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1、Lecture15數(shù)字信號的載波傳輸IILecture15?多進制數(shù)字調(diào)制?MASK?MPSK?MFSK數(shù)字信號的載波傳輸II?正交幅度調(diào)制(QAM)?部分響應(yīng)正交幅度調(diào)制(QPR)?最小頻移鍵控(MSK)?各數(shù)字調(diào)制方法比較多進制幅度鍵控(MASK)多進制幅度鍵控(MASK)??SMASK(t)=??∑ang(t?nTb)??cosωctn?A0,A1,A2,?AM?1??P,P,P,?P?sMASK(t)?012M?1?M?1∑Pi=1i=0多進制相移鍵控(MPSK)多進制相移鍵控(MPSK)π/2相5π/8相3π/8相3π/4相
2、π/4相7π/8相π/8相3π/4相π/2相參考相位π/2相π/4相-7π/8相-π/8相π相0相π相0相π相0相-π/4相-π/2相-3π/4相-5π/8相-3π/8相3π/2相-π/4相?已調(diào)信號-3π/4相3π/2相SPSK(t)=∑g(t?nTb)cos(ωct+?n)n????=??∑g(t?nTb)cos?n??cosωct???∑g(t?nTb)sin?n??sinωctnn多進制相移鍵控(MPSK)QPSK信號的產(chǎn)生?令an=cosφn,bn=sinφnb(1)(0,1)(1,1)??ΔφABSMPSK(t)=???a
3、n∑g(tnT)cosbωctπ/411??na(0)a(1)??3π/401????bnb∑g(tnT)sinωct??n5π/400?可看作兩個正交載波進行MASK調(diào)制后信7π/410(0,0)(1,0)b(0)號的疊加。QPSK信號的產(chǎn)生QPSK信號的產(chǎn)生環(huán)形調(diào)制器1振蕩器s(t)4PSK輸入輸出串/并串/并變換邏輯選相電路帶通濾波器Σ變換器相移π/2四相載波發(fā)生器環(huán)形調(diào)制器2QPSK信號的解調(diào)QPSK信號的產(chǎn)生低通抽樣輸入相位cosφn的sinφn的判決器輸出相乘器濾波器判決器φ極性極性ABn位定時π/4++11振蕩器x(t)
4、串/并變換器3π/4-+01相移π/25π/4--00低通抽樣相乘器濾波器判決器7π/4+-10x(t)=s(t)cos(ωct+?n)多進制數(shù)字調(diào)頻(MFSK)多進制數(shù)字調(diào)頻(MFSK)sMPSK(t)=Acosωiti=0,1,…M-1動態(tài)濾波f1包絡(luò)檢波1采振蕩器f1動態(tài)濾波f2包絡(luò)檢波2樣振蕩器f2開判關(guān)決電器路動態(tài)濾波fL包絡(luò)檢波L振蕩器fL二進制碼控制邏輯電路定時Lecture15數(shù)字信號的載波傳輸II正交幅度調(diào)制(QAM)矢量圖?多進制數(shù)字調(diào)制QQ?MASK?MPSK?MFSKII?正交幅度調(diào)制(QAM)?部分響應(yīng)正交幅
5、度調(diào)制(QPR)?最小頻移鍵控(MSK)(a)16PSK(b)16QAM?各數(shù)字調(diào)制方法比較正交幅度調(diào)制(QAM)時域表達式正交幅度調(diào)制(QAM)調(diào)制SQAM(t)=x(t)cosωct+y(t)sinωct電平LPF乘法器轉(zhuǎn)換x(t)=∑xkg(t?kTb)kCosωcty(t)=∑ykg(t?kTb)二進制L-QAM信號k串-并加法器信息變換Sinωct電平LPF乘法器轉(zhuǎn)換a1a2b1b2xa1a2(0011)(0010)(0001)(0000)+300正交幅度調(diào)制(QAM)解調(diào)(0111)(0110)(0101)(0100)+1
6、01x?(t)a?判決1╳a?l(1011)(1010)(1001)(1000)-110L-QAM信號載波cosωct位同步提取(1111)(1110)(1101)(1100)o-311相移90sinωctb?1╳判決-3-1+1+3y?y(t)b?l1100b1位同步1010b2正交幅度調(diào)制(QAM)解調(diào)正交幅度調(diào)制(QAM)解調(diào)?解調(diào)器兩個支路信號?四電平QAM:L=0,+2,-2x?(t)=∑xkg(t?kTb)?還原出二進制碼k?y(t)=∑ykg(t?kTb)a?1k=x?k(0);ka?2k=x?k(0)⊕x?k(+2)⊕
7、x?k(?2)?用某判決電平L對xk,yk進行判決??0,若xLLk()>xka1ka2kx?k(0)x?k(+2)x?k(?2)xL?k()=?+300000?1,若xLL()-310110k?y(L)k=?-111111?1,若yLL()
8、AM)Xk=∑cixk?ii=0?部分響應(yīng)正交幅度調(diào)制(QPR)N?1?最小頻移鍵控(MSK)Yk=∑diyk?ii=0?各數(shù)字調(diào)制方法比較MSK基本原理Lecture15數(shù)字信號的載波傳輸II?多進制數(shù)字調(diào)制?FSK信