clear all
clc
close all
snr=100; %信噪比
n0=10; %序列长度
f1=20; %载波频率
f2=50;
fs=2000; %采样频率
%%%%%%%%%%%%%%%产生随机码元%%%%
X=randint(1,n0); %产生随机序列
figure(1)
stem(X),grid
title('初始码元序列')
%%%%%%%%%%%%%%产生基带信号，每个码源持续1s%%%%%%%%%
x=[];
for i=1:n0
for j=1:fs
x=[x X(i)];
end
end
figure(2)
k=linspace(0,n0,n0*fs);
plot(k,x)
axis([0,n0,-2,2])
title('基带信号')
xlabel('点数');ylabel('基带码元');
%%%%%%%%%%%% BFSK调制 %%%%%%%%%%%%%%
y0=cos(2*pi*f1*k);
y1=cos(2*pi*f2*k);
y=[];
for i=1:length(x);
if x(i)==1;
y=[y y1(i)];
else
y=[y y0(i)];
end
end
figure(3)
plot(k, y)
grid
title('调制后的信号')
%%%%%%%%%%%%%%5 %经过高斯白噪声的信道后的信号 %%%%%%%%%%%%
n=awgn(y,snr);
figure(4)
plot(n),grid
title('通过信道的信号')
%%%%%%%%%%%%带通滤波%%%%%%%%%%%
b1=fir1(80,[f1/(fs/2)-0.000001 f1/(fs/2)+0.000001],'bandpass');
l1=filter(b1,1,n);
b2=fir1(80,[f2/(fs/2)-0.000001 f2/(fs/2)+0.000001],'bandpass');
l2=filter(b2,1,n);
figure(5)
subplot(2,1,1)
plot(k,l1)
subplot(2,1,2)
plot(k,l2)
%%%%%%%%%%%%% 相乘 %%%%%%%%%%%
p1=l1.*y0;
p2=l2.*y1;
figure(6)
subplot(2,1,1)
plot(p1)
title('相乘后的信号')
subplot(2,1,2)
plot(p2)
%%%%%%%%%%%%%%% 低通滤波%%%%%%%%%%%%%%55
N=80;
b3=fir1(N,10*2/fs,'low');
b4=fir1(N,60*2/fs,'low');
ll1=filter(b3,1,p1);
k=linspace(0,n0,n0*fs);
ll2=filter(b4,1,p2);
figure(8)
subplot(2,1,1)
plot(k,ll1)
title('低通滤波后的接收信号')
subplot(2,1,2)
plot(k,ll2)
%%%%%%%%%%%% 抽样判决%%%%%%%%%%%%%
u=[];
for i=1:n0
if abs(ll2((i-0.5)*fs))> 0.2
u(i)=1;
else
u(i)=0;
end
end
figure(9)
stem(u),grid
title('判决信号')
%%%%%%%%%%%%%% 误码率计算 %%%%%%%%%%
error=sum(abs(X-u));
error_rate=error/n0
