SSB信号调制解调(滤波法)

%SSB信号调制解调

clear;clc;

f0 = 1; %信源信号频率(Hz)

E0 = 1; %信源信号振幅(V)

E = 1; %载波分量振幅(V)

fc = 10; %载波分量频率（Hz）

t0 = 1; %信号时长

snr = 15; %解调器输入信噪比dB

dt = 0.003; %系统时域采样间隔

fs = 1/dt; %系统采样频率

df = 0.001; %所需的频率分辨率

t = 0:dt:t0;

Lt = length(t); %仿真过程中，信号长度

snr_lin = 10^(snr/10);%解调器输入信噪比

%-------------画出调制信号波形及频谱

%产生模拟调制信号

m = E*cos(2*pi*f0*t);

L = min(abs(m));%包络最低点

R = max(abs(m));%包络最高点

%画出调制信号波形和频谱

clf;

figure(1);

%%

%画出调制信号波形

subplot(411);

plot(t,m(1:length(t)));

axis([0,t0,-R-0.3,R+0.3]);%设置坐标范围

xlabel('t');title('调制信号');

set(gca,'YTick',-R:1:R);

subplot(412);

[M,m,df1,f] = T2F_new(m,dt,df,fs); %求出调制信号频谱

[Bw_eq] = signalband(M,df,t0); %求出信号等效带宽

f_start_low = fc - Bw_eq; %求出产生下边带信号的带通滤波器的起始频率f_cutoff_low = fc; %求出产生下边带信号的带通滤波器的截止频率f_start_high = fc; %求出产生上边带信号的带通滤波器的起始频率f_cutoff_high = fc + Bw_eq; %求出产生上边带信号的带通滤波器的截止频率

plot(f,fftshift(abs(M))); %画出调制信号频谱%M：傅里叶变换后的频谱序列

xlabel('f');title('调制信号频谱');

axis([-fc-5*f0,fc+5*f0,0,max(M)+0.3]);

set(gca,'XTick', -10:10:10);

set(gca,'XGrid','on');

%%

%载波及其频谱

subplot(413);

c = cos(2*pi*fc*t); %载波

plot(t,c);

axis([0,t0,-E-0.2,E+0.2]);

xlabel('t');title('载波');

subplot(414); %载波频谱

[C,c,df1,f] = T2F_new(c,dt,df,fs);

plot(f,fftshift(abs(C))); %画出载波频谱

xlabel('f');title('载波频谱');

axis([-fc-5*f0,fc+5*f0,0,max(C)+0.3]);

set(gca,'XTick', -10:10:10);

set(gca,'XGrid','on');

%%

%已调信号及其频谱

figure(2);

subplot(321); %画已调信号

u = m(1:Lt).*c(1:Lt);

plot(t,u);

axis([0,t0,-max(u)-0.5,max(u)+0.5]);

xlabel('t');title('DSB信号');

set(gca,'YTick', -max(u):1:max(u));

subplot(322);

[U,u,df1,f] = T2F_new(u,dt,df,fs);

plot(f,fftshift(abs(U))); %画出已调信号频谱

xlabel('f');title('DSB信号频谱');

axis([-fc-5*f0,fc+5*f0,0,max(U)+0.3]);

set(gca,'XTick', -10:10:10);

set(gca,'XGrid','on');

%%

%滤波法产生SSB信号

[H_low,f_low] = bp_f(length(u),f_start_low,f_cutoff_low,df1,fs,1);%求滤波法产生下边带需要的带通滤波器

[H_high,f_high] = bp_f(length(u),f_start_high,f_cutoff_high,df1,fs,1);

%[H,f] = bp_f(length(sam),f_start,f_cutoff,df1,fs,1);

subplot(323);

plot(f_low,fftshift(abs(H_low))); %画出带通滤波器xlabel('f');title('下边带带通滤波器');

axis([-f_cutoff_low-1,f_cutoff_low+1,-0.05,1.05]);

subplot(324);

plot(f_high,fftshift(abs(H_high))); %画出带通滤波器xlabel('f');title('上边带带通滤波器');

axis([-f_cutoff_high-1,f_cutoff_high+1,-0.05,1.05]);

subplot(325);

plot(f_low,fftshift(abs(H_low)));hold on; %画出带通滤波器

plot(f,fftshift(abs(U))); %画出已调信号频谱axis([-fc-5,fc+5,-0.05,1.05]);

xlabel('f');title('下边带信号');

subplot(326);

plot(f_high,fftshift(abs(H_high)));hold on; %画出带通滤波器

plot(f,fftshift(abs(U))); %画出已调信号频谱axis([-fc-5,fc+5,-0.05,1.05]);

xlabel('f');title('上边带信号');

%%

%----------------经过带通滤波器，产生单边带信号（以上边带信号为例）

samuf = H_high.*U; %滤波器输出信号的频谱

[samu] = F2T_new(samuf,fs); %滤波器输出信号的波形

figure(3);

subplot(321);

plot(t,samu(1:Lt));

axis([0,t0,-max(samu)-0.3,max(samu)+0.3]);

xlabel('t');title('上边带信号');

%%

[samuf,samu,df1,f] = T2F_new(samu(1:Lt),dt,df,fs);%上边带信号频谱

subplot(322);

plot(f,fftshift(abs(samuf))); %画出经过理想带通滤波器后信号频谱xlabel('f');title('上边带信号频谱');

axis([-fc-5*f0,fc+5*f0,0,max(samuf)+0.1]);

set(gca,'XTick', -10:10:10);

set(gca,'XGrid','on');