n=0:N-1; t=n/Fs
ft=Am*cos(2*pi*fm*t+Qm);%调制信号 subplot(421) plot(t,ft) title('调制信号') y1=fft(ft,N)%傅利叶变换 mag1=abs(y1)%取复变函数幅值
f1=(0:length(y1)-1)*Fs/length(y1);%确定频率范围 subplot(423)%子窗口位置
plot(f1(1:N/2/10),mag1(1:N/2/10))%图形输出 title('调制信号频谱')%标题
SAM=(Ac+ft).*cos(2*pi*fc*t+Qc);%已调波信号AM subplot(422) plot(t,SAM)
title('已调波信号AM') y2=fft(SAM,N); mag2=abs(y2);
f2=(0:length(y2)-1)*Fs/length(y2); subplot(424)
plot(f2(1:N/2/5),mag2(1:N/2/5))
title('已调波信号AM频谱') %以上为调制部分 spt=SAM.*cos(2*pi*fcP*t+QcP)%相干解调 subplot(425)
plot(t,spt) title('相干解调波形') y3=fft(spt,N); mag3=abs(y3);
f3=(0:length(y3)-1)*Fs/length(y3); subplot(426)
plot(f3(1:N/2/5),mag3(1:N/2/5))
title('相干解调AM频谱')%以上为相干解调部分
syms FTP ft SAM spt t ftp R C Am fm Qm Ac fc Qc fcP Qcp ft=Am*cos(2*pi*fm*t) SAM=(Ac+ft).*cos(2*pi*fc*t) spt=SAM.*cos(2*pi*fc*t) ftp=int((spt.*exp(t/(R*C))),0,t) FTP=exp(-t/(R*C)).*ftp R=input('输入R') C=input('输入C') Am=am fm=f Ac=ac fc=fo
N=1000; %设显示范围 Fs=100000; %设采样频率 n=0:N-1;
t=n/Fs; %时间间隔
FTP=1/4*exp(-t/R/C).*(-256*Ac*pi^6*R^6*C^6*fm^6-8192*Ac*pi^6*fc^6*R^6*C^6-32768*Ac*pi^8*fc^6*R^8*C^8*fm^2-160*Ac*pi^2*fc^2*R^2*C^2-384*Ac*pi^4*fc^2*R^4*C^4*fm^2+512*Ac*pi^6*fc^2*R^6*C^6*fm^4-2048*Ac*pi^8*fc^2*R^8*C^8*fm^6-4096*Ac*pi^6*fc^4*R^6*C^6*fm^2-2048*Ac*pi^4*fc^4*R^4*C^4-4*Am-4*Ac+16384*Ac*pi^8*fc^4*R^8*C^8*fm^4-4096*Ac*exp(t/R/C)*pi^7*fc^3*R^7*C^7.*sin(4*pi*fc*t)*fm^4-64*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^4*R^4*C^4*fm^3*fc-192*Ac*pi^4*R^4*C^4*fm^4-8192*Am*exp(t/R/C)*pi^7*fm^3*R^7*C^7.*sin(2*pi*fm*t)*fc^4+1536*Ac*exp(t/R/C)*pi^4*fc^4*R^4*C^4-48*Ac*pi^2*R^2*C^2*fm^2-64*Am*pi^4*R^4*C^4*fm^4-128*Am*exp(t/R/C)*pi^3*R^3*C^3.*sin(2*pi*(fm-2*fc)*t)*fc^3-256*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm-2*fc)*t)*fc^3*fm^2+64*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm-2*fc)*t)*fc*fm^4+1024*Am*exp(t/R/C)*pi^7*R^7*C^7.*sin(2*pi*(fm-2*fc)*t)*fc^3*fm^4-4096*Am*exp(t/R/C)*pi^7*R^7*C^7.*sin(2*pi*(fm-2*fc)*t)*fc^5*fm^2-1024*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm-2*fc)*t)*fc^5+8*Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)*pi^2*R^2*C^2*fm^2+32*Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)*pi^2*fc^2*R^2*C^2+192*Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)*pi^4*fc^2*R^4*C^4*fm^2+16*Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)*pi^4*R^4*C^4*fm^4+256*Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)*pi^6*fc^2*R^6*C^6*fm^4+1024*Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)*pi^6*fc^4*R^6*C^6*fm^2+96*Ac*exp(t/R/C)*pi^2*fc^2*R^2*C^2+24*Ac*exp(t/R/C)*pi^2*R^2*C^2*fm^2-16*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^2*R^2*C^2*fm*fc+16*Am*exp(t/R/C)*pi^3*R^3*C^3.*sin(2*pi*(fm+2*fc)*t)*fm^3+128*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(f
m+2*fc)*t)*fm^3*fc^2+32*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm+2*fc)*t)*fm^5+512*Am*exp(t/R/C)*pi^7*R^7*C^7.*sin(2*pi*(fm+2*fc)*t)*fm^5*fc^2-2048*Am*exp(t/R/C)*pi^7*R^7*C^7.*sin(2*pi*(fm+2*fc)*t)*fm^3*fc^4+16*Am*exp(t/R/C)*pi^3*R^3*C^3.*sin(2*pi*(fm-2*fc)*t)*fm^3+128*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm-2*fc)*t)*fm^3*fc^2+32*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm-2*fc)*t)*fm^5+512*Am*exp(t/R/C)*pi^7*R^7*C^7.*sin(2*pi*(fm-2*fc)*t)*fm^5*fc^2-2048*Am*exp(t/R/C)*pi^7*R^7*C^7.*sin(2*pi*(fm-2*fc)*t)*fm^3*fc^4-512*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm-2*fc)*t)*fm*fc^4+2*Ac*exp(t/R/C).*cos(4*pi*fc*t)+Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)+Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)+2*Ac*exp(t/R/C)+384*Ac*exp(t/R/C)*pi^4*fc^2*R^4*C^4*fm^2+512*Ac*exp(t/R/C)*pi^6*fc^2*R^6*C^6*fm^4+2048*Ac*exp(t/R/C)*pi^6*fc^4*R^6*C^6*fm^2-16384*Ac*exp(t/R/C)*pi^8*fc^4*R^8*C^8*fm^4+2048*Ac*exp(t/R/C)*pi^8*fc^2*R^8*C^8*fm^6+96*Ac*exp(t/R/C)*pi^4*R^4*C^4*fm^4+2*Am*exp(t/R/C)*pi*R*C.*sin(2*pi*(fm-2*fc)*t)*fm-4*Am*exp(t/R/C)*pi*R*C.*sin(2*pi*(fm-2*fc)*t)*fc+256*Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)*pi^4*fc^4*R^4*C^4-512*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm+2*fc)*t)*fm*fc^4+128*Am*exp(t/R/C)*pi^3*R^3*C^3.*sin(2*pi*(fm+2*fc)*t)*fc^3+256*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm+2*fc)*t)*fc^3*fm^2-64*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm+2*fc)*t)*fc*fm^4-1024*Am*exp(t/R/C)*pi^7*R^7*C^7.*sin(2*pi*(fm+2*fc)*t)*fc^3*fm^4+4096*Am*exp(t/R/C)*pi^7*R^7*C^7.*sin(2*pi*(fm+2*fc)*t)*fc^5*fm^2+1024*Am*exp(t/R/C)*pi^5*R^5*C^5.*sin(2*pi*(fm+2*fc)*t)*fc^5+8*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^2*R^2*C^2*fm^2+32*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^2*fc^2*R^2*C^2+192*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^4*fc^2*R^4*C^4*fm^2+16*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^4*R^4*C^4*fm^4+256*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^6*fc^2*R^6*C^6*fm^4+1024*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^6*fc^4*R^6*C^6*fm^2+256*Am*exp(t/R/C).*cos(2*pi*(fm+2*fc)*t)*pi^4*fc^4*R^4*C^4+3072*Am*exp(t/R/C)*pi^5*fm*R^5*C^5.*sin(2*pi*fm*t)*fc^4+16384*Am*exp(t/R/C)*pi^7*fm*R^7*C^7.*sin(2*pi*fm*t)*fc^6+16*Am*exp(t/R/C).*cos(2*pi*fm*t)*pi^2*R^2*C^2*fm^2+96*Am*exp(t/R/C).*cos(2*pi*fm*t)*pi^2*fc^2*R^2*C^2+32*Am*exp(t/R/C).*cos(2*pi*fm*t)*pi^4*R^4*C^4*fm^4+512*Am*exp(t/R/C).*cos(2*pi*fm*t)*pi^6*fc^2*R^6*C^6*fm^4-4096*Am*exp(t/R/C).*cos(2*pi*fm*t)*pi^6*fc^4*R^6*C^6*fm^2+1536*Am*exp(t/R/C).*cos(2*pi*fm*t)*pi^4*fc^4*R^4*C^4+8192*Am*exp(t/R/C).*cos(2*pi*fm*t)*pi^6*fc^6*R^6*C^6+32*Am*exp(t/R/C)*pi^3*fm^3*R^3*C^3.*sin(2*pi*fm*t)+192*Am*exp(t/R/C)*pi^3*fm*R^3*C^3.*sin(2*pi*fm*t)*fc^2+64*Am*exp(t/R/C)*pi^5*fm^5*R^5*C^5.*sin(2*pi*fm*t)+1024*Am*exp(t/R/C)*pi^7*fm^5*R^7*C^7.*sin(2*pi*fm*t)*fc^2+16*Am*exp(t/R/C).*cos(2*pi*(fm-2*fc)*t)*pi^2*R^2*C^2*fm*fc+4*Am*exp(t/R/C)*pi*fm*R*C.*sin(2*pi*fm*t)+2*Am*exp(t/R/C)*pi*R*C.*sin(2*pi*(fm+2*fc)*t)*fm+4*Am*exp(t/R/C)*pi*R*C.*sin(2*pi*(fm+2*fc)*t)*fc+2*Am*exp(t/R/C).*cos(2*pi*fm*t)+32768*Ac*exp(t/R/C)*pi^8*fc^6*R^8*C^8*fm^2+8192*Ac*exp(t/R/C)*pi^6*fc^6*R^6*C^6+128*Ac*exp(t/R/C)*pi^6*R^6*C^6*fm^6+96*Ac*exp(t/R/C).*cos(4*pi*fc*t)*pi^4*R^4*C^4*fm^4-1024*Ac*exp(t/R/C).*cos(4*pi*fc*t)*pi^6*fc^2*R^6*C^6*fm^4+2048*Ac*exp(t/R/C).*cos(4*pi*fc*t)*pi^6*fc^4*R^6*C^6*fm^2+512*Ac*exp(t/R/C).*cos(4*pi*fc*t)*pi^4*fc^4*R^4*C^4+128*Ac*exp(t/R/C).*cos(4*pi*fc*t)*pi^6*R^6*C^6*fm^6+8*Ac*exp(t/R/C*R^2*C^2*fm*fc+16*pi^2*fc^2*R^2*C^2)/(1+4*pi^2*R^2*C^2*fm^2+16*pi^2*R^2*C^2*fm*fc+16*pi^2*fc^2*R^2*C^2)/(1+4*pi^2*R^2*C^2*fm^2)
subplot(427) plot(t,FTP)
title('恢复调制信号波形') y4=fft(FTP,N); mag4=abs(y4);
f2=(0:length(y4)-1)*Fs/length(y4); subplot(428)
plot(f2(1:N/2/10),mag4(1:N/2/10)) title('恢复调制信号波形频谱')
参考文献
[1] 张圣勤.MATLAB7.0实用教材.北京：机械工业出版社，2006 [2] 桑林，郝建军，刘丹谱.数字通信.北京邮电大学出版社，2002 [3] 樊昌信，曹丽娜.通信原理.北京国防工业出版社，2008
[4] 邓华. Matlab通信仿真及应用实例详解. 北京：人民邮电出版社，2003