SSB信號(hào)的調(diào)制與解調(diào)

1、SSB信號(hào)的調(diào)制與解調(diào)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 ?二 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0 n二0.1,重新 解調(diào)。實(shí)驗(yàn)原理: 1.單邊帶調(diào)制只傳送一個(gè)邊帶的調(diào)制方式， ssB言號(hào)的帶寬是與消息信號(hào)m（t）相同flx*口曰ft號(hào)刈錯(cuò)k . 2殲啊/crIfix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。1.510.5010.511.5233.544.551.5aI10.5010.511.5233.5

2、44.55O2.5 t2.5 t12 mt sin 2 0t2.單邊帶信號(hào)解調(diào)方法：相干解調(diào)法調(diào)制信號(hào)如圖，調(diào)制信號(hào)為低頻信號(hào)，載波為高頻信號(hào)4 4-7相干解調(diào)迭模型mt COS - .0tmt Sin - -0t Icos 0t112 mt2 mt cos 2 謚制信號(hào)一半。三.實(shí)驗(yàn)結(jié)果與分析1.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？?二 10Hz，如圖:-0.5相干解調(diào)后讓信號(hào)過低通濾波器,取得有用信號(hào)土mt,其幅度為調(diào)-0.5載波信號(hào)-1.50-1.50LPF2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2|1I1IIITI

3、T1 - / / 、 / / / / / / / / ! / / / 1Yy-2iiiiiiiii00.511.522.533.544.55t00.511.522.533.544.5510.50-0.5-1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。3. 調(diào)制信號(hào)、SSB信號(hào)與解調(diào)后信號(hào)頻譜比較：0 -20調(diào)制信號(hào)功率譜2-15-10-505101520fSSB信號(hào)功率譜f調(diào)制信號(hào)功率譜0 *-20-15-10-5101520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，其頻帶 寬度與原調(diào)制信號(hào)相同，頻帶利用率提高。(2) 對(duì)SSB言號(hào)進(jìn)行

4、相干解調(diào)還原出原始信號(hào)的頻譜與原 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，SSBW號(hào)進(jìn)行相干解調(diào)后僅有 mt為有用信 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)：0.6 42240-6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。 function t st=lpf(f,sf,B)%This function filter an input data using a lowpass filter at frequency%domain%Inputs:% f: frequency

5、samples% sf: input data spectrum samples% B: lowpasss bandwidth with a rectangle lowpass%Outputs:% t: frequency samples% st: output datas time samplesdf = f(2)-f(1);T = 1/df;hf = zeros(1,length(f);bf = -floor( B/df ): floor( B/df ) + floor( length(f)/2 ); hf(bf)=1;yf=hf.*sf;t,st=F2T(f,yf);st = real(

6、st);function t st=F2T(f,sf)%This function calculate the time signal using ifft function for the input %signals spectrumdf = 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);functionf,sf= T2F(t,st)%This is a f

7、unction using the FFT function to calculate a signals Fourier %Translation%Input is the time and the signal vectors,the length of time must greater %than 2%Output is the frequency and the signal spectrumdt = 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; f=-N/2*df:df:N/2*

8、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; %f = -NN/2*dff:dff:NN/2*dff-dff;%?e ? ?a 卩十？卩?2 - D? ?a？ SSBclose all ;clear all ;dt = 0.001;%e ?2 e ?u ?fm=1;%D? X ?卩? efc=10;%?2？DD?y ?eT=5;%D?oe 30t = 0:dt:T

9、;mt = sqrt(2)*cos(2*pi*fm*t);%D?%N0 = 0.01; % X ?卩丫 士 ?1|? e ?X ?u ?e %SSB modulations_ssb = real(hilbert(mt).*exp(j*2*pi*fc*t) );B=fm;%noise = noise_nb(fc,B,N0,t);%s_ssb=s_ssb+noise;figure(1)subplot(211)plot(t,mt);%ee ?mt ?2 - D?title(卩十？D?o?);xlabel( t);subplot(212)plot(t,s_ssb);%?-3?SSBD?o?2 D?ti

10、tle( ?2 - D?o?);xlabel( t);rt = s_ssb.*cos(2*pi*fc*t);rt = rt-mean(rt);f,rf = T2F(t,rt);t,rt = lpf(f,rf,2*fm);figure(2)subplot(211)plot(t,mt);title(卩十?D?o?eoo 2)D?subplot(212)plot(t,rt);title(? a ?e ?a oo ?D?o?eoo 2D?xlabel( t) figure(3)subplot(311)f,sf=T2F(t,mt);psfl = (abs(sf).A2)/T;plot(f,psf1);axis(-2*fc 2*fc 0 max(psf1);title(卩十?D?o?1|? e ?x；xlabel( f);subplot(312)f,sf=T2F(t,s_ssb);psf2 = (abs(sf).A2)/T;plot(f,psf2);axis(-2*fc 2*fc 0 ma