Symmetric Window Constraint

Because we are designing a zero-phase window, use only the positive-time part $h\left(n\right)$ :

$$h\left(n\right)=w\left(n\right)\qquad n\geq 0$$ (4.64)

$$w\left(n\right)=\left\{ \begin{array}{ll} h\left(n\right) & n\geq 0\\ h\left(-n\right) & n<0\end{array} \right.$$ (4.65)