E { b t } = lim n → ∞ u − n + u − n + 1 + … + u 0 + u 1 + u 2 + … + u n 2 n + 1 {\displaystyle E\{b_{t}\}=\lim _{n\to \infty }{\frac {u_{-n}+u_{-n+1}+\ldots +u_{0}+u_{1}+u_{2}+\ldots +u_{n}}{2n+1}}}
