ffskdemod.m

用于FFSK解码算法的模拟实现。通过对接收模拟波形的数字滤波处理

function ffskdemod

clear all;
clc;
close all;

fs1=12000;
fs2=6000;

fid=fopen('ffskdemo.wav');
[x1,n]=fread(fid,48000,'int16');
fclose(fid);
t=1:floor(n/2);
xin=x1(2*t-1);

%subplot(2,1,1);plot(t,xin(t));

s=100;
e=floor(n/2-100);
t=s:e;
x=xin(t);

[b,a]=ellip(2,1,40,2*2000/fs1);
x=filter(b,a,x);
e=floor((e-s)/2);
y=zeros(1,e);
t=1:e;
y(t)=x(2*t-1);

%subplot(2,1,2);plot(t,y(t));

[b,a]=ellip(2,1,40,2*1000/fs2,'high');
y=filter(b,a,y);
t=1:e;
subplot(2,1,1);plot(t,y(t));

d1=0;
d2=0;
d3=0;
for t=1:e
    k=round(y(t)*d3/32768);
    d3=d2;
    d2=d1;
    d1=y(t);
    y(t)=k;
end
[b,a]=ellip(1,1,40,2*600/fs2);
y=filter(b,a,y);
t=1:e;
x=zeros(1,e);
subplot(2,1,2);plot(t,y(t),t,x(t));

sgstate=0;
s=1;
uplevelcnt=0;
dnlevelcnt=0;
for t=1:e
   if y(t)>10
       sgstate=1;
   else
       if y(t)<-10
           sgstate=-1;
       end
   end
   if sgstate>0
       if dnlevelcnt>0
           x(s)=uplevelcnt;
           x(s+1)=dnlevelcnt;
           uplevelcnt=0;
           dnlevelcnt=0;
           s=s+2;
       end
       uplevelcnt=uplevelcnt+1;
   else
       dnlevelcnt=dnlevelcnt+1;
   end
end
x(s)=uplevelcnt;
x(s+1)=dnlevelcnt;
s=s+1;
x(1:s)