寬帶播等高質(zhì)量通信（寬帶FMFM）oo/SNoo0AM13imSSNn foo0DSBimSSNn foo0SSBimSSNn fmffm) 1(22oo0FM32ifmSSmNn fn抗噪聲性能抗噪聲性能 WBFM抗抗噪聲性能噪聲性能最好，最好，D