Methods to recover a signal
1. Zero-order intapolation (step function)
$ x(t)= \sum^{\infty}_{k = -\infty} x(kT) {u(t-kT)-u[t-(k+1)T]} $
File:Zero order.jpg. ECE301Fall2008mboutin
2. First-order intapolation
$ x(t)= \sum^{\infty}_{k = -\infty} f_k (t) $
where $ f_k (t)= x(t_k) + (t-t_k) \frac {x(t_k+1)-x(t_k}{t_k+1 - t_k} for t_k < t < t_k+1 $
