qpsk.m

对ASK调制解调进行了仿真,包括程序仿真和模型仿真

function [y, Kmod, fs, fb, fc]=qpsk(x,Kmod,Kbase,fs,fb,fc);
if nargin<6; fc=2;  end;
if nargin<5; fb=1;  end;
if nargin<4; fs=32;  end;
if nargin<3; Kbase=2;  end;
if nargin<2; Kmod=1;  end;
if nargin<1; x=[0 0 0 1 1 1 1 0]; end;
T=length(x)/fb; m=fs/fb; nn=length(x);
dt=1/fs; t=0:dt: T-dt;
Kmod=rem(Kmod, 2); Kmod=Kmod+(Kmod ==0) *2;
Kbase=rem(Kbase,2); Kbase=Kbase+(Kbase ==0) *2;
if Kmod ==1;
    x1 =x*2-1; tstr='QPSK';
elseif Kmod ==2;
    x1=dqpskcd(x); x1=x1*2-1; tstr=['QDPSK'];
end;
I=x1(1:2:nn-1); Q=x1(2:2:nn);
I=pulse(I,2*m); Q=pulse(Q,2*m);
if Kbase ==2;
    I=bshape(I,fs,fb/2); Q=bshape(Q,fs,fb/2);
end;
y=I.*cos(2*pi*fc*t)-Q.*sin(2*pi*fc*t);  y1=y;
n=length(y);
if nargout<1;
    subplot(211);
    plot(t,y,t,I,t,Q,[0 T],[0 0],'b:');
    if Kbase ==2;
        tstr= [tstr 'with the RC filter'];
    end;  title ('Signal');
    n=length (y) ; y=fft(y)/n; y=abs(y(1:fix(n/2)))*2;
    I=find (y<1e-04); Y(I)=1e-04; y=20*log10(y);
    f1=m/n;f=0:f1:(length(y)-1)*f1;
    subplot(223); plot(f,y,'r'); grid on;
    title(' Spectrum'); xlabel('f/fb'); zoom xon ;
end;