2fsk信号调制解调频谱的matlab仿真

2FSK信号的调制解调与频谱绘制的matlab仿真
a=randint(1,16);
t=0.0001:0.001:1;
inisig=a(ceil(t./(1/15)));
subplot(5,1,1)
plot(t,inisig)
axis([0,1,-1.5,1.5])
title('原信号');
%调制
f1=200;
f2=100;
carrier1=cos(2*pi*f1*t);
carrier2=cos(2*pi*f2*t);
modulation_wave=zeros(1,length(t));
for i=1:length(t)
if(inisig(i)==0)
modulation_wave(i)=carrier1(i);
else
modulation_wave(i)=carrier2(i);
end
end
subplot(5,1,2)
plot(t,modulation_wave)
axis([0,1,-1.5,1.5])
title('调制信号');
%2fsk信号加噪
noise_wave=awgn(modulation_wave,100);
%设计带通滤波器
[num1 den1]=butter(10,[2*0.9*f1*pi,2*1.1*f1*pi],'s');
[num2 den2]=butter(10,[2*0.9*f2*pi,2*1.1*f2*pi],'s');
daiout1_h=tf(num1,den1);
daiout2_h=tf(num2,den2);
unmodulation_wave1=lsim(daiout1_h,noise_wave,t); unmodulation_wave2=lsim(daiout2_h,noise_wave,t);
%2fsk信号相干解调
unmodulation_wave1_g=unmodulation_wave1'.*(carrier1); unmodulation_wave2_g=unmodulation_wave2'.*(carrier2);
%设计低通滤波器
wp=2*pi*90;
ws=2*pi*120;
rp=1;
rs=100;
[N Wn]=buttord(wp,ws,rp,rs,'s');
[B A]=butter(N,Wn,'s');
h=tf(B,A);
dsy1=lsim(h,unmodulation_wave1_g,t);
dsy2=lsim(h,unmodulation_wave2_g,t);
subplot(5,1,3);
plot(t,dsy1);
title('经过一路低通滤波器后的信号');
subplot(5,1,4);
plot(t,dsy2);
title('经过二路低通滤波器后的信号');
for i=1:length(dsy1)
if dsy1(i)>dsy2(i)
dsy(i)=0;
else dsy(i)=1;
end
end
subplot(5,1,5);
plot(t,dsy);
axis([0 1.2 -1.2 1.2])
title('解调信号');
%观察原信号频谱
inisig_spectrum=fftshift(fft(inisig));
maxf=1/0.001;
f=-maxf/2:maxf/2-1;
figure
subplot(5,1,1);
plot(f,inisig_spectrum)
title('观察原信号频谱');
%观察调制信号频谱
modulation_spectrum=fftshift(fft(modulation_wave));
maxf=1/0.001;
f=-maxf/2:maxf/2-1;
subplot(5,1,2);
plot(f,modulation_spectrum)
title('观察调制信号频谱');
%观察带通信号频谱
unmodulation1_spectrum=fftshift(fft(unmodulation_wave1)); maxf=1/0.001;
f=-maxf/2:maxf/2-1;
subplot(5,1,4);
plot(f,unmodulation1_spectrum)
title('观察带通信号150频谱');
unmodulation2_spectrum=fftshift(fft(unmodulation_wave2)); maxf=1/0.001;
f=-maxf/2:maxf/2-1;
subplot(5,1,3);
plot(f,unmodulation2_spectrum)
title('观察带通信号100频谱');
length(unmodulation_wave1)
%观察低通滤波器频谱
dsy_spectrum=fftshift(fft(dsy));
maxf=1/0.001;
f=-maxf/2:maxf/2-1;
subplot(5,1,5);
plot(f,dsy_spectrum)
title('观察低通信号100频谱');
信号频谱图
观察原信号频谱
-500-400-300-200-1000100200300400500
观察调制信号频谱
-500-400-300-200-1000100200300400500
观察带通信号100频谱
-500-400-300-200-1000100200300400500
观察带通信号150频谱
观察低通信号100频谱
-500-400-300-200-1000100200300400500观察上图，调制解调的频谱搬移基本正确，调制到高频，又解调回到低频。

观察上图，解调出来的信号不完成正确。

这主要是因为带通滤波器设计的不太好造成的。

From ：qianmyi 0
0.10.20.30.40.50.60.70.80.91-1
1原信号
0.10.20.30.40.50.60.70.80.91-1
1调制信号00.10.20.30.40.50.60.70.80.91-1
1
经过一路低通滤波器后的信号00.10.20.30.40.50.60.70.80.91
-1
1
经过二路低通滤波器后的信号00.20.40.60.81 1.2-1
1
解调信号。