礦大通信原理課件CH 5.1 模擬調(diào)制

1、CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1 1 這里：控制信號稱為調(diào)制信號，被控制信號稱為載波。2. 調(diào)制的必要性/目的CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2 210 l 如： mlMHzfmlKHzfc1,10103103,3010,10103103,3784538 fc B. 提高信道的利用率CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin3 3530KHz1600KHz300 90003. 模擬調(diào)制的分

2、類 CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin4 44.1 模擬幅度調(diào)制 tttAtStAtStmcmc coscos0已已調(diào)調(diào)信信號號載載波波信信號號為為為為待待傳傳信信號號（調(diào)調(diào)制制信信號號）設設CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin5 5數(shù)學表達式CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin6 6h(t)m(t)cosctSm(t) 01coscos00 ，令令AttmttAmtSccm頻域表達式Com

3、municationCommunicationCUMT LIShiyinCUMT LIShiyin7 7h(t)m(t)cosctSm(t)頻域表達式頻域表達式 HMMSccm 21 ttmtScm cos Mtmccct cos 2121FFtftf4. 1.1 常規(guī)調(diào)幅（AM） CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin8 8 ttmtAttmtScccAM coscoscos0 ccAMAS 0 ccMM 21m(t)cos ctSAM(t)A0m(t) tmAtm 0波形圖CommunicationCommunication

4、CUMT LIShiyinCUMT LIShiyin9 9OOttcosc(t) tSAMOtt tmA 0 tmfmmcf mcf mAMfB2 解調(diào)CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1010 tSAM tmA 0 tSAM AM 特點CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin11 11功率分配mcf mcf mAMfB2 CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1212 0)(tm scAMApp

5、tmAtSP2)(22202得得 ttmtAtSccAM coscos0 5. 1.2 抑制載波雙邊帶調(diào)幅（DSB） CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1313m(t)A0cosctsAM(t) ttmtmtSccAM coscos0 ttmtScDSBcos DSB信號的波形和頻譜CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1414cosw0tOtOcc AMS0m 0m MH H OtOt tSAMOt載波反相點載波反相點tSDSB DSBSAM信號的波形和頻譜

6、 ttmtmtSccAM coscos0 ccccAMMMmS 210 ttmtScDSB cos ccDSBMMS 21結(jié)論 MH H CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1515缺點與措施LPFcosctm0(t) tSp ttmtScDSB cos ttStScDSBp cos tmtm210 tcostmtcostmcc2122CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1616缺點與措施CommunicationCommunicationCUMT LIShi

7、yinCUMT LIShiyin1717DSB信號的缺點：信號的缺點：占用頻帶寬，占用頻帶寬，BDSB=2m 。(含有兩個完全相同的邊帶含有兩個完全相同的邊帶) 克服措施：克服措施：將只傳輸一個邊帶將只傳輸一個邊帶 單單邊帶調(diào)制邊帶調(diào)制 DSBSmAMfB2 上邊帶上邊帶下邊帶下邊帶 ccDSBMMS 2121mcf mcf SSBCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1818濾波特性CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1919形成SSB信號的濾波特性H()10

8、ccH()0cc1(a)(b)hSSB(t)m(t)cosctSSSB(t)SSB信號頻譜CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2020SSB信號的頻譜M()HHSM()ccOO 上邊帶 下邊帶 下邊帶 上邊帶ccO上邊帶頻譜Occ下邊帶頻譜SSB信號的數(shù)學式CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2121 DSBSmcf mcf SSBSSSB頻譜頻譜 ccSSBH , 0, 1 SSBDSBSSBHSS ttmttmtsccSSB sin21cos21 結(jié)論Co

9、mmunicationCommunicationCUMT LIShiyinCUMT LIShiyin2222VSBCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2323CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2424DSB、 SSB和VSB信號的頻譜M()2B2BODSB()ccO(a)(b)SSB()OccccVSB()O(c)(d)實現(xiàn)CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2525 HcVSBcVSBHH 常常數(shù)數(shù)，濾波法產(chǎn)生殘留邊帶信號濾波法產(chǎn)生殘留邊帶信號hVSB(t)m(t)cosctSVSB(t)殘留邊帶濾波器必須滿足殘留邊帶濾波器必須滿足特性特性滾將特性CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2626cOcHVSB()HVSB(c)cOcHVSB(c)HVSB(c) HVSB