  We theoretically revisit graphene transport properties as a function of
carrier density, taking into account possible correlations in the spatial
distribution of the Coulomb impurity disorder in the environment. We find that
the charged impurity correlations give rise to a density dependent graphene
conductivity, which agrees well qualitatively with the existing experimental
data. We also find, quite unexpectedly, that the conductivity could increase
with increasing impurity density if there is sufficient inter-impurity
correlation present in the system. In particular, the linearity (sublinearity)
of graphene conductivity at lower (higher) gate voltage is naturally explained
as arising solely from impurity correlation effects in the Coulomb disorder.
