標(biāo)準(zhǔn)文檔實(shí)用文案實(shí)驗(yàn)二（1小班）連續(xù)波MATLAB實(shí)現(xiàn)姓名：買提阿布都拉·奧布力喀斯木學(xué)號(hào)：PB12210174一、實(shí)驗(yàn)?zāi)康恼莆站€性模擬調(diào)制信號(hào)的波形及產(chǎn)生方法掌握線性模擬調(diào)制信號(hào)的頻譜特點(diǎn)掌握線性模擬調(diào)制信號(hào)的解調(diào)方法掌握線性模擬調(diào)制系統(tǒng)的MATLAB仿真實(shí)現(xiàn)二、實(shí)驗(yàn)原理1.AM調(diào)制AM信號(hào)的時(shí)域表示式：頻譜：調(diào)制器模型如圖1所示：圖1AM調(diào)制器模型AM的時(shí)域波形和頻譜如圖2所示：時(shí)域頻域圖2AM調(diào)制時(shí)、頻域波形2.DSB-SC調(diào)制DSB信號(hào)的時(shí)域表示式頻譜：DSB的時(shí)域波形和頻譜如圖3所示：時(shí)域頻域圖3DSB調(diào)制時(shí)、頻域波形DSB的相干解調(diào)模型如圖4所示：：圖4DSB調(diào)制器模型3.SSB調(diào)制SSB信號(hào)的時(shí)域表示式頻譜：分為上邊帶和下邊帶，均為雙邊帶的一半。三、實(shí)驗(yàn)內(nèi)容（任選一）1.用matlab產(chǎn)生一個(gè)頻率為1Hz，振幅為1的余弦信源，設(shè)載波頻率為10Hz，A=2。=1\*GB3①AM系統(tǒng)中，當(dāng)相干解調(diào)器輸入信噪比為15dB時(shí)，系統(tǒng)各點(diǎn)的波形及其頻譜，并對(duì)調(diào)制信號(hào)和解調(diào)信號(hào)進(jìn)行比較分析。主程序：clc;clearall;closeall;A=2;fc=10;t0=1;snr=input('inputsnr');dt=0.002;fs=1/dt;df=0.02;t=0:dt:t0;Lt=length(t);snr_lin=10^(snr/10);m=cos(2*pi*t);L=2*min(m);R=2*max(abs(m))+A;pauseclffigure(1);subplot(321);plot(t,m(1:length(t)));axis([0t0-R/2R/2]);xlabel('t');ylabel('調(diào)制信號(hào)');subplot(322);[M,m,df1,f]=T2F(m,dt,df,fs);[Bw_eq]=signalband(M,df,t0);f_start=fc-Bw_eq;f_cutoff=fc+Bw_eq;plot(f,fftshift(abs(M)));axis([-3301.2]);xlabel('f');ylabel('調(diào)制信號(hào)頻譜');pausesubplot(323);c=cos(2*pi*fc*t);plot(t,c);axis([0t0-1.21.2]);xlabel('t');ylabel('載波信號(hào)');subplot(324)[C,c,df1,f]=T2F(c,dt,df,fs);plot(f,fftshift(abs(C)));axis([-202001.2]);xlabel('f');ylabel('載波信號(hào)頻譜');pausesubplot(325)u=(A+m(1:Lt)).*c(1:Lt);plot(t,u);axis([0t0-RR]);xlabel('t');ylabel('已調(diào)信號(hào)');subplot(326);[U,u,df1,f]=T2F(u,dt,df,fs);plot(f,fftshift(abs(U)));axis([-202001]);xlabel('f');ylabel('已調(diào)信號(hào)頻譜');signal_power=power_x(u(1:Lt));noise_power=(signal_power*fs)/(snr_lin*4*Bw_eq);noise_std=sqrt(noise_power);noise=noise_std*randn(1,Lt);pausefigure(2);subplot(321);plot(t,noise);axis([0t0-RR]);xlabel('t');ylabel('噪聲信號(hào)');subplot(322);[noisef,noise,df1,f]=T2F(noise,dt,df,fs);plot(f,fftshift(abs(noisef)));axis([-151501.2]);xlabel('f');ylabel('噪聲信號(hào)頻譜');pausesam=u(1:Lt)+noise(1:Lt);subplot(323);plot(t,sam);axis([0t0-RR]);xlabel('t');ylabel('信道中的信號(hào)');subplot(324);[samf,sam,df1,f]=T2F(sam,dt,df,fs);plot(f,fftshift(abs(samf)));axis([-202001.2]);xlabel('f');ylabel('信道中的信號(hào)頻譜');[H,f]=bp_f(length(sam),f_start,f_cutoff,df1,fs,1);subplot(326);plot(f,fftshift(abs(H)));axis([-202001.2]);xlabel('f');ylabel('帶通濾波器’);pauseDEM=H.*samf;[dem]=F2T(DEM,fs);figure(3)subplot(321)plot(t,dem(1:Lt))axis([0t0-RR]);xlabel('t');ylabel('理想BPF輸出信號(hào)');[demf,dem,df1,f]=T2F(dem(1:Lt),dt,df,fs);subplot(322)plot(f,fftshift(abs(demf)));xlabel('f');axis([-202001.2]);ylabel('理想BPF輸出頻譜');pausesubplot(323)plot(t,c(1:Lt));axis([0t0-1.21.2]);xlabel('t');ylabel('本地載波');subplot(324)[C,c,df1,f]=T2F(c(1:Lt),dt,df,fs);plot(f,fftshift(abs(C)));axis([-202001.2]);xlabel('f');ylabel('本地載波頻譜');pauseder=dem(1:Lt).*c(1:Lt);subplot(325)plot(t,der);axis([0t0-RR]);xlabel('t');ylabel('混頻后的信號(hào)');subplot(326)[derf,der,df1,f]=T2F(der,dt,df,fs);plot(f,fftshift(abs(derf)));axis([-303001.2]);xlabel('f');ylabel('混頻后的信號(hào)頻譜');pausefigure(4)[LPF,f]=lp_f(length(der),Bw_eq,df1,fs,2);subplot(322)plot(f,fftshift(abs(LPF)));xlabel('f');axis([-151502]);ylabel('理想LPF');pauseDM=LPF.*derf;[dm]=F2T(DM,fs);subplot(323)plot(t,dm(1:Lt));axis([0t0-RR]);xlabel('t');ylabel('LPF輸出信號(hào)');[dmf,dm,df1,f]=T2F(dm(1:Lt),dt,df,fs);subplot(324)plot(f,fftshift(dmf));axis([-3302]);xlabel('f');ylabel('LPF輸出信號(hào)頻譜');pausedmd=dm(1:Lt)-mean(dm(1:Lt));subplot(325)plot(t,dmd);axis([0t0-R/2R/2]);xlabel('t');ylabel('恢復(fù)信號(hào)');[dmdf,dmd,df1,f]=T2F(dmd,dt,df,fs);subplot(326)plot(f,fftshift(dmdf));axis([-3301.2]);xlabel('f');ylabel('恢復(fù)信號(hào)頻譜');subplot(321);plot(t,m(1:Lt));axis([0t0-R/2R/2]);xlabel('t');ylabel('已調(diào)信號(hào));子程序：序列的傅立葉變換function[M,m,df]=fftseq(m,ts,df)%各參數(shù)含義與子函數(shù)T2F中的完全相同，完成fs=1/ts;ifnargin==2n1=0;elsen1=fs/df;endn2=length(m);n=2^(max(nextpow2(n1),nextpow2(n2)));M=fft(m,n);m=[m,zeros(1,n-n2)];df=fs/n;計(jì)算信號(hào)功率functionp=power_x(x)p=(norm(x).^2)./length(x);信號(hào)從頻域轉(zhuǎn)換到時(shí)域function[m]=F2T(M,fs)m=real(ifft(M))*fs;信號(hào)從時(shí)域轉(zhuǎn)換到頻域function[M,m,df1,f]=T2F(m,ts,df,fs)[M,m,df1]=fftseq(m,ts,df);f=[0:df1:df1*(length(m)-1)]-fs/2;M=M/fs;帶通濾波器function[H,f]=bp_f(n,f_start,f_cutoff,df1,fs,p)n_cutoff=floor(f_cutoff/df1);n_start=floor(f_start/df1);f=[0:df1:df1*(n-1)]-fs/2;H=zeros(size(f));H(n_start+1:n_cutoff)=p*ones(1,n_cutoff-n_start);H(length(f)-n_cutoff+1:length(f)-n_start)=p*ones(1,n_cutoff-n_start低通濾波器function[H,f]=lp_f(n,f_cutoff,df1,fs,p)n_cutoff=floor(f_cutoff/df1);f=[0:df1:df1*(n-1)]-fs/2;H=zeros(size(f));H(1:n_cutoff)=p*ones(1,n_cutoff);H(length(f)-n_cutoff+1:length(f))=p*ones(1,n_cutoff);計(jì)算信號(hào)有效帶寬function[Bw_eq]=signalband