基于matlab的2PSK系統(tǒng)的設(shè)計(jì)—課程設(shè)計(jì)報(bào)告圖22PSK信號(hào)波形解調(diào)原理2PSK信號(hào)的解調(diào)方法是相干解調(diào)法。由于PSK信號(hào)本身就是利用相位傳遞信息的，所以在接收端必須利用信號(hào)的相位信息來解調(diào)信號(hào)。下圖2-3中給出了一種2PSK信號(hào)相干接收設(shè)備的原理框圖。圖中經(jīng)過帶通濾波的信號(hào)在相乘器中與本地載波相乘，然后用低通濾波器濾除高頻分量，在進(jìn)行抽樣判決。判決器是按極性來判決的。即正抽樣值判為1，負(fù)抽樣值判為0.2PSK信號(hào)相干解調(diào)各點(diǎn)時(shí)間波形如圖3所示.當(dāng)恢復(fù)的相干載波產(chǎn)生180°倒相時(shí),解調(diào)出的數(shù)字基帶信號(hào)將與發(fā)送的數(shù)字基帶信號(hào)正好是相反,解調(diào)器輸出數(shù)字基帶信號(hào)全部出錯(cuò).基于matlab的2PSK系統(tǒng)的設(shè)計(jì)基于matlab的2PSK系統(tǒng)的設(shè)計(jì)—課程設(shè)計(jì)報(bào)告全文共7頁(yè)，當(dāng)前為第2頁(yè)。圖32PSK信號(hào)相干解調(diào)各點(diǎn)時(shí)間波形

這種現(xiàn)象通常稱為"倒π"現(xiàn)象.由于在2PSK信號(hào)的載波恢復(fù)過程中存在著180°的相位模糊,所以2PSK信號(hào)的相干解調(diào)存在隨機(jī)的"倒π"現(xiàn)象,從而使得2PSK方式在實(shí)際中很少采用.三、源程序clearall;closeall;clc;max=10g=zeros(1,max);g=randint(1,max);%長(zhǎng)度為max的隨機(jī)二進(jìn)制序列cp=[];mod1=[];f=2*2*pi;t=0:2*pi/199:2*pi;forn=1:length(g);ifg(n)==0;A=zeros(1,200);%每個(gè)值200個(gè)點(diǎn)elseg(n)==1;A=ones(1,200);endcp=[cpA];%s(t),碼元寬度200c=cos(f*t);%載波信號(hào)mod1=[mod1c];%與s(t)等長(zhǎng)的載波信號(hào),變?yōu)榫仃囆问絜ndfigure(1);subplot(4,2,1);plot(cp);gridon;axis([0200*length(g)-22]);title('二進(jìn)制信號(hào)序列');cm=[];mod=[];forn=1:length(g);ifg(n)==0;B=ones(1,200);%每個(gè)值200個(gè)點(diǎn)基于matlab的2PSK系統(tǒng)的設(shè)計(jì)—課程設(shè)計(jì)報(bào)告全文共7頁(yè)，當(dāng)前為第3頁(yè)。c=cos(f*t);基于matlab的2PSK系統(tǒng)的設(shè)計(jì)—課程設(shè)計(jì)報(bào)告全文共7頁(yè)，當(dāng)前為第3頁(yè)。elseg(n)==1;B=ones(1,200);c=cos(f*t+pi);%載波信號(hào)endcm=[cmB];%s(t),碼元寬度200mod=[modc];%與s(t)等長(zhǎng)的載波信號(hào)endtiaoz=cm.*mod;%e(t)調(diào)制figure(1);subplot(4,2,2);plot(tiaoz);gridon;axis([0200*length(g)-22]);title('2PSK調(diào)制信號(hào)');figure(2);subplot(4,2,1);plot(abs(fft(cp)));axis([0200*length(g)0400]);title('原始信號(hào)頻譜');figure(2);subplot(4,2,2);plot(abs(fft(tiaoz)));axis([0200*length(g)0400]);title('2PSK信號(hào)頻譜');%帶有高斯白噪聲的信道tz=awgn(tiaoz,10);%信號(hào)tiaoz中加入白噪聲，信噪比為10figure(1);subplot(4,2,3);plot(tz);gridonaxis([0200*length(g)-22]);title('通過高斯白噪聲信道后的信號(hào)');figure(2);subplot(4,2,3);plot(abs(fft(tz)));axis([0200*length(g)0400]);title('加入白噪聲的2PSK信號(hào)頻譜');jiet=2*mod1.*tz;%同步解調(diào)figure(1);subplot(4,2,4);plot(jiet);gridonaxis([0200*length(g)-22]);title('相乘后信號(hào)波形')figure(2);subplot(4,2,4);plot(abs(fft(jiet)));axis([0200*length(g)0400]);title('相乘后信號(hào)頻譜');%低通濾波器fp=500;fs=700;rp=3;rs=20;fn=11025;ws=fs/(fn/2);wp=fp/(fn/2);%計(jì)算歸一化角頻率[n,wn]=buttord(wp,ws,rp,rs);%計(jì)算階數(shù)和截止頻率[b,a]=butter(n,wn);%計(jì)算H(z）figure(4);freqz(b,a,1000,11025);subplot(2,1,1);axis([04000-1003])title('LPF幅頻相頻圖');jt=filter(b,a,jiet);figure(1);subplot(4,2,5);plot(jt);gridonaxis([0200*length(g)-22]);title('經(jīng)低通濾波器后信號(hào)波形')figure(2);subplot(4,2,5);plot(abs(fft(jt)));axis([0200*length(g)0400]);title('經(jīng)低通濾波器后信號(hào)頻譜');%抽樣判決form=1:200*length(g);ifjt(m)<0;jt(m)=1;elsejt(m)>=0;基于matlab的2PSK系統(tǒng)的設(shè)計(jì)—基于matlab的2PSK系統(tǒng)的設(shè)計(jì)—課程設(shè)計(jì)報(bào)告全文共7頁(yè)，當(dāng)前為第4頁(yè)。endendfigure(1);subplot(4,2,6);plot(jt);gridonaxis([0200*length(g)-22]);title('經(jīng)抽樣判決后信號(hào)s^(t)波形')figure(2);subplot(4,2,6);plot(abs(fft(jt)));axis([0200*length(g)0400]);title('經(jīng)抽樣判決后信號(hào)頻譜');四、實(shí)驗(yàn)結(jié)果基于matlab的2P