SSB信號(hào)的調(diào)制與解調(diào)

,.SSB信號(hào)的調(diào)制與解調(diào)一．題目要求：用matlab產(chǎn)生一個(gè)頻率為1Hz，功率為1的余弦信源，設(shè)載波頻率精品文檔放心下載=10Hz，,試畫出：SSB調(diào)制信號(hào)的時(shí)域波形；采用相干解調(diào)后的SSB信號(hào)波形；SSB已調(diào)信號(hào)的功率譜；在接收端帶通后加上窄帶高斯噪聲，單邊功率譜密度0n=0.1，重感謝閱讀新解調(diào)。二．實(shí)驗(yàn)原理：?jiǎn)芜厧д{(diào)制只傳送一個(gè)邊帶的調(diào)制方式，SSB信號(hào)的帶寬是與消息信號(hào)m(t)相同。精品文檔放心下載對(duì)信號(hào)采取先調(diào)制搬頻，再過低通（高通）濾波器取上（下）邊帶的方法進(jìn)行調(diào)制。精品文檔放心下載,.2.單邊帶信號(hào)解調(diào)方法：相干解調(diào)法111mtcostm?tsintcost2mt2mtcos2t2m?tsin2t00000相干解調(diào)后讓信號(hào)過低通濾波器，取得有用信號(hào)1 其幅度為調(diào)謝謝閱讀mt，2制信號(hào)一半。三．實(shí)驗(yàn)結(jié)果與分析信號(hào)發(fā)送端調(diào)制信號(hào)與載波時(shí)域圖形：由題意生成一個(gè)頻率為1Hz，功率為1的余弦信源，設(shè)載波頻率=10Hz，如圖：謝謝閱讀調(diào)制信號(hào)1.510.50-0.5-1-1.50 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5感謝閱讀t載波信號(hào)1.510.50-0.5-1-1.50 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5感謝閱讀t如圖，調(diào)制信號(hào)為低頻信號(hào)，載波為高頻信號(hào)。,.2.假設(shè)信道理想，對(duì)信號(hào)進(jìn)行調(diào)制與解調(diào)：調(diào)制信號(hào)時(shí)域波形210-1-200.511.522.533.544.55相干解調(diào)后的信號(hào)時(shí)域波形10.50-0.5-100.511.522.533.544.55t如圖可知，經(jīng)相干解調(diào)后的單邊帶信號(hào)時(shí)域形狀不變，僅僅是幅度變?yōu)樵盘?hào)的一半。謝謝閱讀3.調(diào)制信號(hào)、SSB信號(hào)與解調(diào)后信號(hào)頻譜比較：調(diào)制信號(hào)功率譜20-15-10-505101520-20fSSB信號(hào)功率譜20-15-10-505101520-20f調(diào)制信號(hào)功率譜10-15-10-505101520-20f,.由信號(hào)頻譜圖可知：（1） SSB調(diào)制是對(duì)調(diào)制信號(hào)進(jìn)行搬頻之后去邊帶，其頻精品文檔放心下載帶寬度與原調(diào)制信號(hào)相同，頻帶利用率提高。（2） 對(duì)SSB信號(hào)進(jìn)行相干解調(diào)還原出原始信號(hào)的頻譜感謝閱讀與原調(diào)制信號(hào)相同，但其幅度減半。從數(shù)學(xué)公式結(jié)合物理角度看，SSB信號(hào)進(jìn)行相干解調(diào)后僅有1mt為有精品文檔放心下載2用信號(hào)，其余頻率成分被低通濾波器濾掉了。4.在接收端帶通后加上窄帶高斯噪聲后從新進(jìn)行解調(diào)：精品文檔放心下載0.60.40.20-0.2-0.4-0.6-0.80 50 100 150 200 250 300 350 400 450 500謝謝閱讀由圖可知，我們明顯看出噪聲對(duì)解調(diào)信號(hào)產(chǎn)生了影響，原正弦信號(hào)波形不再平坦，但幅度仍大約為調(diào)制信號(hào)的一半。感謝閱讀,.function[tst]=lpf(f,sf,B)謝謝閱讀%Thisfunctionfilteraninputdatausingalowpassfilteratfrequency精品文檔放心下載%domain%Inputs:%f:frequencysamples%sf:inputdataspectrumsamples精品文檔放心下載%B:lowpass'sbandwidthwitharectanglelowpass感謝閱讀%Outputs:%t:frequencysamples%st:outputdata'stimesamples謝謝閱讀df=f(2)-f(1);T=1/df;hf=zeros(1,length(f));bf=[-floor(B/df):floor(B/df)]+floor(length(f)/2);感謝閱讀hf(bf)=1;yf=hf.*sf;[t,st]=F2T(f,yf);st=real(st);function[tst]=F2T(f,sf)%Thisfunctioncalculatethetimesignalusingifftfunctionfortheinput精品文檔放心下載%signal'sspectrumdf=f(2)-f(1);,.Fmx=(f(end)-f(1)+df);dt=1/Fmx;N=length(sf);T=dt*N;%t=-T/2:dt:T/2-dt;t=0:dt:T-dt;sff=ifftshift(sf);st=Fmx*ifft(sff);function[f,sf]=T2F(t,st)謝謝閱讀%ThisisafunctionusingtheFFTfunctiontocalculateasignal'sFourier精品文檔放心下載%Translation%Inputisthetimeandthesignalvectors,thelengthoftimemustgreater感謝閱讀%than2%Outputisthefrequencyandthesignalspectrum精品文檔放心下載dt=t(2)-t(1);T=t(end);df=1/T;N=length(st);%f=-N/2*df+df/2:df:N/2*df-df/2;謝謝閱讀f=-N/2*df:df:N/2*df-df;sf=fft(st);sf=T/N*fftshift(sf);,.%dff=df/8;%ff=-50*df:dff:50*df;%mf=sinc(ff*T);%sf=conv(mf,sf)%NN=length(f)+length(ff)-1;精品文檔放心下載%f=-NN/2*dff:dff:NN/2*dff-dff;精品文檔放心下載%??ê??￡?aμ÷??μ?2¨D??°?aμ÷·?·¨SSB感謝閱讀closeall;clearall;,.dt=0.001;%ê±??2é?ù????fm=1;%D??′×????μ?êfc=10;%??2¨?DD??μ?êT=5;%D?o?ê±3¤t=0:dt:T;mt=sqrt(2)*cos(2*pi*fm*t);%D??′精品文檔放心下載%N0=0.01;%°×??μ￥±?1|?ê?×?ü?è感謝閱讀%SSBmodulations_ssb=real(hilbert(mt).*exp(j*2*pi*fc*t));精品文檔放心下載B=fm;%noise=noise_nb(fc,B,N0,t);精品文檔放心下載%s_ssb=s_ssb+noise;figure(1)subplot(211)plot(t,mt);%±êê?mtμ?2¨D?title('μ÷??D?o?');xlabel('t');subplot(212)plot(t,s_ssb);%?3?SSBD?o?2¨D?謝謝閱讀title('??2¨D?o?');xlabel('t');,.rt=s_ssb.*cos(2*pi*fc*t);感謝閱讀rt=rt-mean(rt);[f,rf]=T2F(t,rt);[t,rt]=lpf(f,rf,2*fm);figure(2)subplot(211)plot(t,mt);title('μ÷??D?o?ê±óò2¨D?');謝謝閱讀subplot(212)plot(t,rt);title('?à?é?aμ÷oóμ?D?o?ê±óò2¨D?');精品文檔放心下載xlabel('t')figure(3)subplot(311)[f,sf]=T2F(t,mt);,.psf1=(abs(sf).^2)/T;plot(f,psf1);axis([-2*fc2*fc0max(psf1)]);謝謝閱讀title('μ÷??D?o?1|?ê?×');xlabel('f');subplot(312)[f,sf]=T2F(t,s_ssb);psf2=(abs(sf).^2)/T;plot(f,psf2);axis([-2*fc2*fc0max