%学员:焦志修
%学号:201711612019
clear all;
clc;
close all;
Fs=10000; %抽样频率fs=10000;
t=[0:1/Fs:0.01];
Fc=3000; %载波频率
a=0.5
m=a*cos(300*2*pi*t); %调制信号
X=fft(m);
X=abs(X(1:length(X)/2+1)); %调制信号频谱
frqX=(0:length(X)-1)*Fs/length(X)/2
S = modulate(m,Fc,Fs,'amssb'); %对信号进行调制
Y=fft(S);
Y=abs(Y(1:length(Y)/2+1));
frqY=(0:length(Y)-1)*Fs/length(Y)/2 ;%已调信号频谱
set(gcf,'color','w')
figure(1)
subplot(221) %绘制曲线
plot(t,m)
xlabel('调制信号波形')
subplot(222)
plot(frqX,X)
axis([0 3000 0 max(X)])
xlabel('调制信号频谱')
subplot(223)
plot(t,S)
xlabel('无噪声SSB已调信号波形')
subplot(224)
plot(frqY,Y)
axis([0 60000 0 max(Y)])
xlabel('无噪声SSB已调信号频谱')
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
sn=awgn(S,4); %加入高斯白噪声
sn1=awgn(S,10);
sn2=awgn(S,15);
sn3=awgn(S,20);
sn4=awgn(S,25); %不同信噪比
M1=demod(S,Fc,Fs,'amssb'); %无噪声已调信号解调
MMN=demod(sn,Fc,Fs,'amssb'); %加噪声已调信号解调
MMN1=demod(sn1,Fc,Fs,'amssb');
MMN2=demod(sn2,Fc,Fs,'amssb');
MMN3=demod(sn3,Fc,Fs,'amssb');
MMN4=demod(sn4,Fc,Fs,'amssb');
G1=fft(sn);
G1=abs(G1(1:length(G1)/2+1))
frqG1=(0:length(G1)-1)*Fs/length(G1)/2; %加噪声后已调信号频谱
G2=fft(MMN)
G2=abs(G2(1:length(G2)/2+1))
frqG2=(0:length(G2)-1)*Fs/length(G2)/2 %加噪声后解调信号频谱
set(gcf,'color','w')
figure(2)
subplot(221)
plot(t,MMN);
xlabel('加噪声解调信号波形')
subplot(222)
plot(frqG2,G2);
axis([0 3000 0 max(G2)])
xlabel('加噪声解调信号频谱')
subplot(223)
plot(t,M1)
xlabel('无噪声解调信号波形')
subplot(224)
plot(frqG1,G1)
xlabel('无噪声解调信号频谱')
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
dyi=sn-S; %高斯白噪声
s_ni=var(S)/var(dyi); %输入信噪比
dyo=MMN-M1; %解调后噪声
s_no=var(M1)/var(dyo); %输出信噪比
dyi1=sn1-S;
s_ni1=var(S)/var(dyi1);
dyo1=MMN1-M1;
s_no1=var(M1)/var(dyo1);
dyi2=sn2-S;
s_ni2=var(S)/var(dyi2);
dyo2=MMN2-M1;
s_no2=var(M1)/var(dyo2);
dyi3=sn3-S;
s_ni3=var(S)/var(dyi3);
dyo3=MMN3-M1;
s_no3=var(M1)/var(dyo3);
dyi4=sn4-S;
s_ni4=var(S)/var(dyi4);
dyo4=MMN4-M1;
s_no4=var(M1)/var(dyo4);
in=[s_ni,s_ni1,s_ni2,s_ni3,s_ni4];
out=[s_no,s_no1,s_no2,s_no3,s_no4];
set(gcf,'color','w');
figure(3);
plot(in,out,'+')
hold on
plot(in,out)
xlabel('输入信噪比')
ylabel('输出信噪比')