Plotting a time domain Signal

I want to plot the continuous time domain signal for the following spectrum:

and here is what i have done so far, are there any possible improvments to this?

N=256;
xn=zeros(1,N);
for n=0:1:N-1
    xn(n+1)= 2*(sign(n - -1) - sign(n - 1));
end

%Taking inverse DFT
x_i=ifft(xn);

wk = 0:1:N-1;

plot(wk,x_i);

Answer 1

[Chunru]

N=256;
f=(0:N-1)/N;
xf = 2*sinc(2*f);    % 2*sin(w)/w => 2*sinc(2*f)

x_i=ifft(xf);
plot(f, real(x_i), 'r', f, imag(x_i), 'b');