raisecos.m

数字通信系统中

function raisecos 
Ts=1;
N_sample=17;
dt=Ts/N_sample;
df=1.0/(20.0*Ts);
t=-10*Ts:dt:10*Ts;
f=-2/Ts:df:2/Ts;
alpha=[0,0.5,1];
for n=1:length(alpha)
    for k=1:length(f);
        if abs(f(k))>0.5*(1+alpha(n))/Ts
           Xf(n,k)=0;
       elseif abs(f(k))<0.5*(1-alpha(n))/Ts
           Xf(n,k)=Ts;
       else
           Xf(n,k)=0.5*Ts*(1+cos(pi*Ts/(alpha(n)+eps)*(abs(f(k))-0.5*(1-alpha(n))/Ts)));
       end
   end
   xt(n,:)=sinc(t/Ts).*(cos(alpha(n)*pi*t/Ts))./(1-4*alpha(n)^2*t.^2/Ts^2+eps);
end
figure(1)
plot(f,Xf);
axis([-1 1 0 1.2]);
xlabel('f/Ts');ylabel('升余弦滚降频谱');
figure(2)
plot(t,xt);
axis([-10 10 -0.5 1.1]);
xlabel('t');ylabel('升余弦滚降波形');